# Build a shed Mike's way



## MikeG.

I've put it off long enough!

Hopefully, this will save me hours of repetition:

_*Note that this only applies if your building does not require Building Regulations approval.*_ If it needs to meet the regs, the base will need to be properly designed according to the local soil conditions and tree locations etc.



Code:


[img]http://i637.photobucket.com/albums/uu96/mikegarnham/Shedscan1700x2338.jpg[/img]






The concrete should be laid on:
-clean compacted hardcore, say 100 to 150 thick
-50mm sand blinding (for the protection of the DPM)
-1200 gauge DPM 

Note the golden rule of walls: *The Vapour Barrier goes on the warm side of the insulation!!!!*. The vapour barrier in this drawing is the OSB, which is full of glue and therefore highly resistant to the passage of moisture.

Key features of this design are the brick plinth and the 25mm air gap between the frame and the back of the cladding. In the roof, it is essential that there is a 50mm clear ventilated void above the insulation, and that there is a continuous 25mm gap at the eaves (with insect mesh) to provide air movement. These features are essential to prolong the life of the building, and to keep everything inside dry.

You can omit the floating floor if you wish. My own workshop simply has the concrete slab as the floor.

I imply no structural calculations for the roof! Each roof should be designed individually, and I am always happy to help with that. I would suggest min. 150mm rafters so that you can fit 100mm of insulation in without restricting the airflow, but with some roofs the rafters will need to be much deeper for structural reasons.

The boarding can easily be replaced with render, so long as the airflow behind is maintained, and this is made easier by using a backing of building paper behind the EML (mesh) so that the render doesn't get pushed through too far into the cavity. Note that with boarding there should only be one nail per board per stud position, and that that nail should be situated about 30mm up from the bottom edge of the board.

And now a variation: with *Timber Suspended Floor*



Code:


[img]http://i637.photobucket.com/albums/uu96/mikegarnham/Shedscan21600x1886.jpg[/img]






I like this less, particularly because of the large step up and the resulting taller building (or reduced headroom). This isn't the only way to do this, but the principle is to have the insulation hard up under the flooring, with a continuous ventilated void below the joist. 

The surface of the reduced ground level below the floor should either have a geotextile membrane or a layer of lime laid on it, or it should be treated with a weed-killer. Avoid using this design in wet/ boggy areas because of the reduced ground level below the floor.

I hope this helps.

Mike

Mod Edit:- Thanks to Myfordman for retrieving images.


----------



## mickthetree

Thanks for taking the time to post this Mike. Now watch the questions ensue...

What are the L shaped metal straps for?


----------



## MikeG.

To hold the shed down onto the bricks. Otherwise a good wind could start you thinking of the Wizard of Oz.

Mike


----------



## Krysstel

With the exception of the insulation thicknesses; exactly the way we build wooden houses in Norway, and here it's COLD !
As you say, the really important features are the air gap around the entire construction and that the vapour barrier is on the inside of the insulation.

Mark


----------



## dedee

My vote is for this to be set as a sticky as the information is clear and concise and probably one of the most discussed topics on the forum.

Andy


----------



## MikeG.

I've already asked Philly to sort that Andy..........and I expect to insert the link into a few posts in the future!

Mike


----------



## Krysstel

I posted a similar explanation in an old thread here :-
https://www.ukworkshop.co.uk/forums/timber-house-extension-t25054-30.html?highlight=insulation

Mark


----------



## MikeG.

Mark,

there is a nice breathable external sheathing board now available called Panelvent, which would do a much better job than the plasterboard from your original posting. I use it all the time, but wouldn't bother for a shed because it isn't easily obtainable from local Builder's Merchants.

The pricipal difference between a house and a shed will be in the single skin masonry plinth, which wouldn't do for a house, and in the insulation thicknesses, which also aren't enough. I even specify OSB behind all plasterboard in houses I design......it makes a much nicer wall.

Mike


----------



## Krysstel

The advantage of the waterproof coated plasterboard is it's cheap, quick and easy to use and readily available. But I agree, there's various other, probably better options.

Mark


----------



## Paul Chapman

Thanks for taking the trouble to post this, Mike.

Cheers :wink: 

Paul


----------



## bodgermatic

Thanks Mike!


----------



## MikeG.

No problem guys! It was a simple calculation of self interest, though. How much time will it take me to type the same thing out every week for the next x months, measured against how long it would take me to do a drawing and a posting.

I hope I've saved myself a lot of typing!

Mike

PS Its been stickified now, too, so I will be able to find it again.


----------



## dh7892

Nice to see this "stickied". I'm sure many of us will be refering to this post in the coming months. 

As a small suggestion; on some of the other forums that I visit, they have a "tutorials" section where people can place useful info. Perhaps this would be a nice this to have here.

Few questions about the actual design:

Concrete base direct on top of ground or do you recommend a bit of rubble below it?

Brick plinth butted up to the edge of the slab? I guess this makes it easier to layout the galv. straps when casting the slab. I've seen a few builds where the slab is a bit wider than the shed. Is there any reason for this?

Should the 1200 guage poly, come up the side of the slab too?

When you say that your prefered roof sheeting is Onduline, do you mean the corrugated sheets attached straight on to the rafters? Or would there be some sheet material between?


----------



## MikeG.

I have now added a variation to the original post, with a timber suspended floor in place of the concrete floor. 






dh7892":3psrurml said:


> Few questions about the actual design:
> 
> Concrete base direct on top of ground or do you recommend a bit of rubble below it?
> 
> Brick plinth butted up to the edge of the slab? I guess this makes it easier to layout the galv. straps when casting the slab. I've seen a few builds where the slab is a bit wider than the shed. Is there any reason for this?
> 
> Should the 1200 guage poly, come up the side of the slab too?
> 
> When you say that your prefered roof sheeting is Onduline, do you mean the corrugated sheets attached straight on to the rafters? Or would there be some sheet material between?



You are quite right. The concrete should be laid on:
-clean compacted hardcore, say 100 to 150 thick
-50mm sand blinding (for the protection of the DPM)
-1200 gauge DPM

I reckon that having the slab over-size is simply creating a ledge for moisture to sit on, and is to be avoided if possible. It isn't easy casting concrete exactly accurately, so there will inevitably be a point or two where the concrete is outside the line of the bricks, but in my view this should be kept to a minimum.

