Topping parapet wall - alternatives?

Malc · 29 Jun 2015

Hi,

I've house remodel project and in that I have 2 parapet walls (5deg slope). As they are 1st floor height I don't want to coping stones. I've looked at aluminium coping but these seem to be made order and "loads of money". I've 2 2.1m runs, latest quote was £640! (ex vat). The "cheap" al solution is still ~£200 (ex vat and delivery). Code 4 lead, 6m is under £100 so the al seems well OTT, even the "cheap" one.

Does no one do a cheaper solution, in plastic maybe, off the shelf? Could it be done in lead?

Thanks

oldbutnotdead · 29 Jun 2015

You can do it in lead but the big risk is your local pondlife will nick it. I've used pairs of fibreglass roof trims (think they were A250) on one parapet- screwed down and glued together, been there 2 years and not fallen off yet. Annoyingly expensive at £25 for 3 metres but not as theft-prone as the lead

^woody^ · 29 Jun 2015

You can do it in plastic capping board if things are tight.

Malc · 30 Jun 2015

Good point about the lead. Probably not worth a great deal as scrap if it is only ~£100 bought but might still be a temptation. Do you have a link for the fibreglass roof trims?

Yes, I was wondering about upvc fascia board. The top of wall could be capped with osb screwed to the brickwork with dpc or epm round the edges. This could trap lead flashing too. Then cap it with 2 fascia back to back with a centre joiner. The only issue is how to fix it. polynails would be vertical so I wonder about damp tracking down them to the osb.

White board wouldn't look out of place as the parapets are either side of a glass roof with upvc bars.

oldbutnotdead · 30 Jun 2015

http://www.ecfibreglasssupplies.co.uk/c-981-grp-roof-trims.aspx - these are local for me, there are other suppliers.

I like Woody's suggestion of capping board-your plan of 2 boards back to back is probably the best, makes the job a bit pricier but gives you readymade drip edges and avoids the problem of the top edge not usually being finished. Forget a centre joiner, just use silicon and/or a long strip of that stuff window fitters use to cover up their dodgy measurements. As for water tracking through the pins- unlikely and even if it does it'll not be enough to cause a problem. Rather than OSB you could just use roof battens screwed to the parapet top- they will tolerate damp better than the OSB, are cheaper, come treated, what's not to like?

Malc · 30 Jun 2015

Interest idea of roof battens. I don't know that would work though. The idea of a board across the top is to seal off the cavity, and support the fascia trim. That way I could have thinner upvc which is cheaper. 9mm rather than 18 or 22mm. 9mm works out as 4 x £10 where as 22mm would be double that. Although for 16mm the difference is not anything so maybe roof battens have some mileage. I think the battens would need to run across the cavity to support the joint (between 2 boards) in the middle. But equally I could do with then running the other way to fix the flashing. Hmm.

oldbutnotdead · 30 Jun 2015

You and your modern newfangled ideas- cavity walls indeed! Hadn't thought of that to be honest, my life is mostly solid walls. Ladder of roof batten then (just spike or screw the rungs to the long battens, either in situ or make the ladder on the ground & then fix it as a oner. Valid point on the cost.....

Malc · 30 Jun 2015

FYI floplast have a interesting board, double sided L or U. U354, 9mm thick, 354mm wide, legs 43mm outside so 34mm inside. The 354mm is outside too so 336mm inside. My wall is ~20+100+50+100 = 270mm, maybe another +20mm, so that's 33mm or 23mm overhang which doesn't sound too far out. There's a picture here.

For ends my options are RT6 which is 500mm wide so would need a bit cutting out the middle or 2 x RT4 if I can't get RT6.

I'm thinking I could either screw it down with screw caps and SS screws, or poly nails, or nail plastic strip to board/battens underneath and use solvent glue to stick board to the nailed plastic, for a hidden joint (maybe contact adhesive would bond OSB3 to uPVC?). Of course the later means destroying the board if you need to remove it. Probably getting the polynails out would damage the board too so only the screw solution allows reliable removal.

oldbutnotdead · 30 Jun 2015

That stuff looks perfect for topping 9 inch walls on a budget. 25mm overhang is about right for preventing drip damage. I'd tend towards screws with caps or polynails- contact adhesive if it works would probably bond instantly so you'd have to have the thing spot on when you offer it. Low odds of that in my world.... Polynails are sods to get out- if you pull them with pliers the heads tend to fall off, if you try any leverage you end up compressing the board. But they're cheap and why would you want to remove your coping? (I know, I think like that as well, you might need to one day & while you're doing the job do it once etc etc). http://www.toolstation.com/shop/Scr...Screws/sd2856/Corrugated+Roofing+Screw/p51734 are cheap enough (use a more sensible length screw though). You could use Tekscrews but they might not seal at the low torque you'll get on compressible board.

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Topping parapet wall - alternatives?

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