Roofing Question

I have a flat concrete roof 17m by 12m. whats the best way of roofing this area without adding too much weight or a full pitched roof please?

12 Answers

Best Answer

or as an alternative to both of the above you could install a epdm rubber system which come without any joins and can expand and contract with hot and cold thus lasting for upto 50 years would be applied to screwed down ply and glued to the deck
similar cost to fibre glass but approx a third more than felt but would never need to have it done again in 10 -15 years time

Answered 17th Mar 2012


Member since 5 Jan 2012

Fibreglass with vapour barrier - on OSB3 T&G or WPB ply - but remember if over a habitable room and you are replacing more than 50% of the covering then you need to comply with Approved Document L of Building Regulations (Insulation) and this is not cheap for GRP/EPDM nor Felt

Answered 26th Jul 2012


Member since 26 Jul 2012

cleaned and primed correctly it then can be felted as a normal flat roof, cheapest option and will last, hope this helps, CJ ROOFING SERVICES

Answered 9th Mar 2012

cj roofing services

Member since 21 Jul 2011

Fibre glass/EPDM has no thickness to this membrane.
Why would you use this product? 40 years 50 years? I am very sceptical, stick to the oldest and most recognised system that shows solid 25mml thickness, four year apprenticeships( not learnt in two days ) and still here to this day covering the most of London flat roofs.
Mastic asphalt needs no presentation.

Kerry of Eurolay asphalt and roofing.

Answered 26th Oct 2012

Eurolay Asphalt & Roofing

Member since 4 May 2011

18mm Ply-board or 18mm osb board would be suitable for base of roof, rubber cover fire stone comes in any size so no joints etc and would be my choice as it's easy to use simple to apply and has a long life expandency. Trimming makes all edges look very neat.

Answered 21st Nov 2016

Manchester's Roofing & Guttering

Member since 17 Nov 2016

Clean roof areas.
Apply bitumen primer.
Install high performance capsheet torch on felt.
I highly recommend felt as in my opinion it's the best flat roofing materials to use

Answered 10th Apr 2017

John Cawley (London) Limited

Member since 4 Jul 2014

Hi, You could screw down 18mm ply boards, then cover the roof in fibreglass,
this would be the lightest option. The good thing about fibreglass is you can
mould it to any shape roof you have, it usually come's with a lifetime
guarantee aswell.



Answered 7th Mar 2012

Paul Callaghan Builder

Member since 27 Feb 2012

Felting this roof would be the lightest option as there would be no need for timber decking. Simply clean and prime existing surface then lay the felt underlay and cap sheet. Insulation boards can also be added if it's a warm roof.

Answered 12th Jun 2017

Deltas group

Member since 24 Apr 2017

I would agree with weathertech
Epdm rubber is light weight and is the new option most people are having rather than bitumen green or red mineral which is a lot heavier and thicker than epdm rubber and epdm will last a life time

Answered 11th Oct 2017

Plus-More Property Services Limited

Member since 10 Oct 2017

Phoenix Roofing.
There are 3 ways to do this type of roof.
1. Prime the concrete with a bitumen primer then install a 3 layer felt system . This will give a good 15/ 20 years if done correctly.

2. Lay a 11mm ply over the deck fix and secure with screwing the decking down. Lay a epdm rubber roof, this i would say is the best method. No joints, allows to expand and retract and it will last 50 years with a 20year guarentee.
3. GRP. Deck the roof with 11mm OSB ply. Using OSB allows the fiberglass to grab / stick the decking. This also has no seems or joints. Should last up to 50 years.

Answered 30th Nov 2017

Phoenix Roofing Specialists

Member since 29 Nov 2017


If your roof is over a habitable space it would be a requirement of Building Regulations that the roof is insulated. Whatever Waterproofing you select I would advise it comes with an insurance backed Guarantee.

Whatever the Waterproofing system once installed as a traditional warm roof there would be no need to introduce any plywood. The whole system should be fully adhered.

Dave Middleton

Answered 14th Oct 2013

Middleton Contracts

Member since 27 Mar 2009

3 layer felt system:
1st layer vented
2nd layer underlay
3rd layer mineral finish

Answered 21st Jun 2017

GBG roofing & building ltd

Member since 20 Jun 2017

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