Bubble wrap foil - Cavity Wall Insulation - What can be done?

Hi everyone, First-time post here.
I live in a detached house built in 2000, it has a 10cm cavity between the walls. However, in this cavity, the housebuilders used a roll of “bubble foil” https://ybsinsulation.com/brands/airtec/ <very similar to this.
the rest of the cavity is empty.
I’ve always felt that this insulation was inadequate as the house can get very cold.

I’ve had cavity insulation people out over the years (about 5 or so) and they all tend to say the same thing, you can’t put more insulation in that gap, they say if the foil was to come away from the wall it could create a void and then could harbour damp.

I’ve really struggled over the years to find out:

  1. if the foil is adequate and I’ve been chasing a white rabbit for the last few years
  2. if not, What can be done to top up the insulation if anything

The entire estate is in the same boat as me
I thought I’d try my luck here


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Hi Chris, and welcome to the Carbon Co-op community. This sounds like a really interesting problem, with potentially big ramifications if it includes the entire estate.

I am afraid this is outside of my area of knowledge, but we have a lot of people with different expertise on the forum, so I hope someone is able to offer some insights and considerations.

I will also ask some colleagues who might have a better idea around this.

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I have limited knowledge but given the thin film of foil in a large empty cavity (even if the foil overlaps are airtight sealed) there will be quite a lot of heat loss to the cavity given the surface area. Are there any cavity closures at the top of the cavity wall? I would suggest some before and after (heating switched on) pictures with the IR camera to inform yourself for starters.

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You may want to look into a professional heat-loss survey, but if you are interested we also have a thermal imaging camera which is free for members to borrow. If this is something you are keen to try, just send me an email at matt.franklin[at]carbon.coop and I can send you more details.

It is worth bearing in mind that when using the thermal imaging camera you will want as large a differential between the inside of the house and outside as possible and preferably at least 10 degrees.

Thanks, Matt, I am interested in this to get a better idea of its performance. I’ll drop you an email about that, sounds like getting it over the winter will be useful!

I did get a foam insulator to tell me he could foam fill the cavity as that would exert pressure against the foil and avoid areas where the foil may create a void. However, I wasn’t too sure about this plus he quoted £10,000! not a chance I could ever recoup those costs in any meaning full time.

This is strange. Partial fill insulation should be tight to the inner leaf. Injected top up would be inserted through the outer leaf. How would that cause gaps? If anything it would close them.

Avoid exothermic insulation processes (generally expanding foams) as the heat might damage the existing insulation.

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I think some of their concerns were warranties and that they couldn’t guarantee it it it wasn’t an empty space Etc.

Thus not wanting to touch it with a bargepole!

That is a shame. I know that topping up cavity wall insulation is “a thing” but not how to find a suitable contractor.

There must be millions of houses that could benefit from topping up the cavity wall insulation so there are bound to be niche players out there somewhere.

The risk/ benefit balance. If we had an academic partner we could get a quick project done to do a mock up and check out potential solutions and likely scenarios.