Flat roof solutions
How to choose a flat roof
Flat roof systems
What is the best flat roof ?
I have been fitting new flat roofs, or having contractors fit my flat roofs now for over 30 years. As you can imagine, I’ve seen nearly every type of flat roof in the flesh, from installation until its death so to speak. So if you’re looking for some advice free of sales patter on which is the best flat roof you have just found it.
Calm down it’s only a flat roof
Some times the mere mention of ‘Flat roof’ sends home owners into an illogical state of mind. I’ve had customers spend 15 times the cost of replacing a unseen flat roof, and converting it to a pitched roof to save the cost of putting another flat roof on in later years.
Most modern flat roofs have an average lifespan of 20 years, so you would be lucky to replace it two or maybe three times before you are old or dead. Brutal but honest…
Unless its for aesthetic reasons flat roofs are cheaper, and you can also have a pretty flat roof.
Which is the Best flat roof – Flat roofs compared
A lot of people have asked me this and we could cover a lot of ground here, so let’s narrow it down to the most commonly available flat roof choices and I’ll try to list the positives and negatives in the fairest way possible as I see them. If you read similar articles on the Internet, you will often find huge differences between pro’s and con’s and life expectancy, as the article was either written by a web designer or by a flat roof installer who normally wants to sell their product and rubbish the competition.
Flat roof solutions
Flat roof comparison, here are the most commonly used and installed flat roof systems… EPDM V GRP Fibreglass V Torch on Felt
Felt Roof – ( Polyester reinforced Torch on )
EPDM – E.P.D.M rubber roof
Fibreglass – G.R.P. flat roof
I will describe each roof in order and then explain what you can expect in terms of
- Lifespan
- Cost
- Damage resistance and repair ability
- Appearance
- Installation issues or concerns
- Flexibility
- Vapour transmission or breathe ability
Torch on felt roofing
New bitumen felt roofs can unfortunately still carry a bad reputation from the older and now unused pour and roll systems of yesteryear. Large strides have been made, and continue to be made in flexibility and durability of a modern hot flame applied torch on roofing felts. Typically applied in a 3 layer system consisting of a vapour control layer, a layer 2mm reinforced felt and a 4mm layer of felt called a cap sheet which can be a plain black bitumen finish for a solar reflective paint finish, or a mineral fleck finish in a variety of colours, typically green, brown and a purple/blue.
3 layers of felt are melt welded together with a large blowlamp or torch from where it derives the name torch on.
Make sure any roofing contractor carries the correct insurance to work with hot flame.
- Lifespan – Most guarantees are 10 Years, my contractor guarantees 20 years. I think a well installed Torch-on felt roof could last up to 30 years if looked after and treated well.
- Cost – The cheapest option on the table here.
- Damage resistance – Foot traffic in hot weather may scuff the surface of a mineral finish; this can lead to U.V. damage by sunlight. Window cleaners also put step ladders and ladders on them in hot weather which could damage the surface.
- Repair – Easily repaired but patches on top can look messy, the plain cap sheet with solar reflective paint is the most repairable and popular in unseen and industrial settings for this reason.
- Appearance – Beauty is in the eye of the beholder, but I think a mineral finish is pretty to look at, I like brown and purple.
- Installation issues or concerns – Make sure that any contractor has full insurance to work with hot flame, mine carries 10,000,000 liability – never attempt a DIY installation.
- Flexibility – Modern roofing felt has good expansion and contraction properties.
- Vapour transmission – Roofs are often called on to breathe, thanks to the vapour layer a felt roof will do this. I would however personally never rely on a roof covering alone, especially if you have condensation issues. This should be dealt with in house or roof construction.
EPDM rubber roof
These have stormed the market since being introduced a few years ago in the U.K. A rubber roof can be often installed in one complete layer without the need for joins depending on size, which is often an attractive prospect. It is also extremely light weight, elastic and tough, so it lends itself to many situations. Mostly rubber roofs are glued down to the decking ( wooden substrate ) so if you had a felt roof previously the timber deck may need replacing depending on the system or glue used. Other fixing methods are possible i.e. mechanically fixed, and ballasted ( weighted down with stones ). A well installed rubber roof is a very good option.
