IWI on a cavity wall ??

[Adam Harper]

Hello

I just attended a webinar this evening about Retrofit hosted by a community energy group. There was a chap there billed as an ‘expert’ who operates in Yorkshire as a home retrofit consultant (won’t name any names) who claimed that ‘the only way to further insulate a filled cavity wall without causing condensation is to install internal wall insulation’.

Its a little while since I’ve done dew point calcs, but would internally insulating a cavity wall not move the dew point from the cavity into the inner wall leaf, and therefore increase moisture risk?
I’m sure I’ve read of EnerPhit projects with filled cavity walls that have had EWI installed with no issue, so I’m at a lost to why he’s saying you can’t installed EWI on a cavity wall. Would a appreciate a technical answer as I’d like to challenge this chap is he’s making incorrect statements.

Thanks
Adam

[Paul Jennings]

Hi Adam,

There have certainly been EnerPHit projects with external wall insulation on cavities, but there have also been projects where the removal of existing cavity wall insulation has been proposed to avoid the possibility of such problems.

Unfortunately, I’m not yet skilled with WUFI, so can’t examine this at a technical level.  But I’m doing Joseph Little’s online course in November, maybe I can work this one through as part of that! Maybe someone else can help?

But, maybe we should be naming names? There is far too much incompetence out there, right from the top of the new Green Deal downwards. Get your facts right, do your research, then skewer the guy! But then I am somewhat of an extremist!

Have I shared my solution for the poor quality of newbuild from volume housebuilders? Conversation for adown the pub, whenever that becomes possible again.

Good luck.

Paul Jennings, Aldas

 

[Paul Jennings]

Hi Adam,

https://passivhausrefurb.blogspot.com/search/label/cavity%20walls

I talked with another Adam, Adam Dadeby, who did the excellent EnerPHit refurbishment of Hunters Moon in Dartington.  The link is to his post about removing existing cavity fill (which had suffered from water penetration) and then replacing it with graphite beads before the external leaf was clad externally.  He reckons it took him up to 2 days to vacuum out the old insulation, which he did himself to save money.  Used an industrial vacuum cleaner and some extension pipe, had to work around wall ties, but was made feasible because all the existing windows had been removed.

But clearly was insulating externally on a filled cavity wall. Don’t think he has done any moisture monitoring in the fabric, but no sign of any problems nearly 10 years on.

 

[Nick Owens]

As part of my MSc at University of Kent, I recently modelled 200mm wood fibre EWI on a cellulose-filled brick an block cavity wall, with 0.5 inch wood siding externally externally.  I used DesignBuilder as the simulation tool, which incorporates the EnergyPlus v8.9 simulation engine.

The condensation analysis given by DesignBuilder says “structure is free from condensation”  “number of condensation interfaces: zero” , and “Thermal quality good. Mould growth unlikely”.  And that’s without taking out the old cavity insulation.

So it seems OK, and what’s more I’m going to build it as soon as I can get planning permission.

[Adam Harper]

Hi Nick,

Thanks that sounds interesting.  I see EnergyPlus is a US tool, do you know if it uses ISO standard conventions for the condensation calcs?

Let us know how you get on with the install, which is presumably wood fibre retrofitted onto an existing cavity wall dwelling?

Thanks

Adam

[Adam Harper]

Hi Paul

I meant to reply to say thanks for the advice and suggested link to Hunters Moon. I heard this from a guy called Andy Walker of Sure Insulation. He advises households on retrofit and his company used to install IWI.

Cheers

Adam

[Nick Owens]

Replying to Adam Harper’s post of 20/10/20 7:00pm:

You asked about EnergyPlus and how I got on with the EWI installation.  Re EnergyPlus, sorry I don’t know if it uses ISO standard conventions but I THINK it does – there were no weird units of measure involved.
Re the EWI install, for cost reasons and to match the look of adjacent houses we opted instead for 200mm EPS + white render above the DPC, and 160mm XPS + grey render for 400mm below DPC.  The work was done by a Baumit registered contractor.  Seems to be performing perfectly well, only 1 tiny hairline crack so far, 10 months on. And the energy bills are pretty low!

[Nick Owens]

Just to add, the existing cavity insulation was cellulose fibre and showed as about 90-95% coverage with a thermal camera.  So we didn’t take it out and re-fill, we just kept it in place, but fitted cavity closer batts all along the top of the wall whilst the roof was off to minimise convection heat loss.  Calculations of u-values showed the missing 5-10% would have little effect once 200mm of EWI was added on the outside.

[Nick Parsons]

 

Initially replied as this seemed to describe me, though not my views! However I see I did my seminar on 21st *October*, not 21st Sept.

 

In case anyone is interested in what I said on 21st October: https://selce.org.uk/greening-your-home/

• This reply was modified 4 months, 1 week ago by Nick Parsons.
• This reply was modified 4 months, 1 week ago by Nick Parsons.
• This reply was modified 4 months, 1 week ago by Nick Parsons. Reason: typos and note re EWI
• This reply was modified 4 months, 1 week ago by Nick Parsons.
• This reply was modified 4 months, 1 week ago by Nick Parsons.

[Author]

Posts