17 Sep 2008
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United Kingdom
Have searched the forum but can’t find exactly our situation so sorry if the answer is out there somewhere and I’ve missed it!
We want to increase the amount of insulation in our loft space but are concerned about just increasing the insulation at joist level because of the increased risk of freezing to the water pipes running through the loft. The pipes are lagged but during long cold spells (-12C for 3 weeks in the winters a couple of years ago) the loft space dropped down to zero for long periods which was very worrying.
Increasing the depth of the insulation at joist level also has implications with respect to wiring ‘buried’ underneath and also, as it hides the joists, it makes it more difficult to move around the loft space for routine inspection and maintenance.
Someone suggested we consider adding extra insulating at rafter level so we would reduce heat losses through the roof but retain some heat in the loft space to protect the pipework.
We have been looking into various types of rafter insulation but keep coming across mention of potential condensation problems. Have also seen reference to having to remove the joist insulation when rafters insulation is used.
Our house is stone built with 2’ thick walls. The roof is natural slate, reroofed around 10 years ago using a ‘breathable’ roofing felt over the sarking. The felt used looked like ordinary roofing felt, not like the breathable membrane used in new builds. There are roof vents fitted. The loft space is never going to be converted into a habitable space.
Would appreciate advice on whether rafter insulation is worth considering in our situation, the best products to use, eg foil blankets, or solid blocks, and best practice for fixing.
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How much above are your pipes from the current insulation, if not to much create a loop of unbroken insulation over the pipes. If the subsequent rows are tight to it's neighbor, both sides, then you have a warm pocket round each pipe. Any gaps just drape an insulation cut piece over the space.
Thanks for your reply.
The pipes are about a metre above the loft floor in places as they run over cross members that attach one side of the roof to the other.

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