I don't turn the polythene up the edge of the slab in these circumstances, but it is a bit of an academic exercise. It would be fine to turn it up if you had somewhere to turn it over and trap it, like under the bricks, but by having it loose and turned up, all it can do is trap moisture that runs down the concrete. Ideally, instead of having soil around the edge of the base you would have a trench filled with shingle.

In this design, the edge of the slab can get wet. The point is, being exposed by 50mm min all round, it also dries off. Remember, this is a shed........I wouldn't do this for a house! 

As for the roofing, if I were using Onduline then I would probably using a breathable sarking membrane (Tyvek or similar) and then 50x50 battens.....and omit the ply/ OSB. However, the difficulty with this is keeping insects out of the void. The roof sheet manufacturers make a profiled infil to keep insects and vermin out, but this prevents ventilation. You would still, therefore, need a ventilated void below the Tyvek and above the insulation, open at the eaves.

My own shed roof is a hybrid, having originally been OSB with felt, which I then covered in an Onduline-like product. It was particularly simple to over-clad, so, whilst it may be more expensive, it is perfectly possible to use a sheet material such as Onduline above an OSB sub-roof.

Mike


----------



## wizer

Thanks very much for doing this Mike. I know I'll need it one day and as you say, it'll save lots of repeating yourself. Why don't you stick it in your sig?

Can I also suggest that every time you answer something that's not covered in the original post, that you edit it into that first post? That way the whole thread does not have to bee read to glean all the info we need. Otherwise you;ll continue to get repeat questions.


Hopefully Charley really is doing some work on the rest of this site and it can be added to a specific area. Pigs might fly tho...


----------



## MikeG.

Tom,

I agree with you re adding to the original post...........and I did that this morning with the suspended timber floor variation. As for adding a link in my signature......good idea, but it might take some working out! I'll have a look.

Mike


----------



## yogibe4r

Mike,

Thanks for putting this together.
Below is a design for my workshop roof I plan to build this spring. I would appreciate if you could check my sizings, especially the rafter size ( 6x2). Where the joists stop in the middle I plan to leave the ceiling open. The slightly irregularly rafter spacing in the centre is to ensure they sit above studs.
Regards, JK



[/img]


----------



## MikeG.

yogibe4r":r2cvv1ag said:


> [/img]



Right, let's have a look.......

Seems like you need to re-post your picture, JK. Firstly, you haven't enough postings to get through our spam filter (which I can overcome), and secondly you appear to have 2 [/img] instructions at the end of the image address.

Mike


----------



## yogibe4r

2nd try's a charm...


----------



## MikeG.

OK, that's better.

Before I check the timber sizes, let's look at the principles. Are you hoping to rely on the joists to prevent the walls from spreading? There is a huge amount of good sense in having a hybrid roof like this, because it does enable access into the loft areas from inside the building, and with easy access for longer pieces of stuff than if you try and use a loft hatch. It is exactly what I am planning to do in my new workshop.

If you aren't relying on the joists to prevent spread, then your ridgebeam needs to be structural, and will be huge. If you are relying on the joists then we have to deal with the trusses which don't have ties.

Mike


----------



## yogibe4r

Mike, 
My intention was to rely on the joists to stop the walls spreading. What would be the maximum gap between 'un-joisted' rafters? The wife has already earmarked the 'loft space' for storage.

Regards, JK

edit: The wife has now informed me she is to be referred to as SWIMBO from now on!


----------



## MikeG.

JK,

in which case, we will simply double up the last of the rafters that have a tie, and use a structural ridge beam to span between them. The rafters without a tie will be "held up in the air" by the structural ridge beam, and thus prevented from spreading the walls.

What sort of roofing are you proposing (tiles, felt, sheet-roofing etc)? Are you required to get Building Regulations approval for this shed?

Mike


----------



## yogibe4r

Mike,
The roof will be 12mm OSB covered with felt shingles. Not sure about building regs, as neighbour built a simliar structure and told me he didn't need them. However will be popping down the planning office to make sure. Overall height is 3.85m.
Regards, JK


----------



## MikeG.

I'll sort your timber sizes out when I know whether that this doesn't need BR approval. 

Mike


----------



## yogibe4r

After a brief conversation with the duty planning officer, they have explained that only the electrics may be of concern to them. This I will plan closer to build time.

Regards, JK


----------



## yogibe4r

Not sure if this thread is still being looked at due to recent events, but can anybody else have a look at my roof design to see if it's ok?

Sorry to be a noob without a clue!?!


----------



## 9fingers

yogibe4r":3bm9xi9a said:


> Not sure if this thread is still being looked at due to recent events, but can anybody else have a look at my roof design to see if it's ok?
> 
> Sorry to be a noob without a clue!?!



I can only offer a tiny fraction of Mike's expertise but post some details and we can have a look.
Bob


----------



## yogibe4r

Thanks 9fingers.







Proposed timbers are 6x2 for rafters and joists, 8x2 for ridge beam.
Roofing will be 12mm OSB and felf shingles. All rafters sit above wall studs, hence slightly odd spacing in the centre. The ridge beam isn't to be structural so my concern is whether the amount of space between 'un-joisted' rafters would cause the walls to spread.

Thanks in anticipation, JK


----------



## 9fingers

Such a shame we don't have Mike here for an experienced opinion.

I share your concern on wall bulges. Very attractive to have what must be about a 3m access to the roof but unless you are going to store very long lengths up there, I'd be tempted to close is up to say 2m and make sure the wall plates on top of your studs lay with the widest dimension horizontal to stiffen the walls as much as possible.

Also I wonder if your joists are over spanned at 6x2. If it were my shop, all sorts of stuff would end up there imposing quite a load. I think I'm right in saying if that were a habitable floor you would be looking at least 9x2 to meet regs. So I'd consider 8x2 stress graded timber. Should not add a huge amount to the cost.
Are you going to put a deck up there? It would tie the joists together nicely.

The OSB will tie the rafters and stop them racking.

Thes are just my gut feel - I'm not a professional in this field.

hth

Bob


----------



## yogibe4r

Updated with 8x2 joists, extra joists, deck of 22mm chipboard, and doubled up last pairs of rafter.

Thanks for your advice 9fingers

Cheers, JK


----------



## 9fingers

That looks better to me. Possibly no real need to double up on the rafters though?

Bob


----------



## bucephalus

Many thanks for this useful information - came in very handy when planning my workshop.


