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 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 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.
Can tapered insulation be used on an existing flat roof?
Yes. Tapered insulation can be designed for both new and existing roofs.
For refurbishment projects, the existing roof construction should be assessed before a tapered insulation scheme is designed. The survey and design should consider the existing roof dimensions, drainage points, falls, obstructions, roof condition and the proposed new roof build-up.
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.
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 is a tapered insulation scheme designed?
A tapered insulation scheme is designed around the geometry and drainage requirements of the individual roof.
The design process should consider factors such as:
- Roof dimensions and geometry
- Drainage outlets and gutters
- Existing falls and backfalls
- Rooflights and other obstructions
- Required insulation performance
- The structural deck
- Waterproofing system
- Required roof build-up
-
Upstands and perimeter details
Gradient provides a design service that produces a pre-designed, dimensionally accurate tapered insulation solution with detailed layout drawings.
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.
Speak with our technical experts