GRP roof

[russellsmiler]

I have a small (very small) bay window to my en-suite and have constructed a sloping hipped roof above the window, the window is rectanble so have 2 small hips to the roof, the roof ties back to a timber frame which eventually will be timber clad.
I want to use GRP for the roof, i have watched umpteen videos and have foung online no end of suppliers for the materials needed.

My question is as anyone had experience of GRP on a sloping roof situation, the pitch is about 35 degrees, as i have said its only small with a projection of 550 mm and is 1400mm wide.

Any comments please/

Thanks Russell

 

[oldbutnotdead]

I've only used GRP on flat (or near flat) surfaces. You may get problems with the resin running downhill on your 35 degree pitch, and then again you may not.

Aesthetically it might look a bit cheap and nasty, since you've got a decent pitch why not tile or slate it- cost per sq metre isn't that different, though the hips would make it hard work (which I suspect is why you want to use GRP)?

You'll need to be quite clever at the eaves with getting resin and mat on the edges of the boards and the underside to form a drip edge (don't think any of the manufactured trims are going to work for you except possibly fixing 100mm of flat to the eaves ends of the boards). Again flashing the top of the roof to the wall isn't going to be easy, the trims are all 90 degrees and quite stiff- the hips will be easy, for the top of the main roof you may again have to use some flat fixed to the roof and pushed in to run up the wall and then cover flash over that.

 

[russellsmiler]

Thanks for the very knowlegeable reply, seems like you fully understand my roof!!.
Have worked on the roof over the weekend and feel i will give it a go in GRP, everything is clear apart from making the drip work! I have a 60mm section of fascia from the upvc soffit to the top edge of the OSB were the pitch starts, am planning to use a A170 drip trim and plan to (possibly trim the flange down to 50-60mm) and hopefully pushed tight againgst the fascia it will deform to the pitch and as pressure applied will nail in place, I may however introduce a fillet of osb on the top edge to have the flange of the trim sit at a nice 90 degrees (again though still thinking of trimming the flange to 50-60mm).

What do you think??

By the way slating is not ruled out, aesthetics is something i lose sleep over, and as i write this are considering the possibility of cutting down slate to create a intricate roof. Just a thought!!

 

[oldbutnotdead]

Ahhh, so you have fascia board just above the roof do you? Again aesthetically a single lump may look a bit odd but if it is a continuous run then that can solve the problem of bending the trim (and flashing the top of the roof) by using a bit of AT195 (or if you've got the drip trim already then lose the drip bit), tuck the wall side behind the fascia board and spike the other bit to the OSB. Or use some flat F300 for the job

Putting a fillet at the top of the OSB might look a bit odd and it gives a hard angle that you'll have to resin over (which will give you a weak point which is why those trims exist)

Thinking about the drip edge, if you can cut the edges of the OSB so they're vertical (rather than at 90 degrees to the surface), then fix the offcuts under the OSB (so you have a 36mm thick edge rather than an 18mm edge) you should be able to get the drip trim downstand bit to sit vertically, which means it'll drain properly and look neat and job jobbed. You can probably get the same effect (if you've already cut the OSB) with a bit of roof batten or similar fixed to the underside but projecting so that the effective face is vertical- actually that'll be a lot easier but doesn't give you a flat face to fix the front of the trim to (they can rattle in the wind sometimes)

And cutting slates to do a hip sounds straightforward (especially if you're using artificals) but a millimetre off will stand out like a sore thumb. Plus you've got all the fun of weathering it- in your setup GRP is going to be the way to go