Pottering in the loft: Using multifoil insulation in Ceilings & Skeilings

Pottering in the loft: Using multifoil insulation in Ceilings & Skeilings

Steep pitch - perfect for a loft conversion

The Potters Arms in Poole was originally built in the 19th century by the Architectural Pottery Company for the benefit of their employees – an early Works Social Club! Like so many Victorian pubs it has a steep pitch and a boarded roof – offering plenty of space for a loft conversion.

Dealing with condensation risk

Although it’s recommended (BS 5250: Code of Practice for control of condensation in buildings) that the insulation be continuous from TLX Silver used in the loft conversion of a 19th century pubeaves to ridge at rafter level, this is not always possible or economically desirable, and often the insulation is fitted over ceilings and down the dwarf walls, with only the sloping ‘skeiling’ sections having rafter-level insulation. This then needs some thought as how to prevent condensation in the voids by means of a vapour barrier on the ceiling below and appropriate ventilation.

silver multifoil under rafter solutionIntroducing the vapour control layer

The insulation build-up in the sloping skeiling section will influence the choice of method. If there is a bitumen felt or, as in this case, a boarded roof in place then a 50mm ventilated space is required underneath it, as it is a vapourimpermeable layer. So in this case, if a ridge vent is introduced, then there will be a ventilation pathway from eaves to ridge, and the TLX Silver provides the vapour barrier.

And the result is U 0.18 W/m2Ksilver multifoil skeiling

With 100mm PIR board and 50mm ventilated space above, the rafters are battened-out sufficient to leave a 30mm gap at the bottom. The TLX Silver is stapled to the underside then secured with a 38mm x 38mm batten set crosswise, so that what you end up with is 20mm air gaps either side of the TLX Silver, achieving a U-value of 0.18 W/m2K. Radiant heat is reflected back into the building, yet in summer heat gain is reduced.


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