- Lifespan – Some guarantee for up to 50 years, this seems to be an immensely variable figure from installer to installer and I question whether they plan to be in business or honour a guarantee with a 50 year time frame. From what I’ve seen so far a well installed EPDM roof should last 30 years upwards. I’m happy to guarantee mine for 25 years from what I have seen so far on aging UK installations.
- Cost – Very competitive, expect to pay 20% more for a nice example in relation to a torch on roof.
- Damage resistance – Very tough in most situations and foot traffic, always place something to spread the weight underneath a ladder though. And do not throw food on top of the roof for the birds, as I have seen a roof ruined by seagulls pecking it because of fighting over scraps. Can be repaired easily, but can look a bit like obvious, as it normally involves gluing on patches a bit like an inner tube repair.
- Appearance – For me this is a downfall, personally I’m not keen of the black, black/grey look of the roof, especially if it is to be overlooked from a window. That said a good neat installation helps.
- Installation issues – Unfortunately the easy DIY fitting of this roof has brought the cowboys out to play, some are simply horrible to look at, wrinkly, saggy and withought proper edging strips at drips. Also be aware of roof details, although a roof can be seam free, corners, pipes and complicated drips will mean joins and these should be done carefully and with thought by Trade or a DIY installer.
- Flexibility – You will simply not beat a rubber roof for expansion and contraction, if you have a large roof where this is a real concern, EPDM is for you.
- Vapour transmission – This is dependent on layers that may be underneath, but in normal glued down installs it will breathe less than a torch on felt roof. If condensation is a problem this may have to be designed into the roof construction or elsewhere in the house.
Fibreglass GRP flat roof
These have been around in the UK for well over 20 years but in small numbers, I first came across GRP many years ago when I was asked to supply a no-flame solution for a very awkward roof. Fibreglass roofs have suffered from a bad reputation in the past due to ignorance and faulty installation. A common mistake was using standard boat resins that couldn’t expand or contract properly, or laying fibreglass onto chipboard or smooth plywood. These days’ modern resins and correct installation has helped fibreglass become a real contender for a top flight flat roof. Normally laid in a one, or sometimes a two layer joint less finish with factory made trims and coloured to literally any colour.
- Lifespan – Most guarantees are 25 Years, and there will be no problem for this type of roof to achieve this if properly installed. I have personally seen fibreglass roof that are 30 years old with no visible signs of wear apart from slight UV fading of the top coat ( colour )
- Cost – Normally the most expensive option out of the three due to high material costs as re-boarding is normally required with OSB3.
- Damage resistance and repair – Incredibly resistant to most forms of damage, its extremely tough once cured. Repairs are very easy and can be almost invisible.
- Appearance – For my money the prettiest roof money can buy if installed sympathetically, it can look a bit new and plastic for the first 6 months to a year before the wax finish dulls on the topcoat colour. Lead flashing’s nearly always look better than the GRP flashing’s in my opinion.
- Installation issues or concerns – Make sure that any installer knows what he’s doing, skimping on resin or topcoat can cause pin holes and expansion guidelines must be followed, especially on larger roofs.
- Flexibility – Whilst new specialised roofing resins are flexible they are not as flexible as felt, or certainly not as flexible as EPDM. Roofs over 50 to 100m2 need serious thought and planning before undertaking.
- Vapour transmission – Fibreglass roofs do not breathe well, a bit like glued EPDM, so if condensation is a problem in your property this may have to be designed into the roof construction or elsewhere in the house.
Flat roof comparison at a glance
To sum up the difference between the flat roofs I have compiled a scoring system on points out of Ten, 10 being the best and 1 the worst. I have also averaged out the lifespan to how long it should last if installed by competent tradesman.
As you can see, there is a good reason these flat roofs are popular, whilst they all have a strength or weakness the overall package quite comparable.
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