Help with new roof

[psarinuk]

Hi

Hope all are safe and well. Just need some guidance on a new flat roof.

I have a house with a full flat roof (porch has a flat roof too).

The current felt roof is nearing its end of life, so going for a replacement before it leaks.

I've narrowed on 2 choices:
1. GRP system: The roofer advises that he will install new OSB boards on top of current felt (after cutting/ clearing a few bubbles. Then install GRP on top of that. Should this be OK or a full strip is needed? He says it comes with life long warranty (if there is such a thing).

2. Bowsers 3 part rubber system: Slightly less expensive with 20 years warranty. It allows for movement and is laid as one piece. Not prone to cracking with movement like GRP.

I am attaching a couple of pictures to give you an idea. Any advice would be greatly appreciated.

Roof1

• psarinuk
• 15 Mar 2021

 

[^woody^]

Either will do. The warranty must be insurance backed to be worth anything. Liquid GRP can be laid on an existing cover if the existing is sound, and tends to require regular inspection and maintenance to maintain the warranty.

You may need to update the insulation too at the same time, did the roofers tell you this?

 

[psarinuk]

Thanks Woody,
How can the roofers touch insulation if they are not taking all the existing felt and boards off?

I will check on insurance backing warranty but really doubt it as not one of them has mentioned this.

With your advice and some reports on the noise generated by GRP system, I am probably going for Bowers 3 part rubber system. Is this also known as EPDM?

 

[^woody^]

With roofing, if you are removing a layer, then building regulations dictate that you should take the opportunity to upgrade the insulation at the same time if its practical - ie you can often increase the insulation for little additional cost.

If you don't disturb the roof, then you are not obligated to consider upgrading the insulation.

I'm not familiar with that Bowers product you mentioned. EPDM is normally a single layer system, and Firestone is the market leader.

 

[catlad]

If you are going to keep the old insulation then I would say that is a mistake as there will probably be very little with the age of that construction, now is the time to improve the thermal performance of your home.