----------



## 9fingers

bucephalus":2icp02f4 said:


> Many thanks for this useful information - came in very handy when planning my workshop.



If you ever need to get hold of MikeG, he no longer frequents this forum but can be found via The Wood Haven.

Bob


----------



## bucephalus

Oh, right - I didn't know. I am continually humbled by how helpful everyone is here. Many thanks.


----------



## 9fingers

bucephalus":1b84oov9 said:


> Oh, right - I didn't know. I am continually humbled by how helpful everyone is here. Many thanks.



Ah! we do have a plan though :twisted: 

One day we will come asking for help from you in return!! :lol: 

Happy shavings


Bob


----------



## Andy RV

Bump for a very useful thread!


----------



## Wizard9999

I am in the process of planning my first workshop build. Have been researching on the 'net and this post appears to provide the definitive construction detail. As a complete non-builder type I have one question relating to the initial (extremely helpful post). How do you go about fixing the sole plate to the dwarf wall used to keep the timber off the ground? If I simply plug and screw it won't I screw straight through the DPM / DPC? If I do just screw through them is the impact so small as to not worry about it?

Many thanks in advance for any answers, advice, help...,
Wizard9999.


----------



## Zeddedhed

You're right Wizard, screwing down the sole plate does technically compromise the DPM but as you state it's not significant enough to worry about it.
I build quite a few timber frame buildings, both habitable (houses) and non-habitable (Workshops, pool houses etc) and go for a belt n braces option - drill your hole, squirt in some frame sealant, bang in a decent size frame fixing (Fischer or similar) and when you tighten it up the sealant will effectively remake the continuous DPM.
HTH


----------



## Deejay

Afternoon Wiz

*How do you go about fixing the sole plate to the dwarf wall used to keep the timber off the ground? *

If you look carefully at the drawings, they show galvanised straps bent over the top of the sole plate.

Cheers

Dave


----------



## Wizard9999

Ah, OK Dave, now I get it. The sole plate itself is not fixed to the dwarf wall, but the metal brackets are screwed down onto the dwaft wall - hence the comment through the thread about stopping the shed blowing off the dwarf wall in a big storm. So there is no piercing of the DPC.

Having read your post I did go back and study the original diagram again and I have a couple of further question that I hope somebody can help with.

1. The diagram shows a layer of 500 gauge polythene between the concrete floor and the insulation under the floating floor which then seems to lap up the dwarf wall to the height of the floating floor. This must be running on the inside of the metal bracket, i.e. not between the bracket and the dwarf wall (unless a hole is cut in the polythene for the bracket to poke through) so can't lap over or under the DPC running along the top of the dwarf wall. The floating floor is about the same height as the top of the first brick of the dwarf wall. So, in this structure what prevents damp coming through the the dwarf wall and into the inside skin of the shed (in the diagram this is shown as 11mm OSB)? Or am I now getting too paranoid about damp penetration now?

2. The 1200 gauge polythene under the concrete base seems to just stop at the edge of the base. Am I understanding this correctly, or when I put this down do I need to leave enough to lap up the side of the concrete base to stop damp coming into the side of the concrete where it is in contact with the surrounding soil? But then, if I do lap it up, am I creating a pool which if water ever does get into it will never have anyway of escaping, which I guess may be a reason for not lapping it up?

I'm sure my questions reveal I am a compete novice at this and I apologies if my questions revela utter stupidity, but I really want to understand what I am doing before I think about starting building my workshop. Any help would be much appreciated.

Wizard9999


----------



## Deejay

Morning all

Mike Garnham is posting the construction of his new workshop over on WH2

http://www.thewoodhaven2.co.uk/viewtopi ... 1538#p1538

Cheers

Dave


----------



## johnny

thats an excellent guide Mike and very imformative ...although a bit over the top for a garden shed imo It makes my shed look like a 3rd World shack lol. I guess what we are really talking about here is more a workshop than a shed to store the lawnmower .


The only suggestion that I would make is regarding the detailing around the sub structure brickwork to internal floor juncture. The manner in which the Dpc is sealed to the Dpm to prevent water ingress is so often left unclear or unresolved and is arguably the most critical juncture in any building.
Rain spatters up to a height of 6-8 inches so the bottom two courses of brickwork are going to be constantly wet during spells of heavy or prolonged rain ,Any tear or untaped gap to the Dpc or Dpm around the edge of the chipboard flooring is going to allow the edge of the chipboard to get wet and rot.
My suggestion would be to show the Dpm folded up at the edges and overlapped with, and taped to, the Dpc which should be carried down over the internal edge of the sole plate so that everything below the sole plate is completely sealed like a boat. All joints in both the Dpm and Dpc should be lapped and taped otherwise any significant ground pressure will allow water ingress.

Just a reminder that to be 'Permitted Development' and be exempt from Planning, any garden structure needs to be a maximum of 2.5mts high unless a minimum of 2mts from any boundary.


----------



## Wizard9999

Johnny

If you are interested follow link in post above yours. mike's new build progressing well. He has now explained dpm question. In short, if you concrete plinth is above ground folding up the dpm around would cause it to be damaged by exposure to UV, but if plinth level with ground that is also what he suggests, but folding under brick plinth, not taking up to level of EPC on top of dwarf erick wall.

Wizard9999


----------



## Harbo

Mike doesn't post on here and he is a very experienced Architect.
You will have to follow it on Woodhaven2

Rod


----------



## johnny

Wizard9999":200tivtn said:


> Johnny
> 
> If you are interested follow link in post above yours. mike's new build progressing well. He has now explained dpm question. In short, if you concrete plinth is above ground folding up the dpm around would cause it to be damaged by exposure to UV, but if plinth level with ground that is also what he suggests, but folding under brick plinth, not taking up to level of EPC on top of dwarf erick wall.
> 
> Wizard9999


Thanks Wizard I have been following Mike's new shed build with interest as I am currently constructing one of my own allbeit on a somewhat smaller scale

The waterproof detailing shown in Mikes drawing isn't very clear as shown in the first image. It would probably be clearer if that section was blown up a bit.

I was not so concerned with rising damp tracking through the concrete to the substructure brickwork as the damp ingress through the brickwork into the edge of the flooring .
The juncture between the foundations/sub structure of a building and the DPC must be sealed by lapping and taping to protect the structure and internal finishes. There must be no area unsealed .

