Build a shed Mike's way

[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]

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.]

....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.

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.]

......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.]

......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]

......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.

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.