late to the party, but I would agree with almost everything Tim said, But do have a few questions.
Is the rain water good the only issues preventing you from doing full external insulation? I would say this is by far the most effective in regards to simplicity, and to risk of interstitial condensation with IWI. And close up the cavity.
If it is just the rainwater goods, and not the roof overhang, then i would consider finding a relatvivly easy solution for the rain water goods. It would still need a themral skirt internally, on the party wall with your neighbour.
Regarding IWI. I am always of the opinion that for risk free IWI, a open cavity is better. It means any moisture in the internal leaf is being wicked away. A semi blocked cavity, could provide a mositure bridge from external to internal leaf. it sounds like you have that bridge.
The combo of IWI and EWI means non optimal for one of the build ups. IWI prefers open cavity and EWI closed.
You can of course reduce the risk but using natural vapour open internal inulation, and having a good mvhr for ventilation will do that.
Wow ok, i am clearly bad at this. I mistook tims recent additon to this discussion, as that this feed was brand new! silly me.
interested in hearing the results though.
Hi,
So in the end we went ahead with IWI mainly due to how the internal work had progressed with the builder already stripping most of the plaster on the gable wall. It’s PIR rather than diathonite and we’ve done most of the gable wall apart from the bathroom which may be refurbed later.
Our architect said that they think in our case if we wanted to add EWI later she doesn’t think there would be damp issues and would be prepared to offer some form of indemnity against such issues if we decided we wanted to add it. But the idea was that we would wait till the work was done and see how the house was over winter.
In terms of results, it’s been ok, not amazing. We have a separate issue with our heating being on the same circuit for the downstairs underfloor heating and upstairs radiators and the bamboo flooring having a ‘maximum’ temperature of 27 degrees which we are playing around with and could potentially just fit something to cool down the water before it enters the manifolds (which would be annoying from an energy efficiency POV). But we’ve been comfortable at about 19 degrees in the house during the colder weeks in january with an energy efficiency of 3.0 at the worst and more like 3.7 last week. One niche issue we encountered was we decided to replace the double glazed windows for triple glazed and delays meant that that happened during that cold snap in november, and the low&slow heating method does not work well when all your heat has just vanished through open window cavities - regardless of the insulation on the walls!
I do need to borrow the thermal imaging camera again soon to check what the outside looks like from that perspective too.
Overall I don’t feel like I’ve come out of the project with any confidence that we made the best choices - we’ve got a 19 month toddler to deal with (7 months back when I made this thread!) so we’ve not been operating at peak mental capacity anyway and it’s a complicated topic. I’m not sure we’ll risk the EWI even with the indemnity as it just feels like a large risk for probably not much extra return.
Maybe if we’d had an insulation expert involved from the off we’d have had a better result, but we thought the architect and builder involved were on the same wavelength to start with so it was only halfway through that we stumbled into this issue.
Sorry it’s a bit of a rambly update. Still very much appreciated your input @Tim_Gilbert and I guess my advice for others in the same situation would be to work out the insulation strategy well in advance of the renovations and make sure you have enough sleep (or hire a project manager!)
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Thanks for the update. “Before and after” really helps readers to understand the issues.
Regarding the addition of EWI, the gable end is basically facing north, so it may be worthwhile.
It is generally recommended that if you have both, the R value of the EWI should greatly exceed the R value of the IWI. This is to ensure that any humidity doesn’t condense in the outer wall structure.
For any readers that don’t know,
R value = 1/U value
&
U value = 1/R value
R value is useful because you can add together the R values of different components and then take 1/R to calculate the combined U value of your whole structure.
Yeah, thanks for the update. This is the conundrum of retrofit. Solving problems, and making new problems that have to be solved. I would have been surprised if insulating most of the gable wall and nothing else would have made a significant difference. But incrementally step by step it adds up, so i wouldnt be too dissappointed.
Sounds liek you have been juggling.
Why is it house refurbs and babis seem to arrive at exactly the same time!!!