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UKFR - ROOFING AND INSULATION SPECIALISTS
Ensure your warm deck flat roof lasts with proper installation.
This page streamlines the process, listing products in order and offering expert insights at each stage.
The process begins from the lower deck of the roof and includes vapour barriers, flat roof insulation, warm deck insulation fixings, waterproofing layers, and the essential tools for installing a top-performing warm deck roof.
The first step is adhering a vapour barrier to the subdeck. You must use an approved, high-quality vapour barrier to prevent rot and eventual roof failure. Approved warm deck vapour barriers include:
A premium quality, self-adhesive vapour barrier from Carlisle Construction Materials, a trusted lead manufacturer of flat roof waterproofing.
ALUTRIX is installed on the deck using FG35 Primer to ensure a durable fix. With its foil facing and bitumen backing, ALUTRIX offers versatility.
A high-quality vapour barrier with the same composition & properties as ALUTRIX. Manufactured by Instar, ELOTENE is an excellent alternative product to ALUTRIX.
Use ELOTENE Primer to securely fix the ELOTONE vapour barrier.
Both vapour barriers can be adhered to using an insulation adhesive such as Insta-Stik for use with tissue-faced insulation or mechanically fixed with thermally broken fixings for use with foil faced insulation.
What sets ALUTRIX and ELOTENE apart is their innovative bitumen backings, which self-heals around screws during installation. This ensures the vapour barrier remains uncompromised with superior moisture protection, unlike many other vapour barriers on the market.
Always use ALUTRIX 600 when you need to achieve BroofT4 as this is the only bitumen backed VCL with a BBA certificate.
If you don’t install a vapour barrier or VCL, then warm, moist air from your home will be able to enter the roof space and condense within the insulation layer. This moisture can accumulate and eventually may run back down, leading to damp and mould issues as well as rotting the timbers.
One of the primary causes of flat roof failure is either the absence of a vapour barrier layer or incorrect installation, whether in cold deck or warm deck flat roofs.
The vapour barrier prevents the internal warm, moist air from condensing on the flat roof insulation layer. Without the vapour barrier, condensation would eventually cause dampness and rot in the warm deck roof and joists. One of the primary causes of flat roof failure is either the absence of a vapour barrier layer or incorrect installation, whether in cold deck or warm deck flat roofs.
Once the vapour barrier is installed, a flat roof insulation system will need to be installed above.
You must use an approved flat roof insulation board. Although these boards have PIR cores, they feature a higher compression strength compared to standard PIR boards (150kPa vs 120-140kPa), making them suitable for flat roof applications.
See our approved flat roof insulation boards below:
Rockwool Hardrock achieves an impressive A2 Euroclass Fire Rating, whilst also excelling in sound absorption and thermal properties.
Rockwool Hardrock is mechanically fixed to the roof deck using thermally broken fixings and a single-ply membrane can be adhered to the tissue faced surface, such as EPDM rubber.
It’s also suitable for use with torch-applied felts, pour and roll bitumen, and certain GRP & Liquid systems.
Tissue-faced flat roof insulation boards are highly versatile & easy to install on a warm deck flat roof, easily adhering to the vapour barrier layer below using an insulation adhesive such as INSTA-STIK.
Serving many applications, these boards can be adhered to with most single-ply membranes, such as EPDM, due to their tissue facing. It’s also suitable for use with certain GRP & Liquid systems. For Felt roofs, please use Bitumen-Faced-Boards.
Please check with specific manufacturers for waterproofing guidance.
Foil-faced insulation boards are specifically crafted for mechanically fixed flat roofs. They cannot be adhered to – instead, they must be mechanically fixed to the subdeck and vapour barrier.
For optimal results, we recommend installing these with our thermally broken warm deck fixings. These boards can also be used with a timber upper deck, allowing for a variety of compatible waterproofing systems.
Tapered insulation is designed to improve flat roof performance by creating a fall to ensure efficient water drainage.
These boards come in tissue-faced, foil-faced, and ROCKWOOL-tapered for unparalleled performance.
We also offer a custom tapered insulation scheme – simply fill out our easy form and let our expert advisors create a bespoke design just for you.
There are three main issues you run into when using a non-flat roof specified insulation board in flat roof installation: they don’t have the correct compressive strength required for flat roofs, they are not BBA certified for use in flat roofs, and they are generally foil-faced.
1. Non-flat roof specified boards do not have the correct compressive strength
A standard PIR insulation board has a compressive strength of 120–140 kPa, while a flat roof specification board is rated at 150 kPa. This may not sound like a huge difference, but if the standard board is at the lower end of the range (120 kPa), the flat roof board is around 25% denser. If you’ve ever compared the two side by side, you’ll have noticed this difference for yourself.
2. Non-flat roof specified boards do not have BBA certification
Another important consideration is that standard PIR boards do not have BBA certification for use in flat roofs. Using a non-BBA-certified product can compromise the system’s ability to meet its intended specification.