The reason why you see so many new buildings with the DPM left stuck up in the air ,hacked off and blowing in the breeze is because builders have no understanding of how to tie the DPC's to the DPM so they just hack it off flush with the screed leaving the most critical area of a building unprotected.

Rain splashing up the brickwork will penetrate the brickwork and soak the edge of the flooring in the first construction detail as shown. I think I would prefer to see the restraints on the outside of the brickwork bolted to the edge of the slab on view. That way the condition of the straps is constantly on show and can be monitored and the straps don't interfere with lapping and taping the DPM to the DPC


----------



## ChrisxBates

I am considering constructing a workshop based on Mike’s drawings on page 1. 

Thanks to Mike and all others that have contributed. An excellent, informative thread.

My question is regarding the mineral wool insulation in the walls. This comes in two forms the denser cavity wall type batts and the lighter loft type insulation. 

Firstly…. Which type are people using? 

For the insulation to be effective there mustn’t be an air gap between the mineral wool and the OSB. If there were an air gap, this would allow the cold external air to come into contact with the OSB making the insulation ineffective.

Second….. How do we ensure the insulation stays in place and doesn’t fall away from the OSB overtime? Hence causing an air gap and making the insulation ineffective. 

Previously when I have used mineral wool, it has either been held in place by gravity or sandwiched between two surfaces. 

I would be interested in hearing your views.


----------



## Wizard9999

ChrisxBates":og1q8hay said:


> I am considering constructing a workshop based on Mike’s drawings on page 1.
> 
> Thanks to Mike and all others that have contributed. An excellent, informative thread.
> 
> My question is regarding the mineral wool insulation in the walls. This comes in two forms the denser cavity wall type batts and the lighter loft type insulation.
> 
> Firstly…. Which type are people using?



All in the name isn't it, the cavity wall batts are designed for that job and so have the rigidity needed. Mike did a very long thread on his recent workshop build on TheWoodHaven2 and if you searc for it you will see that is exactly what he used.

Terry.


----------



## SlayWitch

Thanks for posting this, super helpful as I am considering to start on a similar project so it is good to see what kind of approach other people are taking. How is everything going?


----------



## Deejay

SlayWitch":bqkldt7k said:


> Thanks for posting this, super helpful as I am considering to start on a similar project so it is good to see what kind of approach other people are taking. How is everything going?



Mike doesn't post here any longer.

He contributes over on The Woodhaven2.

Cheers

Dave


----------



## SlayWitch

Ah apologies, I didn't realise :S I will check if there has been updates then. Cheers Dave!


----------



## technium

Thanks for this Mike, If I decide to build mine myself then I will try and use this for mine. thanks

Colin


----------



## Muzza80

Very helpful post, thanks!


----------



## Myfordman

MikeG.":2yyxh7gb said:


> I've put it off long enough!
> 
> Hopefully, this will save me hours of repetition:
> 
> _*Note that this only applies if your building does not require Building Regulations approval.*_ If it needs to meet the regs, the base will need to be properly designed according to the local soil conditions and tree locations etc.
> 
> 
> 
> 
> 
> 
> The concrete should be laid on:
> -clean compacted hardcore, say 100 to 150 thick
> - sand blinding (for the protection of the DPM)
> -1200 gauge DPM
> 
> Note the golden rule of walls: *The Vapour Barrier goes on the warm side of the insulation!!!!*. The vapour barrier in this drawing is the OSB, which is full of glue and therefore highly resistant to the passage of moisture.
> 
> Key features of this design are the brick plinth and the 25mm air gap between the frame and the back of the cladding. In the roof, it is essential that there is a 50mm clear ventilated void above the insulation, and that there is a continuous 25mm gap at the eaves (with insect mesh) to provide air movement. These features are essential to prolong the life of the building, and to keep everything inside dry.
> 
> You can omit the floating floor if you wish. My own workshop simply has the concrete slab as the floor.
> 
> I imply no structural calculations for the roof! Each roof should be designed individually, and I am always happy to help with that. I would suggest min. 150mm rafters so that you can fit 100mm of insulation in without restricting the airflow, but with some roofs the rafters will need to be much deeper for structural reasons.
> 
> The boarding can easily be replaced with render, so long as the airflow behind is maintained, and this is made easier by using a backing of building paper behind the EML (mesh) so that the render doesn't get pushed through too far into the cavity. Note that with boarding there should only be one nail per board per stud position, and that that nail should be situated about 30mm up from the bottom edge of the board.
> 
> And now a variation: with *Timber Suspended Floor*
> 
> 
> 
> 
> 
> 
> I like this less, particularly because of the large step up and the resulting taller building (or reduced headroom). This isn't the only way to do this, but the principle is to have the insulation hard up under the flooring, with a continuous ventilated void below the joist.
> 
> The surface of the reduced ground level below the floor should either have a geotextile membrane or a layer of lime laid on it, or it should be treated with a weed-killer. Avoid using this design in wet/ boggy areas because of the reduced ground level below the floor.
> 
> I hope this helps.
> 
> Mike



I've edited the original post to make the vital diagrams visible and make sense of the text. 
Bob


----------



## Hornbeam

There is no reason why insulation quilt cannot be used in walls (most large warehouses use quilt for built up cladding). What you need to do is prevent it from slumping down in the cavity creating voids. One way to stop this is to use stick pins which are long metal pins with an adhesive base. The pins are about 2/3rds of teh cavity depth so dont cause cold bridging. Glass wool is much easier to use than stone wool as fibre length is much longer and so it is less likely to break. I would use a quilt thickness at least 10mm thicker than your cavity and ensure it is fully lofted to fully fill the cavity. Quilt insulation has a slightly lower thermal conductivity than denser batts and willl be easier to fill the cavity , PIR foams insulation has much better insulation than MW so you only need about 60% of the thickness for the same U value. I would not recommend polystyrene due to the fire risk issues

Ian


----------



## dom68

hi mike if i go with the timber floor design how many courses high can the plinth be if i keep it a single bricks width? 

thanks, dom.


----------



## dom68

also would be acceptable if i didnt bring the osb down to the floor? ie could i use one sheet of 8x4 horizontally on the back of my frame then place the frame on top of plinth and fasten down with straps the same as in your diagram? 

thanks.


----------



## MikeG.

The bottom of the sole plate/ DPC should be at least 2 courses above ground level. Three is better.

