Measuring insulation.

Nothing cheap. But you can hire equipment from several good hire companies.

Probably easier to DIY. Not very complex I imagine, just a differential thermometer + servo

• heater + insulation.

Turn on the heater until the temperature on the surface inside and outside the insulation and above is the same, then add the heat flow through the insulation to the heater power to get total heat flow out at any given point.

Won't be very fast, but should work.

Buy an infrared thermometer. On a day when there's a good temperature differential between inside and outside (i.e. middle of winter), measure the temperature of the inside surface of all external walls/ceilings/ windows/doors of the house. If the indoor temperature is about the same everywhere (away from the external surfaces), then the temperature difference between the indoor temperature and the temperature of a surface is roughly proportional to the relative heat loss through that surface.

You can play the same game from the outside of the house too. Measure the temperature of the outside of the walls/roof/windows/doors, and the amount they are above the outdoor temperature is roughly proportional to the relative heat loss through that surface. You should find a good correlation with the figures measured from the inside.

These will give you reasonable relative figures for different areas, but not absolute values.

I would like values.

Plus, the floor is rather hard to get to the other side of. I was very surprised that drilling a tiny hole through and dropping a probe down gave as little as 2C difference in the air temp under the floor and the room. (10C outside, windy, 18C in).

Hmm, I wonder if there is a market for these in small quantities on ebay. Making a servicable meter that reads out directly in w/m^2 lost per meter wouldn't be very hard. Supplemented with an IR thermometer (to check for hot or cold spots) it might be quite handy.

Well, find something for which the value is known, and you can then work out the values for everything else relative to that.

You don't need to. You only need to get to one side.

Temperature under the floor is only partway to the outside. The rest of the way to the outside will be providing further insulation (75% of it in your case with the floor being only 25% of the insulation if we assume temperatures were all stablised, which they never do of course).

I think to do better than the IR thermometer way in place would be very hard.

Yes, it was fascinating to go round the house looking for cold spots. One very cold spot I found was the loft hatch, easily fixed with a piece of insulation layed on the back of it.