Insulating eaves of existing loft conversion

30 Nov 2015
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United Kingdom
Firstly I apologise for the length of the query. I have been reading various forums and have found myself increasingly confused and thought I’d get all the information down in one place. As with all DIY queries my case is subtly different to all the others I have already read about on line!

I’m trying to improve the insulation of an existing loft conversion on a house I have just bought as cost effectively as possible. The loft conversion was built approx. 15 years ago and as such the insulation is not up to current standards and I have found the main room (used as a bedroom) to get cold. I believe most of the cold enters the room through the doors entering into the eaves storage areas which are furthest from the single radiator. The issue does not appear to be just a draught but also general creep of the cold from the eaves into the room (I have already tried to reduce the draught around the doors as much as I can using brushes and foam strip).

I have a contractor booked in early next year to replace the pitched portion of the roof due to other issues. As such I have asked them to also re-insulate the pitched portion which is inaccessible to me and they are planning to do this using Rock Wall. To save costs I have asked them to not insulate the eaves pitch as I will do this myself. The flat roof is not being replaced and consequently there is no access to these rafters. In the interest of keeping costs (and hassle) down I would preferably not want to remove the internal plasterboard and insulate from inside.

The current insulation properties of the room and planned improvements are described in the image attached.

Finally to the questions:

- If using breathable felt is it okay to use unvented PVC soffits and fascias when I replace the existing ones? (I will also be replacing the soffits and fascias myself)

- Should I insulate the eaves roof rafters, the eaves stud wall or both?

- If insulating the rafters shall I insulate between, under or both? If I don’t have enough money for both, which is better? Under, to avoid a thermal bridge across the rafters?

- How much gap needs to be left between insulation and breathable felt to ensure good ventilation? (I have read both 25mm and 50mm)

- How do I ensure continuous insulation where the rafters meet the ceiling joists without compromising ventilation? Is ventilation still an issue for breathable felt?

- How should I insulate the eaves stud wall? Between studs, in front or both?

- If insulating the eaves stud wall is there a decent way of also insulting behind the door to provide some continuous insulation? (I was planning in overlapping insulation board placed in front of the studwork with the gap between the door and frame and placing some insulation board on the back of the door as well)

How do I fit insulation board where I am unable to use friction fit (to the front of the studwork, under rafters or to the back of the eaves door)? Screws and large washers or specialist fittings?

Thanks for any help.

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