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Which Is The Best Flat Roof System, Felt, EPDM Rubber or Fibreglass / GRP? Flat Roofing Systems Compared

Seams are a common failure point


If you want to replace your flat roof, this guide will help. There are a lot of different types of flat roofing materials out there so identifying exactly what sort you have and then identifying the cause of the leak will help you, whether you fix it or get someone in to replace it completely. First things first though if you have a bit of an idea what you're looking at, it will help when you're talking to the roofer so lets take a quick look at what you need to know.


There are different types of boarding. Typically roofs either have chipboard or tongue and groove decking. There are other types out there, but this is what you usually find on older flat roofs, with chipboard being used on the majority. Nowadays OSB decking is used as it doesn't swell and soak in moisture unlike chipboard.

If you're going to climb on your roof for a look, then be careful. If it's chipboard decking on there and the roof has been leaking for a while, then it's usually soft between the joists and you can go through it.

If the decking is tongue and groove or another type of ply, then not only can you usually walk on there fairly safely, but the roof covering can sometimes be removed and another roof system can be put in place on top of the existing boards. This is less messy and causes less disturbance than replacing the boards. If the boards are chipboard, then they will usually need to be replaced.

Can you fix it yourself?

Sometimes it is possible to fix the problem you have. Sometimes the leak is caused by the pointing failing where the material enters the wall. This isn't usually the cause of a leaking roof, but it can sometimes need touching up. This can be done with a trowel and mortar mix relatively easily. The key is to rake out as much of the old pointing as possible without damaging the roof material and then take your time when applying the new mortar. A plasticiser added to the mortar mix will reduce the possibility of it cracking in the future.

If the decking looks like this underneath, then you're past repairing it. It's time to think about a new roof!


If you have a felt roof for example and you don't have a large leak, then it is sometimes possible to use the DIY sealant tubs that you can buy from most DIY shops. This can fix the leak semi permanently and people do sometimes get several years out of these sealant tubs. Ultimately you will need your roof replacing, but they can do the job if you're in a bind and need to stop the leak quickly. If you're going to do this the most important thing to do is get the leak area clean and dry before you start otherwise any repair will not work. Give it a good sweep down, use an old towel then the best thing to get it really dry is a heatgun, or a hairdryer at a push. Heatguns get hotter so will do a better job and they don't cost a lot. You can get them from most hardware shops.

After you've dried your roof and before you attached your flashing or sealant tape, then it can be an idea to warm that up too. It depends on what you're using, but often a bit of heat makes these things more pliable and sticky so you can get it where you need and get it to stick. This isn't so necessary if you're using a gunk, but it can sometimes help those to get runnier and get where you need them. If you're repairing a rubber roof, then a bit of heat helps here too as your primers and glues don't perform well if they're too cold.

This is a tiled garage roof. Usually the most expensive option.


This is a flat roof fitted with felt


This a fibreglass (GRP) roof


This is a PVC roof. The brand of PVC used here is Sarnafil.


This is an EPDM rubber flat roof


Roofing material options

Once you decide to get a new roof altogether, there are different options for replacing your flat roof. These include the following.

New pitched / tiled roof

This is an option that some people like to choose. The advantages are that it can change the look of the property, which some people prefer. The disadvantages are that costs are generally far higher than having a replacement flat roof and installation times are a lot longer. You usually have to get planning permission if you're changing to a tiled roof, although this will depend on various factors.

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Felt roofing

This is a well known system that most people are familiar with. The advantages of this are that it's cheap and if it's done well can last for a few years. It can also be supplied in different colours. These are often covered with stones or painted to try to protect from UV rays. Felt softens when it gets hot in the summer, so can then be damaged and over time tends to get brittle and crack. The main advantage of felt over other systems is that it tends to be cheap.

GRP / Fibreglass roofing

GRP roofing systems can look nice if they're installed properly. Once again they can be supplied in different colours. The cost is significantly higher than felt and the weather conditions have to be just right for these to be installed as they take a day or two to cure. Fibreglass GRP flat roofs are very labour intensive with the mixing of resins and application of gel coats done on site. The quality depends on the person mixing the ingredients & their understanding of the right quantities. These constantly change depending on the current climatic conditions. As the surface is very hard then any rain or hail falling onto the roof can be very noisy which can be a problem, depending on where the roof is located. These roofs can be good, but you have to bear the above in mind when choosing the system you want fitted.

Butyl roofing

Butyl is another material that's often found on flat roofs. It has a rubbery appearance and is usually covered with stones. The stones on the roof can fall into the gutters and block them. The problem with butyl is that it tends to shrink due to UV exposure on the areas where it isn't covered. This tends to pull it away from any walls or edges as it shrinks. This material is not so popular nowadays, but there are a lot of roofs that this has been fitted to so it's a fairly common sight.

PVC roofing

Again a neat finish if done correctly. This system tends to be labour intensive in comparison the other systems as the seams, flashings etc take a lot longer to install than a lot of systems, which usually means that prices are higher. These systems usually have quite a few seams as the material is not available in particularly wide rolls, 1 metre wide rolls are the norm.

