Joist size for lean-to roof over deck

Wilde_37

Planning to build a new deck at the back of the house with a lean-to roof over it. Roof will have slight pitch maybe 1/4" per foot. The joists will be about 10ft long and be 16" centre.The roof will have OSB laid on top (probably 18mm) and covered with felt "shingles". I am also thinking of putting a 6mm plywood under the lower side of the joinst (as a ceiling).

My questions relates to the size of the timbers. Do I go with 6"x2" or would 4"x2" do the job? There is about €500 in the difference, but I am more concerned with stability and safety than price - but also don't want to waste money if the 4" x 2" would do the job!

rje66

At a minimum you'll need something like 7*2, with that weight.

Lumen

Are there any windows above the roof? If so I think you need to account for that in your span calculations as the roof will be a means of escape.

Also, are you sure the felt shingles are designed to be used on a flat roof?

Bonzo Delaney

Shingles won't work on a 1:48 fall about 2 degree

You'll need at least a 8:48 or 1:6 slope for shingles about 10 degrees

Personnaly I wouldnt attempt anything less than a 1:4 slope in an open area which is about a 16 degree pitch for shingles.

So your looking at some form of metal clad , torch on, rubber or fibre glass for a flat low pitch roof covering.

Defo 7x2s depending on your support beam positions

jack of all

+1 on all the above, what you propose is by definition a flat roof, which means a continuous membrane, shingles won't work. Be careful to plan for plenty of strapping/ ties as wind uplift is a significant risk on an open sided structure like that.

maestroamado

https://www.boards.ie/discussion/comment/117745898#Comment_117745898

I have never seen shingles on a roof in Ireland.

It really pisses me off that we are becoming a country that is speaking totally American English, progress.

OP I think 6x2 be best option, i think cladding be good for roof and need less timbers.

I think if i was doing i wouldn't bother with ceiling and make the timbers natural look...

Lumen

@maestroamado wrote

I have never seen shingles on a roof in Ireland. It really pisses me off that we are becoming a country that is speaking totally American English, progress.

Uh OK, I was just repeating the terminology used by the OP.

On that tangent, there's a quite impressive building on the site of Kilquade Aboretum with some nicely weathered cedar (?) shingles, if you happen to be passing. I've used them myself but they were imported from the US, so I guess the terminology was appropriate. I've love to grow my own so that I can replace them when they get worn out, but I fear I'll be too decrepit to be chopping down trees by the time they're ready.

maestroamado

I am in the process of planting some native Irish trees but i will not be turning into shingles.

I wasn't digging but the media are changing to American lingo.

I notice lately the terms being used for court for example Arainment and Layers.

Sport has gone the same way in the last few years, i prefer differences in lingo...

Wilde_37

Thanks for the input. I spoke with the "Shingle" supplier and they said that I needed at least 15 degrees pitch. So that's a rethink. I might go with corrugated sheet instead. The posts will be 8" x 6" and are 6ft apart, set in 2ft of concrete. And I'll definitely be looking at at least 6x2 for joists. Plan was for all joists to be strapped using Simpson Strong Ties for wind protection. The back of the house is very protected already, with 8ft walls either side of the proposed deck and roof.