Topic isn't the whole picture, but this study finds that Insulating the lofts and cavity walls of existing UK housing stock only reduces gas consumption for the first year or two, with all energy savings vanishing by the fourth year after a retrofit,

https://www.cam.ac.uk/research/news/insulation-only-provides-short-term-reduction-in-household-gas-consumption-study-of-uk-housing

I've not looked at it in depth but seems to point to a few things to me -
- our housing stock is terribly insulated so many people live in cold houses
- retrofit isn't being done well enough. (our regulations should be tighter)
- energy is (or at least was) too cheap.

Anecdotally people have been turning down their heating this year - the staff in a DIY store I was in recently were saying they'd had a big increase in people seeking remedy for damp (likely as a result of reducing heating input)

Read a Twitter thread today saying the exact same thing.

Insulating the poorest housing for the lowest percentile does not necessarily reduce energy use, but it gives them a suitably warm living condition at an affordable price. i.e. they spend the same but are warmer.

For CO2 reductions, you need to target the better off with different incentives.

Mmm, not sure I believe that.

If a home doesn't have roof or wall insulation, and basic versions of those are added, it's not difficult to halve the overall U value.

To turn that saving into warmer temperatures instead of energy savings, you'd have to double the HDD, which are around 2500 HDD for central UK.

If the heating season is say 200 days, that means you'd have to increase internal temperature by 2500/200 = 12.5⁰. EG from 17 to 30⁰C.

Doesn't sound likely to me, even acknowledging several shortcuts in the above.

Posted By: WillInAberdeenIf the heating season is say 200 days, that means you'd have to increase internal temperature by 2500/200 = 12.5⁰. EG from 17 to 30⁰C.

It's not quite that simple is it? I'm no expert in HDD but if you increase the temperature, you also increase the number of days you need to heat to reach that temperature, so the temperature rise won't be so great.

Posted By: WillInAberdeeneven acknowledging several shortcuts

You’re completely free to run your own numbers, with a different estimate of the length of the heating season for a newly-insulated house. If you don't like 200 days, then by all means try 250, or even 300. You could also explore some of the other shortcuts, such as incidental gains and precise insulation values. Let us know what answer you get.

Either way, it will take an unfeasibly large temperature rise, to swallow up all the gains from insulating the walls and roof of an uninsulated house.

Posted By: PeterStarckI designed and built my own PH

Posted By: PeterStarckI now live in an 1840s solid stone wall bungalow

What's it like, 'going back'?!

Posted By: Cliff Popebut a rich person would save it

Not just save it (from where it could be retrieved and spent, or invested in some real productive way) but 'invest' it into his/her 'wealth' measured in stock valuation (which e.g. Musk can be wiped out overnight and mostly never returns to be spent or invested in the true productive sense).

The poor person recycles his/her money into the economy where it lubricates and accelerates the velocity of buy/sell exchange, hence felt prosperity mostly locally, as well as increasing national GDP.

The rich person sucks up the money out of the real economy, converts it into paper tokens of control and rent-taking, thus bidding up the overall stock market index to no benefit, from where only a small proportion can ever return to usefuless without crashing the stock market.

Having read the original paper it's becoming a bit more murky:

The authors are professors of politics, policy and economics, so their purpose was not to address the building physics, they were more looking into the social policy implications.

They were not in position to gather their own data, they had to reanalyse someone else's data set for the gas bills in £ of a set of houses, including a few where the owners reported insulation was fitted around 2010. Also some that built extensions or conservatories (ie extra heated space) which caused the total bill for the whole set of houses to drift up over time. There was no data on indoor temperatures or airtightness, or rollout of condensing boilers.

The data (as you'd expect) had a lot of random scatter so they used statistical techniques to get the randomness down to ±10%

The doubtful results for me were that

1) people who reported loft/cavity insulation being fitted around 2010 reported a 4% saving on their bills. We would expect nearer 40% based on 2023 U values, so what level of insulation was actually being fitted back then? Was it really the whole house being fully insulated for the first time, or actually just a few m² of top-up?

2) the biggest bill reductions actually happened 3-5 years before the insulation was fitted (around 2005-7ish). IE the insulation wasn't what had caused the biggest drop in bills.

Those seem like red flags but this study was not focused on investigating those aspects, and probably the gas bills data couldn't tell much about what insulation was physically fitted, or when.

As the average energy bills for the whole set of houses drifted up through the 2010s, possibly due to extension-building or general growth in household wealth, the 4% was soon lost in the noise.

All social policy research involves trying to make sense of lots of incomplete data and it's good that someone does that, but I am very wary that too much is being read into this study in the media. It seems to have been promoted by the university press office as something newsworthy.

It doesn't seem to me like evidence that a deep retrofit to 2023 building standards wouldn't result in long term sustained savings.

TLDR: if you only put a teeny bit of insulation in, you'll soon wish you had some more!

Posted By: fostertom

Posted By: PeterStarckI designed and built my own PH

Posted By: PeterStarckI now live in an 1840s solid stone wall bungalow

What's it like, 'going back'?!

A bit of a shock for the system but more than offset by moving from the SE to North Cornwall.

Posted By: WillInAberdeenThere was no data on indoor temperatures or airtightness, or rollout of condensing boilers.

That's a pretty big omission.

Here in Portugal we didn't add any insulation to the walls of our apartment but changed extremely leaky windows with airtight double glazing + trickle vent and continuous extract ventilation.

This winter we still haven't turned the heating on.

It's zero degrees outside this morning and it's comfortable inside with thermal underwear and a jumper. We were just talking about this and I was saying I was a bit surprised, but my girlfriend informed me that it's because she finally took my advice and stopped swinging the windows wide open simply because it's sunny!