That would be fine with the OSB. The one thing against that is that the panels become very heavy, and the slightest gust of wind at the wrong time can make life very tricky. However, if you've got sufficient help, then yes, that's no problem.


----------



## dom68

great.. so if i build a 8/9 course single skin wall/plinth for the frame to sit on all should be ok? 

my thoughts at this stage are for my 8x6ft shed. im thinking my wall height to be around 2m. the top 1220mm framed and the lower 800mm single skin brick. all approx at the mo..

im also thinking of using new treated scaffold board ripped to 38x50mm to build the framed sections.. retreated after cutting.. does this sound plausible?

dom.


----------



## MikeG.

Hmmm. That's quite tall for a half-brick wall. It could look rather odd, too. That brickwork could be a bit vulnerable around the door opening (and 800 is 10 or 11 courses). You might be OK if you do piers either side of the door which are 215 deep.

50x38 framing would be just about OK for a really small shed, say 6'x4', but it isn't enough for a proper building. 50x50 would be my absolute minimum for any thing bigger than 6'x4', but 75x50 is really the least you'd expect to use for anything you'd work in.


----------



## dom68

how about 8 courses of bricks with piers by the door and 75x38? or is 38 just too thin? sorry to be a pest :roll:


----------



## MikeG.

75x38 such that the wall was 75 thick? Do-able, depending on the dimensions of your shed. You might need some noggins. 

75x38 such that the wall was 38 thick. No.


----------



## dom68

thats good news mike.. yes meaning the walls would be 75mils thick. i was planning dimensions of 8ft x 6ft but this can be adjusted if need be.. will i need a rethink?


----------



## ObservantGround28

Incredibly helpful info in this thread.

I'm looking at a version of M's Shed clad in Plastisol coated box profile roof sheets on the back and sides rather than feather edge, etc. as I want to get it as close as possible to the boundaries and not worry about maintenance. Fences will be as tall as the walls so in theory it should be well protected at the back and both sides by any direct rain, snow, etc.

Anyone else looked at using plastic coated steel sheeting for this purpose and would you recommend it?

Thanks


----------



## MikeG.

That'd do a lovely job. If you are using this vertically, then you'll need horizontal battens, and they should be on vertical counterbattens........all of which alters the thickness of the wall and the junction detail with the plinth. Just be very sure of your insect mesh detailing, because the profile will make that a little more complicated than with a board. It's quite a big deal, too, because wasps or bees in your wall could actually render your workshop unusable for a summer.


----------



## ObservantGround28

Thanks Mike. I'll look into this and post back what I'm going to do for anyone else thinking about this.


----------



## Angel1058

Hi

Looking at an 11m by 5m shop - and based on this, will have a concrete base. Do I have to have reinforcement steel in the base - those grid like rebar things?

Cheers


----------



## ObservantGround28

ObservantGround28":7juxtjug said:


> Thanks Mike. I'll look into this and post back what I'm going to do for anyone else thinking about this.


. I ended up building it out of blocks and put a fibreglass roof on it. Exhausting work - figured I’ve lifted over 10 tonnes excluding all the digging I did.


----------



## That would work

Hi
My projected build will be going up to a boundary fence. Therefore I need to make the outside on that side sealed. I am intending to cover an outer skin with osb and seal this with bitumen and felt. It will be built in 8x4 sections each one being stood on a couple of courses of brick. So, as I will have a sealed exterior skin, should provide ventilation on the inside skin osb? I'll be insulating in the cavity.


----------



## MikeG.

On the boundary? Then if you are above 15 square metres you'll need to comply with Building Regs, which means fire-resistant materials within a metre of the boundary.....which would rule out OSB.


----------



## That would work

Hi
Unfortunately not, its 11.5 sq m. I was thinking of sealing the outsides of each panel and then also standing corrugated bitumen sheets between the boundary and the outside wall (of workshop) that sit under a draped flashing from the roof and in turn have their bottom edge sat in guttering (well below dpc) which then runs off of the upstanding base. This should ensure that not only the external timber is sealed but also kept completely dry with the corrugated sheets... and also allowing airflow between. So should I ventilate the voids in the wall with vents on the inside skin that is. It will be a 75mm cavity.


----------



## MikeG.

If this was a store shed, it wouldn't matter. But if it is to be heated and you are going to work in it, then ideally the OSB would be on the inside, and a breathable membrane would be put on the outside, battened out, then a ventilated void created to whatever rainscreen you intend. You could fix the corrugated sheets direct to the (counterbattens & battens on the ) wall, rather than propping them in an ad hoc way, but you would need to add horizontal battens to your vertical battens. I strongly advise against felt and bitumen on OSB as your outer wall. Maintenance would be virtually impossible, and the necessity to get ventilation in behind it makes the detail difficult.


----------



## That would work

Ok, interesting, Hadn't thought about using the sheet for the outside, automatically giving plenty of airflow. So a 3x2 stud frame with corrugated on the outside... and could let each sheet drop just over the brick base top edge on the outside. I should also be able to arrange a decent vertical overlap as I can screw from inside the stud frame to pull them together. What insulation would you recommend?


----------



## MikeG.

Careful, though. It doesn't just give airflow, but access for insects and vermin. You'll need to design in some insect mesh.

Insulation? Mineral wool/ fibreglass is fine for a shed. If you want something more expensive but a better insulator, then Celotex.


----------



## That would work

yes, will do, Ill fill maybe half and push some kind of mesh in the remaining. 
Many thanks.... You have saved me a lot of mess and felt!

Cheers,
Tim


----------



## DBT85

Mike,

Was originally thinking pent roof but now looking at apex with a structural ridge. If only I knew anything about any of it! ha.

I'm sure you've answered these many times before but am I right with

a) a pent roof will need bigger rafters than a apex roof. 
b) a non structural ridge (board) needs the walls tied together with rafter ties (do these have to be on top of the wall plate or can they be further up?)
c) a structural ridge (beam) needs its weight (and the weight it bears) transferred down into the end walls, but does not need rafter ties.

I'm fortunate that my back garden is around the 300sqm mark so even at the biggest I'd only be losing just over 10% to a workshop. 

