Prefabricated houses and house components are one way of achieving a very high standard of insulation and air tightness in a building as well as making for a very quick build. Solid Insulated Panels (S.I.P.s) are insulated, pre-fabricated constructional panels used to create the walls and roof of a house.
If you then want to put a double skin flue through a SIPs panel it is important to maintain air tightness and not create a cold bridge.
A Deks airtight insulated roof penetration kit consists of an EPDM grommet on an adhesive backing sheet and a foil backed insulation sleeve that is fitted 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, if it is a pitched roof or you are going through a wall at 45*, cut to the correct angle at both ends before being put over the pipe.
Usually the joists or rafters are trimmed around a roof penetration to create a box which the pipe passes through. A loose fill of non-combustible rockwool insulation can be added around the insulating sleeve to fill up the spaces that will be left in the corners.
It may be necessary to support the flue at roof level. If it is required to take the weight of the flue system then a Selkirk roof support needs to be used. This is placed at the top of the rafters. The insulating sleeve is brought up to the bottom of that bracket and then a 50mm gap must be 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 only lateral support that is needed, and the weight of the flue run is carried elsewhere, then a wall band can be used at the top of the rafter to secure the flue beneath the flashing. The insulation arrangement should then be the same as above.
When passing through a wall horizontally or at 45* the EPDM grommet is fixed to the airtight membrane and a trim plate is used inside on top of the plasterboard to cover the 50mm gap between the pipe and the plasterboard.
In certain circumstances two airtight membranes may be used, one on the inside of the insulation and one under the exterior wall covering. In that case an Deks airtight grommet is fixed to both membranes.
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.