What if I cannot provide all of the information required for thermal calculations of a specific project?
It is possible for us to make certain assumptions when performing a calculation, but this can reduce the accuracy of the final result. Assumptions are routinely made about the types of fixings to be used, but we will always try to inform you if a general figure has been used where more accurate data could affect the calculation result.
What is a Vacuum Insulation Panel or VIP?
VIP is the abbreviation of Vacuum Insulation Panel. A Vacuum Insulation Panel generally comprises a microporous core material (e.g. based on fumed silica), which is introduced into a high barrier multilayer foil envelope. The envelope is then evacuated and sealed, obtaining a near vacuum inside the envelope.
Because of the microporous core and the absence of air, excellent thermal properties are obtained. For our Vacuum Insulation Panel as such (Core-VQ®) we can declare a lambda value of 0,006 W/mK, which is typically 3-5 better than traditional insulation materials.
Vacuum Insulation Panels have already been used for several decades in high demanding applications, especially when stringent requirements for thermal insulation are set (e.g. refrigerators). As the thermal insulation of buildings has become increasingly important over the last years, Vacuum Insulation Panels have been introduced in buildings to meet the high standards.
Recticel Insulation offers the following products:
What is a warm flat roof construction?
A warm flat roof is a roof construction where the insulation is positioned above the structural roof deck, keeping the deck and structure on the warm side of the insulation.
A typical warm roof build-up may include the structural deck, vapour control layer, insulation and waterproofing system. The exact arrangement depends on the roof construction and waterproofing system being used. Warm roof construction can provide continuous insulation across the roof, helping to reduce heat loss and improve the thermal performance of the building. The complete roof build-up should be designed to meet the required thermal, moisture, structural and fire performance criteria.
What is tapered insulation?
Tapered insulation is insulation manufactured or designed with varying thicknesses to create a fall across a flat or low-slope roof.
Rather than using insulation of a constant thickness, a tapered scheme uses different insulation thicknesses to form designed falls that direct rainwater towards outlets, gutters or other drainage points.
Gradient provides bespoke tapered insulation solutions designed around the individual roof geometry, including new and existing roofs.
What is the best way of achieving an air and vapour barrier when using PIR insulation panels?
As per the literature supplied with the product - an effective air and vapour barrier can be achieved by the taping of board joints using suitable insulation tape, the inclusion of a separate proprietary vapour control layer or the use of a foil backed plasterboard all of these methods are acceptable forms of air/vapour control.
What is the difference between a U-value and an R-value?
U-values take into account all elements of a construction, including thermal bridges. They can only be worked out by calculation. The R-value, or thermal resistance, is a measure of the insulation board on its own, dividing the thickness (in metres) by the thermal conductivity (lambda value, W/m.K). The R-value can be used to compare how different thicknesses of products with different lambda values perform comparatively.
What is the difference between U-value, R-value and thermal conductivity?
U-value measures how easily heat passes through a building element such as a roof, wall or floor. It is expressed in W/m²K. A lower U-value generally indicates better thermal performance.
R-value represents the thermal resistance of a material or construction. A higher R-value indicates greater resistance to heat flow.
Thermal conductivity, represented by the Greek letter λ (lambda), describes how readily heat passes through a material. It is expressed in W/mK. A lower lambda value generally indicates a material with better insulating properties.
Importantly, the U-value of a roof is determined by the performance of the complete construction, not simply the lambda value of the insulation product.
What is vacuum insulation and how does it work?
Vacuum insulation panels, or VIPs, are high-performance insulation panels designed to provide a high level of thermal resistance within a relatively small thickness.
Gradient's VIP technology uses a core based on pyrogenic silica enclosed within a gas-tight multilayer film. The panel is then protected within a high-density, pressure-resistant PIR casing in the Deck-VQ® system.
The vacuum and core structure significantly reduce heat transfer through the insulation, allowing very high thermal performance from a relatively thin panel.
Vacuum insulation is particularly useful where there is insufficient space to accommodate the thickness of conventional insulation.
What problems can a flat roof survey identify?
A visual survey can identify issues such as defective membrane laps, splits, blistering, damaged areas, deteriorated upstands, damaged edge details, blocked outlets and visible ponding water. Ponding is specifically recognised in NFRC guidance as an issue requiring consideration on flat roofs, although its presence does not necessarily mean that a roof has failed.
What U-value should a flat roof achieve?
There isn't one U-value that applies to every flat roof.
The required performance depends on factors including whether the project is a new build or refurbishment, the type of building, the construction and the applicable Building Regulations and design requirements.
For example, the 2026 Approved Document L Volume 2, covering buildings other than dwellings in England, gives a maximum U-value of 0.18 W/m²K for roofs for new or replacement elements. For new dwellings, the 2026 Volume 1 gives a limiting U-value of 0.16 W/m²K for all roof types.
However, a project may require a different target U-value, so the required performance should be established by the project designer or energy assessor.