# Some more questions re. shed



## John Brown

I've got two thirds of the OSB3 floor down on my 3M x 4.5M shed, and now it's covered in a tarp and the weather seems set to rain for the next 40 days. I think I'm going to have to think about a tenting exercise, but don't really have enough space at one end for effective guy-rope angles and a ridge tent design. Also no trees or buildings nearby.
I'm wondering if I could build "skeleton" walls, strong enough to supports tarps, and then flesh them out when they're up.
I would really welcome any constructive advice.


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## MikeG.

Yep, you can do that John. It is critical with any tarp arrangement that there is a high centre, fully supported, so a good ridge beam for instance. Otherwise you will get a swimming pool full of water on the tarp before it collapses.


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## John Brown

Thanks.
What size timber would you recommend for a ridge, Mike? I'm only thinking felt or EDPM for the roof. Not as nice as slate or shingles, but budget is tight.


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## MikeG.

It's not as simple as that John. The whole roof needs to be looked at as one. If there are ties, for instance, then there doesn't technically need to be a ridge at all. If you're only spanning 3m then your timbers only need to be quite small structurally, but might be forced larger to give you the depth of insulation necessary. Describe the roof structure you have in mind.


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## John Brown

I was hoping to follow your guidelines for the roof, although you don't specify rafter spacing, if I recall. Also, would 18mm OSB be necessary under the felt for what is a fairly small shed?
Ties, yes. I was planning to have ties at eaves height, or a bit above. I will probably need the storage space.


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## MikeG.

OK, then, 145 x 45 rafters at 600 centres, max (allows for 100 or 125mm of insulation at rafter level). 120 or 145 x 45 ties to each pair of rafters, bolted (these must be in the lower 1/3rd of the rafter length). If you leave out only one tie to give yourself access to the storage space, then your ridge can be a piece of 200x25 sawn board. If you want to leave out more ties you'll need a beefier ridge. You must allow continuous eaves ventilation (with insect mesh) under your 18mm OSB. And definitely, definitely go for EPDM over felt...but don't buy the expensive plastic trim. It's not necessary. Line the inside with 9 or 10mm OSB.


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## John Brown

So EDPM rather than Onduline, which you recommend?
I did spec felt for PP, but I think I'd get away with Onduline.


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## MikeG.

Onduline is fine. EPDM is much better. You'll have no issue with Planning over using it in preference to mineral felt.


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## John Brown

Thanks.
Another few questions: 
How do I attach the breathable membrane to the studwork? Is it held in place by the battens that the cladding is nailed to?
Is there a cheaper alternative to Tyvek housewrap?
Since Travis Perkins only seem to sell Tyvek in 100M rolls, is it good for walls and roofs(rooves)?


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## MikeG.

You can use roofing membrane for the walls (but you can't use the wall membranes for a roof). There are always half-rolls etc on Ebay, and you can save quite a lot of money that way. You just staple it in place initially, and then the counterbattens hold it permanently.


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## Fitzroy

I built under a tent. Ridge line was a rope with a frame on the left and a tree on the right. A simple A frame at each end to tension the ridge line would also work.





However one of my sides did not have enough slope, you can see it’s a bit saggy inside.





The outcome of heavy rain, balls




The tent allowed me to build frames on the deck. The on a good day it was action stations to go frames up and roof on, the tarp went back over the top.





Cheers

Fitz.


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## clogs

great Bitish weather......!!!
hasn't rained here since March....


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## John Brown

MikeG. said:


> You can use roofing membrane for the walls (but you can't use the wall membranes for a roof). There are always half-rolls etc on Ebay, and you can save quite a lot of money that way. You just staple it in place initially, and then the counterbattens hold it permanently.


Thanks. I've looked on eBay, looks like buying 100m of 1.4 is cheaper than most eBay offerings. 
Just out of curiosity, why is it OK to use roof membrane on walls, but not vice versa?


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## MikeG.

Dunno. They're tested for their BBA Certificates, and it's at that point that their useages are set in stone. It's not impossible that Housewrap would be fine on a roof (I suspect it isn't robust enough to cope with the wear of roofer's boots), but the manufacturer wanted it to be wall-only, as they already have multiple roofing membranes. I'm just speculating, and there could be multiple other reasons.


