What should I know about flat roofs?

Jun 1, 2022 | Building Issues

If you have an extension on your house or own a garage, you might have a flat roof on your property, however you may or may not understand the complications that are part and parcel with certain types of flat roof.

What is a flat roof?

To create a flat roof a waterproof exterior layer is necessary – mandatory in fact! – to ensure that the building can withstand the full force of rain and hail.

This can be made using layers of mineralised felt impregnated with bitumen or EPDM rubber, among other materials. They will include multiple layers to ensure a water-tight seal.

Although the name would suggest a completely flat surface, a flat roof is not entirely flat and instead has a gradient of 2-4 degrees. This is done to ensure the proper drainage – you don’t want water collecting in one area, that could be disastrous in the long-term!

Why do people opt for a flat roof?

Flat roofs are often a design choice – you will find a lot of new homes boast flat roofs as well as extensions and newly built garages because visually they give a more modern aesthetic that complements contemporary homes.

Having said that, the main reason people opt for a flat roof is they are a cost-saver. Flat roofs are less expensive to build than a pitched roof, with upfront costs for the materials and labour costs being lower as flat roofs are easier to erect and require less work.

What is the downside of a flat roof?

Despite their usefulness, flat roofs made from bitumen can actually have quite a short lifespan. This can be a result of sunlight and ineffective materials. Sunlight, for example, contains ultra-violet light – also known as UV light – hardens and dries materials, and in the case of flat roofs, can cause cracking and shrinkage leading to unwanted leaks.

Felt can also be easily torn and punctured either by human interference (people walking on the roof) or by Mother Nature (branches, stones, and damage from storms). The seams between layers are also a soft spot, as they can become weak or open over time, which leads to leaking.

They can also have issues with drainage despite the slight gradient that they are built with. Flat roofs are not as efficient as a pitched roof. Pitched roofs offer natural drainage from the steeper angle at which they are set, while a flat roof can still have rainwater gather on it, forming puddles. A badly-formed, uneven roof surface will not drain effectively either. Moss growth is also common and then slows the drainage. This water build-up can lead to water damage and leaks.

How long do flat roofs last?

Typically, flat roofs made using felt have shorter lifespans as a result of these issues, with leaking being very common. These types of roofs will usually last about 15 years, although in some exceptional circumstances they only last 5 years.

How to prevent issues

The best way to prevent issues is by regularly checking for signs of wear or damage as this will help avoid problems occurring and help to identify minor issues before they become larger. Minor leaks can lead to hidden rot so checking for leaks should be a priority.

Don’t forget to include the cost of maintenance in your calculations and future repairs when considering a property with a flat roof. Scaffolding or similar equipment will need to be factored in for repairs on roofs at high levels, in addition to the inspection and then repair costs – which can add up.

If you need to walk on your roof crawling boards are a must. This will help prevent rips or holes from shoes – stones stuck in the soles of your shoes are a big culprit here.

Modern Roofs

Modern flat roofs made from EPDM rubber can have the durability to last for around 40 years – a lot of which is down to being supposedly resistant to UV light – however, with that comes a higher cost. Having said that, if you have a straightforward installation it can be easy and not as pricey in the long run.

Make sure that when you buy a property that has a flat roof, or when you are considering extending your current one, and if you require a flat roof, you understand the commitment of the different materials. You don’t want to be paying out down the line for a poor-quality flat roof that needs to be replaced in 5 years.

Les Long FRICS FISVA Principal, Eyesurvey

Contact EYESURVEY Chartered Surveyors here for all your professional property services and needs.