Thermal Design

Thermal design focuses on managing the flow of heat and water vapour through the roof structure. This consideration is crucial for maintaining the roof’s performance and its components. Designers must evaluate insulation levels to minimise heat loss and prevent condensation issues.

Insulation

Choosing the right insulation is vital for flat roof performance. It should be compatible with the waterproofing system and meet fire resistance standards. Accessibility for maintenance during and after construction is another critical factor to remember.

Condensation

Understanding condensation is critical to effective flat roof design. The dew point is the temperature of the air, which is fully saturated with moisture. When the warm air meets a cold surface, it’s cooled, and the temperature drops well below the dew point and gives up moisture in the form of surface condensation. This condensing moisture can enter the waterproof membrane and affect the system’s integrity. Appropriate product selection is key.

Deck Types

The materials used for the roof deck should comply with standards like BS:6229 2018. Appropriate materials ensure durability and performance, so designers must consult relevant guidelines.

Creating Falls for Drainage

Building regulations require that flat roofs facilitate proper rainwater drainage. Following BS 6229 & BS 8217, a minimum fall of 1:40 is necessary to ensure adequate water runoff. This applies to both roof areas and internal gutters.

Drainage Systems

Flat roofs must incorporate efficient drainage solutions through internal rainwater outlets, downpipes, or external guttering systems. Even small roofs should ideally have at least two drainage points to mitigate the risk of blockages.

Fire Resistance

Building regulations dictate fire safety standards for flat roofs. Testing under TS 1187 assesses the performance of the complete waterproofing system against external fire penetration and flame spread, ensuring safety compliance.

Wind Load Design

Calculating wind load is crucial for flat roof integrity. It helps confirm that the roofing system can withstand pressure and uplift forces based on the building’s design, height, and location.

Locating Rooftop Equipment

For optimal integrity, rooftop equipment should be placed directly on the waterproofing membrane to minimise interruptions that could lead to water ingress. Equipment is often supported by paving slabs with protective layers underneath.

Foot Traffic and Access

Regular foot traffic on flat roofs necessitates protective measures to safeguard the waterproofing surface. Properly defined walkways and protective materials are essential for maintenance access and fire escape routes.

Rooflights

Incorporating rooflights into flat roofs can significantly enhance natural light within the building. Various designs and glazing finishes are available, but specifications must align with relevant building regulations.

Edge Protection

Safety is paramount, especially when accessing flat roofs. To ensure safe access for maintenance or emergencies, architects should consider edge protection when designing a flat roof, whether with a designed parapet, guard rail at the roof edge or a permanently protected walkway.

Assessing Refurbishment Needs

Before starting a roof renovation project, thoroughly appraise the existing roof and identify any areas needing repair to unravel the best next steps and approach for remedial actions.

Overlaying Existing Waterproofing

To overlay an existing roof system, the existing waterproofing must be sound and suitable for the new overlay. Ensuring the underlying structure is dry and free from damage is essential for a successful application.

Upgrading Insulation

Enhancing thermal insulation during refurbishment reduces energy consumption and benefits the environment, making it a sensible investment for any building owner.

In summary, flat roofs offer a multitude of advantages and design opportunities. With careful consideration of thermal performance, drainage, fire safety, and access, they can transform new builds and refurbishments into practical and aesthetically pleasing spaces.