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## John Brown

Fitzroy said:


> I built under a tent. Ridge line was a rope with a frame on the left and a tree on the right. A simple A frame at each end to tension the ridge line would also work.
> View attachment 90609
> 
> However one of my sides did not have enough slope, you can see it’s a bit saggy inside.
> 
> View attachment 90606
> 
> The outcome of heavy rain, balls
> View attachment 90607
> 
> The tent allowed me to build frames on the deck. The on a good day it was action stations to go frames up and roof on, the tarp went back over the top.
> 
> View attachment 90608
> 
> Cheers
> 
> Fitz.


I will probably have to do the same, but I have no trees in the right places, and not quite enough room at one end for a good guy rope angle. I'm thinking maybe I could use my ridge beam on a couple of A frames, with guys at one end, and some diagonals added.


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## John Brown

Big shoutout for the guys at Shoplands sawmills in Clevedon, BTW. C16 and C24 seem to be like hen's teeth at the moment, but they came up with the goods at a fair price, and will deliver.
The accounts I've opened with Selco and Travis Perkins have so far been wasted time.


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## MikeG.

Is it really that important? It doesn't matter if the structure gets wet, so long as you can keep you tools dry. The structure will go up in a matter of days, and you can work in a semi-sheltered way under your new roof.


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## MikeG.

John Brown said:


> C16 and C24 seem to be like hen's teeth at the moment......



That's a strength grading system, and irrelevant to your needs unless you have a roof right on the the limits of its span sizes. Just buy the timber on size.


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## John Brown

MikeG. said:


> Is it really that important? It doesn't matter if the structure gets wet, so long as you can keep you tools dry. The structure will go up in a matter of days, and you can work in a semi-sheltered way under your new roof.


It's the OSB floor I'm concerned about.

And yes, I know... I shouldn't have done things this way.
If I was to start over, I'd know a lot more, but I doubt I'll ever build another shed.


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## MikeG.

That'll survive 3 or 4 years of being left out in the sun and rain. I wouldn't worry about it for a second.


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## Lons

John
If you are using OSB, be careful of your rafter spacing as a lot of OSB sheet is still being supplied in 8x4 sheets (2440x1220) and you could find yourself cutting every sheet which is a pita.

My apology if that's already been pointed out.


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## John Brown

MikeG. said:


> That'll survive 3 or 4 years of being left out in the sun and rain. I wouldn't worry about it for a second.


Really? I was under the impression that once the edges got wet it would be compromised.


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## John Brown

Lons said:


> John
> If you are using OSB, be careful of your rafter spacing as a lot of OSB sheet is still being supplied in 8x4 sheets (2440x1220) and you could find yourself cutting every sheet which is a pita.
> 
> My apology if that's already been pointed out.


Thanks, Lons. I'll keep that in mind.


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## John Brown

I keep reading that EPDM is suitable for flat or low pitched rooves. My proposed and PP approved design has a 40 degree pitch. What are the implications of this, if any, please?


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## Fitzroy

My only thoughts are it may slip/slump with time if it was a mono pitch, how would you fasten at the top. If it sloped both sides this wouldn’t be an issue.

Other thought is, it’s normally used because a more robust longer lasting option is not available, ie you can’t slate or tile a flat/low pitch roof. 

Fitz


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## MikeG.

It's only ever fitted over a ply or OSB base, so it's fine on a pitch. It is glued down with a none-setting gum-like adhesive which holds it in place nicely, and you use a contact adhesive around complicated shapes or changes of pitch. One of my sheds has a c.40degree pitch and has EPDM on it. It's perfect.......but you can see the roof covering. When it's flat, you can't actually see what's on a roof. There is nothing longer lasting or more robust than EPDM in terms of single-ply roof coverings. I'd be surprised if it needed changing in 50 years time.


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## John Brown

Thanks both. I doubt I'll be around in 15 years, let alone 50, but I'll give it some thought.


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## John Brown

1. Horizontal studs?(I'm sure they're not called that...). Do I need them? If so, what spacing?

2. Internal OSB sheathing. Portrait or landscape? Shed is 3m by 4.5m by 1.9m at eaves. Wastage seems roughly equal. If landscape, I guess that answers 1.

3. Tyvek or equiv. Does it need stapling to a horizontal frame member? If yes, then I guess that answers 1.

4. When I fit the window frame, how do I line up the outside surface of the frame? Flush with the framing? Flush with the outside of the counterbattens? Somewhere else? I'm planning on waney edged larch cladding. Window frame is around 75mm deep, studs are 95mm.

5. Do I really, really need 18mm OSB3 on the roof, rather than 11mm? It's going to be a real struggle getting it up there..


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## MikeG.

1/ Noggins. Not absolutely necessary (but see 2/, below), but stiffens the wall up nicely and I would certainly suggest using them.

