# My "shed" build (first timer!)



## Muzza80

Hi all, 
Just wanted to start a thread for the workshop/shed I've started.
I have to admit this is the first time doing anything like this and no doubt I may have done/plan to do things incorrectly so please feel free to steer me in the right direction if you see any vital errors, I'd really appreciate any advice anyone can offer along the way.

So the story is we've just moved from a top floor flat to a lovely fully refurbished and extended ex-council end terrace 3 bed house and finally we have some outside space for us all to enjoy, my 4 year old son love having a garden and simple things like being able to wash our own cars, hang out washing, put on a BBQ and so on are just so nice, it's amazing what simple pleasures you miss living in a flat!

So, I really need a decent size outdoor building, the tin shed at the bottom of the garden is leakier than a leaky thing and has to go ASAP as all my camping gear, expensive bikes, power tools and so on are currently at the mercy of the weather and we want to utilise that space in a total revamp of the garden starting next year. Ideally the previous owners kept a caravan at the bottom of the drive, it's an area built up with sleepers and ideal for the 14x9 "workshop" I've started. Sadly I'm limited to 2.5m max height as the building will be within 2 foot of the neighbouring property.

I've looked at pre-fab "sheds" and have either been extremely unimpressed or blown away with the cost of some of them and I'm convinced I can do as good, or hopefully better than the offerings and for a lot less then some of the higher end stuff, I'm keen to keep it under £1500 (not including some tools I've purchased) and it's to be fully insulated with power and more than a shed, would be nice to have a proper little outdoor "room" that can house an iMac computer, all my tools, good workbench space and so on. I have amassed a fair amount of tools over the years, mostly car related as i work on my own and friends cars regularly but I have the essentials I need for doing this too I think.


Anyway, on to some pictures which I'll explain on the way:


This is the area in question, picture does not show it very well here but essentially minimal slabbing, approximately 18 foot long by 9 and a bit foot wide (retaining sufficient space to access the cars and drive and get the bins out). 










So the groundwork starts, removed nearly 2 tonnes of chips from the area alone, the ground under them was very uneven and they just threw as many chips as it took to level it out I think







Originally I'd planned building it 16 x 9 and much closer to the monoblock drive and also having a wood store to the rear however upon lifting the existing slabs and breaking up the mortar pads they sat on I uncovered a bloody manhole cover, and a new one at that!?? Odd thing was that our drain is further down the garden and upon opening the manhole it was pretty obvious it had not been in use for a very long time, there was debris, bits of brick and all sorts in the channel where the waste would run, so why the new cover?? So a quick email to the previous owners and it was explained that many years ago the council re-routed the system and this had been "decommissioned", the reason for the new cover was that there was a very old, large and thick domed iron cover on it and they changed it to a low profile one simply to allow them to get their caravan in there and they simply fitted it and then slabbed on top of it!!?













Anyway, wouldn't be at all comfortable building on top of that, knowing my luck they would want in there at some point and the shed would have to be dismantled so now unfortunately it's got to be 14 x 9 and further down.

So I put up a little shuttering just to section off the area and keep the chips from collapsing in and ended up excavating down about 6 inches or so in total and made it as level as i could by eye, got 3 tonnes of type 1 sub base, lined the bottom with a layer of driveway fabric/weed control barrier and started barrowing in the sub base then borrowed a whacker from my neighbour and whacked it down. Took the full 3 tonnes to get it to the level I wanted too! 
































So, sub base sorted and i had to decide if I wanted to go the poured slab route or re-use all the 2x2 and 3x2 "council" concrete slabs I had dotted around all over the bottom of the garden, in the end for cost reasons I decided on the latter, may as well use them and save the £300ish I was quoted it would have cost in having concrete delivered. Also saved me the hassle of having to get rid of all these slabs at the same time. 

So I ordered up a tonne of sharp sand and some bags of cement and laid the slabs on a 6/1 dry mortar mix, now this again was the first time doing this and a couple of the slabs were off level a bit, certainly not perfect but I have a plan for that which I'll explain in a bit but on the whole not awful for a first attempt I hope?








So next up was to get the timber for the base, gone for tanalised 4x2" framework which is sitting on 4 - 4x2" tanalised bearers laid flat to spread the load and support the joists whilst giving a clear 2 inches of ventilation space under the whole base, I'm hoping that is sufficcent?












And here's the finished base framework, the joists are at 16" on centre spacing.








Now you can probably see that I've chosen to screw it together rather than nail. I've since been reading that possibly this is not ideal and nails are better however I wanted to be able to correct any errors I made easily and as I'm going to be doing this over a period as and when the weather allows the cost of hiring a Paslode for a day or two at a time, multiple times, was going to just be too expensive. 

I've gone for TurboUltra A2 Stainless 90mm screws with pilot holes and used 3 per connection, I hope I'm not making a terrible mistake doing this, seem to be mixed opinions, plenty use them plenty say not to?

So that's where I'm at, I've 5 sheets of 18mm exterior plywood waiting to go on just as soon as my 50mm polystyrene insulation sheets arrive in the next couple of days and I can fit them.

I've also got 250m of C16 treated 4x2 timber coming tomorrow for the rest of the framework and roof.

