GRP vs EPDM (Fibreglass vs Rubber)

JohnA666 · 21 May 2007

I'm currently deciding how to replace two flat roofs at home.
They are about 15sq m each, and the felt is falling apart (no leaks inside yet though!)

I've had a couple of felt specialists, Fibreglass and Rubber as well.
Each one thinks their own product is the stuff of dreams, and the other alternatives are inferior.

I've seen the fleece-back EPDM and the Firestone stuff next to it. They both seem thin to me and cat or fox claws would easily poke holes in them (in my opinion). Plus they are pitch black, so in hot summer days they will be far from ideal. In the States they sell special water-based products to paint them white, so heat must be an issue.

The GRP stuff seems slippery enough to deter cats from damaging it, and in light grey colour will reflect a lot more sun than black rubber.

EPDM is quite elastic and will follow some roof movement, while GRP is not flexible and may crack if there is movement.

Both need OSB boards laid underneath them and neither will have any seams in my roof dimensions. If the weather is dry while fitting, both stand the same chances of successful installation (rain can seriously muck up fibreglass from curing)

They all cost similar money, so I am at a loss as to which one is best for domestic use.

Any ideas from the trade?

masona · 21 May 2007

Is it possible to put a low pitch roof with roof tiles instead?

JohnA666 · 22 May 2007

I don't think so, the pitch is not steep enough in the kitchen. It starts off roughly where the pitched roof of the rest of the house ends.
The garage slopes a bit more, but no more than 15% I'd hazard a guess.

masona · 24 May 2007

JohnA666 said:
I don't think so, the pitch is not steep enough in the kitchen. It starts off roughly where the pitched roof of the rest of the house ends.

Can you do a photo?

JohnA666 · 4 Jun 2007

I finally decided to go for GRP.
I think it has an edge over rubber on sun reflectivity and robustness in general.

We'll see how it goes.

adybuttress · 9 Jun 2007

shame you went for the grp. Alot of contractors are jumping from that system to epdm. There have been alot of grp roofs failing due to cracking. At first glance the product looks ideal, but it doesnt allow for any movement.

As for claws going through the rubber. Its never happened in 30 years, so i dont see why it should start now.

The white paint hat can be applied to reflect sun is in areas where the sun gets really hot, such as the states, Arabia, spain etc. Its not very popular here, as we just dont have the climate.

Hope these comments help

JohnA666 · 12 Jun 2007

I still haven't done it, last weekend was meant to be wet (although it wasn't) and as we know installing GRP in the wet is a no-no

I'm not sure if these cracking incidents are due to faulty installation. If it rains while the fibreglass is curing then it will crack.
The thin layer of rubber (like a car's inner tube) just doesn't feel as robust to me, maybe I'm being paranoid...

Deluks · 12 Jun 2007

JohnA666 said:
The thin layer of rubber (like a car's inner tube) just doesn't feel as robust to me, maybe I'm being paranoid...

Have you ever had a problem with a car inner tube letting water in?

adybuttress · 12 Jun 2007

I know what your saying.Alot of people think this. Its specifically made for flat roofing. Simular to fishing nylon, not very thick but more than does the job. because it is fully adhered if it was damaged, say due to a falling slate, it can be repaired within 5 minutes at a cost of about a tenner.

Ive been involved with this product for 9 years and to honest repaired perhaps 3-4 if that.

Zeberdee · 14 Jun 2007

How do you rubber and waterproof any boxes on a flat roof? the ones that conceal any pipes coming out the wall etc?

adybuttress · 14 Jun 2007

Theres a flashing tape called formflash. Its a semi cured rubber tape tahts self adhesive. You prime the rubber first and then it goes on to vulcanise.
Its very easy

Zeberdee · 14 Jun 2007

so you do the whole box in tape? some boxes can be rather big. Isn't it best to use offcuts of rubber then seal?

adybuttress · 15 Jun 2007

sorry I didnt explain myself properly. You bond rubber to as much area as possible, then flash off all the joints etc with the tape.

hope this clarifies. If you follow this link there is an instalation guide that explains how the whole system goes together http://www.leaking-flat-roof.co.uk/

Hope this helps[/url]

west187 · 16 Jun 2007

Hi,
Just thought ild advise you to go G.R.P all the way . As long as BBA approved resins are used then cracking will not appear.Also you can get 20 ltrs to cure in 5 mins if you wish , so it aint as risky as you think.I been installing G.R.P roofs for over 10 years. plz dont hesitate to email me for any advice.

G.R.P Roofs last forever!
west

JohnA666 · 18 Jun 2007

Well during to inclement weather the roofs are still undone.

I still haven't seen any compelling argument against GRP, and during hot sunny days I'd much rather have a light grey shiny surface rather than a black matt surface. In the winter it doesn't matter ofcourse.

My cats could get really nasty if they found a soft surface where their claws adhere to, and EPDM might well be such a surface (can't say for sure though)
I also have three soil pipe supports that will need to be screwed into the new surface. The GRP would create a sealed surface around the screwholes, not sure how the rubber would be like.

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GRP vs EPDM (Fibreglass vs Rubber)

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