Multifoil insulation: speeding up your loft conversion


Loft conversions have been around a long time, but Building Regs change

Loft conversions have been around a long time. But the Building Regs requirements for insulating them haven’t! And so there are a lot of properties around where the loft rooms with sloping ceilings are very cold, yet the owners do not want the chaos that would result from removing the plasterboard to install rafter-level insulation. Very often these older properties only have 75mm deep rafters in any case, and if there is a bitumen felt rather than a breather membrane there would be a requirement for a 50mm ventilated space, leaving only 25mm available for insulation.

Airtightness is important too

Some contractors have tried to work from within the eaves or loft void space, feeding insulation down between the rafters. Using PIR in this way is unsatisfactory, as not only are the boards usually too long to handle within the void space in the first place, but when inserted, gaps result between the boards and the rafters, and insulation without airtightness is of limited benefit. Where mineral wool has been used, all too often an eaves void full of the material is found as it simply slips down the rafters to end up at the bottom.

It’s not always necessary to remove the Plasterboard

Homeowners often do not realise that there is no need to remove existing plasterboard - insulation can be fitted directly over it with another plasterboard layer below (space permitting). By fitting 25mm deep battens onto the existing ceiling, stapling TLX Silver onto it then securing with a 38mm deep batten set crosswise, the room benefits not only from the insulation value of the TLX Silver and the adjacent air gaps but also the airtightness it confers. So when the wind blows through the rafters and the tiny cracks in the ceiling, the room inside remains draught-free. An additional and perhaps surprising benefit is that the TLX Silver also keeps the temperature cooler in a hot summer, for not only does its shiny surface reflect heat back across the air gaps, it does not pass the heat on by emitting it either.

Loss of headroom can be reduced

TLX Silver loft conversionBecause the TLX Silver compresses to 2mm between the battens, the total loss of headroom is 65mm plus plasterboard. It is also possible to use TLX Silver directly against the existing plasterboard but secured by a 50mm deep batten, though this only makes use of a single 20mm unventilated air gap to reflect heat. An extra bonus is that the air gap under the plasterboard can be used as a service cavity to run wiring through.

Saving around 80% of heat loss

It is hard to give the exact U value that would result as this would depend on the roof covering and rafter depth, but using TLX Silver as described above should save around 80% of the heat loss, and increase comfort levels - an important consideration when you spend 8 hours a day there!

Vapour barrier vs. heatloss

Ideally the TLX Silver would be continued under the flat ceiling. Even if there is some loft roll on the floor of the loft void providing some protection against heat loss, water vapour will migrate into the loft void, where it could condense if not adequately ventilated. Since TLX Silver is an excellent vapour barrier, this risk is greatly reduced - and there is no need to use foil-backed plasterboard.

TLX Silver multifoil can be used on solid walls, sandwiched between two 25mm deep battens to achieve a U value of 0.47 W/m2K. This is particularly popular where there are stone walls with uneven surfaces, as the combination of battens and the flexible blanket enables the adjustments necessary to achieve a flat internal finish.

So for a speedy solution – consider TLX Silver!

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