The plan is to fit 2 second hand UPVC windows door on the side and one UPVC window at the bottom end, thinking this should work nicely and pretty cheap to pick up on Gumtree and the likes, because of the height restrictions I'm limited to the roof will be pent sloping using 4x2 C16 but I'll double it up full length or use sister joists giving me the span strength and maximising internal head room as much as possible (I'm already going to be 8 inches to floor level with the ply on!) plus the C16 4x2" was a fantastic price on special from my local timber place. I'm hoping that doubling up is acceptable? 

One question I do have.....

As I mentioned a couple of the pavers are a little lower than the others where the bearers run over them, I've taken some 4x4 slices from a tanslised fence post and I've treated them both sides with Ensele End Grain Preservative (same as I used on the cut ends of the tanslised framework), I was going to shim the areas that are a little low with these treated slices, it's just a few areas maybe 1cm or so, am I bonkers doing this or is that acceptable?

Anyway I'll update as I go, appreciate all comments good or bad and any advice would be greatly appreciated.

Thanks!


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## adidat

Looks good, if I where you I would have carried on regardless and made and access hatch above the drain. Also it would be good to put a membrane between the slabs and timber, as they will rot quite quickly from rising damp.

Adidat


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## flying haggis

nice work so far, but before you go too much further can I suggest that you purchase some DPC, the 6in wide rolls, not the large sheets and put that under any bearers that are in contact with the slabs. that will stop any moisture seeping up into the wood. if you can fix it at each end and not have any fixings along the length so much the better

edit adidat types quicker than me....


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## Fitzroy

My roof is 6x2 on 600mm centre with 18mm Osb on top, span is 308cm and walking on it is fine. If you look up joist span tables online they will give you a better idea on your plan. You may be better have narrow joist spacing rather the doubling up each joist. I'd do a test with a few lengths between bricks at the expected spacing and see what you think. With 150mm floor and ceiling joists on my build there would have been noway to stay under 2.5m.


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## Muzza80

Cheers for the replies.

I was originally thinking the same re: DPM but the timber merchant I got it from assured me as it's pressure treated tanslised timber that there was no need, they're specifically designed to be used outdoors just like their sleepers they sell for garden use? I suppose it's next to no cost so I may as well do it, thanks for the heads up!

Re: the drain, it's too high with the cover on, I'd need to raise the enture area aother 2 inches and that would eat right the overall height, the only way would have been to remove the cover entirely, take a layer of the brick course away and cover it with a steel plate or something and that's a faff and too permanent for my liking. so the plan now actually is we're going to utilise that area there as a bin store, the council have now given us 4 full size wheelies to use as of October so we can tuck them away around there out of the way and close to the street rather than sitting in the garden. Might even manage a little woodstore in there too.

*Fitzroy* - Regarding the roof span, according to the tables even at 16" centres (400mm) I'm limited to less than 2m, but at my 9 foot span (assuming you take the span as the distance between the supporting walls with no overhang included) I'm actually 2.75m. In the same boat as you regarding the height limit so every inch counts, hence either doubling up on the 4x2 C16 or maybe screwing and gluing ply to one side of each. It's not going to be a heavy roof by design, I think I'm going to go 12mm ply and EPDM but we can get a lot of snow here. I like your suggestion though, if I went to 12 inch centres I bet that would be fine, not sure where to check that to be certain though as the tables show fixed centres?

Cheers!


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## Halo Jones

Good start!



> In the same boat as you regarding the height limit so every inch counts



The rules in Scotlland are different from England so you might get away with more than you think:


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## Fitzroy

There is an online calculator called the sagulator which does the bending calculations for shelf sag. Using this I compared the sag on a 4.5 X 14.5 beam vs a 4.5 X 9.5 beam. For the same span and loading the shallower beam deflected 3.6 times as far, which shows why beams are deep. All the maths is linear so you'd need 3.6 times as many joists for the same deflection. So if 6x2 is ok for 600mm centres you'd need 4x2 at 170mm centres. 

Edit: I've a bit of spare time this morning I'll see if I can find some other calcs.


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## Phil Pascoe

I wouldn't shim with timber, I'd either find some slates or bed the timbers in mortar where they need building up - I wouldn't chance small sections of timber in a place where they can't be replaced without serious work. Sleepers are treated for years of full ground contact, treated 4" x 2"s aren't. When you look at your cut ends, you'll see where the colour changes - that's where the protection ends, which is why you treat the ends. It doesn't take more than a little damage or for much of a crack to open up to get through this layer, which is why it's wise to use a DPM.
It's a pity this Country doesn't use a H Rating system like NZ, where you know what you're buying. H = hazard, and it goes from one to six, with six being for permanent ground contact. So simple.

For above ^^^ -
http://www.woodbin.com/calcs/sagulator/


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## Muzza80

*Halo Jones* - I cant believe I never seen this before, this could change everything, looks like an apex roof is definitely an option then, I'll need to do some calculations, thanks!

*Fitzroy* - Thanks for that info re the sagulator, that helps loads cheers, certainly confirms that doubling up will work but looks like an Apex might be on the cards anyway, never realised Scotland's PP rules were different!

*phil.p* - That sounds like wise advice and as it happens I've a load of slates sitting at the back of the garden, brilliant idea, thanks!


