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How to avoid a cold bridge when penetrating a roof

Deks Airtight Insulated Roof Penetration Kit

With today's emphasis on high insulation values and airtightness in modern buildings it is important to ensure that, when penetrating a roof or ceiling with a flue, a cold bridge or air leak isn't created.

The Deks airtight insulated roof penetration kit consists of an EPDM grommet on an adhesive backing sheet and a foil backed insulation sleeve that fits around the pipe. The EPDM grommet is fixed onto the airtight membrane where the flue passes through it and the 50mm thick foil backed sleeve is cut to length and to the correct angle at both ends before being put over the pipe.

It is common to trim the rafters around a roof penetration creating a closed box through which the pipe passes. In this case a loose fill of non-combustible rockwool insulation can be added around the insulating sleeve to fill up any spaces.

It can be necessary to support the flue at rafter level. If the support is required to carry the weight of the flue system then a Selkirk roof support needs to be used and is placed at the top of the rafters. The insulating sleeve is brought up to the bottom of the bracket and it must be ensured that either a 50mm gap is maintained around that last section of pipe or a piece of the insulating sleeve is used to fill any space left. Other insulating materials must not come within 50mm of the pipework.

If it is just lateral support that is needed at rafter level, and the weight of the flue run is carried elsewhere, then a wall band can be used at the top of the rafter. The insulation arrangement should then be the same as with a rafter support.

The kit can be used in the same way with a 'cold loft' where the flue passes through a horizontal insulated ceiling.

Dektite EPDM flashing - 24 - 44 inc VAT
Silicon - 5.75 inc VAT
Rockwool Sleeve - 41 inc VAT
EPDM Adhesive Grommit - Price and availability coming soon.

For further technical advice, chimney and flue design and consultancy please contact us on 0845 226 5754

If you would like us to design your flue system then please go to the flue design service section of this site.

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