Roof Insulation Board

What are Roof Insulation Boards?

Roof insulation boards are rigid, pre-formed panels engineered to provide high thermal resistance within roof structures.

Unlike loose-fill or flexible blanket insulations, these boards offer a dense, stable, and often load-bearing solution.

They are manufactured from various materials, primarily closed-cell foams - such as polyisocyanurate (PIR) and extruded polystyrene (XPS) - which are chosen for their thermal properties and ability to withstand the demands of roof environments, including moisture management and compressive strength. 

These boards are integral to constructing "warm roofs" where insulation is placed above or within the roof structure, keeping the building's thermal envelope continuous.

How They Work

Roof insulation boards typically function by combating three modes of heat transfer:

• Conduction: The primary insulating material (e.g., PIR, XPS) has an extremely low thermal conductivity. This means heat struggles to pass directly through the solid material of the board.
• Convection: The rigid, closed-cell structure of most insulation boards traps gases (often specialised blowing agents or air) within tiny, isolated pockets. This prevents convection currents (the movement of heat through circulating air) from occurring within the insulation layer.
• Radiation: Many roof insulation boards, particularly those with foil-backed facings, incorporate a low-emissivity surface. This reflective surface reduces radiant heat transfer, bouncing heat back towards its source (e.g., reflecting internal heat inwards in winter, or external solar radiation outwards in summer), provided there is an adjacent airspace.

Applications: Flat Roof vs. Pitched Roof Insulation

Roof insulation boards are fundamental to both flat and pitched roof constructions, though their installation methods and specific product requirements vary.

Flat Roof Insulation

Flat roofs commonly utilise insulation boards to create "warm roof" or "inverted roof" systems:

• Warm Roof (Above Deck): Insulation boards are installed directly on top of the structural roof deck (e.g., timber, concrete, metal), beneath the waterproofing membrane. This keeps the deck itself warm, preventing condensation. PIR boards with various facings are commonly used here.
• Inverted Roof: The insulation boards are placed above the waterproofing membrane, protecting it from UV radiation and temperature fluctuations. This requires insulation with exceptional moisture resistance and high compressive strength, making XPS boards the material of choice.

Pitched Roof Insulation

Insulation boards in pitched roofs contribute to "warm roof" constructions, integrating insulation at rafter level:

• Between Rafters: Insulation boards are cut and friction-fitted between the timber rafters. This method requires careful cutting to ensure a snug fit and prevent gaps.
• Over Rafters: Insulation boards are installed continuously over the top of the rafters, creating a highly effective uninterrupted thermal layer that minimises thermal bridging through the timber. This often uses larger format PIR boards.
• Combinations: Often, a combination of between-rafter and over-rafter insulation is used to achieve very low U-values.
• Below Rafters (Insulated Plasterboard): For internal finishes, insulated plasterboard (plasterboard factory-bonded to PIR or XPS) can be fixed directly to the underside of rafters, providing insulation and a ready-to-decorate surface in one go.

Benefits 

• Reduction in Energy Consumption: The primary benefit of roof insulation is its impact on your building's energy footprint. By establishing a thermal barrier, these rigid boards dramatically curtail heat transfer through the roof. This translates directly into less energy expended on heating during colder months and a reduced need for air conditioning in warmer periods, leading to substantial, measurable savings on your annual utility bills.
• Internal Comfort and Climate Stability: A well-insulated roof ensures a more consistent and comfortable internal climate. It minimises temperature fluctuations, eradicating cold spots and drafts commonly associated with uninsulated or poorly insulated roof spaces. This results in a more pleasant and stable indoor environment, regardless of external weather conditions.
• Optimised Thermal Performance: Meeting or exceeding modern building regulations for thermal performance is often directly dependent on the effective use of these high-performance insulating boards, contributing to a building's energy performance certificate (EPC) rating.
• Moisture and Condensation Management: When correctly specified and installed, particularly those boards featuring integrated vapour control layers or used within appropriate systems, roof insulation boards play a critical role in preventing interstitial condensation. By controlling the migration of warm, moist internal air into cooler roof cavities, they mitigate the risks of timber decay, insulation degradation, and the development of unhealthy mould and mildew within the building fabric.
• Increased Property Value and Market Appeal: An energy-efficient property with a well-insulated roof is a highly attractive asset. It signals lower running costs, improved comfort, and compliance with modern standards, making the property more desirable to potential buyers and often bumping its resale value.
• Assured Regulatory Compliance: Modern building codes and energy efficiency directives mandate specific U-value targets for roof constructions. Utilising certified roof insulation boards is typically essential for ensuring your building project (whether new build or renovation) meets these stringent regulatory requirements, avoiding potential delays or costly rework.
• Exceptional Durability and Long-Term Stability: Rigid roof insulation boards are manufactured to be highly durable and dimensionally stable. Once installed correctly, they resist slumping, settling, or degrading over the building's lifespan. 
• Space Utilisation: The high thermal efficiency of materials like PIR allows for the achievement of impressive thermal values with relatively thinner boards. This is particularly advantageous in scenarios where maximising internal head height or preserving loft space is crucial, offering high performance without excessive bulk.

Types of Roof Insulation Boards We Offer

We stock a comprehensive range of roof insulation board solutions, tailored for various applications and performance requirements:

PIR (Polyisocyanurate) Insulation Boards

• Characteristics: PIR boards are a highly efficient, rigid, closed-cell foam insulation. They offer an exceptionally low thermal conductivity (typically around 0.022 W/mK), providing excellent thermal performance for their thickness. They are known for their strong compressive strength and good fire performance, often forming a char layer when exposed to flame.
• Common Facings: PIR boards are frequently supplied with foil-backed facings (multi-layered aluminum foil), which enhance radiant barrier performance and serve as an effective vapour control layer (VCL). They can also come with coated glass tissue faces on both sides, providing a robust, non-wicking surface ideal for bonding with various waterproofing membranes.

XPS (Extruded Polystyrene) Insulation Boards

• Characteristics: XPS boards are a rigid, closed-cell foam insulation product renowned for their outstanding moisture resistance and very high compressive strength. They typically have a thermal conductivity around 0.033-0.036W/mK. Their closed-cell structure makes them virtually impermeable to water, crucial for inverted roof applications.
• Ideal for Inverted Roofs: Their inherent resistance to water absorption makes them the preferred choice for inverted flat roof systems, where the insulation is placed above the waterproofing membrane.

Specialised Facings 

Beyond the core material, the facings applied to insulation boards are key to their application and performance:

• Coated Glass Tissue Face on Both Sides: These facings provide excellent dimensional stability, a durable surface, and are often ideal for direct bonding with a range of waterproofing systems, including single-ply membranes or built-up felt systems, without the need for additional layers.
• Foil Backed Boards: As detailed with PIR, foil facings are critical for optimising radiant heat reflection (when facing an air gap) and acting as a primary vapour control layer, preventing condensation within the roof structure.
• Torch-On Compatible Solutions: Some insulation boards (often with specific bitumen-coated glass tissue facings) are designed to withstand the heat of torch-on waterproofing membrane application. These specialised boards ensure sufficient adhesion and system integrity when using this popular flat roofing method.