How we insulated under our floors

Regular readers will know about my plan to get our house to an A rating by 2020, and net zero by 2025. I missed the 2020 deadline due to the government mis-handling the Green Homes Grant, but this week the underfloor insulation went in. I won’t be commissioning a new Energy Performance Certificate to confirm it, but it’s now pretty comprehensively in the A zone.

Homes lose heat in all directions. We’d already insulated the loft, a double layer with insulation rolls and then foil. We’ve got double glazing in the windows and fitted a more efficient front door. External wall insulation went on last year. The floor, generally responsible for 10-20% of heat loss, was the last bit to do.

The problem is that our 1920s home has wooden floors suspended over a small crawl-space. I have got under there, but there’s barely enough room to move around. It would be very difficult to manhandle insulating panels or rolls down there and get them into place. The only other way to do it would be to tear up all the floorboards, which is difficult when you’re already living in the house.

In 2018 I came across a possible solution – a company called Q-bot that has developed a crawler robot designed to fit in floor voids, map the underside of the floor and then apply a spray-on insulating foam. They weren’t doing the domestic market at the time, but I’ve kept an eye on them and the Green Homes Grant was a great opportunity to get the job done with a little financial help from the government.

On monday, the Q-bot team parked their van outside the house. They put up a gazebo next to it, and set up a table with a monitor and a set of controls. Inside, I removed three short sections of floorboard to get the robot in. It’s like a robust radio controlled car, with a power cable and a chunky blue hosepipe attached.

Off it went. I heard a hissing from under the floors as it worked its way back and forth. Otherwise I carried on working from home as usual. An extractor fan drew out any fumes as the insulation dried, and there was no discernible smell at the time or afterwards. It’s the least disruptive bit of work we’ve had done on the house, by a considerable distance.

One thing that I found interesting was the whole job was computerised and documented. The robot scans and maps the floor, and can see exactly where to put the insulation and how thick to apply it. This is recorded by its onboard cameras, and the data is all visible in an app. This same app records details about the property, before and after photos, and a bunch of information that would be helpful in monitoring performance or settling any issues later. More construction companies should do this.

I am aware that as a new process, I’m doing something of an experiment on the family home. A friend who works on buildings management gave me a list of things to consider, and I did my homework on the process, the composition of the insulation, the effects on the wood and so on. Like the external wall insulation, it is not risk free and any problems may not reveal themselves until well down the line. Neither is it waste-free, as that insulating foam is not a natural product. There are compromises here.

Nevertheless, it has an estimated lifespan of 30-80 years, and should save at least 10% of heating costs – and carbon emissions – in that time. Given the urgency of getting homes to zero carbon, I didn’t want to reject a good solution and wait for a perfect one.

We’ll have to judge its effectiveness next winter, but Q-bot’s installation proccess has been excellent. And I’m aware that we’re among the lucky ones to have got through the Green Homes Scheme before the government hoovered the money back out of it.

What’s next on the way to net zero? We’ve still got the gas boiler. So far all our efforts have been around reducing the need for heating in the first place. The next task, as and when we can afford it, will be to move to a renewable heating source.

If you’ve got any questions about the grant or the installation, drop it in the comments and I’ll help if I can.


  1. This is really interesting. We’re hoping to move next year into a forever home where all of the insulation will be closely looked at and fixed. Nice to know about Q-bot, though.

  2. Jeremy, great article and great to hear of your experience of Q-Bot from the customers perspective. It is always pleasing to hear from happy customers, Q-Bot are very grateful for your comments.

    Q-Bot have also calculated the carbon impact of our underfloor insulation (UFI) measure using the Climate Impact Forecast tool from

    The full carbon cost of a single installation is approximately 777kg/CO2e (this includes the foam, the manufacture of the robot, transportation of components as well as transport to site and application). The carbon saving through energy savings (an average of 2600kwh annually, based on Gas Central Heating) is 655kg/CO2e. Therefore the carbon payback period is 1.2 years for an average property.

    The expected lifetime impact (based on the insulations life of 42 years) for a single home is therefore -26,741kg/CO2e, this is the equivalent of planting 1,216 trees. Or would offset driving a car around the world 3.3 times.

    Your work towards getting to Net Zero is commendable. Adding a battery and signing up to a dynamic time of use is also a great step to further decarbonising your electricity usage (if you haven’t already!).

    i recently came across this low carbon heating solution – it might also be of interest.

    Good luck on the rest of the journey.

  3. Jeremy

    I’m interested in this but slightly worried about damp rotting the wood due to a lack of air movement over it. Also the underneath our floors is like the surface of Mars. Very uneven and full of rubble. I’m also interested in what you did to your door.

    Thanks Neil

    1. Hi Neil – I had a good look into that very issue, because I’m aware that spray insulation in lofts can go badly wrong. There is a key difference between them though: in lofts, the insulation puts the timbers on the cold side and makes them more vulnerable to condensation and damp. Under the floor, the insulation brings the timbers into the warm envelope and has the opposite effect. The wood is warmer and drier, and Q-bot have commissioned third party studies that have found an overall reduction in damp where their process is used.

      You do still need good air circulation under the floor, which we have and which I improved during installation, just to be sure.

      As for the door, we have a fairly standard composite front door. It opens into a small porch area where we have a second door into the house, and this ‘airlock’ keeps the warmth it quite effectively.

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