Are thermal calculations done in the same way for all building elements?
Generally speaking, yes - all calculations are done by the 'combined method'. However, ground floors differ slightly from other building elements in the information that is required. If requesting a calculation for a ground floor, please ensure that you provide a floor area and length of the exposed perimeter (i.e. the length of new floor along outside-facing walls). This allows us to calculate a perimeter/area ratio, which is crucial in the floor calculation.
Can a breather membrane be laid directly over insulation boards?
Different breather membrane manufacturers have different guidelines for their products, and these should always be consulted prior to installation. It may be possible to lay the breather membrane on the insulation, but with a counter batten airspace above.
If you would like to discuss application of any specific project, please contact our Technical Services.
Can I get a U-value calculated for my flat roofing project?
Absolutely! Please contact our freephone technical helpline on 01543 678777.
Can I recess cables into PIR insulation boards?
Cables should not be recessed into the insulation boards. They may be laid between two layers of boards with the cabling oversized to accommodate for an increase in operating temperature. If cables penetrate an insulation layer, PIR will have no detrimental effect on cable sheathing.
Further guidance on the above should be obtained from a qualified electrician.
How thick do I need to insulate?
We recommend that you seek advice from your architect, designer, energy assessor etc. to determine the appropriate insulation thickness. If you already know the desired performance, you can contact our Technical Services team for U-value calculations or look up the required R-value and corresponding thickness in the technical datasheet.
The cleanest energy for heating and cooling, is the energy you do not have to use. That is why we recommend to insulate a flat roof to a higher standard than the minimum requirement. We recommend a minimum of 45 mm Deck-VQ® (Lambda (λ) = 0,009 W/mK) for renovation and 60 mm (Lambda (λ) = 0,008 W/mK) for new build.
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What air gap is required between insulation and breather membrane?
This should be confirmed in the membrane manufacturer's BBA certificate, though 25mm to 50mm is typical.
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 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.