2/ Doesn't matter, but if you do landscape, then you need noggins at the level of the long edge join.

3/ No.

4/ I line up with the outside of the studwork framing, and then put a small window lining board over the counterbattens and board ends.

5/ On the top of the roof....yes. As a lining inside, then no. 9/10/11mm is fine there. Without reading the whole thread, I presume you are planning on a roof covering such as EPDM. Of course, if you are tiling etc then you don't need any board on top of the roof at all.


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## John Brown

MikeG. said:


> 1/ Noggins. Not absolutely necessary (but see 2/, below), but stiffens the wall up nicely and I would certainly suggest using them.
> 
> 2/ Doesn't matter, but if you do landscape, then you need noggins at the level of the long edge join.
> 
> 3/ No.
> 
> 4/ I line up with the outside of the studwork framing, and then put a small window lining board over the counterbattens and board ends.
> 
> 5/ On the top of the roof....yes. As a lining inside, then no. 9/10/11mm is fine there. Without reading the whole thread, I presume you are planning on a roof covering such as EPDM. Of course, if you are tiling etc then you don't need any board on top of the roof at all.


Many thanks.
Can I wrap, stuff and sheath one wall at a time, or is the strength of Tyvek compromised if I don't wrap the entire structure in one run?


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## MikeG.

One wall at a time is fine, so long as you leave enough overlap.


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## clogs

John 
doing one wall at time is OK....It's the overlap u need to be aware of...more the better.....
preferance would be to do the North and West facing walls together, they get the brunt of the weather ....and there would be no join......
then do the rest as and when ur ready.....
when I worked in California the whole house was done at once but then there was a crew to do it....
Pay particular aten to the openings and their flashings....also use the proper tape.......
plenty of good how to's on line...
do it right do it once......


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## John Brown

Thanks. And do I need special staples?
Tape?


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## MikeG.

No. The staples are a temporary fixing (but left in permanently). The membrane is held in place by the counterbattens, in the same way that roof membrane is stapled first, but actually held permanently by the tile battens.


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## John Brown

MikeG. said:


> No. The staples are a temporary fixing (but left in permanently). The membrane is held in place by the counterbattens, in the same way that roof membrane is stapled first, but actually held permanently by the tile battens.


Got it. What's your view on tape, Mike?


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## MikeG.

Unnecessary on a shed.


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## John Brown

Great. Counterbattens are 25mm, from your drawings, but 25 by 25? 25 x 50?


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## MikeG.

You can get away with 38x25, but it's best to use 50x25, especially if you are going to end up needing butt joints to the boarding. It's hard to get nails from two boards into 38mm.


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## John Brown

MikeG. said:


> You can get away with 38x25, but it's best to use 50x25, especially if you are going to end up needing butt joints to the boarding. It's hard to get nails from two boards into 38mm.


Thanks. 50 x 25 it is then.


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## John Brown

I've made a lenght of sill/cill with a slope and a drip groove fro a shed window, but of course it projects from the frame of the shed(or it will, when I fit it). So I'm thinking that wrapping will be difficult. I was planning on supporting the sill on the "cripples"(sorry if that's an American term), but now I'm thinking maybe I need another noggin at the bottom of the window aperture, wrap and fold the Tyvek into the aperture, and then fit the sill. Am I overcomplicating this?


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## MikeG.

Cripples isn't an American term..they're studs which don't go to the wall plate but instead support a lintel.

I'm afraid I don't follow the rest of your question. But let me give you a few principles......the membrane sits flush with the outside face of the studs, other than at openings where is gets folded into the structural opening. Window openings in the studwork have a lintel above and a cill plate at the bottom.


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## John Brown

MikeG. said:


> Cripples isn't an American term..they're studs which don't go to the wall plate but instead support a lintel.
> 
> I'm afraid I don't follow the rest of your question. But let me give you a few principles......the membrane sits flush with the outside face of the studs, other than at openings where is gets folded into the structural opening. Window openings in the studwork have a lintel above and a cill plate at the bottom.


Ok. Well I've done it now, but my cill has a sloping section that projects aprox 50mm from the other framing. So I added another piece of 4 x 2 that wiil sit between the cripples and the cill, so that I can fold the wrap over, and then fit the cill with the sloping, projecting edge.


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## MikeG.

I can't see how you'll make that work. I'd knock that out and just put in a flush piece of 4x2. This gets boarded over, so I can't picture a decent detail if it stuck out. You'd never keep it watertight.


