Insulating gap above cavity in 1930's property
Information, help, tips and advice on cavity walls, ceilings and lofts etc....

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SteveD54321
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Insulating gap above cavity in 1930's property

by SteveD54321 » Sun Nov 26, 2023 3:57 pm

Existing house has no insulation around top of cavity wall. House is 1930s with a 75mm cavity which has been filled with polystyrene balls. The cavity is closed at the top with the middle row of bricks you can see in the photo. I have access as scaffolding up and roof being stripped and re done.
Not sure of best way to insulate- possibly remove brick bridging cavity and stuff rock wool into cavity so it comes up to meet loft insulation? Or leave brick in and stick rigid insulation to side of top inside leaf brick and wall plate?
Any ideas or has anyone dealt with anything similar??
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stoneyboy
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Re: Insulating gap above cavity in 1930's property

by stoneyboy » Tue Nov 28, 2023 10:04 pm

Hi steved54321,
It would be unusual for a 1930’s house to have any cavities let alone 75mm ones.
The closing bricks will be providing a cold bridge but removing them will create ventilated cavities which is not good. Suggest you lay as much (in terms of thickness) mineral wool insulation up and into the loft space but don’t forget to provide a ventilation gap.
Regards S

SteveD54321
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Re: Insulating gap above cavity in 1930's property

by SteveD54321 » Wed Nov 29, 2023 9:29 pm

Thanks, ok well maybe it’s more 1940s but it def has a smallish cavity that’s been fully filled with EPS balls.
Therefore if I remove the bricks capping it off at top the cavity won’t become ventilated. It would then mean I could continue insulation with no thermal break however I’m beginning to think it’d be a lot of work for little gain. Maybe best to add rockwool above brick and accept small thermal break.

stoneyboy
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Re: Insulating gap above cavity in 1930's property

by stoneyboy » Thu Nov 30, 2023 9:59 pm

Hi steved54321,
The cavity fill does not form a sealed barrier - it a load of balls with gaps between. Go with the proposal in your last sentence.
Regards S

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