Flat roof

[Ade234]

Looking for some information. Currently have a garage converted into an office but it wasn't done well. Time has come to replace the flat roof properly, I want to put an insulated warm roof on instead of the felt shed roof it currently has.

Garage is attached to the house and is single skin brick built with piers, was wondering about raising the joists about six inches to provide more headroom. I would need a plate fastened to the brick outer wall of the house for the joists to hang off. Existing joists are set into brickwork so would be cut back, could sit plate on that and still bolt it. Could this just be bolted with M12 sleeve bolts and could six inches of timber be fastened to the top of the existing walls for the joists to be fastened to? This would create the height I need.

Brickwork was done in the 70's and all appears to be in good order. Should I be worried about the weight compared to the roof that is already there?

 

[Notch7]

Do you have the space for firings, 125mm of insulation, OSB board on top of new joists?

Yes you can bolt timber plate to house wall.

You can't really bolt a timber plate to the top of a wall - are you meaning the garage walls? I'm confused.

 

[Ade234]

Yes - I had a builder out who suggested a wooden beam on top of the three garage walls to lift it the six inches, he was going to strap it to the piers and fix the joists to that. Easiest option would be to just put a warm roof on to existing structure but was hoping to increase internal height slightly.

 

[cdbe]

I raised my lean-to garage roof by 6 inches (a long story involving a caravan). I jacked up rafters and wall plate as one and inserted 2 courses of bricks under. At the house end there was enough movement in the truss clips that I didn't need to do anything there but I think mine was slightly different in that it started off as a shallow pitched roof and ended up as a flat roof which I re-did in EPDM. If you use timber you'll need a tall fascia or some cladding to weatherproof it outside.

 

[Ade234]

Wow, that is impressive, my work is for a whole new roof as deck is showing signs of water damage so wouldn't need any jacks.

 

[noseall]

I raised my lean-to garage roof by 6 inches (a long story involving a caravan). I jacked up rafters and wall plate as one and inserted 2 courses of bricks under. At the house end there was enough movement in the truss clips that I didn't need to do anything there but I think mine was slightly different in that it started off as a shallow pitched roof and ended up as a flat roof which I re-did in EPDM. If you use timber you'll need a tall fascia or some cladding to weatherproof it outside.

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I like the use of 50mm truss clips as joist hangers.

 

[^woody^]

I like the use of 50mm truss clips as joist hangers.

They are actually Australian hangers

 

[cdbe]

I like the use of 50mm truss clips as joist hangers.

If they're free, and they look vaguely right they'll do me. You'll probably sigh at the (free) 9mm osb decking but with the rafters at 400mm centres it's all nice and solid.

 

[Ade234]

@Notch7

Wasn't really explaining myself well - the current roof is fastened to the exterior of the house which is where the wall plate would go - the current rafters go across and just sit on top of the wall. The suggested solution to raising the roof at that side was to put six inches of timber full length on top of the bricks and pillars and put new rafters on. This would give a deep plinth but has been suggested by more than one builder now, I have asked building regs for guidance and will go from there. Thanks.

 

[Ade234]

Have a new builder looking at this and he has suggested new load bearing inner skin stud wall plonked on the existing concrete slab, and then build up outside with new brickwork - this would allow the insulation and plasterboard I need but I dont know if the concrete slabe would take the weight of this and the new roof. Anyone know how thick the concrete would need to be for this to work?