I'd probably look in the direction of 6.5x4.5m ish with the 6.5m ridge so i imagine that's a large lump of tree to take the load or just use a steel. That'll be fun to lift :shock: I imagine a ridge board and rafter ties 1/3 of the way up the rafters is the substantially simpler solution at the cost of a little ceiling height (that my 186cm frame won't be using anyway :lol: )

I note that in Dom's thread (in a reply a year ago!) you say 


> Depending on your ground conditions, you may well not need anything below your slab other than sand blinding (to protect the DPM). Hardcore or Type1 /2 are for consolidating soft or wet ground, or for building up levels. If you don't have those conditions, then don't use it. As soon as spring arrives, you should dig yourself a trial patch in the area of your workshop, and see what the soil conditions are like. Ideally you'll remove the topsoil and bed directly onto the top of the subsoil, and if that is firm enough, just put an inch of sand over everything.



Can you elaborate on "ground conditions"? For example when calcs and things were done for the GSHP install 100m down the road we were told that its clay all the way down to something daft like 300m. I don't have to dig more than 75mm in my garden to hit clay. 

Also you obviously mention MOT type 1 as the aggregate. If I have a handy mountain of brick/concrete laying around on the farm and I also happen to know a man with a crusher, is that an option instead?


----------



## MikeG.

DBT85":1wahzzx2 said:


> ....Was originally thinking pent roof but now looking at apex with a structural ridge. If only I knew anything about any of it!......



Don't worry. I'll tell you what you need to do.



> a) a pent roof will need bigger rafters than a apex roof.



Probably, because the span is much further, but on smaller buildings the depth required for insulation is usually much greater than the depth necessary for strength.



> b) a non structural ridge (board) needs the walls tied together with rafter ties (do these have to be on top of the wall plate or can they be further up?)



The walls need tying (or prevention from splaying), but there are lots of ways of achieving this. You can for instance have one or two principle trusses and purlins. You can tie with a wire or rod. The ties can indeed be raised up the rafter, and the rule of thumb there is that they should be in the bottom third of the rafter length.



> a structural ridge (beam) needs its weight (and the weight it bears) transferred down into the end walls, but does not need rafter ties.



Pretty much, albeit you could have a large principle truss somewhere near the middle also supporting it. The whole point of doing a structural ridge beam (ridge purlin) is to avoid the use of ties.



> I'd probably look in the direction of 6.5x4.5m ish with the 6.5m ridge so i imagine that's a large lump of tree to take the load or just use a steel. That'll be fun to lift :shock: I imagine a ridge board and rafter ties 1/3 of the way up the rafters is the substantially simpler solution at the cost of a little ceiling height (that my 186cm frame won't be using anyway :lol: )



That's nicely under the 30 sq.m ceiling for buildings exempt from Building Regs. 
Finding a piece of wood 6.5m long would be your first issue. That would likely be either a timber "I" beam, or a glulam beam. However, if you put one principle truss in the middle of that span you could use two shorter ridge beams. The other approach, which I used in my workshop, was to have an orthodox tied section at each end of the roof, and then a gap spanned by a structural ridge beam. This gave me some really useful and easily accessible storage.



> I note that in Dom's thread (in a reply a year ago!) you say
> 
> 
> 
> Depending on your ground conditions, you may well not need anything below your slab other than sand blinding (to protect the DPM). Hardcore or Type1 /2 are for consolidating soft or wet ground, or for building up levels. If you don't have those conditions, then don't use it. As soon as spring arrives, you should dig yourself a trial patch in the area of your workshop, and see what the soil conditions are like. Ideally you'll remove the topsoil and bed directly onto the top of the subsoil, and if that is firm enough, just put an inch of sand over everything.
> 
> 
> 
> 
> Can you elaborate on "ground conditions"? For example when calcs and things were done for the GSHP install 100m down the road we were told that its clay all the way down to something daft like 300m. I don't have to dig more than 75mm in my garden to hit clay.
Click to expand...


With clay you need to look at the proximity of trees. If there are trees (or hedges) nearby, then you need to beef up the slab a little, because the clay will move up or down in changing conditions. This is precisely what I have here.



> Also you obviously mention MOT type 1 as the aggregate. If I have a handy mountain of brick/concrete laying around on the farm and I also happen to know a man with a crusher, is that an option instead?



Perfect! However, I say again, if you dig down and arrive at a solid base (ie no vegetative matter, no topsoil, no roots, no soft or wet patches), then you don't need hardcore/ Type 1 / Type 2. Your 6.5m x 4.5m slab on clay, assuming no trees and decent ground conditions, should be 150 thick, minimum, and have some steel mesh set in the bottom of it (40/50mm up). As you want 50mm above ground, your dig need only be 100mm deep. If that gets you to an even bed of clay, and there are no trees nearby, then you don't need any hardcore. If you are still in soft stuff at that depth, then dig through that to whatever depth is necessary to get to solid even clay, and build the levels back up to 100mm below ground level with consolidated hardcore.

A site photo and a drawing would be handy. It might be worthwhile starting a new thread.


----------



## DBT85

Thanks for all the details Mike.

Given the location vegetation is indeed an obstacle to bear in mind. It's a farmhouse so there is literally a hedge or tree on every border! The corner I'd most likely build in is where you can see the shed in this image. As you can see from the other google maps image, area to build in isn't a problem.

I'd most likely apply for planning anyway just to be able to build closer to the boundary than 2m while also going over 2.5m in height, that obviously negates any real need to stay under 30sqm but it's still a more than acceptable size. I'll go dig out your build thread and have a re read. I'll also be going through as many others as I can find to see what other pearls have been dropped in!















Naturally the 3 trees between myself and the shed would all be removed anyway (my mother in law was the brain behind planting trees in the middle of a %£&ng lawn) many years ago.

I absolutely will start a thread when i feel like its something i might actually start within 6 months or so. I don't want to go starting anything and then not get near it for 3 years! 

Given the vegetation and thereore (im guessing) likely need of substrate for the slab, would I also be looking at an even thicker slab? On the subject of the thicker edges how much thicker are we talking? 

Given that I have lots of spare time when I'm not actually at home to do anything (yay work) I would like to get as much of the build visualised in sketchup before I started any work other than an investigative hole. I think I've actually already made one to similar sizes including the individual bricks somewhere but the file may be gone.

I already have access to things like mini diggers via the farm as well as a tower of 50mm pir (oddly pale blue, no foil) at least 30ft tall. It naturally wouldn't be a cheap project but if I REALLY wanted to get it done this year I think I could manage it. Maybe.