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## Halo Jones

Things may have changed slightly since I last looked at permitted development but the current booklet can be downloaded here:

http://www.gov.scot/Publications/2016/06/2685/downloads

I think it is a very handy booklet!


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## Muzza80

Thanks for the link, confirms what you said, good news!  


Took the advice from the first two posters and fitted a DPM to the 4x2 bearers. I used stainless staples to secure it and also a bead of silicone right along the external edge and ends, the DPM edges on the outside will be overlapped by the cladding anyway but better to be safe than sorry I guess.








You might have spotted the Paslode, it's an IM350+ and I picked it up on Gumtree yesterday for the bargain price of £200 in superb condition and I used it to secure the bearers to the frame from the bottom (now protected by the DPM) which has made the whole thing extremely solid and holding square perfectly, great tool, will make this whole build a lot easier I think. 

Also took delivery of nearly 250m of 4x2 for the rest of the framework/roof and whatnot, probably ordered too much but I'll use the extra elsewhere once this is done.


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## Fitzroy

Muzza, I don't want to be the bearer (no pun intended) of bad news but pretty sure the DPM needs to be between the concrete slabs and the bearers. The issue is that the ground and concrete slabs are fundamentally porous, so moisture will be continually wicked up through the slabs and into your bearers, so the bearers will be constantly wet which will shorten their life. Yes, you can get rain on top of the dpm, that will soak into the bearers, but this will be an occasional and temporary issue as there should be some airflow under the shed that will dry this situation out between inclement weather periods.

Envious of the pasload, i looked out for one on gumtree for my build for ages but one never came up at a good price. Ended up nailing my by hand, with the resulting blisters for my keyboard jockey hands, bet you never knew you can use Compeed on your hands, it works a treat to get back to nailing when the weather is good and you have to keep going.

F.


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## pcb1962

Fitzroy":1timfrkd said:


> Muzza, I don't want to be the bearer (no pun intended) of bad news but pretty sure the DPM needs to be between the concrete slabs and the bearers.


ITYF he's turned the base upside down to attach the DPM.
I would have just laid it on the slabs, not stapled it to the bearers.


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## Fitzroy

Hmmm, now i feel stupid  . So temping to delete my post


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## Muzza80

Fitzroy":3ohvu8f0 said:


> Hmmm, now i feel stupid  . So temping to delete my post



Not at all, I'll make daft errors along the way I'm sure so please feel free to point anything out no matter how obvious! 

Yes that's the base upsides down, I needed to attach the bearers to the base anyway and rather than toenail from above, seeing as I was going to be lifting it and fitting a DPM anyway I decided to do it all neatly and essentially encapsulate and seal the bearers from the elements, I was thinking thinking laying strips of it on the slabs and just laying the bearers on top would potentially allow run off water, rain, snow melt over the top of the DPM and then in turn into the bearers? 

Mabye over thinking it but not much extra effort to do it this way and it's nice and neat too 




Fitzroy":3ohvu8f0 said:


> Envious of the pasload, i looked out for one on gumtree for my build for ages but one never came up at a good price. Ended up nailing my by hand, with the resulting blisters for my keyboard jockey hands, bet you never knew you can use Compeed on your hands, it works a treat to get back to nailing when the weather is good and you have to keep going.
> 
> F.



Yeah it was a great buy at that price, I'm planning doing some fencing and decking in the garden too next year so it will pay for itself I'm sure, I'll always be able to sell it on, probably for more than I paid for it once I'm finished with it too, win win really.


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## Muzza80

Insulation arrvied.

It's 50mm EPS70 and i got 18 sheets for £150 delivered, not bad.








Weather's been horrendous so no more progress on finishing the base, so this morning I went on the hunt for windows, picked this up from a local UPVC place for £45.







It was a mismeasured unit, frosted glass, tilt and open, 850x750, brand new with sill, handle, vents and so on, ideal for the end wall.

Also got a lead on one double wide one, opens out, again brand new with sill and so on, £50, ideal for the side facing the house where the door will also be.


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## Muzza80

So, finally a couple of days of decent weather this weekend, managed to get the base insulated and covered with 18mm exterior grade ply.

Also built 3 of the walls and test fitted the window I picked up last week.




































Need to find a door now, cant continue until I do, also need to pick up the double wide main window I sourced on Gumtree.

To give you an idea of what I'm aiming to achieve, this is pretty much what I want but without the door on the end.


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## Muzza80

So a little update if anyone's interested.


Got the other window, door, 9mm OSB for outside sheathing, Permavent breather membrane, batton for the cladding (yet to be purchased) and also decided to go with 6x2 for the roof in the end.














So yesterday I enlisted the help of a friend and for all the walls up, sheathed and wrapped in breather.....
























The windows and door I'm wrapping in a dark grey vinyl for a more modern look rather than the brown, I've done a fair bit of wrapping on cars in the past so windows and doors are pretty straight forward in comparison, here's something to give you an idea....









Now to make a start on the roof!


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## MattRoberts

Wow - great progress! Coming along really well. Although seeing the chop saw and stand filling up the footprint really gives it perspective


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## Muzza80

MattRoberts":ggav2eq4 said:


> Wow - great progress! Coming along really well. Although seeing the chop saw and stand filling up the footprint really gives it perspective




Cheers!