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## John Brown

MikeG. said:


> I can't see how you'll make that work. I'd knock that out and just put in a flush piece of 4x2. This gets boarded over, so I can't picture a decent detail if it stuck out. You'd never keep it watertight.


So how do I ķeep the rain from running down the window, and getting behind the cladding, which is 25mm out from the framing?


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## MikeG.

That's the job of the window cill.


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## John Brown

MikeG. said:


> That's the job of the window cill.


Now I'm confused. You just told me to ditch the window cill...


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## MikeG.

No, you said you'd got a protruding bit of the frame, I thought. That's what I told you to ditch. If you haven't, you can't.

I think we're both confused.


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## John Brown

The window unit had been removed for a house which was being extended. It does not have an integral cill. So I made one from a piece of 145 x 47. I put a 25 degree slope on the edge and a drip groove below. I was planning to fit this underneath the window frame.


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## MikeG.

That's fine, so long as it isn't part of the studwork/ framing. You make a wall with a hole in it, then insert a window with an attached cill.


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## John Brown

MikeG. said:


> That's fine, so long as it isn't part of the studwork/ framing. You make a wall with a hole in it, then insert a window with an attached cill.


Ok. So if I attach the cill to the window frame, before I fit the window it's OK? I was planning on fixing the cill to the framing(after wrapping) and then fixing the window to the cill, but I am happy to do the former.


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## John Brown

And I apologise for being such a nuisance, especially at the weekend, but I am trying to make the most of the dry spells.


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## MikeG.

John Brown said:


> Ok. So if I attach the cill to the window frame, before I fit the window it's OK?



Exactly.



> I was planning on fixing the cill to the framing(after wrapping) and then fixing the window to the cill, but I am happy to do the former.



No, the cill attaches to the window, not the framing.


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## John Brown

I've been looking for details about how to fix insect mesh. So far, no luck. I am not at that stage yet, but don't want to do anything that would compromise the operation later. I skimmed through Mike's a different place thread, but may have missed the insect mesh action..


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## MikeG.

Go back to that thread, John, as there are detailed photos of the mesh.


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## John Brown

I can only find the mesh at the bottom, stapled to your wedges that kick the feather edge out. I was wondering about at the top of the cladding.


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## MikeG.

There is no mesh at the top. There is no specific air admittance gap. The various gaps around and through the boarding are sufficient.


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## John Brown

I have some minor confusion with respect the the gable ends. I have the end rafters sitting at the extremities of the top plate. Since they are "portrait" in cross-sectional view, I have a discrepancy between the gable studs and the rafter, because the rafters are 47mm in the ridge direction, while the studwork is 95mm in that direction. I'm trying to understand:
a) how I should secure the top edges of the inner wall OSB on the gable ends.
b) How I fix the inner OSB on the roof to the end rafters.

I'm sure there's a simple solution to this, but I can't see it right now.


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## MikeG.




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## John Brown

MikeG. said:


>


Thanks, my reading of this is that the studs are stepped at the top tp sit under the rafter, and the "extra rafter" pieces are 47 by 47mm. I guess the celing OSB has to be fitted before the gable inner OSB?


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## MikeG.

If you do the gable first then you'd need to plant another piece of timber on the gable to take the end of the ceiling OSB. Whatever suits your order of work is do-able.


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## DBT85

John Brown said:


> Thanks, my reading of this is that the studs are stepped at the top tp sit under the rafter, and the "extra rafter" pieces are 47 by 47mm. I guess the celing OSB has to be fitted before the gable inner OSB?


Not sure if you csn see it in my build, but I did the walls first and then the ceiling. I just put a length of batten on the gable osb for the ceiling osb to secure to.

And yes, the studs are notched to sit under the rafter and protrude up the face of it and then some 50*50 to infil.


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## John Brown

Thanks both.
John


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## John Brown

The 18mm OSB for the roof arrives tomorrow. I am figuring out how to get it up onto the rafters, but that's another story.
As my roof pitch is 34 degrees, I am wondering what is the best way to mate the boards at the ridge. Should I cut them at an angle - a sort of mitre joint? Have one side stick out by about 18mm, and but the other up to it? Some sort of filler strip?
I am open to ideas.


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## MikeG.

John Brown said:


> ........Have one side stick out by about 18mm, and but the other up to it? ......



This.

And be careful. It's hard to stop the boards slipping off the roof. Nail on some temporary battens, or get a couple of helpers.......and don't stand underneath them, ever.


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## John Brown

Thanks. That was my first choice, but I thought I'd better check.
I will be very careful. At one side I have space to take a couple of lengths of 2 x 4, and extend the roof slope all the way to ground level, which I think will make things easier. At the other side, I don't, so I'm still pondering.


