Spray Foam For Flat Roof Insulation

Enverge Spray Foam Insulation is commonly used to insulate flat roofs either above the deck or below and it can offer numerous benefits over pre-manufactured insulation materials. Speed of install, airtightness and durable thermal performance helps to make Enverge Spray Foam one of the most popular choices for flat roof insulation either externally from above or to the underside of the deck from within the property. When Posi-Joists are used as the flat roof structure, the spray foam insulation can be installed between and through the joists to provide a seamless, monolithic thermal layer.

Enverge Spray Foam Flat Roof Insulation Benefits

Flat Roof Insulation

The Enverge range of spray foam insulation products are BBA-certified and suitable for use in flat roof insulation projects. Whether you are looking to insulate externally onto the deck, internally below the deck or between and through posi-joists, spray foam insulation can offer a robust, airtight, thermal solution that ensures your flat roof insulation project meets building regulations. Although PIR board is generally used above deck, Enverge Nexseal LE Closed Cell Spray Foam Insulation can be used as an alternative that bonds to the surface to add excellent adhesion and durability. When using Enverge Spray Foam Insulation below deck, either Nexseal LE Closed Cell or Sucraseal Open Cell may be suitable provided a robust vapour control layer is used.

Fast Install





Strong Adhesion

Nexseal Flat Roof Insulation

Sucraseal Flat Roof Insulation

Vara Vapour Control Layers

We’ve partnered with Partel to provide the VARA range of Intelligent Vapour Control membranes as part of the moisture management strategy in flat roofs. It is vital to protect the structural assembly and insulation materials from the impacts of interstitial condensation so that thermal performance is maintained, mainly when high-resistance flat roof membranes are used above deck as a waterproofing layer. VARA Intelligent Membranes come in a sheet form or spray-applied liquid version to ensure insulation protection and enhanced airtightness. Vapour control layers are an essential part of any flat roof insulation strategy, and our technical team is on hand to help design your bespoke insulation system that meets thermal compliance and reduces air leakage and moisture management following BS 5250.

Flat Roof Insulation Solutions

Enverge Spray Foam insulates flat roofs above deck, below deck and between posi-joists to provide a continuous, airtight, thermal layer that bonds to the substrate and provides excellent durability. Where pre-manufactured insulation materials require carefully fitting into place and the use of airtight tapes to seal the joins to prevent air leakage, Enverge Spray Foam Insulation is designed to achieve natural airtightness in a single application. Spray-applied to the substrate as a liquid, spray foam insulation rapidly expands to fill the void to meet thermal targets and comply with building regulations. Whilst the use of traditional, pre-manufactured insulation materials may appear easy to install, spray foam insulation offers enhanced durability, structural integrity, and reduced airgaps to ensure that moisture cannot penetrate the flat roof assembly and cause future problems.


Check our Enverge BBA-Certified Spray Foams For Flat Roof Insulation

The Enverge range of spray foams include leading brands, Sucraseal Open Cell and Nexseal Closed Cell. Utilising recycled materials, manufactured sustainably with the environment in mind and containing HFO, water-based blowing agents, Enverge products offer thermal, airtightness and durability.

This low exothermic, high-lift closed cell foam boasts a fast installation time, offers incredible thermal performance and improves the structural integrity of a building. Loved by installers for its fast rise, Nexseal is ozone-friendly and holds BBA Certification.

One of the leading open cell foam systems now available in the UK. Sucraseal combines peace of mind British Class 1 fire safety with exceptional thermal performance and is fully certified by the BBA. Sucraseal is installed exclusively by ThermoFoam-approved contractors only.

Flat Roof Insulation Customers

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Is Enverge Spray Foam Approved for Use?

Yes! Enverge Spray Foam Insulation has been tested to UKAS standards and certified by the BBA (British Board of Agrement) for use in new and existing homes. It is essential that any flat roof insulation project is designed in accordance with BS 5250 to ensure that moisture is managed correctly, and this is why we generally recommend the use of VARA Vapour Control Layers. Flat roof insulation is installed by our own network of ThermoFoam-approved contractors who know what it takes to get compliant results.

Is Enverge Nexseal LE Closed Cell or Sucraseal Open Cell Better?

When insulating a flat roof from above, only Nexseal LE Closed Cell spray foam is recommended because it has structural integrity and can usually be walked upon without damaging it. Sucraseal is a low-density, sponge like material that offers no structural integrity. When used internally to the underside of the flat roof deck, either Nexseal LE or Sucraseal can be used depending on the space available. It’s worth noting that Nexseal LE has better thermal performance which means a smaller depth can be used whereas Sucraseal requires a greater thickness. With that said, Sucraseal is considerably cheaper, even at a greater thickness.

Do I Need to Create Ventilation Between Flat Roof Deck and Insulation?

When insulating the flat roof deck from above, this is known as a warm roof and does not require an airgap. When insulating the flat roof deck from below, proper hygrothermal modelling will be required to determine whether a vapour control layer can manage moisture or whether a ventilated cavity void is required. This will be determined during the initial product specification and the structural roof assembly may need to be constructed accordingly to provide ventilation.

What Is A Vapour Control Layer?

Vapour control layers can be crucial in flat roof insulation projects because they protect the structural assembly from the impacts of interstitial condensation that forms within the property. This moisture is unable to escape from the flat roof due to the waterproof, non-breathable layer on top of the roof deck. A vapour control layer is usually a plastic sheet that stops moisture from penetrating the structural assembly, therefore, preventing timber rot of roof joists and the flat roof deck. Whilst a vapour control layer won’t stop moisture from forming, it stops it from entering the insulation assembly and it will usually disperse through other ventilated openings within the property.

What Waterproof Layer Should Go on Top of Externally Applied Spray Foam?

Most flat roof systems will incorporate a GRP fibreglass, bitumen felt or EPDM rubber membrane to provide robust waterproofing of the flat roof deck. These membranes are usually high resistance to moisture and non-breathable. To protect the fabric of the flat roof structure and to prevent timber rot from occurring, a robust, seamless, and well-sealed external roof membrane will be required.

Is Spray Foam Faster to install than Pre-Manufactured Insulation Materials?

Spray Foam Insulation can be up to 5 times faster to install than pre-manufactured insulation materials. Pre-manufactured insulation materials require cutting to size, fixing into place and then the seams joined with airtight tapes. Spray Foam Insulation is spray-applied and expands to fill the flat roof joist void to the required depth. Depending on the type of flat roof insulation required, up to 150 metres of spray foam insulation can be installed in just one day