To be fair the saw/stand are big, but no, it's not a huge building, just 14ft x 9ft but really very adequate for what I need and should be nice and light with the windows and door being quite big.


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## Fitzroy

Looking good, i was about to say you need to crack on with the roof. I had a tarp up in a similar fashion and with the angle of the roof it was impossible to get the tarp tight enough to stop water pooling, eventually it collapsed (in the middle of the night). If you can't get the roof on before rain arrives I found a couple of 4x2 lengths could be used as uprights to push up the middle of the tarp and create the angle required to ensure water couldn't pool.


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## Muzza80

Cheers for the tip, we're due some rain tomorrow actually so have propped it up in the middle with a long pole which will hopefully do the trick.



Had a couple of hours spare tonight so wrapped one of the windows, turned out good I think:


*BEFORE* 








*
AFTER*


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## Dandan

That looks really neat, the colour is much more modern.
Did you disassemble the unit at all before wrapping? I only ask because I wrapped a window frame in situ and found it very tricky to get a good stick on some of the small returns, it would have been nice to be able to wrap into some of the joins. That was only on the interior side of a window and it started to shrink away from some of the edges after only a few weeks.
To be fair, it was a thick, laminated, full-colour print, I guess you used a decent wrapping vinyl and heated it after application? (I used to be a sign maker too!)


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## technium

Looks great mate. Can I ask where you got your eps70 insulation so cheap as I need to order some insulation for my workshop.

thanks

Colin


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## Muzza80

Dandan":21ltpuwy said:


> That looks really neat, the colour is much more modern.
> Did you disassemble the unit at all before wrapping? I only ask because I wrapped a window frame in situ and found it very tricky to get a good stick on some of the small returns, it would have been nice to be able to wrap into some of the joins. That was only on the interior side of a window and it started to shrink away from some of the edges after only a few weeks.
> To be fair, it was a thick, laminated, full-colour print, I guess you used a decent wrapping vinyl and heated it after application? (I used to be a sign maker too!)



Hey mate, thanks, yeah looks ok.

So this window I obviously removed the vents and the mini-sill then simply opened up fully, did the window first then the frame after with the window closed, the double window I'll need to remove the windows from the frame I think as they dont open out enough.

It's proper automotive grade vinyl and I carefully wiped down everything with IPA first, I actually didn't use heat at all, that way it shouldn't shrink. Just used a very sharp craft knife for the cuts.





technium":21ltpuwy said:


> Looks great mate. Can I ask where you got your eps70 insulation so cheap as I need to order some insulation for my workshop.
> 
> thanks
> 
> Colin




Hi Colin, yes sure it was from eBay here: http://www.ebay.co.uk/itm/272051628415

When it arrived it's actually Jablite branded "Classic EPS70" , good stuff, closed cell so not too messy to cut up using a very sharp carving knife which I re-sharpened every dozen cuts or so.


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## technium

Thanks mate, will add it to favourites and look into getting some once I return from holiday as workshop not arriving until 23rd October so bit of time yet.


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## Paul200

Loving the wrapped windows. Learn something new every day....


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## Muzza80

Made some good progress in the last 48 hours.

Got the roof made, went 6x2 600mm centres with a decent overhang front, smaller one rear and sides, the sides I hung an extra joist using a timber "ladder" supported by a triangular frame on each side wall.

I cut birdsmouth's on the joists and also used truss clips, no noggins as yet but may add them depending on advice?

I finished up the OSB to the sides and finished the wrap too.

I've roughly fitted the door as a temporary measure, sealed the frame against the wrap using a decent waterproof tape along the join just up to the second layer of breather membrane to keep it all watertight and allow me easy access for now, of course I still need to wrap the door and other window in vinyl before fitting properly.

I only put 4 of my roof OSB sheets up for now just with a few screws to secure them, I need to plan the roof properly and do a few cuts plus it started to rain last night and I just needed to get it covered ASAP. We're now due 5 days of heavy rain and it's already windy I just hope the tarp stays put, it's stapled on all the way round and nice and tight so fingers crossed! 

All comments appreciated! 


































And a little panoramic shot of inside, not sure how this will display being so wide...


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## Fitzroy

Looking great! Very similar to mine, but you're about equal with my progress even though you stated later so you'll be ahead of me soon. I'm starting to regret my decision to make my windows! I found my roof did not need noggins except at the edge of the roof boards. With the 18mm Osb screwed at 150mm inetervals the whole lot is solid, just needed noggins to support the Osb edges. What are you finishing the roof with?

Fitz.


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## Wizard9999

Just read from the first post through, very tidy work indeed =D> 

One question / concern. Why did you clad the outside with OSB before putting the membrane on? My understanding is that OSB is so full of glue it is basically a vapour barrier, so having that directly next to the membrane appears somewhat self defeating as no moisture will get through the OSB. I had understood that the OSB goes on the inside face of the walls, then the insulation, then the membrane, then the cladding. That way any moisture that gets past the OSB vapour barrier into the insulated cavity can escape through the breathable membrane.

I have just checked and it is covered in this post, Mike no longer posts here but he is an architect and he knows what he is talking about.
build-a-shed-mike-s-way-t39389.html

In the post Mike say "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. "

Sorry for pointing this out after the membrane has gone up, but as I say, only just read the thread.

