Cavity wall extra insulation

Stubod · 23 May 2018 at 5:02PM

Hi, our house (as built 30+ years ago) has polystyrene blocks in the cavity, and there is an air gap of about 25 mm.

Recently a company has been round as part of a "govt. initiative" offering (free) extra insulation to fill the gap?

I was always advised "never" to fill in the cavity wall completely. Not sure if its a scam as no money has been requested. Just wondering if this is the right thing to do?

many thanks

Furts · 23 May 2018 at 5:31PM

Your house is a puzzle. 30+ years ago partial cavity fill was rare and I suggest the gap should be 50mm. Regardless, leave the gap unfilled because it is there for a purpose.

Stubod · 23 May 2018 at 7:06PM

.hi and thanks for the reply.....yes gap should read 50mm.

I also understood that the gap is there for a reason...it just seems odd that somebody would like to fill it for free?

Interestingly the neighbor (same house build) has had it done and the company turned up in an old van with no company name, logos or telephone numbers on...just seems a bit "iffy" to me?

Furts · 23 May 2018 at 8:26PM

Your home is way beyond the NHBC 10 year warranty but drilling and injecting is 100% against NHBC rules. Since this is a standard reference for all home building take the hint, and do not do it. As for your neighbour, I am left at a loss for words. Who with any degree of sanity allows door to door knockers to cause damage to their home? But they have also made their home unsaleable - no Surveyor will sanction what has been done. So what happens when they try to sell?

armchaireconomist · 24 May 2018 at 12:30PM

Don't do it. Lots of horror stories out there about these kind of jobs causing damp issues - the gap was left for a reason.

"Company" doesn't care, all they need is anything to fill with insulation so they can tell the government they've made your house warmer and get paid.

molerat · 24 May 2018 at 12:40PM

Furts wrote: »

Your house is a puzzle. 30+ years ago partial cavity fill was rare and I suggest the gap should be 50mm. Regardless, leave the gap unfilled because it is there for a purpose.

I am sure in the 80s & 90s they were throwing up block inner walls with 1" polystyrene sheets attached then the outer brick or block skin leaving a 1" gap.

Furts · 24 May 2018 at 1:27PM

molerat wrote: »

I am sure in the 80s & 90s they were throwing up block inner walls with 1" polystyrene sheets attached then the outer brick or block skin leaving a 1" gap.

Jablite was one of the early partial fills and I first came across this on a 1981 building. But this was high spec build for a hospital, and private homes were a generation behind this.

Jablite is a poor product for cavity fill, relative to PIR which seems to have come along after. If you know of 25mm sheets these would have been a nightmare to install - which means the build and insulation is going to end up iffy.

With OP's home being 30+ years old partial fill is an unusual case, or at least in my region of the UK.

Stubod · 25 May 2018 at 5:39PM

Hi all and thanks for the feedback. I have contacted our local council and they have advised that these schemes are ligit....just a bit concerned about the technicality as to whether or not you should actually "fill in" the gap?

Cavity wall extra insulation

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