In the Victorian era, flat roofs were incredibly rare, with architects and engineers favouring pitched designs for optimum drainage and decoration. However, in the present day, flat roofs are a popular choice, especially if you’re adding an extension to your house and working with an architect to create something dramatic and different.

With this in mind, are flat roofs actually completely flat? The answer is actually “no”. We explore why below.

Flat roofs explained

While flat roofs are almost completely level, they are not totally flat. When a flat roof is being installed, it will be laid to a fall with one side lower than the other. They are usually designed to have a minimum fall of 1:40. Some technical handbooks describe a flat roof as having a slope that  “does not exceed 10º from the horizontal.”

Why aren’t flat roofs actually flat?

Flat roofs have a very minor slope so that rainwater can drain off to one side. This is to ensure that water, snow, and any other debris doesn’t accumulate on the roof and cause problems such as damp, rotting, leaks, and even serious structural damage.

Pros and cons of flat roof systems

Before adding a flat roof to your home or when planning an extension, you might want to weigh up the pros vs. the cons of installing a flat roof. We’ve explored a few of them below.


  • Flat roofs tend to be less expensive to construct
  • Flat roofs are easier to clean and maintain
  • Access to your roof is much easier
  • Internal space doesn’t have to be affected
  • Some people consider flat roofs to be more modern than pitched ones


  • The drainage from flat roofs is not as good as from pitched roofs
  • Flat roofs have historically been linked to more leaks and issues
  • If the falls on your flat roof are inadequate, you can end up with ‘ponding’ on the roof which is where small puddles of water accumulate on the surface
  • The lifespan of a flat roof might not be as long as a pitched one

When considering the pros and cons above, it’s important to remember that many problems only exist as a result of poor installation and construction. When you opt for a reputable roofing company, you can often benefit from guarantees and quality workmanship.

Flat roofing repairs and maintenance in south London & Surrey

With decades of experience in the construction and maintenance of flat roofing, South Thames are the trusted, reliable, and reputable roofing experts in your local area. Serving the whole of south London and Surrey, our expert contractors are on hand throughout the likes of Richmond and Epsom.

Whether you’re looking to have a flat roof fixed, removed, cleaned or installed, our experts are equipped with the best tools for the job. We are proud to be highly rated on both CheckaTrade and Google, giving customers complete peace of mind that their property is in safe hands.

To arrange a site visit or get a quote, get in touch by calling 020 8397 2900, or send an email to [email protected].