The seams are heat welded together, which can be a downside as if the seam gets too hot then the material turns brittle and if not hot enough they won't join correctly. These can shrink as well, but are usually fastened down to try and prevent this from happening. Once again, these roofs can have a nice finish, but be aware of the pros and cons when considering them as an option.

EPDM roofing

EPDM is a rubber membrane. It comes in very large sheets, so most domestic roofs can be installed in one piece without seams. It is fully adhered to the deck. There are several advantages of EPDM over other roofing systems. Firstly it's fairly quick to install so the roof can be made watertight quite quickly. It is also easy to repair if you ever have anything fall on or pierce the roof. It is also flexible, so if there is any movement in the building as temperature fluctuates throughout the seasons, instead of cracking or splitting, it will move with the building. As it is resistant to heat and light, there is no need to cover it with any protective membrane or stones. It also is hardwearing and has an extremely long lifespan. It is not affected by UV rays so it doesn't shrink or crack. As it lasts fifty years plus, although installation costs are usually a bit more than felt for example, it usually pays off as the roof doesn't need fitting again.

These are a few different options that are available to you. The most important thing is to remember that installation of any system has to be done correctly or any of these systems will fail. Ensure that you get an approved, experienced roofer to install your roof. If your budget is tight, you can get by with sealant, but it won't do the job forever.

  • Flat Roofers Nottingham
    Rain Defence Roofing are flat roofing specialists, based in Nottingham. They install and replace flat roofs, using EPDM rubber membrane.


john pflugfelder on July 23, 2020:

i need a new roof. Flat row home

Rain Defence (author) from UK on February 12, 2013:

There are some decent felts and felters out there, the same as fibreglass and all of the other systems. There are also bad installers of all. One thing EPDM does have going for it is that it is quite common to use a single sheet for the whole roof. If you're talking a garage or simple extension, it's pretty hard to get that wrong even if the fitters aren't great!

As usual, getting decent experienced fitters is the most important thing, regardless of which system is used, although there are certainly some systems that are superior to others on my opinion. Thanks for your comment.

Jon Burr on February 11, 2013:

Most modern felt system are extremely good and high performance systems which are commonly used by reputable companies are either SBS based or polyester / glass fibre torch on systems and mainly consist of three layers, a base layer (3B glass fibre based usually nailed or a 3G which is a perforated layet partially bonded then a 2 mm glass/ poly torch on underlay then a plain or mineral coated cap sheet fully torched all edge detail to be enveloped with 2mm undetlay (wall abutments primed prior to this) verge drips and front (gutter drips fully heat welted with a minimum of 100mm returned and sealed down on to the flat roof surface.

With these modern membranes if they are fitted correctly will surpass many of the single ply rubber, butyl and fibre glass systems as themodern "felted" membranes are a world awau from what most laymen and some so called surveyers and architects omsgine them to be. They can take up thermal movement teally efficiently and can be fixed in most applications simply and quickly without any major problems with low temperatures etc

Rain Defence (author) from UK on February 09, 2013:

Nice attempt at a link! Unfortunately they're no follow on this site, but keep it up..

Virginia Lawrence on February 08, 2013:

This is so great, thanks so much for the info. Now correct me if I'm understanding wrong, but I'll need an epdm membrane? Or am I misunderstanding? Would this be a good place to get one?

Rain Defence (author) from UK on December 07, 2012:

Thanks for your comment!

tipstoretireearly from New York on December 07, 2012:

Very good information. Its the best article on flat roofing materials that I've come across!

James Cartwright on December 03, 2012:

Great post, this has been really helpful! Focusing on the 'Can you fix it yourself' section of this post, I have been getting routine checks done on my roof once a year to make sure the cold months haven't caused any major issues. I found a useful guide on access platforms as I realised the ladder I wanted to buy found here was not going to be suitable for me

So I opted to find someone to operate one of these and inspect the roof for me

Rain Defence (author) from UK on October 10, 2012:

It's always better to get a professional in when it comes to structural maintenance in my opinion. DIY is alright for non essential repairs, but your roof is pretty important really..

dommcg on October 10, 2012:

Great article, it's really cleared up some questions I had. I still think I'll get a professional in tho

jamesedmunds on August 30, 2012:

Very nice article. Thanks for sharing this useful tips for metal roofing. Colorado springs roofing companies also provides best and quality metal roofing service.

Maren Elizabeth Morgan from Pennsylvania on June 17, 2012:

Thanks - I am doing research for major roof repair/replacement.

Natasha from Hawaii on March 04, 2012:

Thanks - yesterday it started raining in my closet!

Rain Defence (author) from UK on December 21, 2011:

Thanks. It's more of an information piece about available options than a guide on exactly how to fix what you have at the moment. I went off in a different direction once I started writing!

Dreamer at heart from Northern California on December 13, 2011:

This should help some people who have questions about repairs. Good information.

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