Flat roofs are often specified for a variety of reasons; aesthetics, cost and functionality. IKO highlight the important things to consider when designing flatroofs.

While their conceptual and visual simplicity is undoubtedly part of the appeal, specifiers should be aware of the complex detailing and required design to achieve a solution that is fit for purpose and provides long-term protection. Adding to the complexity of the design process, there is a number of different flat roofing materials and systems available – each with its own individual characteristics and technical requirements.

There are three different types of flat roof construction; warm, cold, and inverted and each has multiple layers in their build up to get right.

Common mistakes made when designing flat roofs
Particular attention should be paid to project sequencing and preceding trades. For example, the detailing of roofs around openings and reveals needs to be completed before doorways, rooflights and clerestorey windows are installed. Achieving adequate long-lasting weather protection around these critical junctions can be very difficult if these elements are already in place.

Advantages and disadvantages of cold and warm roofs
Cold roofs are less popular in the UK due to the need for increased depths of insulation required to meet current U-values and the requirement for cross-ventilation. It’s more a question of whether to specify a warm or inverted roof. An inverted roof places the waterproof layer directly over the roof deck and beneath the closed cell thermal insulation and ballast where it is less susceptible to damage and UV-degradation.

On the downside, the waterproofing can be difficult to access in the case of water ingress, it needs to be ballasted which increases the overall weight of the roof and is generally installed on to a concrete deck adding overall roof construction cost.