andyscotland Posted July 5, 2019 Share Posted July 5, 2019 Will soon be ready to start on our GRP roof, have two queries about detailing that I'm struggling to find answers to. First, it's actually a low pitch (10ish degrees) L-shaped hipped roof on three planes. I'm not sure what to do at the three (gentle) ridge junctions. I don't otherwise need an expansion joint, and I don't really fancy the look of the "rolled" ridge/expansion joint trims sticking up. Can I just put flat trim over it? Or just bandage it as if it was any other butt joint? Second, I'm building rooflight kerbs on top. The sides will be faced in GRP with trim at the top up into the rooflight flashing. Do these need wall fillet / angle trims at the bottom where they meet the roof deck, or again can they just be bandaged and laminated over? Link to comment Share on other sites More sharing options...
scottishjohn Posted July 5, 2019 Share Posted July 5, 2019 a bit more accurate detail think is really needed what are the walls made out of that the semi flat grp is going join too? maybe lead flashing into brick wall onto the flatish roof -plenty of length,but also a flashing on roof below grp finished edge of it going up under the wall flashing --? plenty of overlap on everything and no flat area to puddle . Link to comment Share on other sites More sharing options...
Russell griffiths Posted July 5, 2019 Share Posted July 5, 2019 All I would add is when I did my grip roof I was told fit the eaves trim flat on the roof deck and then bandage on to the main roof, I always thought this would create a ridge that water sits behind, as it is such a small lip I was told it’s not a problem. Well it certainly creates more of a lip than I am happy with and I wish I had cut a rebate for the eaves trim to sit in so the bandage wouldn’t have created a lip. Glad this is on the house we will knock down and not on my new one. Link to comment Share on other sites More sharing options...
andyscotland Posted July 5, 2019 Author Share Posted July 5, 2019 @scottishjohn @Russell griffiths sorry - I've maybe not explained it very clearly. I've attached a drawing from the original 1980s garage plans - best image I have that shows the roof shape. The slightly unusual rafters have been altered / sistered a bit now as part of the conversion, and there's insulation going on top, but the basic shape is staying the same. I'm happy with the abutment to the house - the roof butts up to the brick walls, below the soffit overhang. I'll put wall fillet / simulated lead flashing there (although by the time the roof is built up, the section along the side of the house will be quite close to the soffit - so I'll probably enclose that area anyway since it will otherwise be very awkward to paint / maintain that bit of the soffit in future). The hip joins I'm asking about are the two diagonal ridges, running up to the house from the left / right corners of the wall facing you in the isometric. The original roof was corrugated sheeting with flat ridge pieces over that join. Does that make more sense what I'm asking? Link to comment Share on other sites More sharing options...
Russell griffiths Posted July 6, 2019 Share Posted July 6, 2019 I don’t really have an opinion on your hip ridge junction, you will probably need to be led by manufacturers recommendations. My only opinion related to the eaves where I was led to believe a small lip will not be an issue, I have since found a video that showed a bloke cutting a flat area for the eaves trim to sit down in. So no lip when you bandage over the top. Link to comment Share on other sites More sharing options...
andyscotland Posted July 6, 2019 Author Share Posted July 6, 2019 @Russell griffithsthanks - been trying to get an answer from the manufacturer for a week or so but not had much luck so far. Is your roof quite flat? I've seen that detail (routing out for the edge trim to sit flat) but had thought my roof is steep enough it wouldn't matter. Link to comment Share on other sites More sharing options...
Russell griffiths Posted July 6, 2019 Share Posted July 6, 2019 I found it was not a case of water run off, as that is fine, what it is is the dirt it leaves behind, the lip has a continuous build up of a residual muck left behind i get on the roof once every six months and give it a good scrub. My roof is very flat probably 5degrees. 1 Link to comment Share on other sites More sharing options...
andyscotland Posted July 6, 2019 Author Share Posted July 6, 2019 @Russell griffiths that's good to know - I'll maybe rebate it in then. Link to comment Share on other sites More sharing options...
