Is GRP a good roofing material?

GRP flat roofing Prose and cons


  • Now easily available in DIY shops
  • Good and strong
  • Tested over many ears to perform
  • Comes in any colour
  • Can be formed into any shape
  • Will hold standing water


  • Very rigid and brittle if laid to thin
  • Has to be laid by experienced people
  • Has to be built up to form a good surface and this takes time and materials
  • Weather and temperature dependable

Other options to consider

  • 3M SD650
  • GacoRoof
  • Kemper

All three are based on the principles of GRP resins and glass fiber but they have been modified to be flexible.

My opinion.

If the GRP roof is laid correctly and to the correct depth they are good roofs however I only ever see well laid GRP roofs when Im down the coats these are normally laid by boat builders and are formed from may layers of GRP,  forming a good strong shell.

If you have lots of money and want a really nice looking roof then GRP is the way to go.


Problem with Green flat roof

Green flat roofs may be nice on the environment and nice to look at but when you get a problem they can be very expensive.

This green flat roof is probably going to have to be completely striped as the flat roofing membrane under it is leaking somewhere and we cannot find the problem.

Realistically under a green flat roof you don’t want to have joints that can go wrong at sometime, most new flat roofing materials will last for many years but when they do go wrong they will alway go wrong where there is details.

Remove the details remove the problem.

liquid rubber SD650 By 3m flat roofing 8

Garden Office Shed roof.

Hi,I saw your videos on You tube and was impressed.

I have a garden office, just installed bu it only has a temporary tyvec cover on at the moment (the company only did felt roofs and we asked for a shallower pitch to the roof for extra height height).

It’s under a tree, the floor space is 15m2 (3.75m x 4m) so the roof is slightly larger due to overhangs. Due to height restrictions, I cant’ do a warm roof, so it will be insulated inside with a boatload of cellotex I have.

Do you work in Se London? Is the best form of roofing for this fibreglass (GRP?). Do you have any idea how much it would cost? The access is through the house (it’s a victorian terrace) but it shouldn’t be a problem and the are no parking restrictions and we work form home.

Any advice on the insulation and the amount of air gap I need to leave would also be appreciated.

Many thanks,

Reply from:

London Flat Roofing.

GRP flat roofs or Glass Reinforced Plastic flat roofs, have in the past been a good alternative to the older tar based flat roofing materials such as Asphalt and mineral felt.

Time has moved on, second generation Liquid roofing systems evolved from older GRP systems, a glass fiber matt impregnated with a resin, the resins had been modified to stay flexible unlike Traditional GRP that’s rigid.

Third generation liquid flat roofing systems have no glass fibber matt to reinforce them, new resins bond together giving a tough durable materials that’s stays flexible but also very strong.

If you have not already seen the 3M video that promotes there new flat roofing system go and have a look they show there old system at the start with the glass fibers this system was good and flexible  the new system douse away with the glass fiber saving the material cost and the time but most of all removing a procedure that if not carried out correctly could over time be the downfall of the system.

The new system being easier to install means that there are less procedure to undertake on site, less chance of a mistake being made, less chance of a failure in years to come.

The 3m System on 13m2 will cost around £1500+vat

No air venting is needed if this is a warm room. Warm flat roof video

Yes we will work out your way

Send me some photos of what you have  I’m in office all-day today if you want to call 078023 00099

EPDM rubber will be cheaper still very good  around £1000.00+vat   black and not as good looking.

Estimate for new EPDM roof or 3M Scotchkote Urethane Roof Coating SD650 liquid roof.

Information from customer regarding his leaking flat felt roof.


We have a leak on a felt flat roof extension in London NW6 4SS, which is about 10 square meter. We are looking to replace with EPDM. Could you please come around for a quote?

Reply By email from London Flat Roofing.

EPDM over felt is not recommended as its black and attracts the heat in the summer melting the felt and making the rooms under the roof uncomfortable. To stop this happening the roof will need a OSB Board overlay  before the EPDM then flashing’s so I would suggest a price of £1400.00 +flashing’s and scaffolding if needed.

An alternative roof is the 3M Scotchkote Urethane Roof Coating SD650  the finish is light gray  so reflects the heat, although much more expensive that EPDM rubber, easier to lay and now over boarding needed  so would suggest a cost of around £1000.00+vat + any flashing’s and scaffolding needed
Both prices will be subject to how clean the old roof is and its accessibility.
All +vat
Guarantees up to 25 Years are available
Have you got access to the roof, if so can you send me some photos? if So can you send me a photo from outside the property
If you also send me the address I can look this up on Google earth.
These may be of intrest to you.

Time-laps video of a new flat roof

Cleaning a old asphalt roof

liquid rubber SD650 ny 3m flat roofing 8

liquid rubber SD650 ny 3m flat roofing 8 (Photo credit: EPDM Rubber Flat Roofing)

First coat detail round skylight

EPDM rubber roof northwood 6

EPDM rubber roof northwood 6 (Photo credit: EPDM Rubber Flat Roofing)