Terry.


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## Fitzroy

Terry, Muzza and I seem to have had the same shed dream as our builds are so similar! With regards the Osb on the outside it is not there for a vapor barrier just as a structural element. Sheathing in Osb then wrapping in breather membrane allows you to get the structure solid and weather proof very quick. You can then clad at your own pace and as the weather permits. When the inside is completed it will need an internal vapour barrier (more Osb) or foil backed plaster board between the interior and the insulation. 

Well that's my understanding anyhow!

Fitz.


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## Harbo

On my shed build, because of bad weather, I installed the membrane first ( which kept out the rain ) then the insulation (from the inside), then the internal OSB and finally the battens and outside cladding. No need for two layers of OSB.

Rod


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## Wizard9999

Fitzroy":2350c67q said:


> Terry, Muzza and I seem to have had the same shed dream as our builds are so similar! With regards the Osb on the outside it is not there for a vapor barrier just as a structural element. Sheathing in Osb then wrapping in breather membrane allows you to get the structure solid and weather proof very quick. You can then clad at your own pace and as the weather permits. When the inside is completed it will need an internal vapour barrier (more Osb) or foil backed plaster board between the interior and the insulation.
> 
> Well that's my understanding anyhow!
> 
> Fitz.



Fitz

The problem is that even though you have it there as a structural element it is a vapour barrier. So, if any moisture gets into the wall cavity it will become trapped by the outer layer of OSB? I have just looked it up and the risk you run with that wall structure is called interstitial condensation (I've seen that phrase used on here in past workshop discussions). The inner lining of OSB will give all the structural rigidity you need so once that is on the outer layer performs no function but does risk causing you a problem. Plus two layers of OSB costs twice as much as one layer.

Not trying to be difficult, just trying to save you a problem down the line. But hey, maybe it is one of those theoretical things that won't materialise in any of our life times  

Terry.


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## Muzza80

Wizard9999":2ii78pmu said:


> Just read from the first post through, very tidy work indeed =D>
> 
> One question / concern. Why did you clad the outside with OSB before putting the membrane on? My understanding is that OSB is so full of glue it is basically a vapour barrier, so having that directly next to the membrane appears somewhat self defeating as no moisture will get through the OSB. I had understood that the OSB goes on the inside face of the walls, then the insulation, then the membrane, then the cladding. That way any moisture that gets past the OSB vapour barrier into the insulated cavity can escape through the breathable membrane.
> 
> I have just checked and it is covered in this post, Mike no longer posts here but he is an architect and he knows what he is talking about.
> build-a-shed-mike-s-way-t39389.html
> 
> In the post Mike say "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. "
> 
> Sorry for pointing this out after the membrane has gone up, but as I say, only just read the thread.
> 
> Terry.




Hi Terry, cheers for the reply.

Yes you're quite right and I had originally planned to build it with no sheathing on the outside however I needed to give it structure, quick, the weather has taken a really bad turn for the worst here and we had some heavy wind there on Friday just after I managed to get the roof up and tarped. This way the build is totally weather proof at an early stage and I can deal with the cladding, insulation, electrical work and interior final finish at my leisure.

For the extra £100 odd for the 9mm OSB3 it seemed like the way to go and I'm glad I did because I doubt my breather membrane would have survived the wind we've had here over this weekend had it just been fitted to the framework.

Of course I'll be fitting a proper VCL internally too, I've read that actually OSB is pretty vapour permeable?

So a little extra cost, yes, but it's allowed me to beat the weather and I can now continue inside in dry conditions as and when I have the time which is what I needed


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## Fitzroy

Wizard9999":uu76o936 said:


> Fitz
> 
> The problem is that even though you have it there as a structural element it is a vapour barrier. So, if any moisture gets into the wall cavity it will become trapped by the outer layer of OSB? I have just looked it up and the risk you run with that wall structure is called interstitial condensation (I've seen that phrase used on here in past workshop discussions). The inner lining of OSB will give all the structural rigidity you need so once that is on the outer layer performs no function but does risk causing you a problem. Plus two layers of OSB costs twice as much as one layer.
> 
> Not trying to be difficult, just trying to save you a problem down the line. But hey, maybe it is one of those theoretical things that won't materialise in any of our life times
> 
> Terry.



Terry,

It shouldn't particularly matter, you will have a thermal gradient through the insulation, if the temperature at any point falls below the dewpoint of the air permeating out of the building then condensation will occur. The outer Osb layer would make it more difficult for the insulation to dry out when the weather conditions are more favourable, however I'd expect if you are getting condensation within the insulation it's all a moot point anyhow. Hence the vapour barrier goes on the warm side. I think what I will do though is go overboard on the vapor barrier, rather than just rely on the foil backed plasterboard! 

Mine's been 'OSBed' for a while so no getting rid of it on my build now! Interestingly on nearly all the sites and vids I found on vertical cladding (my covering of choice) there is an outer layer of Osb, or similar. History will be the judge 

Thanks for the thoughts. 

Fitz


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## Muzza80

Fitzroy":c0r8jjs5 said:


> Looking great! Very similar to mine, but you're about equal with my progress even though you stated later so you'll be ahead of me soon. I'm starting to regret my decision to make my windows! I found my roof did not need noggins except at the edge of the roof boards. With the 18mm Osb screwed at 150mm inetervals the whole lot is solid, just needed noggins to support the Osb edges. What are you finishing the roof with?
> 
> Fitz.




