What is a roof substrate board?

A roof substrate board is a board placed over the structural deck of the roof. All the other roofing components such as membranes, insulation, roof cover boards and the waterproofing layer, are placed above the roof substrate board.

What are the advantages of using a roof substrate board?

Roof substrate boards can add a variety of benefits when specified with a flat roof assembly. They may increase the overall fire resistance and structural integrity, improve acoustic performance and can promote an improved bond with the insulation layer.

The fire performance of the roof may be enhanced due to the thermal barrier provided by the roof substrate board. If a fire breaks out inside the building, this thermal barrier can help to slow the spread of heat along the underside of the deck and provide additional protection to the insulation layer above. This can be especially beneficial where combustible insulation is present.

Roof substrate boards can also increase the structural integrity of the deck by adding extra weight and rigidity to the deck. The extra density provided by the boards can also improve the overall acoustic performance by reducing the noise transmission through the roof. The level of improvement will depend on the density of the board chosen and the design of the other roofing components.

The smooth flat surface provided by the roof substrate boards over a profiled metal deck can provide more bonding area for compatible membranes or insulation and enhance their bond strength to the roof increasing the resistance of roof to effects of wind uplift.

Where breather membranes or vapour control layers are used over roof substrate boards, the membranes can have the ability to create an extra level of weather protection early in the build process. Advice should always be sought from the membrane manufacturer(s) as the specific levels of protection that are possible. In such situations the roof substrate boards do not add to the weather protection however, they can provide a solid surface on which to store roofing materials as the roofing work progresses.

What type should I choose for my roof?

Many of the advantages of using a roof substrate board will depend on the type of material from which the board is made.

The properties of non-combustible boards allow them to offer additional fire resistance. The density and composition of roof substrate boards can offer some acoustic advantages as well as providing additional structural strength to a roof build up.

Georgia-Pacific offer a range of DensDeck^® mat faced gypsum core roof substrate boards. They are widely used and are present in many FM Approved roof assemblies. If you would like to discuss how the DensDeck^® Roof Board range could be suitable your next project, please contact one of our team today.