It may also void any guarantees with the manufacturers, as guarantees are usually based on the full build-up being installed correctly. If it can be seen that a non-certified product has been used, then it is more likely that manufacturers will be able to deny the guarantee if failure occurs.
You will also fail to meet the BroofT4 standard that building control needs with non-BBA approved products.
3. Non-flat-roof specified boards are generally foil-faced
Standard PIR boards are also foil-faced only, which means they cannot be bonded directly to the waterproofing layer above, as the foil-facing would just peel away. As a result, a timber deck becomes necessary, which can eventually rot in the unventilated warm deck roof build-up.
Properly securing insulation to the warm deck roof vapour barrier layer is crucial for durability. The choice between insulation adhesive and thermally broken fixings depends on the flat roof insulation installed. See our approved warm deck insulation fixings below.
Timber Deck Insulation Fixings
Timber deck thermally broken fixings are used when securing your flat roof insulation boards to an 18mm timber subdeck. Timber can be any suitable plywood or OSB boards.
Required for foil-faced flat roof insulation boards or any mechanically-fixed system.
Steel deck thermally broken fixings are used when securing your flat roof insulation boards to a 0.7mm – 1.2mm steel subdeck.
Required for foil-faced flat roof insulation boards or any mechanically-fixed system.
Concrete Deck Insulation Fixings
Concrete deck thermally broken fixings are used when securing your flat roof insulation boards to a concrete deck.
Required for foil-faced flat roof insulation boards or any mechanically-fixed system.
INSTA-STIK insulation adhesive is used to secure a tissue-faced flat roof insulation board to a fully bonded vapour barrier layer, such as ALUTRIX or ELOTENE.
The choice between insulation adhesive and thermally broken fixings depends entirely on the insulation you use.
If you use either a foil-faced or Rockwool Hardrock flat roof insulation board or any mechanically-fixed system, thermally broken fixings are required. These are designed to prevent thermal bridging, improve energy efficiency, and contribute to a longer roof lifespan. They are also a legal requirement from building control as of the start of 2024.
If you use a tissue-faced or bitumen-faced flat roof insulation board, it can be adhered to the vapour barrier layer using an approved insulation adhesive such as INSTA-STIK.
Thermally broken fixings have been required since early 2024, following a change in building regulations. This requirement was introduced to address the many failures in flat roofs caused by screws running directly through the roof from top to bottom, including thermal bridging, moisture problems and eventual rot.
A standard screw that extends from the top of the roof down into the roof space can conduct heat. When it’s cold outside and warm inside, condensation can form on the exposed part of the screw beneath the VCL. This, in turn, can lead to the usual problems of damp, mould, and timber rot.
This is why thermally broken fixings are required, as they prevent this condensation from forming. Thermally broken fixings are primarily designed to prevent thermal bridging, improving energy efficiency, while also contributing to a longer roof lifespan in other ways.
When combined with other incorrect techniques, such as using a timber deck and the wrong insulation, the impact of not using a thermally broken fixing is much more severe.
For example, with a GRP system installed over a timber deck with the incorrect insulation, normal foot traffic during installation or maintenance can compress the insulation. This causes screws to push against the GRP layer, which would eventually lead to cracking or puncturing of the waterproofing layer. Using a thermally broken fixing would at least minimise this risk as the tubes create a space between the screw and the top deck, ensuring that the screw can’t puncture the waterproofing layer.
Once the waterproofing layer is compromised, the roof can begin to leak. Added moisture accelerates the previously mentioned issues, eventually leading to the GRP system and insulation needing repair or replacement. In some cases, we’ve seen this happen in as little as 18 months after installation.
This is not just unique to GRP roofs, other systems, including EPDM, PVC, liquid-applied membranes, and even felt, can be punctured in the same way.
Once you’ve installed your insulation board, you will need a flat roof waterproofing membrane. Your chosen flat roof covering depends on the compatibility of the flat roof insulation board used.
Protect your warm deck flat roof for years to come with our selection, including ClassicBond, ClassicBond Pro & RESITRIX. They all have BBA Certificates and boast impressive expected lifespans of over 50 years, ensuring long-lasting performance for your warm deck roof.
Enter your roof dimensions, trim type, deck type, system type, and we’ll price up the available options for you.
ClassicBond is a versatile single-sheet system that can be installed onto a variety of deck types. They’re available as 1.2mm and 1.5mm thicknesses, with large single sheets (up to 9.15m x 30.5m), minimising time spent on joint detailing.
Pair it with tissue-faced insulation boards or Rockwool Hardrock using full-contact adhesive. For foil-faced insulation boards on timber decks, a water-based adhesive is suitable.
RESITRIX is one of the most advanced and top-rated single-ply roofing systems on the market, at 2.5mm thick with hot air-welded joints. Its self-adhesive bitumen backing and reinforced EPDM hybrid design make it perfect for warm deck flat roofs.
RESITRIX can be installed onto a multitude of warm deck roofs, including Rockwool Hardrock, tissue-faced insulation boards and timber decks using the FG35 Primer and a heat gun.