Your windows are a work of woodworking art, extremely impressed and I'm sure they will be well worth the work!

I'm going EPDM same as you, seems like the simplest/most reliable solution. Can I ask what you used as a sub-facia at the front and rear ends of your roof joists? I was going to use 2 extra lengths of 6x2 I had but starting to think 2" is too much and I might be better off with a 1x6 tanalised facia board, I intend to use the classicbond kerb edge and gutter trims for finishing the EPDM but they're quite small so I need something weather proof to fit them too and something that's a minimum of 6 inches to finish the ends of the roof properly, does that make sense?

P.S where did you buy your EPDM kit from? Best I've found myself is nearly £340!

Cheers!


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## Fitzroy

Haha, I had to google sub-fascia! Mine is a piece of 6x2, mainly just because that's what I built the rest of the roof out of. I'm sure 6x1 would be fine and would be easier to man handle into position. I did however keep the OSB back 18mm from the edge of the 'sub-fascia' and added a 18mm quadrant trim to the roof edge to give it a rounded over look.

I've not used any trim on my roof, the thought being the front and side edges will not see any real flow off of them as all the water will fall to the rear. On the rear my roof drips (will drip) onto 40-50mm Scottish pebbles which will hopefully prevent splashback onto the woodwork, if not I’ll install a gutter. So far the roof is glued to the main deck but not to the sub-facia as I’d not entirely got my mind around how it was going to work, your post has pushed me to work it out the details!

So my plan is the edges on my roof are being glued to the sub-facia’s face and under edge, then having a ‘drip strip’ tacked on the underside with a larch strip (offcut of cladding) fastened with a stainless fastener, then the soffit (google again) is located a centimetre or so back from the drip strip. The idea is to have zero penetrations through the EPDM when it is on a face with active water flow, I’m basically trying to minimise the possibility of rain water getting to my woodwork. See images below, as they say a picture is worth a thousand words.

Because I did not need a kit I bought the roof membrane from ebay, link below, this was the cheapest I could find EPDM without buying 0.75mm pond liner which I thought was too thin and couldn’t convince myself of its UV properties. Anyhow, I bought a piece 7mx4m and my roof is 6.2mx3.6m, I have lots of overhang to the sides, but it’ll be close front and back to get the wrap under the edge and drip strip in place.
http://www.ebay.co.uk/itm/FIRESTONE-RUB ... Y2tXnKt3BA

I bought the water-based adhesive 5L (used on the main deck) and contact based adhesive 2.5L for the edges and vertical elements direct from Permaroof (same supplier as the ebay listing but the membrane is more expensive on the website). The quantities of adhesive were plenty, I could probably have gotten away with a smaller pack of contact adhesive (1.5L) but they did nothing smaller.

Total including vat and delivery was £272, my roof is 22.3m² so £12.20/m², your sheds 70% the length of mine so prorated you’d be at £190, £340 sounds pretty steep.

Fitz.

Roof details


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## Muzza80

Thanks for all the info Fitz, much appreciated.

You're right, a lot of that cost is in the trims and also despite the 30% difference in size, I still need the 5L of WBA and the 2.5L of contact adhesive.

I've been back and forth to a few suppliers and I've managed to get that price down considerably through pricematching/beating, currently with Rubber4Roofs with a ClassicBond 1.5mm premium membrane, all the edge trims, corner trims and gutter trim, fixings, adhesives and so on for £306 delivered or £275 if I go for the "standard" 1.2mm membrane (I'm tempted with the thicker for no other reason than it seems not a lot of money extra). For the same prices (through price matching) I can get the Firestone system from Permaroof although that's using their own adhesives and I've read on here that some have had issues with them and bubbling? Firestone's own stuff is supposed to be superior but it's a fair bit extra where as with the Classic Bond option, that's supplied with manufacturer adhesives and better quality trims which might just sway it for me. 

I really like your plan to cover your facias with the membrane and tuck, and the 18mm quadrant will make a nice smooth transition between facia and roof deck, good thinking, can I ask though, did you trim 18mm off your roof boards to accommodate the quadrant? If I was to do similar (given it's such a good idea!) I'd have to or the boards would not sit in line with the roof joists and therefore wouldn't be supported properly, not a big deal to trim off 18mm I guess.

The reason I think I will go for the trims is that unfortunately, one side and the back wall are right next to ground level sleepers, if I didn't trim then the splash from those sleepers would be an issue I'm sure, really I need to have edge trim and guttering at the rear but I may do a combination of both, trims and also full length membrane covering the facias, that way like you rightly point out you're properly protecting the facia timbers, they will never need treated and it should look pretty good too I think.

One thing, fully overlapping the full roof down the facias, you will be left with excess at each corner, kind of a "flap" if I'm, getting it right? What's your plan for that, cut it out then seal the seam with sealant or fold the "flap" back against the facia and bond it on there?

Thanks again for the reply, it's all very helpful! 

Murray.


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## HOJ

Fitz, I am not sure about your flat roof design, I fear that wind blown rain will not obey your theory of water just running off to the rear, and as such will be pushed or pulled against the walls either by force or suction. 

