How to choose your flat roof specification.

Flat roofs are an effective way of keeping the rain out whilst minimising the height of the roof.

They have a poor reputation due to poor installation and neglectful maintenance. Today’s properly installed flat roofs are no more susceptible to leaking than pitched roofs and should be the first choice for many situations where the height is limited by planning law.


Typical issues when designing for loft conversions.

Planning permission is needed if you want to raise or build anything higher than the top of your ridge tile level. If planning permission is not forthcoming, it is possible to get the ceiling height you need by lowering the floor. However, this means that the ceiling below will also need to be reduced, which is not always desirable. The ceiling height dimension will depend on the building the loft conversion is within. If the loft conversion is a self-contained flat, the ceiling height will need to be 2.5m, although 2.3m may be acceptable. For loft conversions that provide ancillary bedrooms, the ceiling height ranges from 2m up.

Flat roofs are the simplest way of stopping the rain from coming in. Flat Roofs are also used for extensions and are a great way of minimising the height of the roof and maintaining clean and straightforward lines. Early modernist architects favoured flat roofs for their simplicity and clean horizontal lines.


For us at G.A. Architects, there are two essential considerations to be aware of when deciding your flat roof design.

  1. The appearance of the roof
  2. The performance of the roof



The appearance of a flat roof

The appearance or aesthetics of your flat roof is the primary consideration because we firmly believe that what you look at affects your mood and, ultimately, your general outlook. If you are pleased with what you see, you will generally be a happier person. And we believe more comfortable people lead more fulfilled lives.

The design of the roof is inseparable from the design of the building or extension as a whole.

How can a flat roof make us happy?

To answer this question, we need to understand our client’s intuitive preferences.

We ask our clients particular questions which will inform us as to their preferences. Do they prefer traditional or modern design? Are they looking for something more calming or something more functional?

These are not opposites for some people, and people can be made calm by more functional design. Do they want it to blend in or stand apart?

The answers help us to consolidate the design ad choose particular ways of doing things. A more modern approach would be a metal roof for a flat roof, perhaps a standing seam zinc roof. For a more traditional approach, a lead roof could be the answer. A more utilitarian approach would be a felt roof, a rubber, GRP or a single-ply membrane.

A more contextual roof could be a green roof, and these vary between tall grass (extensive) or sedum matting (intensive) roof coverings.

The roofs’ design should always complement the design as a whole and should always be carefully considered within its context for the best result.

The question regarding the roof’s performance is the next consideration.

Lead flat roof build-up

Flat roof performance

The performance of a flat roof is concerned with its structural design and thermal efficiency.

The structure required to support the roof depends on the weight of the roof and the type of structure, whether it is steel, timber or concrete. The structural design will help to determine the overall thickness of the roof.

The overall thickness of the roof will determine the overall height and the internal ceiling height.

The roof build-up must accommodate thermal insulation for a roof to meet the minimum thermal insulation standard (U value). There are many different thermal insulation manufacturers on the market, and they vary in quality, thermal efficiency, density and longevity. The best thermal insulation products can achieve the same thermal efficiency with thinner insulation which has clear benefits for maximising your ceiling height.


There are many questions and considerations, and we at G.A.Architects, dedicate ourselves to informing our clients and helping them make the right decisions.

Rainwater hopper

GRP flat roof
PD Rights for householders