Please Note – For those seeking a mechanical fix system, RESITRIX MB presents an excellent option. It can be utilised with foil-faced and Rockwool Hardrock insulation. Feel free to reach out to our sales team who will be able to help.
ClassicBond PRO sets itself apart as a premium performance fleece-backed solution for a flat roof covering.
Utilising pressure-sensitive 3-inch joining strips with the easy-to-handle 1.52m rolls, installation couldn’t be easier.
The ClassicBond PRO can be adhered to timber decks using water-based adhesive or to other surfaces such as tissue-faced insulation or ROCKWOOL Hardrock using the ClassicBond PRO PU adhesive.
Install your EPDM membrane with the right tools. We supply DIY and professional kits complete with everything you’ll need for an effective installation. We also supply these tools as standalone.
Liquid roofing is the newest roofing system on the market. Utilising PU and PMMA, they are becoming an increasingly popular flat roof waterproofing solution as they are easy to install (requiring no additional tools) and have a seamless finish.
ARBOFLEX PU Liquid Roof Calculator
Enter your roof dimensions, trim type, deck type and we’ll calculate a kit based on your exact specifications, so you only pay for what you need.
Arboflex PU combines a 225g matting with the innovative PU liquid to create a durable flat roof covering. Its popularity among professional roofers stems from the inclusion of a UV topcoat, ensuring a durable and UV-stable finish.
This liquid roof waterproofing system is easily installed onto a timber deck. However, if you plan to install onto Rockwool Hardrock or tissue-faced insulation boards, then please contact our sales team, as you will need a carrier membrane.
GRP fibreglass roofing is a well-renowned seamless system used by many flat roofers. While it offers durability for warm roof decks, proper installation with thermally broken fixings is crucial. Without them, thermal bridging can lead to deck rot over time, causing screws to puncture the GRP warm roof construction with roof movement.
Our thermal broken fixings mitigate this risk by reducing thermal bridging and potential rot. They also feature a telescopic function, allowing for movement without piercing the waterproofing layer. These fixings also minimise excess noise and creaking in flat roofs.
If you want to keep your seamless finish we recommend recessing the fixing into the top deck with a forsner bit or router.
Enter your roof dimensions, deck type and system type, and we’ll calculate a kit based on your exact specifications, so you only pay for what you need.
GRP Roof 1010 is a seamless fibreglass roofing system with a lifespan of 20 years. This is an excellent option for your GRP warm roof construction when used on a timber OSB3 T&G deck.
When using GRP roof 1010 in a mechanically fixed system, it is crucial to use thermally broken fixings to prevent flat roof failure.
As one of the only flexible GRP fibreglass roofing systems on the market, the FLEXITEC 2020 is highly rated amongst roofers.
Featuring a seamless finish with easy detailing, this system is ideal for a GRP warm roof construction when installed onto a timber OSB3 square and T&G deck as well as concrete decks.
This system is also ideal for overlays and warm deck roofs with tissue-faced PIR and a carrier membrane used. Its flexible properties make it ideal for these types of applications where standard GRP’s can’t be used.
Install your GRP roof with the right tools. We supply basic and Flexitec 2020-specific kits complete with everything you’ll need for an effective installation. We also supply these tools as standalone.
Once you’ve laid the waterproofing membrane, you can complete your flat roof.
For EPDM systems:
For GRP & Liquid Roofing systems:
If you don’t plan on installing a timber deck, but need to walk on your roof regularly, you should install rubber promenade tiles or pedestals with paving tiles, either as a dedicated walkway or covering the full roof. This is essential for highly trafficked areas, as walking directly on any waterproofing system will eventually cause wear.
If foot traffic is only for occasional maintenance, such as accessing solar panels, rooflights, or AC units, a walkway can be installed to these areas. All high-quality waterproofing membranes and insulation boards are designed to withstand this type of limited foot traffic.
While some commercial specifications may call for additional non-degradable boards over the insulation, these are not timber.
UKFR are industry experts in warm deck flat roofing, with over 50 years of experience. Our knowledgeable team is dedicated to ensuring all warm deck flat roof constructions are installed correctly and successfully. Our experienced customer service team are on hand to answer any questions you may have about warm flat roofing.
A warm deck flat roof is where the insulation layer is above the joists and subdeck.
A warm deck flat roof is installed in the following order: subdeck, vapour barrier, insulation layer, and waterproofing layer.
There are many benefits to a warm deck flat roof, including cost effectiveness, reduced energy bills and when installed correctly, they are very efficient at preventing damp problems associated with cold flat roofs.
Warm flat roofs are also much easier to install and allow the joist space to be used for electrical wiring.
Warm deck roofs are now standard in UK construction for new builds, offering advantages over cold roofs.
They allow for utilisation of the joist area for wires, downlights, or open joists, and ensure an unventilated, enclosed envelope with insulation placed above the deck.
This setup preserves the integrity of the vapour barrier, unlike cold roofs.
Additionally, warm deck roofs minimise thermal breaks, ensuring thermal efficiency across the entire roof space.
