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The following questions provide an outline of common queries regarding Gradient Insulation’s products. For further information, please see our product literature and detailed installation guides, or contact the Gradient service helpdesk.

It is good practice to seal board joints as it controls the rate of passage of water vapour and improves the airtightness of the building envelope - an increasingly important element of the Building Regulations Approved Document L.

One common method is to use a self-adhesive aluminium foil tape. Depending on the proposed construction, taped board joints may act as a vapour control layer (VCL) on their own or be used in conjunction with a conventional sheet VCL like polythene.

Abutments with other construction elements should be sealed with a low modulus silicon sealant.
Please contact our technical support team on freephone 0800 0854079 or see the U-value section here
Our U-value calculation software also models condensation risk in accordance with BS 5250: 2011, and it forms part of the calculation as standard. We will always aim to provide appropriate technical advice if a proposed construction is showing a condensation risk. However, please bear in mind that the calculation service is not a design service - we can only work from the information provided to us.
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.
The surface temperature of a lamp can reach 2000C. Without adequate ventilation to allow the escape of heat, downlighters can cause fires. Recticel recommends the following measures are taken when installing downlighters:

Downlighters should not be recessed into insulated ceilings if they penetrate the vapour control layer (VCL). This will result in them drawing warm moist air into the roof space where it could condense and drip back out of the fitting, causing a potential fire risk.

Where downlighters are to be used they should be fitted into a false ceiling below the structural ceiling.

Overheating can occur where thermal insulation is laid over existing downlighters and any associated transformers that are not designed to operate under these conditions. Cables and other electrical equipment should not be covered by insulation.

In all cases, the downlighter manufacturer's instructions should be followed. They should specify the amount of space to be left around the back of the fitting, its fire rating, whether it can be covered with insulation, and the type/wattage of suitable lamps.

If in doubt, consult a qualified electrician.
BS 5250:2011, the British Standard for the control of condensation in buildings, does not recommend installing insulation between timber joists as well as above the deck.
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.
Eurowall Cavity is certified for use in conjunction with a 25mm cavity. However, some warranty providers will not accept this and require a 50mm cavity, as do Scottish Building Standards. A wider cavity should be used in exposed locations.

If in doubt, seek advice from your Building Control Officer.


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