Cavity wall insulation after 39 years

syrok · 15 May 2011

We have recently moved to a 1960s built house which had cavity walls insulated in 1972. The material that was used is Rentokil Rockwool and the procedure was performed by Rentokil Limited which doesn't seem to trade any more.

I was thinking that 40 years is quite a long time. Can this rockwool deteriorate or get compressed over such period of time thus loosing it's thermal characteristic?

I was also thinking that since 1972 technology should be improved and probably some better materials are currently on the market.
I am really keen on getting the house properly insulated as I am putting underfloor heating together with air source heat pump and any improvement in thermal insulation would be really beneficial.

Would it make sense to get the old rockwool out and pump a new insulation in instead?

freddiemercurystwin · 16 May 2011

I'm intrigued to understand how would you propose you remove the existing insulation?

JohnD · 16 May 2011

syrok said:
Would it make sense to get the old rockwool out and pump a new insulation in instead?

no

unless you have reason to believe that it was badly installed and you have cold or wet areas.

rockwool fluff is about the same as still used, though at that age I don't know if it would have a water-repellent treatment. Mine did round about 1980.

syrok · 16 May 2011

freddymercurystwin said:
I'm intrigued to understand how would you propose you remove the existing insulation?

similar to this http://www.askjeff.co.uk/cavity.html

syrok · 16 May 2011

JohnD said:
syrok said:

Would it make sense to get the old rockwool out and pump a new insulation in instead?

Click to expand...

no
unless you have reason to believe that it was badly installed and you have cold or wet areas.
rockwool fluff is about the same as still used, though at that age I don't know if it would have a water-repellent treatment. Mine did round about 1980.

i have no idea how it was installed to be honest but when i look into PU foam insulation they claim that k-value is almost double of rockwool

JohnD · 16 May 2011

you can't insert foam slabs without taking the bricks off.

it is extremely difficult and costly to remove old insulation, and the real cause of damp spots is usually mortar dropped down the cavity by clumsy bricklayers, not insulation.

problems with cavity insulation are very rare, though scare stories are quite common.

the website you looked at uses the words "the recent fad for cavity wall insulation" which gives us a clue to his prejudices.

syrok · 16 May 2011

JohnD said:
you can't insert foam slabs without taking the bricks off.

it is extremely difficult and costly to remove old insulation, and the real cause of damp spots is usually mortar dropped down the cavity by clumsy bricklayers, not insulation.

problems with cavity insulation are very rare, though scare stories are quite common.

the website you looked at uses the words "the recent fad for cavity wall insulation" which gives us a clue to his prejudices.

i was thinking about self expanding PU foam. you simply pour it into cavities similar to injecting mineral wool

JohnD · 16 May 2011

has been withdrawn for post-build cavity insulation. Some people say the evaporating solvent causes health problems, others that the rigid foam cracks and water tracks through the cracks by capillarity.

syrok · 16 May 2011

JohnD said:
has been withdrawn for post-build cavity insulation. Some people say the evaporating solvent causes health problems, others that the rigid foam cracks and water tracks through the cracks by capillarity.

Just spoke to a company who does expandable PU foam for cavity walls and while they confirmed that PU is much better material for cavity insulation the cost of getting rockwool out would be much higher than to put it in.

peterperfection · 15 Jul 2012

I know this is a oldish post- but some info for whoever else is looking wont do any harm
The way they used to put rockwool in is- it was blown in --same as lofts.
very common in houses built around 1970-mid 80s (ish).

HOWEVER-- after maybe 10 years the rockwool 'settles' and compacts -leaving voids in the cavity. I know this through when I changed my windows and ther was a 400 mm + gap below window board downstairs and more upstairs.
I would not consider removing the rockwool- because of the messing about -but- 'my personal opinion' is- if you want to top it up- that's ok.
Be aware though- you still need ventilation--ie-air bricks to the outside .
Airbricks were ignored in 1970s-- maybe explains why some people are coughing and wheezing these days ?.

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Cavity wall insulation after 39 years

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