When completing a home insurance quote, you may be asked whether any part of your roof is flat and, if so, what percentage of the total roof area it represents.
For many homes, especially those with extensions or integral garages, this can be surprisingly difficult to answer. Most properties are not entirely pitched or entirely flat, and you are not expected to provide an exact measurement.
This guide explains what insurers mean by a flat roof and how to estimate the percentage accurately and consistently.
For insurance purposes, a flat roof usually means any section of roof that is not traditionally pitched and tiled or slated. Flat roofs often have a slight fall to allow water to drain, but they appear flat when viewed from ground level or above.
Common examples include:
Flat roofs are commonly covered with materials such as felt, fibreglass (GRP) or rubber (EPDM), although the material itself is assessed separately from whether the roof is flat. Homes with mixed roof types are often treated as non-standard construction for insurance purposes.
The percentage refers to the proportion of the entire roof area of the main building that is flat.
This includes:
It does not include:
The percentage is based on roof area, not the number of roof sections.
You do not need exact measurements. Insurers expect a reasonable estimate.
A simple way to work it out is:
For example:
Rounding to the nearest sensible figure is usually fine.
Often have a pitched main roof with a flat roof over a rear extension. Flat roof percentages commonly fall between 20 and 30 percent.
Flat roofs are often found over garages, utility rooms or side extensions.
May combine pitched roofs with flat sections, particularly on extensions or balconies.
Flat roofs are more common and may make up a significant proportion of the roof area, depending on the building design.
During a quote, you may also be asked whether the roof is made entirely of slate or tile, and whether any part of the roof is made of felt. These questions are linked, so the answers should be consistent.
Percentages are always calculated against the entire roof area, not just the flat section. If you are working out multiple roof materials, you may find our guide to calculating construction percentages helpful.
As an example, if a rear extension has a flat felt roof that makes up 25 percent of the total roof area, you would normally expect:
If you are not confident, there are a few ways to sense-check your estimate:
If you are looking for official planning records, the Planning Portal explains how planning and building work is typically recorded in the UK.
If you are still unsure, it is generally better to provide a cautious and honest estimate rather than guessing too low.
Flat roofs behave differently to pitched roofs. Drainage, maintenance and materials can all affect how insurers assess risk. You can read more about this on our flat roof insurance page.
Providing an accurate and consistent estimate helps ensure your quote reflects the construction of your home and avoids delays or follow-up questions later.
Many homes have some flat roof, particularly where extensions or garages are involved. You are not expected to calculate precise measurements, only a reasonable estimate based on the whole roof of the main building.
Taking a few minutes to check and ensure your answers are consistent across roof type and materials can make the quote process smoother and more accurate.
Usually yes, if they form part of the main building’s roof. Many quote journeys treat porches, conservatories, extensions and integral garages as part of the main building for roof calculations.
Usually no. Detached garages, sheds and other outbuildings are typically excluded if they do not form part of the main structure of the building.
No. Felt is common, but flat roofs can also be covered with rubber (EPDM), fibreglass (GRP), asphalt and other materials.
Usually not. If any part of the roof is flat, the roof is not entirely slate or tile. You would normally select the additional roof type or material and provide an estimated percentage.
If you cannot estimate confidently, you can use satellite imagery, plans or paperwork to help. If you are still unsure, it may help to seek advice from a roofer or builder, or provide a cautious estimate that reflects your best understanding.
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