Types of Flat Roof

If you could go back only a few decades you would see that flat roofing, as a whole, did not have the best reputation. Often getting damaged, letting water in and needing replacing. However, the times have changed, and with new materials developed to offer them far greater strength and durability these types of roofs have had somewhat of a resurgence.

Not only do they take less time to build than their pitched alternatives, but they also require far fewer materials. Two key features that can severely limit their costs. It is because of this that they are particularly favoured amongst those looking to build garages or extensions – with average costs ranging between £1200 – 2000 (Single – double garage) versus roughly double that for a pitched. It is not a question of whether or not flat roofs are worth it then, but rather which type is best suited for you.

Cold vs Warm Roofs

Less of an argument than an important to know bit of trivia, the two most common builds of flat roof can be separated into cold or warm. The big difference between the two is insulation and, more specifically, where that insulation is placed. On a warm roof, your insulation sits right on top of the structure with a membrane lain over that. This keeps the structure warm and by doing so greatly limits the risk of damp and mould related damage.

Cold roofs are only slightly different, with the insulation instead sitting between the rafters and underneath any covering. This limits the height of your building and can, in some cases be easier to install, though does come with the downside of a poor thermal efficiency. In part of because of this, these days the majority of constructions will be warm roofs for longevity’s sake with cold typically being employed when dealing with height restrictions.

Of course, these two are not the be all and end all. Various ‘Hybrid’ constructions can also be employed which can include additional elements such as ventilation gaps to further limit moisture build-up. At the end of the day, however, what’s important isn't necessarily which type of construction you use but rather that it adequately protects your building's structure - both from air leakage and water ingress.

Flat Roof Coverings

Air leakage can be controlled with insulation and ventilation, though water ingress is another matter entirely. It cannot really be discussed without mentioning another key element in any flat roof construction (or replacement), that is its covering. Different coverings can offer not only vastly different levels of protection but also varying lifespans. It is important to know your felt from your rubber to make sure you are not spending too much, or worse, too little on your next project.

Felt

Perhaps the most traditional covering of them all, roof felt is often a misunderstood material relegated to the bottom of the barrel and not given a second look. There is good reason for this, felt (like flat roofs) have been known to be unreliable at times with life expectancies barely touching double digits. However, it is precisely because of this that quality manufacturers now know what to avoid.

Modern roof felt is more commonly made using bitumen technologies and thus resists the same UV damage that so often caused its predecessor to need to be replaced. Creating a stronger material has also led a more sophisticated application method using a blow torch. Each layer of felt (typically three) is heated and then melted onto your roof with the third and final layer often being reinforced for even greater protection.

Approximate life span: 20-30 years

Asphalt

Joining felt in the category of most traditionally used, Asphalt comes in at a slightly high price point but makes up for it with a fantastic level of flexibility. Suitable for use on all manner of timbre and steel structures, it can be lain whilst still hot and thus moulded around even the most awkwardly designed roofs with great results.

To achieve this great result, however, can take quite a bit of work. Something else asphalt is known for is its weight. Of course, this first means that weak of flimsy structures are out of the question but also that transporting and handling it can be far more difficult than the alternatives.

Approximate life span: 30-40+ years

EPDM

Otherwise known as Ethylene Propylene Diene Monomer or simply rubber roofing, EPDM has become a very popular choice for professionals and DIYers alike thanks to its relative ease of installation. Unlike felt it does not require an open flame and unlike asphalt, it is remarkably lightweight. The synthetic materials can be adhered directly to your roof deck, with trims fitted around the edge for a smooth and neat finish.

Especially useful for larger roofs, EPDM’s most standout feature is its elasticity which enables it to handle expansion and contraction in response to changing temperatures with little issue or damage. Although, this does not mean it can’t be damaged at all. While it is resistant to a lot of different forms of impact and general wear and tear, there is always the risk of it being cut or pierced, especially around any protrusions in your roof. In these cases, as EPDM is generally only installed in a single layer, any damage can leave the roof vulnerable and would need to be repaired as quickly as possible.

Approximate life span: 50 years

GRP (Fibreglass)

A material that finds its origins being used to making hulls for boats, you can be sure of GRP’s (glass-reinforced plastic) waterproofing properties. Lightweight, low maintenance and offering a joinless finish, GRP flat roofing can truly be considered a modern alternative, having nearly eliminated the risk of bubbles or faults forming in your roof. This in turn greatly limits the chance of damage and the need for repairs, with the only thing that really needs to be kept on top of being occasional cleaning.

Another significant draw of GRP is that it is DIY-friendly, mainly due to its excellent durability. Most GRP roofs can withstand foot traffic, alongside being cut or ripped and so the risk of accidentally damaging it when installing it yourself is quite significantly reduced. Most will be guaranteed to at least two decades but with a proper installation, can last even longer.

Approximate life span: 40+ years

Single Ply

More of a general term for an array of materials than a specific material in itself, single plies are, as their name would suggest, coverings fitted with only a single layer. These can include PVC, TPO, TPE and PIB though they all share similar features. For a start, they are lightweight, flexible, and easy to handle. Beyond this most also boast good chemical and UV resistance whilst also being able to combat most forms of turbulent weather.

 However, with all these benefits, the cost factor does come into play with most single plies coming out on the more expensive end when compared to the likes of felt. Due to the number of models out there, nailing down the life expectancy you want can also be a bit of a challenge. Most will come guarantee for 20 years however some, PVC in particular, can last almost twice that.

Tiles

In instances when your flat roof is expected to withstand regular foot traffic (such as a terrace or balcony), you’ll likely have to consider tiles. These are available in a wide array of different materials each with their own benefits, drawbacks and life expectancies but what they will likely all have in common is that they will require a substantial structure on which to be installed. If you are looking to build a terrace or convert a pre-existing building, make sure it is strong enough to hold this weight.

Green Roof Systems

A type of flat roof coming up in conversations more and more, green roofs brand themselves as a living environment – in essence, a whole layer of vegetation planted over the top of your waterproofing system. Especially popular among those with visible flat roofs, they offer something drastically different from your standard grey, black or green square whilst also touting some fairly significant environmental benefits.

Separated into extensive, intensive and semi-intensive depending on the amount of soil, growing medium and maintenance requirements (intensive requiring irrigations and drainage systems) all green roofs are able to absorb a certain amount of carbon dioxide in the atmosphere and provide habitats for insects and birds to thrive.

You may be thinking that while these sound great, they must also require a lot of work to keep, especially given they are on your roof. This is not the case. Though it may be true that many models require care and attention, just as many require none at all. The opposite in fact with some even being pre-grown and fully self-sustaining - A boon to the planet without the need for you to lift a finger after their installation.