The roofing membrane sits above the rafter, held in place by roofing battens and tiles. The purpose of the membrane is to offer a breathable but protective layer that allows moisture to escape from within a building whilst preventing the ingress of moisture from the outside.
Modern membranes are strong but thin, therefore, during the insulation phase, they can become damaged if not treated with care. Pre-manufactured insulation such as Rigid PIR, requires a 50mm air-gap between the roofing membrane and the insulation. This is to allow interstitial condensation to escape the building and not becoming trapped between the insulation and membrane.
If an air-gap is not considered for pre-manufactured insulation, moisture can become trapped in a very tight space, causing it to sweat and potentially degrade the timber rafters. The air-gap provides ample airflow that will help to dry and remove moisture.
Spray Foam does not require an air-gap because it is spray-applied to the membrane and becomes an extension of the substrate with no opportunity for moisture to become trapped. Whilst this is a significant benefit that helps to save space in the rafter, respecting the integrity of the membrane is essential during installation.
The process of spraying foam might look reasonably easy but for installers who treat the customers property with respect and take pride in their work, it’s a highly technical procedure that takes care and consideration. Unfortunately, not every installation company understands or respects the building and on occasion, this can lead to property damage. When choosing spray foam for your project, you should ensure that the installation company you choose are competant and experienced applicators.
To ensure a successful installation of spray foam insulation, we are knowledgeable about roofing membranes and how best to retain their integrity. Although a major benefit of spray foam is its speed of application, you definitely don’t want to choose and installer who puts speed ahead of accuracy.
Modern roofing membranes are often thin and flexible which means they can be easily damaged. To overcome this, we spray a thin flash coating of ThermoFoam to the central drape of a membrane. This process helps the membrane retain the natural sag and prevents it being pushed up towards the roofing tiles – something that would inhibit the performance of the air-gap.
Once the centre of the membrane has a light coating of foam, we then coat the edges to leave a thin, monolithic layer of foam. At this stage, further layers can be added gradually until the correct thickness of spray foam is achieved. Spraying too thick, too fast will simply put too much pressure on the roofing membrane and could cause it to crumple, push against the tiles or tear.
If you are considering the use of spray foam to insulate a new roof, don’t be put off by the pit falls. Generally speaking, whichever industry you’re in, things can go wrong when installed by inexperienced people.
When choosing your installer, ask them about how they retain the integrity of the roofing membrane during installation. An experienced installation company should be able to give you the right answer.
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