Insulate roof space of dormer bungalow

8 Jan 2009
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United Kingdom

I have a dormer bungalow and need to increase the amount of insulation.

The sloping ceilings of the rooms has been well insulated with Celotex and Tri-iso. I have also insulated the walls of the rooms using Celotex.

I have a crawl space all around the outside of the rooms, this has currently 6" of rockwool. I plan to increase this by -

- adding another layer of rockwool across the joists where I can
- adding a layer of Celotex underneath the existing crawl boards. This will increase the insulation without raising the height too much.

Currently the gap underneath the floor of the rooms is not insulated, this means that warm air is rising and leaking out into the cold roof space.
My question is should I leave an air gap for ventilation between the ceiling and walls so that air can get to the floor joists or can I safely close this gap with insulation?

Any thoughts or advice would be great.
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