Also not wishing to start a debate on the merits of OSB "inside or outside", I build timber frames structures for residential use,
I use construction methods defined by Trada and also design analysis for thermal calculations, all of which give me compliance with Building Regulation requirements, although none of which is applicable to sheds

The following texts are exerts from Trada Specifications which may be of use: 

"All timber frame walls are designed to 'breathe'. The term 'breathe' refers to the ability of a wall to allow water vapour to diffuse through the structure.

This is an important consideration to the long term durability of the timber structure.

*The breather membrane performs a number of functions in a timber frame wall:*
• It protects the fabric of the building from rainwater penetration during construction before external claddings are completed.

• It provides a second line of defence against water penetration during the life of the building as most claddings act as rainscreens, rather than as complete barriers.

• It allows water vapour to escape from the construction.

• It can also contribute to air sealing the wall and reducing ventilation heat losses and wind washing through insulation layers. This aspect is of increasing importance as air leakage is now an important part of the thermal performance requirements under building regulations. 

• It should be lapped and detailed to deflect water away from the timber frame, e.g. at cavity barriers, cavity trays, window openings etc.


*A breather membrane is required to protect timber frame walls:*

• where the outer sheathing of a conventional timber frame wall is oriented strand board, plywood or certain types of medium board – this is the usual method in the UK
• where the sheathing is on the inner face of the wall, so-called ‘reverse wall’ construction
• where additional layers of insulation are installed over the outer face of the timber frame structure.

*A conventional timber frame wall design, generally comprises (starting on the inside): *

• plasterboard
• a service void may be present containing additional insulation
• vapour control layer
• solid timber studs with insulation between
• oriented strand board (OSB) sheathing
• breather membrane
• drained and vented cavity
• external cladding.


*Condensation risk*
There are two types of condensation – surface and interstitial (within the wall structure).
Surface condensation is visible to and largely generated by the actions of occupants. The risk of surface condensation is also increased with the presence of thermal bridging (e.g. at junctions between elements). NHBC guidance note Condensation in homes [3] explains how to control surface condensation.

Interstitial condensation is condensation that occurs within the structure of wall (or roof or floor). There is a rule of thumb to ensure that interstitial condensation cannot occur – the vapour resistance of the layers on the warm side of the insulation should be at least five times that of those on the cold side. This controls the flow of water vapour by ensuring that it escapes more quickly through the outer layers of the wall than it can enter through the inner layers."



Hope this helps in some way.


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## Muzza80

Helps greatly HOJ, thanks.
Thankfully confirms Fitz and I are not bonkers for sheathing the outside in OSB.

Thanks again!


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## Wizard9999

I agree that the post by HOJ is really interesting and helpful. If I understand the extract correctly the key is that if you have OSB on the outside of the frame you can't rely on OSB alone on the inside, as by definition the vapour resistance will be 1:1 and not the recommended 5:1. But from your post you are using a 'proper' vapour control barrier on the inside which I presume is designed to give exactly what is needed.

Terry.

Edit: weather came on just after I posted this, certainly sounds like a good thing that you have structural integrity as it sounds like it is going to get seriously windy later this week!


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## Muzza80

Wizard9999":2u4hlisx said:


> I agree that the post by HOJ is really interesting and helpful. If I understand the extract correctly the key is that if you have OSB on the outside of the frame you can't rely on OSB alone on the inside, as by definition the vapour resistance will be 1:1 and not the recommended 5:1. But from your post you are using a 'proper' vapour control barrier on the inside which I presume is designed to give exactly what is needed.
> 
> Terry.
> 
> Edit: weather came on just after I posted this, certainly sounds like a good thing that you have structural integrity as it sounds like it is going to get seriously windy later this week!




I say that but I have not picked anything as yet, I'm assuming a polythene sheet material will do the job, I'll need to have a look.

You're right about that, even last night it was gusting up to 50mph here, I'm seriously concerned about this tarp I've currently got on the roof, really need to get the roof boarding finished and EPDM down ASAP, looking like Sunday (incidentally, my birthday) is the only dry day for the next while so hopefully get it done then, the wife's not going to be happy as she wanted to go out for a nice lunch haha, sorry dear!

I ended up ordering a 4m x 5m, 1.2mm membrane Classic bond kit from rubber4roofs with everything I need including edge kerb and gutter trims, arrives tomorrow, not too bad at £280 delivered.


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## HOJ

Wizard9999":1xrjintz said:


> I'm assuming a polythene sheet material will do the job,



The vapour resistance of a material is a measure of the material’s reluctance to let water vapour pass through. The vapour resistance takes into account the material’s thickness, so can only be quoted for a particular thickness of material. It is usually measured in MNs/g (“MegaNewton seconds per gram”).

Typical values are as follows: (I have put the values in order of permeability)

Breather Membrane 0.6 MNs/g
Vapour check plasterboard 60 MNs/g
0.12mm polythene sheet 250 MNs/g
0.25mm polythene sheet 500 MNs/g
Aluminium foil 7500 MNs/g

Again, hope this helps.


