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.

 

[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.

 

[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.

 

[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.

 

[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.

 

[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.

 

[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.

 

[MikeG.]

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

 

[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)?

 

[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.

 

[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.

 

[clogs]

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

 

[John Brown]

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?

 

[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.

 

[John Brown]

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.

 

[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.

 

[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.

 

[MikeG.]

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.

 

[John Brown]

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.

 

[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.