Should I Buy a House With a Flat Roof?
- Flat roofs do come with some added risks, but you should weigh these against the benefits
- You can still get a mortgage on a house with a flat roof
- If you decide to go ahead with your offer, make sure you get a survey before you sign contracts
What is the downside of a flat roof?
Drainage
The main concern with a flat roof is drainage. While flat roofs have a slight angle to direct the water off the roof, it is not nearly as efficient or reliable as a standard pitched roof. Due to the gentler slope, stagnant rainwater often pools on the roof, and even a slight build-up of fallen leaves or moss can prevent proper downflow.
On a pitched roof, if the drains become blocked, the water will still fall off the roof, whereas a flat roof can turn into a bit of a paddling pool. The problem with this pooling water is that it can lead to leaks and damage to the roof. Sitting water will also wick away the heat faster than a dry surface.
Stability
Triangles are the strongest shape there is, which makes pitched roofs incredibly sturdy and increases the structural integrity of the whole building. To compensate, a flat roofed building will need additional structural support.
Ever wondered if you should buy a house with gable straps?
Lifespan
Flat roofs need regular maintenance. Older roofs that use traditional felt have a lifespan of 10-15 years, but modern plastics like polyurethane and polycarbonate can increase this. EPDM rubber roofing can last closer to 50 years, however, it is important to note this is much more vulnerable to puncture than a solid slate tile.
The payoff is that flat roofs are relatively cheap initially and access is easy, meaning you can carry out most maintenance without the cost of scaffolding. However, they can become more expensive in the long term. The best approach is to inspect them regularly (once in spring and once in autumn, plus after any heavy storms where debris may have struck the roof). Keep the roof clean and clear of obstructions (including moss and vegetation) and tackle any signs of leaks as soon as possible.
Heat absorption
Flat roofs typically allow more heat transfer, making your home hotter in the summer and colder in the winter. This is partly due to the full surface area being exposed to the sunlight (on a pitched roof, it is often only half the roof at a time, except for the very height of the day), heat-absorbing materials and less insulation space; imagine a typical house shape with loft insulation on both the floor of the loft space and under the angled roof, with the loft cavity in between, versus a flat roof with a single layer of insulation at whatever spec was required by building regs at the time.
This is less of a concern if the roof is over a garage or garden room which is mostly unused in the colder months, but may pose more of an issue if the roof is over living space or bedrooms, especially with rising energy costs.
Flat roof, green roof?
One option to consider if the roof can support the extra weight is installing a green sedum roof. This is an extra insulative layer, although it is better at keeping the house cool in summer than warm in winter due to the water it holds. Added benefits of a green roof include:
- Microclimates for insects and birds, including rare species.
- Limits the 'urban heat island' effect where standard construction materials reflect and retain heat, creating problems with energy costs (e.g., for air conditioning), air pollution levels, and heat-related illness and mortality.
- Reduced surface run-off taking pressure of drainage infrastructure, which can contribute to surface-water flood prevention.
- Sound insulation; the substrate deadens lower frequencies while the plants themselves absorb higher ones.
- Increase the lifespan of the roof's waterproof membrane by protecting it from the elements.
- Improve air quality.
- You can even create a roof garden for leisure or veggies and herbs.
Space
Flat roofed houses have no loft space, which may be a problem if you're short on storage. However, flat roofed extensions make the most of the limited height allowed under permitted development, which means you'll get the most room-space out of the maximum height that the previous owners were able to build to.
Is it OK to buy a house with a flat roof?
There are loads of benefits to buying a house with a flat roof: they're often cheaper; they don't impede the view; you can install air conditioning, solar panels, satellite dishes or external water tanks on them; and you may even be able to convert yours into a balcony or patio.
If you have weighed up the pros and cons of buying a house with a flat roof and you love the property, you should move forward with your offer. As we recommend for any purchase, you should have a thorough home survey conducted by a professionally accredited surveyor to inspect for any potential defects before you sign contracts.
Remember that modern flat roofs have come on leaps and bounds from what they were like in the past.
Caragh is an excellent writer and copy editor of books, news articles and editorials. She has written extensively for SAM for a variety of conveyancing, survey, property law and mortgage-related articles.