Liquid rubber flat roofing SD650 by 3M

liquid rubber SD650 ny 3m flat roofing 37liquid rubber SD650 ny 3m flat roofing 36liquid rubber SD650 ny 3m flat roofing 35liquid rubber SD650 ny 3m flat roofing 34liquid rubber SD650 ny 3m flat roofing 33liquid rubber SD650 ny 3m flat roofing 32
liquid rubber SD650 ny 3m flat roofing 31liquid rubber SD650 ny 3m flat roofing 30liquid rubber SD650 ny 3m flat roofing 29liquid rubber SD650 ny 3m flat roofing 28liquid rubber SD650 ny 3m flat roofing 27liquid rubber SD650 ny 3m flat roofing 26
liquid rubber SD650 ny 3m flat roofing 25liquid rubber SD650 ny 3m flat roofing 24liquid rubber SD650 ny 3m flat roofing 23liquid rubber SD650 ny 3m flat roofing 22liquid rubber SD650 ny 3m flat roofing 21liquid rubber SD650 ny 3m flat roofing 20
liquid rubber SD650 ny 3m flat roofing 19liquid rubber SD650 ny 3m flat roofing 18liquid rubber SD650 ny 3m flat roofing 17liquid rubber SD650 ny 3m flat roofing 16liquid rubber SD650 ny 3m flat roofing 15liquid rubber SD650 ny 3m flat roofing 14

Via Flickr:
The words Liquid Rubber are what most people perceive liquid roofing products to be, realistically out of the 15 or so liquid roofing materials on the market there is only one Liquid Rubber liquid roofing material that I know is actually liquid EPDM rubber, all the rest are liquid emulsion liquid polymers, or some other kind of material.
We are using 3M Scotchkote Urethane Roof Coating. SD650 is a two component, elastomeric, solvent-based urethane for flat roofs and its good, very good! Exactly what you would expect from 3M. It comes with a 25 year guarantee from 3M, when installed by a trained contractor, and yes, we are trained contractors. So if you need any info on the system please don’t hesitate to contact me: Steven Dickinson 07802 300 099 at London Flat Roofing Ltd.

This is a link to some of the videos on Youtube we have, showing this flat roofing system.
Time lapse video of a new flat roof
Cleaning an old asphalt roof
First coat detail round skylight

Camden Kensington Hammersmith Highgate Holborn Belsize Park Bloomsbury Camden Town Chalk Farm Covent Garden (also partly in Westminster) Dartmouth Park Fitzrovia Fortune Green Frognal Gospel Oak Hampstead Haverstock Highgate (also partly in the London Borough of Islington and the London Borough of Haringey) Holborn Kentish Town Kings Cross Peckwater Estate Primrose Hill Regent’s Park Estate Saffron Hill St. Giles St Pancras Somers Town South Hampstead Swiss Cottage Tufnell Park West End of London West Hampstead St Johns Wood

Estimate for a new flat roof


Your website and videos are very good; very reassuring.
This is an old mineral felt flat roof I need an approximate quote for a cold roof repair please. Cold roof because of a window that sits on the flat roof; a warm roof is not possible.

It’s a typical Victorian north London terrace with rear addition. The flat roof is about 3m x 6m in size and situated above the rear addition, with two edges against brick walls and two open. Access is from the back garden, i.e. through the house. I can supply photos.

I will insulate from below (the ceiling is down) and would need you to do the following please:

old flet roof on a flat in Hammersmith

  • Remove two layers of mineral felt/boards (i.e. it has been re-roofed before and the original roofing boards – planks – are still in place but should be replaced)
  • I’ll supply a skip
  • Re-roof (cold) with one of the membrane options you offer.
  • Build the ventilation along the wall/parapet edge.
  • Finish detailing around all four edges including flashing, replacing fascia boards and re-pointing.
  • I’ll sort the guttering.

This is a bog-standard configuration – there must be 100,000 houses like this in north London. Are you able to give approximate quotes, for the different options, without a visit please?

Thanks in advance.

Reply to Email

Thanks for the email and the photos of the roof.

It’s a felt roof that looks quite good. I can’t see the back or the right hand side but as you state there are thousands of roofs like this, probably with a parapet along the back and a drip into the gutter, right hand side.
Yes, it’s the window that gives you the problem with turning this into a warm flat roof.
If you don’t insulate then we can cap the roof using a liquid system; basically this just goes over the existing roof. Although this is classed as a capping system, it will not trigger Part L1b and you don’t have to insulate the roof. The system I would suggest is the 3M SD650 system, as 3M give it a 25 year guarantee. Also we can possibly do the work using harnesses for health and safety.
As you are aware, if you insulate the flat roof from below, the new flat roof will have to be vented front and rear, which will definitely mean we will need scaffolding.
The option of turning this into a warm flat roof is still there; we could insulate over the felt and leave a box gutter in front of the window, we will still have to raise this area by 25mm to stop any thermal bridging.
The existing lead flashings look good so they can be re-used, although what I cannot see are the back and side details.
I would suggest that these will be OK. There will be a cost to clean the roof and carry out preparation before the roof can be laid. I do need to see the job and would like to see the some more photos, I’m assuming work can be carried out through the window?

New EPDM roof over an old asphalt roof

We want to place a new EPDM roof over this Hi,
I’ve looked at the photos of the flat roofs you sent me. Both flat roofs will have to have hand rails around them before any work can be carried out. Realistically a working platform would be the best option, around 500mm down from the ridge, as the ridge tiles will have to be removed so that the flat roofing material can be dressed up and over the top of the ridge.

Both flat roofs will need to be cleaned then overlaid with OSB board before the new flat roofing EPDM Rubber can be installed. An alternative material that could be used is the 3M Scotchkote Urethane Roof Coating SD650. This is a two component, elastomeric, solvent-based urethane for flat roofs and is very light in colour so it reflects the heat of the day in the summer. If you are not going to insulate the roof then this is the best option. It goes directly over the old asphalt, with no need to lay the OSB, so the saving there covers the cost of the slightly more expensive system.