Insulation in 1970's Chalet-Style House Information, help, tips and advice on cavity walls, ceilings and lofts etc....

[JonThompson]

I live in a 1970's chalet style house. The two upstairs bedrooms are effectively a loft conversion. The soffits are open to the eaves and the floor void. I know the roof space needs ventilation, but this is really open. What can I do to insulate and stop draughts?

[stoneyboy]

Hi jonthompson
Insulating the room is easy, line all walls and ceiling with 100mm celotex, fit plasterboard on top and plaster.
The floor is more difficult because you will need access to the ground floor ceiling/first floor void and this you will need to seal at both ends. Use the celotex offcuts and use expanding foam to ensure an airtight fit.
Regards S

[JonThompson]

Thanks for your help. The ceiling, sloping bits and walls all have 100mm rigid insulation. It is the floor void I need to sort. So, I can seal them off, they don't need ventilation? And whether I can close off the eaves from the roof? The draughts are impressive. A few pictures to demonstrate. They're in reverse order but you get the idea.

[stoneyboy]

Hi JonThompson,
You must maintain ventilation of the area between the rafters i.e. below the sarking felt and above the plasterboard. You can seal the area between the dormer floor and the ceiling below it. The simplest way would be to seal the ends of this area working within the crawl space and pack loft insulation in the ends.
This is always a difficult one when done retrospectively but unless you do stop draughts you will have a cold floor in the dormer room and a cold ceilings in the rooms below.
Regards S

[JonThompson]

Hi, im going to see if I can drop the pvc soffit down to access the void from outside, might save my knuckles! Thanks for your help.

[paulca]

Hi,

Sorry to hijack, but StoneyBoy what you described regarding the cold floor and ceiling in the dormer described my issue perfectly. I've been searching for how to fix it, but every posts seems to be about insulating the dormer itself.

If I could be as bold as to show you my issue, in the image works.

I tried to create a diagram showing what I mean as it's a bit confusing.
The part of the loft outlined in orange is insulated on it's lower side with 300mm glass wool.
The part of the loft outlined in blue is inaccessible and not insulated.
The blue line along the window shows the air gap for the dormer.
The blue arrows show the ventilation path which leads directly from my bedroom into the upper loft and out the vent.
It should be noted that the ceiling just inside the front door is stone cold to the touch, that bit of loft is COLD.


The cold air literally "pours" through the window sill of the dormer and across the bedroom floor. It actually "sounds" like a window is open.

This is since I got the loft insulated and the vented slates installed. It was no were near this bad last winter. Middle of the night without heating on, the dormer can get as cold as 13*C, only 7 above outdoor ambient.

Are there any solutions to stop that air flow while maintaining enough ventilation for the lower roof AND the dormer?