Period insulation advice.

[FamilyWiggs]

I need to insulate the sloping roof of a room I'm restoring.

The sloping rafters are about 75-80mm deep, so I guess I have about 50mm to play with as I want to be able to see some of the beams, rather than board over the whole thing. The room is above the porch, walls are solid random rubble. There are three external walls and single glazed (leaded) windows in each aspect. Room is about 6 feet square, with floorboards onto the original exposed joists over an open porch. Traditionally it has thus been rather chilliy in the winter. I'llbe trying to get a small radiator in there too. It will become a small TV/games console room for the gene puddles.

Questions:

a) What is the best insulation to put between the rafters? ie most thermal property.

b) do I need to leave an air gap between the insultation and underside of the felt?

b) I will need to put insultation between the joists to help keep the room warm in winter. Again what is best for this? I'll board over underneath and probably have 100-120mm to play with.

Something tells me some sort of block/board that I cut to fit will be an easier instalation than something on a roll, as i will be working from below for both jobs.

Any advice?

Thanks

Robin.

 

[FamilyWiggs]

I should have added that the sarking felt is non-breatheable. Which probably means I will have a ventilation issue... The eaves don't appear to be open.

I can't (don't want) to lift the tiles and lay a breatheable membrane. I also don't want to lose head height in the room. I could at a push put in a suspended ceiling, but even this would have to be halfway up the slop of the rafters, so I'm still left with the same issue for half of the room on each side.

Any bright ideas, guys?

 

[garnett]

Hi

Nothing to say on the insulation but can I suggest you google lapvents for the ventilation? They can be retrofitted into non breathable felt and are completely invisable.

I use them all the time.

Garnett

 

[FamilyWiggs]

Garnett - many thanks. They look just the job for ventilation.

I'm wondering if I install lots of those (as I have little/no between-rafters airflow) if maybe a smaller air gap and then some Kingspan or similar would be OK.

Hope this isn't classed as advdertising on the site:

http://www.lapvent.co.uk/fitting-instructions.html

 

[robgil]

I would go with Kingspan/celotex, most bang for your buck with such a tight space. Not very green initially but will 'green' itself many times over with the amount of energy you save.

 

[AMc]

I'm with robgil. Pay attention to air tightness to see the best effect from the insulation you can squeeze in there.