Becoming Dr. Love: Part 2 (what occupants do)

Jenny Love, UCL Energy Institute

In my previous post here, I described the process of PhD data collection and some of the odd things which can happen when carrying it out. After publishing that post I went quiet for a bit to concentrate on the small matter of turning the data into a 90,000 word thesis. Having done that, and then recovering by alternating between sleep and eating nutella out of the jar, I am ready to face the world again. So in this post and the next one I’ll be describing some of my findings.


In this post I’ll talk about what light was shed on the complexities of occupant behaviour in the context of retrofit: how occupants change their heating behaviour afterwards, and why internal temperatures increase.  In the next post I’ll report some implications of this concerning whether our current retrofit strategy for social housing goes far enough.

What was I trying to find out?

There is a general concern that retrofit, here referring to insulation of dwellings, doesn’t save as much energy as it should for all the effort of wrapping a house up in a blanket. That’s because it is suspected that instead of what  is ‘supposed’ to happen (i.e. the occupants keep the heating at the same level after the retrofit and save energy), occupants will take this chance to heat to higher temperatures or for longer, and not save much energy after all. This is especially expected to happen in ‘fuel poor’ households: those who before retrofit struggle to heat their home to the temperature they would want, for whom insulation might mean they can be warmer.

As I described in more detail in the last post, instead of looking at just outcomes of retrofit  (i.e. these people saved X kWh of energy, or it was X degrees warmer in their house afterwards), I looked also at what actually happened in the homes: what did occupants think the retrofit was all about; how had they changed their use of heating since; were they using their home differently and was this requiring more or less energy? So the sort of things I was measuring were: their use of radiators, air temperature and humidity, and use of space;  I also interviewed the occupants before and after.

Variety in occupant reactions

When you wrap up a building in a big pink jumper (see photo below), it will lose heat less quickly afterwards, and so its average temperature will increase without the occupants doing anything.


But how occupants then react to this natural temperature increase is different in different households. I found three types of occupant reaction, ranging from occupants practically eliminating their use of heating to occupants using more hours of heating:

1. Temperature increase from the building, counteracted by occupants

Two of the case study households turned down the heating so much that the temperature went down after retrofit. However, they reported feeling warmer. How could both of these phenomena have come about? Here’s what I could gather from my data…

Both of these households had an income cut around the time of the retrofit and were really struggling for money. Also, before the retrofit they were both expecting the retrofit to lead to a warmer house with less heating needed. This could explain why they turned the heating down so much. But why did they feel warmer? I looked in the air temperature data: had the particular rooms they used got warmer at the times they used them? Or had the daily minimum temperature they experienced increased, say, when they got up in the morning? Neither of these had occurred. I had to conclude that there must be other comfort variables at work, like radiant temperature.

2. Temperature increase from the building, no change in occupant behaviour

These occupants carried on using the heating in pretty much the same way as before: they didn’t turn anything down, and they didn’t turn anything up. As was mentioned above and will be further explained below, this still leads to an increase in internal temperature.

3. Temperature Increase from the building, then occupants used more heating

Two different and interesting processes were seen in households who used the heating more after retrofit.

In one flat,  the occupant didn’t really bother with the central heating before the retrofit since the building was so leaky that it didn’t seem to make a difference. He heated the living room with a gas fire and stayed in there. After the retrofit he started using the central heating since it now actually did something.

In another case, even though the insulation made the house warmer, different rooms warmed up by different amounts. This had the effect of making the occupants’ bedroom feel cold, as it hadn’t warmed up as much as some other rooms. So they started heating the whole house all evening, so that their bedroom would be warm enough by the time they wanted to use it.

Turning heating up, down, the same…does that mean that anything can happen?

Yes. I will argue in my next post that with this type of ‘shallow’ retrofit (10 cm of insulation), it’s very difficult to predict the outcomes since you leave a lot of room for different outcomes to be possible, especially when new occupants move in. However we only started to see a glimpse of the range of possible outcomes. With the same people living there after retrofit as before, occupants probably aren’t going to massively increase their energy use after retrofit so we probably aren’t going to see those kind of outcomes.

Also, just because occupants reacted in a variety of ways, doesn’t mean that how they reacted totally determined the outcome. As we’ve seen, the building theoretically has a lot to do with it. We can try to quantify its influence in a few ways…

In most houses there was a temperature increase. What was it mostly caused by?

The answer is not the occupants but the building itself. How can I know this? By looking at when it occurred…

Firstly, most of the temperature increase compared to the previous year occurred when the heating was off. That is, the times when the heating was off, post-retrofit, were warmer than the times the heating was off pre-retrofit. I had a fancy equation to calculate how much of the temperature increase occurred during unheated hours, and it turned out to be 77-87% across the houses.

Within this, quite a bit of the temperature increase happened at night. It’s possible to see the houses cooling down slower at night, when the heating was off, whilst the occupants are fast asleep and therefore not thinking, ‘I know, I’ll increase the temperature in my dwelling’.

In some houses, the hours in which the heating was on got warmer after retrofit (accounting for 5%-23% of the temperature increase). This wasn’t due to people turning up the thermostats. It was either that the thermostat was at a sensible setting and the building was too leaky to get that warm before retrofit, or the thermostat was at a non-sensible setting like 30C (for whatever reason) and the heating system tried its hardest but still couldn’t reach it.

