Block shed flatroof questions

[Ryan_The_Bodge]

Hi I've recently built myself a 4.4 x 3.6m block shed. I'm now at the point when it's time to stick the roof on.

The shed will eventually be rendered, so I'm going to have to leave a gap between the fascia and the blocks to take the render.

How much of a gap should I leave? I thought about overhanging the joists by 20mm then nailing an 18mm osb to the front of the joists as a sub fascia then using 9mm capping. Would that leave me enough room for the render?

Also, I'm not sure how straight the wall is. So when it comes to fitting the joists should I place the two end joists on first over hanging the 20mm and run a sting line across the face of the joists and butt the others to the line?

One last question. I'm using osb3 2440 x 1220 am I right in thinking I should do 16" centers?

Thanks

 

[Ryan_The_Bodge]

What spell do I use to summon woody? Abbra kadabra?

 

[Alastairreid]

Looks much better with a soffit.

 

[Ryan_The_Bodge]

Looks much better with a soffit.

Won't be having a soffit on it, I'm afraid.

 

[Notch7]

Hi I've recently built myself a 4.4 x 3.6m block shed. I'm now at the point when it's time to stick the roof on.

The shed will eventually be rendered, so I'm going to have to leave a gap between the fascia and the blocks to take the render.

How much of a gap should I leave? I thought about overhanging the joists by 20mm then nailing an 18mm osb to the front of the joists as a sub fascia then using 9mm capping. Would that leave me enough room for the render?

Also, I'm not sure how straight the wall is. So when it comes to fitting the joists should I place the two end joists on first over hanging the 20mm and run a sting line across the face of the joists and butt the others to the line?

One last question. I'm using osb3 2440 x 1220 am I right in thinking I should do 16" centers?

Thanks

As Alastair says, it would look better with a soffit.

If you are rendering, I would recommend a roof overhang of say 100mm or more overall - as that will help reduce rain dripping onto the walls - which on render might make it look dirty after a few years.

All you have to do is build a "ladder" which is the convential way of doing gable end overhangs pitched tiled roofs.

If using 18mm osb3 do 400mm centres.

 

[Notch7]

Won't be having a soffit on it, I'm afraid.

You need to be careful with your detailing to avoid leaks in that case.

Me personally, I'd have a soffit.

 

[Ryan_The_Bodge]

As Alastair says, it would look better with a soffit.

If you are rendering, I would recommend a roof overhang of say 100mm or more overall - as that will help reduce rain dripping onto the walls - which on render might make it look dirty after a few years.

All you have to do is build a "ladder" which is the convential way of doing gable end overhangs pitched tiled roofs.

If using 18mm osb3 do 400mm centres.

I see what you are saying. I already have the joists ordered and the length of them is 3.6m. My roof is slightly under 3.6m so no chance of a 100mm overhang on both sides. The only way I could do that is to extend the ends of the joists with short bits of 7x2 which sounds like a pain in the arse.

 

[Ryan_The_Bodge]

You need to be careful with your detailing to avoid leaks in that case.

Me personally, I'd have a soffit.

Where would you be expecting these leaks to be?

It's a flat roof, epdm with all the plastic kerbs and drips. I'm using furrings on top of the joists, followed by OSB3 18mm. I will cut down some OSB3 boards to use as a sub fascia. I will then place a single batten around the perimeter level with the top of the deck osb. Might put a double batten on the drip side of the roof. The fascia will then be nailed butted up to the underside of the batten I stuck round the perimeter.

Is there something I'm missing here that would cause a leak? You have me nervous lol

 

[Ryan_The_Bodge]

Well I've listened to your advice and decided to add a bit of a soffit. It's not going to be much of one but it's better than nothing. I only have 36mm over hang front and back of the joists. But it should make it easier when it comes to the rendering. Thanks guys

 

[Alastairreid]

Good decision, rainwater tracks down facings and barge boards and tracks down the walls without soffit or verge oversail...can cause problems in the long term.

 

[Ryan_The_Bodge]

This might be a stupid question and I don't think it really matters either way. But I'm using flat white soffit, at most it's only going to be two inches wide. Is it worth using a J trim at all?

 

[Alastairreid]

Gives a better finished edge.

 

[Ryan_The_Bodge]

Gives a better finished edge.

Is it worth it though If I'm just going to render up to the soffit?

 

[Alastairreid]

Forgot you were rendering it...I wouldn't bother.

 

[Ryan_The_Bodge]

Forgot you were rendering it...I wouldn't bother.

That is what I wanted to hear thanks.