Shed roof construction

[noseall]

Sorry, I’m not sure what you mean?

I'm forgetting it's a shed. I'm thinking one end is abutted to a building, doh.

 

[noseall]

Im putting a vented soffit around the perimeter and from what I have researched for a warm roof there needs to be a 50mm ventilation gap above insulation before the OSB.

That's a cold roof. Yes there needs to be a gap above the insulation and said gap requires venting.

So I was then thinking if the noggins (spaced at every 1500mm or so) are tight under the OSB is this not going to stop the ventilation gap and form cold spots?

Use shallower noggs. The whole area above the insulation is a cold spot on a cold deck roof. You may also need to under-draw the ceiling with insulation too.

 

[11Tommy11]

Oh yes cold roof is what I meant.

Ok great thanks. I’ll go with 6 x 2 noggins if I decide to go with the 8 x 2 rafters then.

 

[noseall]

Oh yes cold roof is what I meant.

Ok great thanks. I’ll go with 6 x 2 noggins if I decide to go with the 8 x 2 rafters then.

Won't the diminishing strips create a wee bit of space above the noggs?

 

[11Tommy11]

If I was starting from scratch I would definitely use firrings as that seems the easy option but as the wall structure is already built (the back is one block higher than the front to create a slope) I’m not going to interfere with that.

 

[Harry Bloomfield]

If I was starting from scratch I would definitely use firrings as that seems the easy option but as the wall structure is already built (the back is one block higher than the front to create a slope) I’m not going to interfere with that.

Lack of adequate slope, might be at the root of your present problem, that a slight dip, causes pooling on the roof.

 

[stevie888]

Insulation is a new factor: still going to just be a shed? Without heating insulation is of dubious value.

If you're going to renew the whole thing why not go warm deck though: much easier and more efficient.

1 block (225?) in 4800 is plenty of fall for a flat roof so don't be worrying about that.

 

[11Tommy11]

Insulation is a new factor: still going to just be a shed? Without heating insulation is of dubious value.

If you're going to renew the whole thing why not go warm deck though: much easier and more efficient.

1 block (225?) in 4800 is plenty of fall for a flat roof so don't be worrying about that.

I want to use it as a more functional gym and storage area so will be plaster boarding and finishing more like a conventional room as opposed to a shed.

I probably will add some sort of heating to take the chill off in the winter months.

The only downside of warm roof, is it not going to me huge depth at the end. 8 x 2 plus 150mm insulation, 2 lots of ply/OSB and then roof covering. I was thinking I’ll be looking at 400mm fascia.

Not completely against it though, just only ever done the cold roof system in the past so happy for any advice!