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## John Brown

Last question for the weekend.
I'm almost decided on EPDM, but not 100% sure how it will look with waney edge larch cladding in this Cotswolds AONB. I like the idea of a 50 year life span, but I really won't care that much when I'm 117. So I'm wondering what the cons are of bitumous felt shingles.


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## DBT85

Bit late but given you're going with waney edge larch on the walls and in a AONB, I'm surprised you'd go with either over something like cedar shingle or slate/fibre cement slate.

What did you choose in the end?


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## John Brown

Felt shingles. My PP application stated felt, but I decided I wanted something a bit nicer (in my opinion).
Today, I am cursing the decision, and wishing I'd had the budget for slate, as I can't really reach across a row of 4 shingles from my roof ladder, and it all takes soooooo long, up the ladder, down the ladder, move the ladder... you get the idea. My over-the-road neighbour(who at 73 is 6 years my senior) is slating his oak framed car port, and is nimbly dancing around on the roofing battens. 
Anyway, I've made my bed, so.I'll have to lie in it. I don't really have the budget for cedar shingles or Welsh slate. And I don't see how I could have managed a giant sheet of EPDM by myself. Added to which, it would have highlighted my crappy ridge line.

Still curious about the ex willow wielder...


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## John Brown

I am a bit confused re. breather membrane and fitting window frames. If I search the internet, I can find about 126 different opinions on how to do things.
I have some oak window frames that I am repurposing. I made a rough and ready cill with a sloping edge and a drip groove, which I have affixed to the bottom of the frames. 
I am not particularly bothered about the top of the window frame, as it is tucked away under the eaves, so unless the rain is blown upwards it should be OK. Also, I guess the cladding can overlap the top of the frame.
I figure I will have vertical battens that bridge the join between the shed frame and the window frame and which but up agains the ends of the cladding boards.
However, various internet sources say I should fold the Tyvek around the sides/not fold round the sides, fold over the bottom of the aperture/not fold over the bottom...
My inclination is to not fold any of the breather, and to seal any gaps with framing sealant.
What does the team think?


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## DBT85

If in doubt, look at Mikes build or ask Mike.

Neither of which are here.

From what I can see in his photos he folded the membrane over for the bottom of the window but not the sides. You can drop him a PM at the other place and he'll only be too glad to help.


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## John Brown

I just started cladding. Thought I'd begin with the end that has no windows or doors for simplicity. It does, however, have a gable end, and I'm wondering what happens at the top, in order to preserve the airflow under the cladding.
I guess I have to leave a gap, and add some more insect mesh, but what then?
Do I have to add more timber, i.e soffits?

I'm asking here first as I don't have login credentials for the other place on my phone, BTW, before you advise me to ask MikeG... I'll post over there when I have access to my desktop.


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## DBT85

Have you got a photo John? My gable ends just went right up to the roof. You might be able to see it in my thread.


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## John Brown

DBT85 said:


> Have you got a photo John? My gable ends just went right up to the roof. You might be able to see it in my thread.


No photo, as I've only nailed on two boards at the bottom so far. Just thinking (barely) ahead.
I will check your thread.


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## John Brown

I checked your thread, doesn't really answer my question re. airflow, but has reminded me that I probably need battens under the verges.


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## DBT85

I didn't do anything for airflow up there. I secured a 50x50 to the gable rafters as something for the barge board to secure to (I later had to add an extra 22m filler on top). The battens along the gable were placed below that 50x50.

Theccladding boards then go upto the 50x50 and the barge board goes over the top butting against the underside of the roof. 

I've forgotten what cladding you're using.


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## John Brown

I'm using waney edged larch.
My roof is 18mm OSB, which overhangs the rafters by 75mm or so.
Seems strange to try and maintain that 25mm air gap under the cladding, and then seal it off at the gable. Not that it will be hermetically sealed...


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## Sheptonphil

As MikeG said on many threads, lapped boards do not need venting at the top as there is sufficient air leakage all over to give good circulation without the vented top.
My shed construction has a vented bottom with insect mesh, 25mm gap all the way up, then at the top there is battens following the verge line to carry the barge fixings. Air will flow through the thin gaps between board overlaps.

If you were using sheet material like steel sheet etc which is not ‘leaky’, then you would need vented top.


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## John Brown

Ok. I understand.
Seems like the insect mesh might be a waste of time, though, since there will almost certainly be gaps big enough for a wasp or two.
Thanks for the reply.


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