What to make of all this

The first point is that if the temperature increases in someone’s home after retrofit, it’s not necessarily their fault or their intention. To get the temperature not to increase, occupants would have to shorten their daily heating period by quite a few hours. Even when they increase their hours of heating, most of the temperature increase is still attributable to the building cooling down more slowly. So we can stop occupant-blaming.

not guilty

Secondly, there was quite a large range in terms of how occupants reacted, and whether they turned heating up or down, which makes it difficult to predict outcomes. However, this was a small range compared to what could have happened. I haven’t explained this statement yet, as I explore this further in the next post, where I talk about the effect of new tenants moving in over time –  and how the current way we do retrofit means we can’t guarantee energy savings afterwards.

That’s all for now – but feel free to get in touch with me if you would like any more detail on the sort of mechanisms I uncovered or if you have any questions:


13 thoughts on “Becoming Dr. Love: Part 2 (what occupants do)

  1. Hi Jenny, this is a nice follow on to your talk at the Lolo Conference last week. Perhaps the other variable is also increased airtightness after retrofit. Do you have blower door tests pre/post or did the HA not do this? Also, anecdotally, we had our flat roof insulated at the weekend and we noticed that the difference in room temperature upstairs/downstairs is more pronounced, as the heat is more retained upstairs. ( our bathroom could never reach over 16C in winter WITH heat on; it has been 17/18 now). The only thing is that when I now go downstairs (I work upstairs) I find the thermostat at 18 or 19 C and it ‘feels cold’ (and colder than 18/19 C) because it is 20 or 21 upstairs, yet before I would find 19C downstairs totally acceptable – so it is just the perception and difference that is more pronounced now. I think I need to play with my upstairs radiator thermostats and turn them down! 😉

  2. Jenny,

    A really interesting summary. You are now in my RSS feed (feedly) so keep up the good work.

    Mark Brinkley

  3. Shallow retrofits are problematic for the reasons you’re uncovering. Here are some of my empirical findings.

    One of the things I have noticed about people who are fuel-poor and retired is that they typically only heat the rooms which they’re using. Two of my elderly relations (a married couple) only used their front room in summer, because it was such a cold room to heat in winter. Once they’d installed insulation on my suggestion—multifoil under the floorboards, a new double glazed patio door and 80mm of external insulation on the outside walls of the entire house—they now use their front room all year round, but in addition to the rooms they used before. Arguably, if the aim was specifically to reduce fuel use, it would have been better to concentrate on insulating just the external and internal walls round the rooms they actually used and then continue living as before but with lower bills. They would have found this very acceptable and their fuel savings would have been much greater.

    This same couple only use one of their three upstairs bedrooms to sleep in so have the radiators switched off in the other two. Again, with no insulation on internal walls, their potential heat saving is compromised because much of the heat loss is to the other rooms (which are now warmer; but to what purpose?).

    What I’m coming round to saying is that if we are ‘shallow retrofitting’ we need to think more about the way people live in a house. In this case I would suggest it’s as important to have insulation in/on the walls between internal rooms, as it is in/on external walls. What’s more, without insulation between downstairs and upstairs, once external insulation is added, loft insulation improved and the downstairs rooms are heated to say 22C, it can often be found that the upstairs becomes so warm that people will open bedroom windows to cool rooms down for sleeping.

    I should add that the couple I describe above have seen the cost of their gas bill drop, but not by as much as would have been possible if the way they use their home had stayed the same. But they’re happy with the improvements to their 30s, solid-walled house, even though the retrofit cost them £17,000 from their savings in total.

    A last comment. A thing to watch out for is that just living in a house will create a certain level of heat—from computers, TVs, washing machines, lighting and cooking activities. A human body gives off about 60W too—which can add up if you have a family of 4 living in a house. Of course in a leaky and poorly insulated house that ‘waste’ heat is too insignificant to be noticed, due to the speed it’s being lost. But add insulation and it starts to become a greater percentage of the heat available to keep the house warm. Frankly my philosophy is to insulate as far as you can—and then go further. You’ll never regret it as it’s the disruption and the labour which is the big cost. In other words; if you’re putting in 80mm an additional 40mm of insulation costs peanuts. Fuel costs can only go up!

    • Hi there,
      They were built after the 2nd world war, using Wimpy no-fines construction. A supervisor of mine described Wimpy no-fines walls as, “like a nut bar”, in that they’re essentially full of holes. I wouldn’t wish them upon anybody.

  4. I love your post, Jenny.

    For the occupants who through they were warmer even though the rooms were cooler, I wonder if reduced draughts could have been a factor, since having a cold draught around your feet is a sure way to feel chilly.

    • Hi Nicola, thanks!

      I did ask them about draughts and none of them seemed to think they were a problem pre-retrofit. Interestingly the only comments about draughts were as a result of having trickle vents put in with the double glazing. But I don’t know a way to measure whether there are draughts around the floor, that would be interesting…

  5. I am also working on retrofitting but my PhD topic is focused on Modern Movement residential buildings (listed). Nevertheless, our team has a project more focused in social housing and we are interested in deepening on this aspect. Do you have anything published about it? How far are you already with your PhD?

    Kind regards from Spain,

  6. Pingback: Becoming Dr. Love: part 3 (does behaviour matter?) | energyandlife

  7. Pingback: Reflections on energy and housing | energyandlife

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