Insulation of chalet bungalow Information, help, tips and advice on cavity walls, ceilings and lofts etc....

[Papa]

My first post!
I'd like to follow on from the last post in this topic (started in May 2024) contributed by TheTeaBoy and mostly responded to by stoneyboy.

I too have a chalet bungalow style house of 70s vintage and for years have struggled with the correct approach to refurbished the entire insulation of the property to improve it's thermal performance and lower heating costs. Is there someone out there who can advise?

I have a specific question as a starter and I'll refer to TheTeaBoy's excellent graphics if I may of his parents' house shown at
parent-s-chalet-bungalow-insulation-plan-t55250.html

In the fifth graphic on the page showing all the different coloured insulation areas, TheTeaBoy refers to the Pink area being the insulation that seals the rectangular gap between the floor joists, the upper floor floorboards and and the ground floor ceiling thereby cutting off the airflow in the Orange spaces from the crawl spaces. This is my current challenge. Do I completely seal those empty spaces or do I almost fill them with PIR but leave a ventilation hole in the PIR? It's not a surprise that the downstairs rooms suffer from cold more than upstairs rooms as these gaps are along the entire length of the house but If I were to block up the pink gaps entirely would I then create a condensation problem in the Orange spaces which I don't have at the moment? Hey ho. Any advice would be much appreciated.

[stoneyboy]

Hi Papa.
You can and should seal the ends of the pink areas under the dormer walls. This will effectively create sealed and hence insulated chambers. Damp in the vapour phase from below will pass through the chamber. You will need to insulate the purple areas between the floor joists, either with fibre insulation or pir boards. Either way leave the top open so damp can escape.
Regards S

[Papa]

Dear stoney boy,
Thank you for taking the time and trouble to respond. If I understand correctly, the chamber(s) as you call them will be the spaces contained by the floor joists on each side, the ceiling below, the floorboards above and if we block up the holes at each end, the insulation that we put in to isolate the chambers from the crawl spaces. Are you saying that moisture would escape as vapour from this enclosed chamber and through which of those materials would it permeate through?

As I see it, there are two ways of blocking up the holes at each end to ensure the chambers are insulated:
1. To use a tightly fitted PIR which has no way of letting through moisture or vapour
2. To use Rockwool type insulation which I believe is breathable and would allow moisture/vapour to get through to the crawl spaces.

I would imagine option 2 is the way to go?

[stoneyboy]

Hi Papa,
Yes damp in the vapour phase will pass through the plasterboard and through floorboards above which enclose this chamber (couldn’t think what else to call it but it’s probably called a ceiling void).
Your aim should be to stop this void being ventilated by the air in the crawl sections (the triangular spaces either side of the dormer room). Either of your methods 1 or 2 would work and both are a compromise..100mm pir insulation sealed in place with expanding foam would seal and insulate the ceiling void. You could use Rockwool slab insulation (for rigidity) to seal the ends of the voids and combine this with Rockwool roll insulation for the adjoining areas.
Whichever way you pick the triangular crawl spaces will have to be ventilated to remove damp permeating the Rockwool..
Regards S

[stoneyboy]

Hi Papa,
Having thought about your suggestion of using Rockwool this is probably the best option. Use Rockwool in slab form - this is easy to trim to size using a carving knife.
Regards S

[Papa]

Thanks stoneyboy. Go Rockwool!