how to install flat roof joists on top of brick wall

21 Sep 2013
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United Kingdom

I'm putting a new flat roof on a single story building and just wanted to sanity check it please.

One end of the joists will be attached to the 2storey end of the house using a 7x2 wall plate bolted to the wall (m12 bolts) then joist hangers from that to the joists.

The other end will attach to the top of a single skin brick wall. I was thinking of sitting the joists on top of the wall and using tie down straps to secure. I'd use paint on DPC to cover the ends of the joists. The building control guy suggested building the wall up 2 courses and then using joist hangers (so there was brick between the joist ends and outside for damp), however I'm not convinced about using joist hangers right on top of the bricks - seems they're meant to be built in. Does it make a difference if you put a timber wall plate on top of the brick then joist hangers from the timber?

Any thoughts/suggestions?

Thanks in advance
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Normally you would have a 4x2" as a wall plate strapped down your wall then you would skew nail your rafters to the wall plate.
You can either fix a wall plate as suggested or use twisted straps fixed to the joist ends and a series of end noggings creating a solid bridge.

I'd go for the strapped down wall plate.
As you are pitching on single skin wall, assume it is a cold deck with no insulation or air circulation required.
If this is the case and roof is cross fall, then pitch straight on to wall, beam fill up to top of joists, facia 25mm deeper than joists and drip fillet to facia. Twisted hold down strap every other joist.
Regards oldun
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Thanks very much for your replies. Glad that you all seem to agree to use the wall to rest the joists on and not joist hangers... now just to convince building control.

Hopefully wrapping the end of the joists in DPC should calm any of his fears about condensation.

FYI, it will be a warm deck, so insulation above the joists and the wall insulation extending up between the joists to meet it.

Out of interest, I was planning on putting an 18mm ply deck on top of the joists then insulation on top of that, but just noticed on Celotex website that they say you can put their roof deck boards straight on the joists?! Anyone with experience of using these?

Thanks again for the comments.

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