Can a flat roof survey tell me if my insulation is adequate?
Not necessarily. A visual survey may identify information about the apparent roof build-up, but it cannot reliably confirm the condition, moisture content or thickness of concealed insulation. Where this information is required, further investigation such as core sampling may be necessary. The applicable thermal requirements also depend on factors including the building, the work being undertaken and which Building Regulations provisions apply.
Can I get a U-value calculated for my flat roofing project?
Absolutely! Please contact our freephone technical helpline on 01543 678777.
Do I need an intrusive survey or core samples?
Not every roof survey requires intrusive investigation. If the purpose is to identify visible defects or drainage issues, a visual assessment may be sufficient. However, where the condition of the underlying roof build-up, moisture levels or insulation needs to be established, intrusive investigation may be recommended. The appropriate scope will depend on the condition of the roof and the reason for the survey.
Does thicker insulation always provide better thermal performance?
Increasing insulation thickness will generally increase the thermal resistance of the insulation layer, but thickness alone does not determine the thermal performance of a complete roof.
The thermal conductivity of the insulation, the other components within the roof build-up and the construction details all contribute to the final U-value.
Different insulation materials can therefore achieve similar thermal performance at different thicknesses.
This is particularly relevant where roof build-up height is restricted, because high-performance insulation can help achieve a required thermal target without simply increasing the thickness of conventional insulation.
How can I improve the thermal performance of an existing flat roof?
Improving an existing flat roof's thermal performance may involve adding insulation as part of a refurbishment or overlay system, subject to the condition and construction of the existing roof.
The appropriate solution depends on factors such as:
- Existing roof construction
- Existing waterproofing
- Available build-up height
- Required U-value
- Moisture and condensation considerations
- Drainage
- Existing roof condition
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Upstands and junctions
Where available space is restricted, high-performance insulation such as vacuum insulation can provide an option for achieving improved thermal performance without requiring the same thickness as some conventional insulation products. Gradient's Deck-VQ® has been used in refurbishment projects where existing roof height and parapet constraints limited the available build-up.
How do I prevent thermal bridging through a flat roof?
Thermal bridging occurs where heat can flow more readily through part of a building element because of a change in material, geometry or construction.
In a flat roof, thermal bridging can occur around areas such as junctions, penetrations, parapets, rooflights and structural elements.
Good design should aim to maintain continuity of insulation wherever possible and address junctions and details appropriately.
The thermal performance of the complete roof build-up should be assessed rather than considering the insulation product in isolation. Accurate U-value calculations can help determine the thermal performance of the proposed construction. Gradient states that its U-value calculations are based on the relevant calculation methodology, including BS EN ISO 6946 for building elements.
How should I store Insulation boards?
Our boards are supplied in polythene shrink wrap which is designed for short-term protection only. It is accepted that storing boards indoors is not always possible – when outdoor storage is necessary, boards should be stored clear of the ground, on a level surface, and under cover to protect them from prolonged exposure to moisture or mechanical damage.
Speak to our technical experts
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 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.