----------



## MikeG.

DBT85":3phfajyc said:


> ......I'd most likely apply for planning anyway just to be able to build closer to the boundary than 2m while also going over 2.5m in height, that obviously negates any real need to stay under 30sqm......



Not so. You are confusing two entirely separate issues: Planning Permission and Building Regulations approval. Planning has no set limits on size, but Building Regs does. If you stay under 30sq m (internal floor area, and walls can take up a surprising amount of space) then you don't need Building Regs approval. If you go over 30 sq m you will need to put this building on orthodox foundations or on an engineer-designed raft, and this adds massively to the cost and trouble.


----------



## MikeG.

DBT85":27gdv87l said:


> ......Given the location vegetation is indeed an obstacle to bear in mind. It's a farmhouse so there is literally a hedge or tree on every border!.........
> 
> Given the vegetation and therefore (I'm guessing) likely need of substrate for the slab, would I also be looking at an even thicker slab? On the subject of the thicker edges how much thicker are we talking? .....



Ask a structural engineer and you'll get a 300-ish deep slab with an edge thickened to 500 or 600 ish all around, all reinforced with a cage in the edges and steel mesh top and bottom. My qualifications and insurance don't allow me to calculate these things myself, but if I were building it in those circumstances (clay and adjacent trees) I would make the slab 250 thick and have A142 mesh 40/50mm from the bottom and the top. This makes pouring the concrete a bit more awkward, and you should make sure you hire an electric (not pneumatic or hydraulic) poker to vibrate the concrete as it is poured.


----------



## DBT85

MikeG.":1ieiknp6 said:


> DBT85":1ieiknp6 said:
> 
> 
> 
> ......Given the location vegetation is indeed an obstacle to bear in mind. It's a farmhouse so there is literally a hedge or tree on every border!.........
> 
> Given the vegetation and therefore (I'm guessing) likely need of substrate for the slab, would I also be looking at an even thicker slab? On the subject of the thicker edges how much thicker are we talking? .....
> 
> 
> 
> 
> Ask a structural engineer and you'll get a 300-ish deep slab with an edge thickened to 500 or 600 ish all around, all reinforced with a cage in the edges and steel mesh top and bottom. My qualifications and insurance don't allow me to calculate these things myself, but if I were building it in those circumstances (clay and adjacent trees) I would make the slab 250 thick and have A142 mesh 40/50mm from the bottom and the top. This makes pouring the concrete a bit more awkward, and you should make sure you hire an electric (not pneumatic or hydraulic) poker to vibrate the concrete as it is poured.
Click to expand...

Thanks again Mike. I think it'll all have to be given careful consideration. A raft that thick and I could start thinking about what I'd need to do to go bigger and make a garage out the front which would all need planning and calcs anyway.

When you say 250mm think I assume that also means with thicker edges as well. 

Having never poured any volume of concrete let alone vibratediit, I'd maybe look to get the pour and labour done by others as its not a small easy pour. If I screw up the framing I can fix it but the options aren't as open for the slab.


----------



## MikeG.

DBT85":clttpf2t said:


> .......When you say 250mm think I assume that also means with thicker edges as well.......



No. Just a flat pour. It's one of the things an engineer always wants, but with a light building like these I have never had an issue with just a flat slab, and I reckon that at least 200 sheds/ workshops around the world have been built following the guide in this (and other) threads. My suggestion of 250 depth pre-supposes you find tree roots in the dig. If you don't, you could reduce the thickness to say 200mm.


----------



## DBT85

MikeG.":3kkt11rg said:


> DBT85":3kkt11rg said:
> 
> 
> 
> .......When you say 250mm think I assume that also means with thicker edges as well.......
> 
> 
> 
> 
> No. Just a flat pour. It's one of the things an engineer always wants, but with a light building like these I have never had an issue with just a flat slab, and I reckon that at least 200 sheds/ workshops around the world have been built following the guide in this (and other) threads. My suggestion of 250 depth pre-supposes you find tree roots in the dig. If you don't, you could reduce the thickness to say 200mm.
Click to expand...


OK, not quite so bad then. I'd be surprised if there are no roots, even the bloody bay tree that was in the middle of the lawn had sent inch thick main roots out in almost compass like precision. Though I don't think they were that deep. The difference in cost on a 250mm or 200mm isn't enough to worry about though.

My bigger worry is that the nearest a truck can get is probably 15m beyond the bottom left of the aerial photo.

7 cubes by barrow is a pitb and a pump only adds extra cost. Though I would easily be able to squeeze a small dumper through the opening to the field which would make life much easier and they look cheaper than the beer vouchers I'd need to hand out to barrow voulenteers :lol:

I'll ruminate further and get back to you with more!

While you sit eagerly waiting to give away your heard learned and earned knowledge for free, how long could I leave between the pour and starting further work? Is there any reason (I don't think there is) it couldn't be done now and not covered with workshop based entertainment for another 6 months?

I'm also still wondering about insulation in the slab or on it. If in it I'd go for the power float though maybe not to ice rink polish!


----------



## MikeG.

You can put insulation under the slab if you want, but maybe the best idea is a floating floor, with say 50mm of insulation above the slab and a ply or chipboard flooring on top of that. 

You can leave the concrete as long as you like before building on it. The longer you leave it, the stronger and harder it gets (well, you know, within reason). A dumper is a brilliant bit of kit, and more people pouring their own slabs should consider hiring one.


----------



## DBT85

MikeG.":2gwxytdu said:


> You can put insulation under the slab if you want, but maybe the best idea is a floating floor, with say 50mm of insulation above the slab and a ply or chipboard flooring on top of that.
> 
> You can leave the concrete as long as you like before building on it. The longer you leave it, the stronger and harder it gets (well, you know, within reason). A dumper is a brilliant bit of kit, and more people pouring their own slabs should consider hiring one.


 I was quite surprised to see a day rate for one being less than a cube of concrete. My back feels better just looking at it!

Can I ask why you have a penchant for Onduline? When I first saw the product I assumed it would be just dismissed with "get a proper roof".

Maybe I'll consider getting the slab down and then leave a few months getting everything else together.


----------



## MikeG.

That's really old, the original post. I think there are much better products now, even at the budget end of the scale. Don't get me wrong, in the right circumstances Onduline and its copies make a great roof for not much money, but I wouldn't really be advocating it today in the way I did way back then.