Onoff Posted July 6, 2019 Share Posted July 6, 2019 13 hours ago, andyscotland said: and there's insulation going on top Insulation going on top....of the roof joists? A wild idea but could you carry that on and down the walls on the OUTSIDE as ewi? A more seamless thermal envelope, more space inside etc. Maybe a f'glass roof with hidden edge gutter and hidden vertical gutter detail like @Barney12 did on his dormer. Link to comment Share on other sites More sharing options...
andyscotland Posted July 6, 2019 Author Share Posted July 6, 2019 @Onoff I would love to, would have made a bunch of stuff easier internally. Unfortunately the existing wall is hard up to the boundary already ? Link to comment Share on other sites More sharing options...
scottishjohn Posted July 6, 2019 Share Posted July 6, 2019 (edited) probably me being thick ,but surely you just make ALL the roof in one go -going round the hips etc as you lay the GRP not section it -If so then that will be no problem . I have made a lot of additons in GRP to my main garage building and used grp for funny bits and nothing has ever moved in 25 years. I have a 3ft dis extraction pipe going up through it( for spray booth ) -and i used a sheet off the roof to make a mould to make up a half sheet of roof with a 3ft hole in it with an 6" upstand around the pipe this was fixed to roof with 2 lines of sealer under edges and fixed directly onto the plasticoated steel roof panels +glassed to the extraction pipe for good measure--never any sign of any leaks or movement all I can see now is some loss of resin from top surface as i did not us an UV top coat on the grp ,just a very resin rich lay up -so it was glossy -which was a mistake --but its all still there and fine. keep polyester resin away from insulation ,it will melt it-no gaps in sarking boards for it to run through use expoxy resins if you want to use it with foam -- thats was how the wing on our europa home build aircraft wing and things was made --blue foam core and west expoxy system and fancy bidirectional cloth . like making a suit Edited July 6, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
andyscotland Posted July 6, 2019 Author Share Posted July 6, 2019 @scottishjohn yes planning to laminate the whole thing in a single operation. Just wasn't sure if the hips needed treating differently from any other butt joint. Obviously would be easiest to just bandage over if that's sufficiently robust. Link to comment Share on other sites More sharing options...
scottishjohn Posted July 6, 2019 Share Posted July 6, 2019 3 minutes ago, andyscotland said: @scottishjohn yes planning to laminate the whole thing in a single operation. Just wasn't sure if the hips needed treating differently from any other butt joint. Obviously would be easiest to just bandage over if that's sufficiently robust. why bandage? just glass over ,apply a bandage first if you like to give more thickness at change in shape. are you not intending to do it all in one session anyway? -or do a section over the joint first then just glass over the whole roof ,wet it out well and the glass will conform to shape no problem Link to comment Share on other sites More sharing options...
Ferdinand Posted July 6, 2019 Share Posted July 6, 2019 (edited) Might be worth capping the edges on the corner of the hips with something. That is the thing that will crack if someone up there ever stands on it. Not sure how, but possibly the metal angles from corrugated roofs glassed in at the edges or right over (?). Or perhaps glued on afterwards, or just sat on the resin as it sets. F Edited July 6, 2019 by Ferdinand Link to comment Share on other sites More sharing options...
Onoff Posted July 6, 2019 Share Posted July 6, 2019 44 minutes ago, Ferdinand said: Not sure how, but possibly the metal angles from corrugated roofs glassed in at the edges or right over (?). I'd be careful. Well known issues with the non factory fitted, fibreglass X Packs etc on Ford Capris back in the day. People would affix them with metal rivets then skim over with filler, prime and paint. Over time these little fixing points would become super hot spots on Sunny days to the point of bubbling the paint and expanding to the point the kit panels could eventually loosen. Link to comment Share on other sites More sharing options...
andyscotland Posted July 6, 2019 Author Share Posted July 6, 2019 5 hours ago, scottishjohn said: why bandage? Just that's the manufacturer's spec for butt joints (which this will obv be) 1 hour ago, Ferdinand said: Might be worth capping the edges on the corner of the hips with something. That is the thing that will crack if someone up there ever stands on it. Not sure how, but possibly the metal angles from corrugated roofs glassed in at the edges or right over (?). Or perhaps glued on afterwards, or just sat on the resin as it sets. F Thanks - given @Onoff comment too I'll have a think what I could glue on - maybe even include a thin bit of polystyrene/scrap insulation or something as a compressible layer. Also it's unlikely there'll be anyone but me walking on the roof in the foreseeable future so can probably get away without capping it at least at first. Link to comment Share on other sites More sharing options...
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