Posted: May 10th, 2022

Typical Small Housing Estate: Flat Roof

Typical Small Housing Estate: Flat Roof
I. Current Construction types for design and material selection
Most households have a garage attached to their property, while others are within the property boundaries. Traditionally, garage roof materials’ requirement was keen using felt, bitumen, and asphalt, which has changed over the years. The typical recognized construction types and design options of a flat roof for the garage involves keen consideration of material and technology selection and building regulations. A flat roof has a maximum slope angle of 5 degrees. The main recognized designs of flat roof construction for the garage include warm, cold, and inverted.
For garages, warm roof construction involves the location of principal thermal insulation above the structural decking. This design allows that results to the structural deck and the support structure at a temperature close to the garage’s interior. A warm flat roof has no requirement for roof void ventilation and cold bridging through the system, eliminating interruptions from the structural supports. In the warm flat roof design for garages, there is usually continuous support for the flat and stable structure directly over most profiled metal decking. A warm flat roof is the most used type of flat roof construction for garages due to its simplicity and suitability for garage spaces and designs.
Cold flat roof for garages involves the use of timber joists and a plywood deck. The waterproofing layer constitutes the vapor control layer on the cold side of the insulation. There is a high risk of harmful interstitial and surface condensation. The essential risk of interstitial condensation should be utilized to specify appropriate materials at the design stage.
II. Building regulations, the thermal design which includes the position of insulation and prevention of condensation
Thermal design involves the flow of both heat and water vapor through roof construction and any subsequent effect on the roof’s performance. In consideration of the flat roof, insulation comes in the form of a rigid board above the deck and a fibrous quilt immediately above the ceiling. According to the Building Regulations, BS 5220, Cold flat roof construction is not recommended for the garage due to the difficulty of formation and maintenance for the effective AVCL below the insulation and provision of sufficient cross-ventilation above the insulation. For the cold flat roof of garages, a fully waterproof breather membrane should be installed on the cold side of thermal insulation. The membrane provides both an external air-leakage barrier and protection to the insulation layer against detrimental environmental factors.
III. Provision for Falls and Drainage
It is required by Building regulation for garage flat roofs that adequate provision for carrying rainwater from the roof of the garage. Following the regulations BS 6229 and BS 8217, the flat garage roof should be designed with a minimum fall of 1:40 with ensures that a finished fall of 1:80 is achievable. The applications of the general roof areas come along with internal gutters. Garages should have a design fall of 1:80 for their flat roof. Under detailed structural analysis accounts for construction tolerances, settlement, and deflection under load. Recessed and fitted in sumps are used to prevent ponding on the garage flat roofs. Drainage for garage flat roofs should be provided through internal rainwater outlets and downpipes. Garage flat roofs being considerably small should at least two drainage points if one gets blocked. The regulation BS EN 12056-3 provides the rainfall calculations that should be undertaken for garage flat roofs and design principles for gutters and downpipes.
Reference
García-Solórzano, L.A., Esparza-Lopez, C.J. and Al-Obaidi, K.M., 2020. Environmental design solutions for existing concrete flat roofs in low-cost housing to improve passive cooling in western Mexico. Journal of Cleaner Production, 277, p.123992.

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