Has anyone had a happy experience with retrofitted cavity wall insulation?

Wootcanaw

Our house is a detached bungalow, built in 1931 with an F rated EPC.  It’s an unusual layout as most of the rooms have three external walls.  

As you can imagine, we’re keen to improve its energy efficiency.  We were unsure whether the house had cavity wall insulation or not (it’s rendered so we couldn’t see from outside). We asked an insulation company to check and they put a camera through the air bricks and established we had insulation but that it was very old and had degraded.  We arranged for them to remove the old insulation with a view to replacing it a few weeks later (they said we needed to wait so that it would have dried out properly).   It’s a reputable, well-reviewed company.  I asked advice about the suitability of CWI for our sort of house and the owner of the company was very reassuring.  He pointed out that the last thing he would want to do would be to put CWI into an unsuitable property and that he was happy from the inspection to go ahead.   We currently have a house covered in holes and with all the ground level air bricks removed awaiting filling with Rockwool.  

I’ve started to get very nervous again about it, having read countless horror stories.  What’s particularly bothering me is that the small internal temperature/humidity monitors that we have in several rooms are all showing vastly increased humidity levels - anything from 65 - 80% humidity. This happened pretty much immediately after removing the insulation and has baffled me as, if anything, I would have imagined the humidity levels would decrease after the removal of failed insulation.

We’re desperately keen to insulate as much as possible but also very worried about potential damp issues.  

Wondered if anyone had any reassuring experiences of retrofitting CWI?

BTW - we are about a mile from the coast though not the west coast and in a fairly sheltered position so we don’t really have an issue with wind driven rain.

Mutton_Geoff

Wootcanaw said:

several rooms are all showing vastly increased humidity levels - anything from 65 - 80% humidity. This happened pretty much immediately after removing the insulation and has baffled me as, if anything, I would have imagined the humidity levels would decrease after the removal of failed insulation.

Humidity is relative and as air cools, the % level will rise for the same amount of moisture in the air (until it reaches the dewpoint when it condenses, eg as on a bathroom window or the clouds in the sky). Did the temperature fall as well, if so, that explains the increase in relative humidity that you are seeing.

DougMLancs

Our house has had CWI since 2011 with no issues and we’re in wet, wild Lancaster.

EssexExile

Ours was done about 20 years ago, all fine so far.

Wootcanaw

Mutton_Geoff said:

Wootcanaw said:

several rooms are all showing vastly increased humidity levels - anything from 65 - 80% humidity. This happened pretty much immediately after removing the insulation and has baffled me as, if anything, I would have imagined the humidity levels would decrease after the removal of failed insulation.

Humidity is relative and as air cools, the % level will rise for the same amount of moisture in the air (until it reaches the dewpoint when it condenses, eg as on a bathroom window or the clouds in the sky). Did the temperature fall as well, if so, that explains the increase in relative humidity that you are seeing.

Thanks Mutton Geoff, hopefully that explains it.  It was removed in September and I think the temperature dropped quite a bit after the summer - it was just alarming that it seemed to coincide with the CWI being removed.  Appreciate your reply.

Wootcanaw

Good to know Doug, thank you.

Do you mind letting me known what sort of filling do you have? I’ve read mixed reports about Rockwool though I like to idea of its sound insulation properties as well as thermal.

Wootcanaw

Thanks EssexExile.

Don’t suppose yours is Rockwool is it? The insulators recommended it, especially as we’re on a main road as apparently it’s good for sound insulation too but some websites claim it holds water.

DougMLancs

Wootcanaw said:

Good to know Doug, thank you.

Do you mind letting me known what sort of filling do you have? I’ve read mixed reports about Rockwool though I like to idea of its sound insulation properties as well as thermal.

Ours was a Knauf blown mineral wool that was fitted with a 25 yr guarantee. I’ve also seen CWI horror stories but more often than not when fitted in areas with strong driving rain. There were also a lot of cowboy installers around back when you could get a grant/subsidy for it.

I don’t know how much the technology of the products has evolved in recent years but if you look at Knauf’s most recent products then they say they’re completely water repellent and can be used even in the most extreme situations. Rockwool say something similar. Manufacturer claims can’t always be taken at face value but I would be surprised if the products haven’t improved in the last 20 years.

An alternative to the mineral wool products are glued eps beads which are slightly more expensive to install but impervious to water. 

If you don’t have an issue with driving rain though then personally I would think the mineral wool products would be fine providing they’re correctly installed and your pointing etc is in good condition.

EssexExile

Wootcanaw said:

Thanks EssexExile.

Don’t suppose yours is Rockwool is it? The insulators recommended it, especially as we’re on a main road as apparently it’s good for sound insulation too but some websites claim it holds water.

I've no idea! It's fluffy stuff like loft insulation.

jonnydeppiwish!

I have bonded EPS beads as well, though I didn't have them installed. No damp and the house is easy to heat with minimal heating on