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.


Liquid roof covering by GacoRoof over a parapet wall

In this video I show you just how flexible the GacoRoof covering is

We have just covered an old asphalt roof in wembley with the new liquid waterproofing system, we dressed the parapet walls with the system so we didn’t have any flashing details to deal with.

No flashing no messing about complete encapsulation, the flexible roofing system will allow for expansion and contraction  over the seasons





Preparation before a new liquid flat roof

We are on day to of this roof, the old roof is an old asphalt roof and was leaking from several places.

In this video I walk you around the roof showing you the condition of the old roof, some of the cracks and detailing.

The new liquid roofing system we are about to use on this roof is imported from the USA and is relatively new to the UK

It’s a silicon-based flat roofing materials called GacoRoof and one of its biggest advantages over other flat roofing materials is its amazing flexibility

Before we cover the old flat roof with the new roofing system we have given it a good clean and repaired all the damage that has happened over the years.

This old roof had Ponding or pooling water all down the center, although a problem to the old roof its not a problem to the new liquid silicon roof.

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?

Cost of EPDM rubber roofing is coming down

I hope everybody understand that I love EPDM Rubber.

I never knock it as a roof covering is really good.


It must be used in the correct places  and by people trained in EPDM rubber.

Recently we got trained in yet another flat roofing system Triflex its a liquid covering and its reinforced it amazing however its expensive.

The most expensive flat roof coverings  apart from metal coverings such as lead copper  zink and so on  are:-

Not so expensive for us to buy but expensive for us to fit.

Liquid Plastic
Expensive for us to buy and slightly expensive for us to lay.

Expensive for us to buy and slightly expensive for us to lay.

Expensive for us to buy and slightly expensive for us to lay.

EPDM Rubber
Cheep for us to buy and quick and cheep for us to fix.

All of the other flat roofing  suppliers are putting up their prices however because of the amount of EPDM rubber being laid the price seems to be falling for the EPDM.


Problems with lead roofs

In this new video I show some problems that I see more and more, the lead is oxidising because of lack of ventilation.

Todays building methods and materials mean that if you don’t ventilate your roof correctly the roofing membrane will stop all movement of air and water vapor this can then lead to sweating when the conditions are correct.

The new EPDM rubbers and some of the liquid rubbers are vapour permeable however this does not mean you don’t have to vent the roof it just means that a small amount of water vapor can move through the membrane

New Roof cost

New page added to the site today all about how much a new roof costs I also have a roof cost estimator being launched next month this will help people find out just how much the different roof materials cost.

I’m asked all the time how much a new roof cost and realistically nobody puts their prices up on the net  I don’t understand this!

Anyhow I’m going to change this the new roof price estimator will work out the price of a new roof based on criteria entered by the user, it will collect the information then send the  user a PDF with prices and options of several different new roof materials.

Speak soon