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## Wizard9999

HOJ":2msjprai said:


> Wizard9999":2msjprai said:
> 
> 
> 
> I'm assuming a polythene sheet material will do the job,
> 
> 
> 
> 
> The vapour resistance of a material is a measure of the material’s reluctance to let water vapour pass through. The vapour resistance takes into account the material’s thickness, so can only be quoted for a particular thickness of material. It is usually measured in MNs/g (“MegaNewton seconds per gram”).
> 
> Typical values are as follows: (I have put the values in order of permeability)
> 
> Breather Membrane 0.6 MNs/g
> Vapour check plasterboard 60 MNs/g
> 0.12mm polythene sheet 250 MNs/g
> 0.25mm polythene sheet 500 MNs/g
> Aluminium foil 7500 MNs/g
> 
> Again, hope this helps.
Click to expand...


As the outside is clad in OSB (9mm of I understand correctly) to ensure 5:1 presumably these guys need to know what the 'score' that gets in MNs/g. Is that available? And do you just take the highest score between the OSB and membrane, add the OSB score to the membrane score or something more complicated?

Terry.


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## Wizard9999

Muzza80":2wpv48vu said:


> You're right about that, even last night it was gusting up to 50mph here, I'm seriously concerned about this tarp I've currently got on the roof, really need to get the roof boarding finished and EPDM down ASAP, looking like Sunday (incidentally, my birthday) is the only dry day for the next while so hopefully get it done then, the wife's not going to be happy as she wanted to go out for a nice lunch haha, sorry dear!
> 
> I ended up ordering a 4m x 5m, 1.2mm membrane Classic bond kit from rubber4roofs with everything I need including edge kerb and gutter trims, arrives tomorrow, not too bad at £280 delivered.



I used EPDM on my workshop roof, brilliant stuff. I started laying mine with not a cloud in the sky, before I had finished a hail storm had come out of nowhere! Luckily it did not seem to affect the end result. Good luck and ccasion4: for Sunday

Terry.


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## Muzza80

Ok so been a productive weekend!

Roof EPDM on, kerb and gutter trims fitted, windows in and flashed, door frame wrapped, fitted and flashed just the door to wrap now but I'm watertight and secure at last hooray! 













































By pure coincidence the bostick flashband I've used to seal the reveals around the windows and door is exactly the same colour as my wrap which makes sealing it up a doddle as I can just overlap slightly around the frames without it looking shoddy, looks a little odd now but when clad it should be barely noticeable unless looking very closely. 

Next up I need to work out what I'm going to do about the roof facia's all round, thinking of just using the extra EPDM all round to face them but I need to come up with a plan for the sofits, how to support them and whatnot first.

Anyway, as always all comments welcome!


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## Stanleymonkey

Just noticed the view from your back garden - lucky sod!!

Fantastic work mate - your little lad must be very impressed with you


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## Wizard9999

Stanleymonkey":2e9h9986 said:


> Just noticed the view from your back garden - lucky sod!!



+1 window placement fully understood now :wink:


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## Muzza80

Stanleymonkey":3f7p7kjs said:


> Just noticed the view from your back garden - lucky sod!!
> 
> Fantastic work mate - your little lad must be very impressed with you






Wizard9999":3f7p7kjs said:


> Stanleymonkey":3f7p7kjs said:
> 
> 
> 
> Just noticed the view from your back garden - lucky sod!!
> 
> 
> 
> 
> +1 window placement fully understood now :wink:
Click to expand...



Cheers, yeah cant complain, here's the view from that little window on the end!


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## Norfolk75

After reading every reply here & apart from a couple of school boy errors I think you've made a fantastic job & take my hat off to you Well Done.

Was hoping to see the project completely finished, not sure if you've posted it somewhere else but would love to see it finished.


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## CRAFTY

Yeh super job man well done =D> can't wait to build my own


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## Muzza80

Cheers for the comments chaps.

To be totally honest I've not touched it since the last update.

Being secure and waterproof before the winter fully set in was the main priority, as it happens, just today I've made a start on clearing the garden and I'm dismantling the old tin shed this afternoon.

I'll get the cladding ordered up shorty and get cracking with it, I'll be sure to post updates as soon as I have them.


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## Sherman1973

Ive been talking about doing this for the last 5 years lol you have put me to shame  looking forward to update pictures


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## Muzza80

So I thought I'd better post a little update.

Would you believe, it's taken me 11 months to get around to cladding this! 

I've been super busy with a complete garden overhaul and as the build was completely weather proof it got put on the back burner there until this past weekend!

I had intended using Larch cladding but having just done over 40m of fence, a huge deck and 20m of sleeper retaining wall in green pressure treated timber I thought it might look a little odd, plus the cost of Larch in the profile I wanted was excessive. I've ended up with very nice 22mm thick pressure treated shiplap, total cost for cladding was about £450 delivered so really not too bad at all and I'm really pleased with the quality and look.

I still need to detail the corners, around the windows and door and the underside of the roof sides.

I'll fit vents front and back on the underside of the roof projection and the read will also get guttering.

Still need to wrap that door in the vinyl to match the rest of the windows/doors and also build a little 2 step unit for the front door.

Next is wiring out to the build from the house and then from the build down to the decking at the bottom of the garden, I've run armoured cable down there during the landscaping.

Here's a quick picture of the weekends progress.


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## Fitzroy

Looks great!


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