[signaturefish]

The whole bill of work is as follows:

* Full external-wall-insulation (180mm thick) with brick slip dressing so it doesn't stick out like a sore thumb amidst all the brick houses in the road.

* Triple-glazed windows and doors throughout, replacing single-glazed original units which are at end-of-life.

* 300mm deep loft insulation, replacing poor-quality and patchy 80-100mm insulation.

* Full airtightness sealing (i.e. the house should leak almost no warm air to the outside world), ...with heat-recovering mechanical ventilation so we don't all suffocate.

* Air-source heat pump to replace the gas boiler, driving underfloor heating in place of the wet-circuit radiators.

* 12-panel solar photovoltaic install on the roof (plus batteries etc).

Fully agreed on decarbonizing heating, but it's not an either/or thing, both approaches work and are to some extent necessary. Any heat you're not losing to the outside world doesn't need to be replaced by the heating system, is the theory. Here in the UK, I'm working to AECB (Association of Eco-Conscious Builders) standards: we cant quite hit PassiveHaus without knocking the whole thing down and rebuilding, but we can get pretty close.

There's a whole separate argument to be had about subsidy of electric heating vs subsidy of gas heating, if I recall correctly. A good electric heating system should be just as effective as a gas system, but in the UK it can cost up to four times as much to run because of the current mess of subsidies. That needs sorting out, as well, as telling people they have to pay much more for a somewhat more eco-conscious system isn't going to fly with the general population.

[kieranmaine]

That's an impressive list! Hats off to you. It would be really interesting to know which gives you the greatest benefit/cost ratio. I live in flats built in 1969 and they're generally fairly warm. However I'd really like to push for improved insulation, so any info on what works best would help me argue my case.

Also it might be worth looking at the following trial:

https://www.ovoenergy.com/smart-home/zero-carbon-heating-tri...

I'm not sure if they're still accepting participants but if you want to help push the boundaries on decarbonising heat it would be a good thing to get involved in.

[signaturefish]

Looks like that trial's currently not accepting new participants, but thanks for the link - I'll keep an eye on it in case that changes.

The retrofit plan that an eco-retrofit architect is currently drawing up for me indicates that the biggest benefits are on the "windows=>triple-glazing" (3->2 tonnes Co2e/year) and "external-wall-insulation" (2->1.1 tonnes CO2e/year) steps, but I don't have cost data to establish a cost-benefit ratio for them yet. I'd always suggest that someone who's looking to make their house slightly more efficient start with good triple-glazed windows, though - single glazing and some types of older double glazing can be really surprisingly lossy. The airtightness and MVHR work is spread out among several stages, so is harder to analyse, but older houses leak like sieves and anywhere you can feel a breeze in the winter you can be fairly sure that you're paying to heat air that's escaping the house.

"What works best" is really a bit of a rabbithole. The standards I'm working to are here: https://aecb.net/aecb-retrofit-standard/ and the AECB site in general is full of information though it can be quite dense and jargonized. You may also find https://passivhaustrust.org.uk/news/detail/?nId=867 interesting - it's a report on retrofitting an entire block of flats by stripping and rebuilding the interior using /Internal/ Wall Insulation instead of the more common EWI - it's less popular because it can be a pest to do electrical and plumbing work around, but it's an option. The three strong pillars of eco-retrofit, at least as I've seen them to be so far, are airtightness (and ventilation!), wall insulation and triple-glazing, and competently made and installed glazing will be the easiest sell to the management company I imagine (if you don't already have it). The other two are more involved.

[kieranmaine]

Thanks for the very comprehensive info. I think external wall insulation would be a hard one to get all the tenants to sign up for, but we're definitely due replacement windows in the next few years, so I'll push for triple glazing. Good luck with your retrofit!