Flat Roof Design

Flat roof designs are more suited to the creative use of outdoor areas. Many designs feature gardens, outdoor spaces and terraces. If this type of installation is incorporated, construction must be upgraded to account for the additional weight requirements of equipment and/or people. In these cases the thickness of the plywood substrate must be greater and the use of tongue and groove edges is incorporated. This makes the panel system more rigid and less prone to deflection. The roof support system must also be strengthened by using larger sized joists as well as closer spacing.

The design and construction of the underlay system is important for a long lasting and well-functioning flat roof. This base is the platform to which the flat roof membrane is adhered to. The membrane is the water-proof layer that keeps the roof from leaking. There are three methods for attaching the membrane: semi-independent, independent and fully adhered.

Semi-independent membranes are only partially bonded to the underlying platform. This is ideal in installations that are not completely stable or when the bonding surface is partially damp. In this application the underlay is either perforated or applied in strips. If a separate adhesive is used (versus material where the membrane is pre-coated), a technique known as trickle application is used. The result of all these semi-independent methods is a system that enables the membrane to partially flex and adapt to roof movement.

Independent membranes are simply laid on top of the substrate. To keep the roofing membrane from sticking from the sun’s radiant warmth, a thin fiber barrier is laid between the base and the membrane. This is most often used on concrete substrates (either poured slabs or pre-cast panels). This type of installation makes it difficult to identify the source of leaks as the water can run a significant distance under the membrane from the penetration to where the leak is actually detected.

Fully adhered membranes as the name suggest, are completely attached to the substrate surface. In order for these systems to provide maximum protection, the underlayment must be completely stable and have almost no flex. Fully adhered membranes are slightly elastic and highly resilient in order to combat any movement. As an added way to resist a flexing substrate, strips of the membrane material are used to cover the seams in the plywood. This provides a more stable substrate on which to apply the water proof membrane yielding a roof system more resistant to pedestrian use and contraction and expansion due to heat or freezing weather.

All and all the new technology and materials used in today’s flat roof systems make them suitable for just about any climate and installation.

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