----------



## DBT85

MikeG.":24i1foyx said:


> That's really old, the original post. I think there are much better products now, even at the budget end of the scale. Don't get me wrong, in the right circumstances Onduline and its copies make a great roof for not much money, but I wouldn't really be advocating it today in the way I did way back then.


Ah OK!

Have you ever considered adding a short YouTube series to your catalogue? Could show photos of others builds to highlight things, answer common questions, explain a bit more the choices you have made? I think it would be a slow burner but it would get views for years and years.


----------



## MikeG.

DBT85":3l626uon said:


> Have you ever considered adding a short YouTube series to your catalogue?........



Erm........no.


----------



## DBT85

So I emailed Cemex who are all for a mile away for a quote. I think I'd need about 7m3

RC40 - 20G - S2 SLUMP - CEM1 – WRA

@ £113 per M3 + vat

Part load is £55 per M3. 

They only have 6m3 trucks, so that's £1280. :shock: 

It's been an off week for financial stuff with some ir35 decisions being taken at companies to work for as well as the in laws deciding that they don't want to help my kids nursery fees any more. So while I'm going to continue my planning and budgeting to get an idea of where I need to be, it may not be this year


----------



## DBT85

MikeG.":1uwpgdr9 said:


> DBT85":1uwpgdr9 said:
> 
> 
> 
> ......I'd most likely apply for planning anyway just to be able to build closer to the boundary than 2m while also going over 2.5m in height, that obviously negates any real need to stay under 30sqm......
> 
> 
> 
> 
> Not so. You are confusing two entirely separate issues: Planning Permission and Building Regulations approval. Planning has no set limits on size, but Building Regs does. If you stay under 30sq m (internal floor area, and walls can take up a surprising amount of space) then you don't need Building Regs approval. If you go over 30 sq m you will need to put this building on orthodox foundations or on an engineer-designed raft, and this adds massively to the cost and trouble.
Click to expand...


Mike, on this note. 

https://www.planningportal.co.uk/info/2 ... tbuildings



> Outbuildings and garages to be single storey with maximum eaves height of 2.5 metres and maximum overall height of four metres with a dual pitched roof or three metres for any other roof.
> Maximum height of 2.5 metres in the case of a building, enclosure or container within two metres of a boundary of the curtilage of the dwellinghouse.



So from a permitted development perspective. If building within 2m of the boundary, I can only go to 2.5m in height, correct? 

PP can give me permission to go to 4m and say only 30cm from the boundary regardless of its size? My mistake in the original quote was conflating 30sqm with PP rather than BR.

I am in the midst of making my own thread on the subject but Covid-19 and IP35 are likely to end all hope of doing it this year.


----------



## MikeG.

There are no numerical limits on what you can apply for under the Planning Permission regime. Each local council will have its own planning policies, in addition to the national ones, and these will inevitably talk about the form, massing, and relationship of the proposal to existing buildings. In other words, judgement on what is appropriate is down to the council.

As for your reading of the Permitted Development guidelines......As you said, if building within 2m of the boundary you are limited to 2.5m height unless you go for Planning Permission.


----------



## space.dandy

@MikeG. I'm building a shed which will be close to a boundary on two sides, so no access for maintenance. What would you recommend for the cladding on those sides? I see someone asked about Plastisol in 2018 further up the thread, is that the best option?


----------



## MikeG.

I've no idea what Plastisol is....but it sounds like it might be plastic-based. If it is, I wouldn't use it.

There are squillions of options if you look at a sheet material such as aluminium paneling (rainscreen)/ crinkly tin roofing, or cementitious boards, or render, or Onduline-type products, or EPDM. I lot is going to depend on whether you have access to fit the material after the wall has been built, or whether you've got to fix it to the wall then lift the wall into place.


----------



## space.dandy

MikeG. said:


> I've no idea what Plastisol is....but it sounds like it might be plastic-based. If it is, I wouldn't use it.



Some kind of plastic coated corrugated steel, I think. ObservantGround28 mentioned it above and you seemed fairly approving of it at the time.



MikeG. said:


> There are squillions of options if you look at a sheet material such as aluminium paneling (rainscreen)/ crinkly tin roofing, or cementitious boards, or render, or Onduline-type products, or EPDM. I lot is going to depend on whether you have access to fit the material after the wall has been built, or whether you've got to fix it to the wall then lift the wall into place.



I’ll have to fix first then lift in to place.


----------



## Sheptonphil

space.dandy said:


> @MikeG. I'm building a shed which will be close to a boundary on two sides, so no access for maintenance. What would you recommend for the cladding on those sides? I see someone asked about Plastisol in 2018 further up the thread, is that the best option?


I had that dilemma, I went with Hardie Plank cement based boards that look like painted timber cladding. The twenty plus colours have a fifteen year life before even considering any maintenance at all. That assumes you will have access for one day to actually fit the boards. I was at least able to add the membrane and counter battens as I built the framing panels. this meant the sides were weatherproof straight away.


----------



## ObservantGround28

space.dandy said:


> Some kind of plastic coated corrugated steel, I think. ObservantGround28 mentioned it above and you seemed fairly approving of it at the time.
> I’ll have to fix first then lift in to place.


Suggest you go down the plastic coated metal sheeting route. I ended up building out of dense blockwork with a fibreglass roof, but even now I'm 50/50 on that decision.


----------



## Crumblybiscuit

Just wanted to say thanks for all the information in this thread. I completely stumbled across the forums when looking for shed ideas. And it has been great. 

I work in IT and putting my mind to such a different task has been almost therapeutic. Although I am still unsure on a million things!


----------



## Lancashire Wood Studio

Super info, thanks.


----------



## HAMMERHEAD

FANTASTIC..... Just what ive been looking for... im literally just starting out as a hobbyist/ diyer and my little outhouse/ shed has very quickly filled up with just the basic tools , i now wish to purchase a table saw, thicknesser/planer and maybe a small lathe, so now i have to build a tidy size workshop
Thanks for taking the time to draw, illustrate, explain the process and sharing it....top man.


----------



## Myfordman

Mike no longer visits this forum but can be found on the woodhaven2 - the gentleman’s woodworking forum lol


----------



## kenpem

Many thanks, @MikeG. I'm just embarking on my own build (very slowly, so don't expect regular updates), and this thread will be invaluable.


----------

