Loft insulation

28 Oct 2005
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United Kingdom
I would like to nail insulation horizontally across the sloping roof joists in the loft together with a vapour barrier. There will be a free space between the joists and under the insulation for outside air to circulate.This is instead of placing insulation on the loft floor as this is used for storage. In this way, can I insulate right down to the loft floor thus blocking outside air from entering the loft space? I am not sure if this will satisfy condensation requirements. If I leave a space at the bottom at the eaves, it is possible that any moist air that enters the loft could get under the insulation and cause condensation.
Advice would be appreciated.
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Will this not give you a warm loft and cold house? Kind of defeating the objective i.e. keeping the heat in the main house and living areas.

My advice would be to increase insulation at the loft floor, granted in maybe a pain.
Thank you. I take your point, but I would still be interested in whether it would cause condensation problems if I insulate the roof right down to floor level thus stopping outside air from entering the loft space.
cause condensation problems If I insulate the roof right down to floor level thus stopping outside air from entering the loft space.

Yes it will.

That apart, from a practical point of view i.e. wasted money/heat, your idea is ridiculous.
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There is some insulatiuon under the boarded up loft floor, just not the recommended thickness. The entire floor space is used for storage and the area is freezing cold in the winter and boiling hot in the summer. What exactly would be the problem in insulating the roof down to floor level? Isnt that what happend when you have your loft converted?
Insulating both ceiling and rafters is a total waste of money and time because the heat that gets through the initial insulation is quite small and by the time this is diffused in the cold loft, the amount of heat then saved by the rafter insulation is negligible.

You are spending a considerable amount of money to raise the loft temp by less than 1 C ( just a guess ).

If you have a loft conversion, you are creating new living-space which must be heated: it is no longer just storage space.
Okay, thank you. I understand that. But can you comment on the remaining question of whether sealing off the rafter space with an air gap and vapour barrier would cause any condensation or other issue (apart from waste of money etc).

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