Free Cavity Wall Insulation "Upgrade" - worthwhile? Who really gains?

Martyn-F

We recently had a knock on the door from a cavity wall insulation installer who is offering free insulation based on a government ECO grant, even for houses that already have cavity wall insulation and don't qualify for grants based on various measures of income support. I've checked it out and it is all legitimate. It's called ECO Flex and 25% of the grant money available to the local council can be used for households that wouldn't normally qualify.

No issues there, but about the planned work, I do have questions & concerns.

We have mineral wool insulation at present, backed by a 30-year guarantee (house built in 1999), so it has 8 years remaining. The door-to-door seller said that it is prone to problems like settling and gaps appearing etc. (The guarantee says otherwise of course!) They will drill & vacuum out the old, and pump in their replacement insulation which they say is much better. This is made from polystyrene beads (EPS beads) and they say they are much better. A new EPC (energy performance certificate) would be produced for the house too. Removal of old is about 1.5 days and putting in the new is about a day, so around 2.5 days of disruption, and lots of holes in the outer walls which of course they'll fill and match to colour of current mortar.

Being forever a cynic, I did a little research. General findings:

- Most sources I have read put mineral wool and EPS beads as having the same thermal rating (U-value). A few cite EPS beads as fractionally better (e.g. 0.28 vs 0.30 W/m²K)

- Both types are cheap options, EPS beads being less environmentally friendly in the long run.

- Both should be fine at not carrying water between the outer and inner wall to avoid damp (we're not in a high-risk area from driving rain - Midlands)

- Some sources say EPS beads can cause problems if pumped in with too much or too little glue.

So my question is - do I bother going ahead? Will the end result be worth the hassle for me? Or is this just a 'box-ticking exercise' for the local council/government (hitting targets), and a way of turning profit for the installer by blitzing as many properties in an area before moving on? All I gain is a small risk of problems in future which I don't have now, possibly fractionally better insulation, plus two days of noise and commotion.

Has anyone else has experience of similar 'upgrades' and how did you find it? Did it make your house noticeably warmer? Was it worth it?

We agreed to a survey - this involved a person taking about 200 photos of the house - every window (open & closed), gaps under internal doors, every light fitting, shower, loft, boiler - you name it. Also drilled a few test holes on the outer walls. Fairly normal stuff but a bit intense with the photography. Now waiting for the council to accept their application before we get an installation date booked in - if I choose to go ahead with.

Thanks for any thoughts or input. I don't want to miss an opportunity to improve our environment impact and energy efficiency, but I also don't want to go through unnecessary hassle if it's really for someone else's financial gain.

grumbler

Martyn-F said:

We have mineral wool insulation at present ....  They will drill & vacuum out the old...

This is really hard to believe. IMO they will get money for making noise for two days.

Martyn-F

Apparently they drill holes at regular intervals, starting from 10 bricks high, then 20, 30 all the way up to the roof, including the gable ends. This is not the company involved, but it's explained a little way down this page for example:

https://www.thegreenage.co.uk/can-remove-cavity-wall-insulation/

Ectophile

If they are getting a grant for doing the work, then they don't really care if it's necessary.  Once they have claimed the money and gone, they don't really care if your house is any warmer than it was before.

grumbler

Martyn-F said:

Apparently they drill holes at regular intervals, starting from 10 bricks high, then 20, 30 all the way up to the roof, including the gable ends. This is not the company involved, but it's explained a little way down this page for example:

https://www.thegreenage.co.uk/can-remove-cavity-wall-insulation/

If the holes are as small as in this picture, no way can they "vacuum out the old" mineral wool. If the holes are much bigger, do you really want your house resembling a colander without any good reason for this? Most, if not all new houses built on industrial scale now still have mineral wool insulation in their cavities.

daveyjp

I live close to a over 55s social housing development of two storeys, built about 30 years ago.  There will be about 50 flats.

Over the summer they had work done to replace the original CWI which did involve vacuuming out the old fill as in the photo and then replacing.

The process did also require the company to remove bricks at regular intervals.

No idea why they did it, but I assume there were problems as I can't imagine a cash strapped housing association spending money on such an extensive projecf if it wasn't needed.

https://youtu.be/REgNYIKETGI

stuart45

Normally they remove some bricks at the bottom to vacuum it out and drill holes higher up to air blast it down.
If you don't have any problems with it, I wouldn't bother with removal.

casper_gutman

Did they build houses with loose fill mineral fibre cavity insulation in 1999? I would have assumed it would be solid mineral wool batts, and I can't see them being too easy to vacuum out through little holes!

stuart45

Walls were normally built with either full(batts) or part(boards) back then, although some new builds got retro filled. 
Removal is done from whole bricks removed.

Martyn-F

casper_gutman said:

Did they build houses with loose fill mineral fibre cavity insulation in 1999? I would have assumed it would be solid mineral wool batts, and I can't see them being too easy to vacuum out through little holes!

Pretty sure our house has loose fibres, yes. Having recently had our boiler replaced & relocated to the loft, I saw the white, cotton-wool-esque insulation hanging around the gaping hole before it was filled. Also around an extractor fan vent when making a fix.

Thanks for all the replies. They didn't mention removing any bricks, but makes sense given the job at hand. I'll try calling the original installer soon. Maybe they can give an honest opinion, maybe not.

ComicGeek

I definitely wouldn't replace existing mineral wool that isn't causing any current problems. Normally the mineral wool would be a partial fill, which then allows the cavity to drain properly. Fully filling the cavity with EPS beads then provides a route for water penetration that didn't previously exist.

Have they confirmed U-values for before and after? Assuming say 0.35 W/m2.K for existing, and 0.28 W/m2.K for the EPS beads, you would be looking at absolute minimal difference in heating requirements and running costs. I really wouldn't take that level of risk for what might be a couple of pounds per month!

The only people who benefit from this are the installers, who get paid for unnecessary work and prevent the grants being used for homes that actually need it.