Earth Notes: Thermal Imaging Survey: DIY vs Professional

Learn how a thermal imaging survey can spot real problems, and is a trained operator useful?
thermal images tiled 5x1

Twice the Fun

In February 2011 I managed to borrow a thermal camera for a few hours on a chilly evening to check for big problems at home such as unexpected thermal bridging. (Many thanks to Chas Warlow c/o the Street Champions project and the Ham and Petersham Low Carbon Zone!)

Thermal imaging cameras are sensing infrared (IR), often alonside visible light, and are using the IR to estimate the temperature of objects in the field of view. Occasionally they may described as 'thermographic'. IR thermometers are effectively single-point or single-pixel versions!

In March I engaged a professional to repeat the survey to see how effective my DIY attempt was (and see what else might need fixing) at a cost of under £200 all-in visiting me on a chilly Sunday morning!

Obvious Problems

cold spots from steel fixing screws

My amateurish attempts, and Sustainable Lifestyles' (SL) more practised eye, both discovered big problems such as the cold front door and loft hatch. Equally, both of us could see that our house is doing quite well (eg losing a lot less heat than neighbouring properties), though it turned out that I was too complacent and should have worked harder to pick out other issues.

loft hatch still needs work

One interesting feature that stood out dramatically in both surveys was the (expected) thermal bridging of the aerogel drylining in our living room with the steel fixing screws. With some styles of rigid drylining such as Kingspan K17 where dot-and-dab adhesive fixing to the wall is possible, such bridging can be avoided.

cold air leaking in the front door

Even though the loft hatch has been draught-stripped, and I glued some insulation to its top side (the box for a small solar panel with its expanded polystyrene packing!) it remains a clear weak point thermally. It may be possible to make a backing from some of the left-over aerogel; something should be done about it in any case.

The fact that our newly double-glazed front-door would still be relatively cold was not astonishing, nor that our door curtain is still useful to have, but possibly the colder external temperatures and a bit more slippage since my own survey made the effect of the poor seal at the door's foot rather dramatic in SL's survey and this time I was nudged to investigate. (In the end a catch needed to be re-tightened to fix the problem.)

Using the Thermal Camera

The FLIR Systems b40 that I used was small and light and easy to use, at least superficially, and with some fiddling around I was able to get the images onto my Mac when I'd finished my survey, making use of the removable memory card and a reader (I seem to recall; the device was not recognised over USB).

The thermal camera is deceptively simple point-and-shoot but with some caveats:

So if intending to DIY you need not be intimidated, but should definitely give yourself plenty of time to work through the camera modes and features to get the best out of it, maybe a whole day or more, and try and do it on a pretty cold day to maximise the visibility of heat leaks.

Things that I had Missed

SL did spot many things (often subtle) that I'd overlooked such as:

Air Infiltration above Ceilings

air infiltration above living room ceiling causing cooling

There seemed to be a consistent and unexpected pattern of infiltration above the ceiling from the east/west walls to the first transverse joist in all rooms, and consequent heat loss. Above the first-floor ceilings, since there will have to be some ventilation of the loft space to avoid moisture build-up and rot, that may be partly unavoidable, but downstairs it may be fixable, and I'm particularly keen to avoid it in the living room which we have gone to huge trouble to superinsulate and make the "warm refuge" room for winter.

This '60s house's external walls were probably not designed for air-tightness, so some infiltrations/leaks are not at all astonishing, and some ventilation is needed to keep the structural elements dry. But possibly we could make some special effort in the living room without endangering the building fabric, and in particularly cold spots elsewhere.

Holes in Loft Insulation

insulation hole at NW corner insulation hole at NE corner
insulation hole under loft boards near hatch one of the insulation holes above the bathroom ceiling
Problem cold spots at ceiling height.

I suspected that the current loft boards would be a weak point thermally, though could not see it on my own survey.

(There are boards for a small amount of storage above the small rear bedroom, and for safe working access to the solar PV inverters in two places.)

Not only did the SL survey show that fairly clearly, but also really dramatic holes in the existing glass/rock wool insulation, presumably where both the first and second and round missed areas. These are typically at hard-to-reach external edges and corners.

It's also clear from the SL survey that in several places joists are thermal bridges, cooling down the strip of ceiling directly beneath them. That will be hard to do much about right at the ends at external walls, but the rest in the first floor could be improved by better and more consistent insulation above them in the loft.

Heat Loss from above Windows

window bleeding heat above

This was something that I had not noticed at all during my survey, and would be worth at least a simple investigation if it can be done without too much mess or cost or disruption, just to see if something as simple as squirty foam would help, eg stopping unwanted air infiltration and convection beside and above frames.


Given that a survey doesn't necessarily cost anything if you can borrow, and not much even if someone comes round to do it for/with you, then it is quite likely that you can recoup your time and effort in energy savings in a reasonable time. And it's interesting!

I'd recommend getting in someone familiar with the equipment if you can, since it's not quite as point-and-click as a normal digital camera even though it almost seems to be.

Since renting a thermal camera may cost no less than getting the expert to bring their own and do all the leg work, then it may well be worth getting the trained brain along too.

None of this is to say that my own initial survey was a waste of effort, and indeed at the very least if I do a repeat in (say) a year's time, I'd have a better idea of what to concentrate on.


2011/03/07: the SL survey pointed out that our new front door is not sealing properly at the bottom, so I asked the company that installed it (Warmlite) to come and adjust it, which they did 2011/03/11 in 2 minutes (needed a catch adjusting); no charge.

I'm getting the loft insulation gaps sorted out and insulated loft boards put in to replace the current standard ones. (2017 note: I believe that we used B&Q Insulated Timber Loft Board (L) 1200 x (W) 320 x (D) 123mm, thermal resistance R-value is 3.50m2K/W EPS + 0.1286m2 K/W particle board, total loft board R value = 3.6286m2K/W rather than Knauf Space Board Insulation.)

As a longer-term project I'll think about reducing the air infiltration above each ceiling (especially that of the superinsulated living room) while being careful not to set myself up with condensation/rot problems for the house's timber frame.

(2011/10/21 note: when re-plumbing the rads in the rear bedrooms, now both hung on the internal partition wall to reduce direct external heat loss through exterior walls, the builder squirty-foamed the space to the outside wall to reduce infiltration at least from that section and around the radiator pipework which could be especially significant for heat-loss.)

Another project would be trying to fix the heat loss seen above the windows; maybe it would be possible to take out the reveal and do some simple remedial work such as foam filling of gaps and so on. And if we are ever replacing windows outright then we can pay extra attention to thermal bridging and losses around the frame.

(2011/10/04 note: when drylining exterior wall of rear bedrooms, the builders added lashings of squirty foam around window since there was quite a lot of air penetration, ie huge gaps you could stick a finger through, which may explain heat losses seen in the thermal imaging.)

~1712 words.