After watching two assessors make a right dog’s dinner of measuring the energy performance of his house, Jeff Howell suspects a little extra training may be in order

To mark the introduction of Hips on 1 August, I had two energy performance surveys carried out on my house, a 19th-century cottage I have renovated using environment-friendly materials. I have insulated it to the highest possible standards, while retaining the original features. I have used traditional “breathable” materials, sourced locally where possible, and achieved an energy use of less than 200kWh/m2 a year.

So I was a bit miffed, and greatly concerned, that two qualified domestic energy assessors should dismiss my house as having “very poor” energy efficiency and “very poor” environmental performance. They estimated my energy use to be 850kWh/m2 – more than four times the actual recorded figure.

After all the time and effort I have put into insulating the house, it was galling to be told it had no wall insulation, no floor insulation and only 50mm of loft insulation. They gave it an energy-efficiency rating of 17 out of 100 and an environmental impact (CO2) rating of only 14/100. Both assessors also missed the fact that the house has underfloor heating, despite the thermostats being clearly visible.

Even more alarming is the fact that these energy performance certificates were posted on a government website within hours of the surveys taking place, and without the building owner (me) having any chance to challenge their validity.

To be honest, I didn’t expect them to find it plain sailing, but there were clues aplenty. The walls, for example, are insulated with hemp-and-lime, which sounds hollow when tapped. I thought they’d assume this was plasterboard and – taking into account the overall wall thickness – that they might be looking at internal insulation finished with dry-lining. But both assessors ticked the box marked “solid brick, as built, no insulation”.

The floors are traditional Suffolk brick, formerly laid directly onto the clay sub-soil. But I had dug them out and insulated with 225mm of “limecrete”, laid electric underfloor heating and bedded the bricks back on top.

An assessor recommended I upgrade my fan-assisted electric night-storage heaters to the very type of heaters I already have

Now, to the uninitiated, this might give the impression of being a traditional, solid brick floor. But these guys are not supposed to be “uninitiated”; they are supposed to be trained energy performance assessors. Had they noticed the thermostats, they might have deduced that underfloor heating was in place and that nobody would bother to install underfloor heating without insulating below it.

Curiously, not only did the assessors fail to spot any of this, but they recorded the floor type as, “suspended, no insulation”. A suspended brick floor? What kind of training have these guys been getting? Further investigation revealed that the computer software might be to blame. The assessors’ field sheets do not actually have a tick-box requiring them to register the type of floor in a house. The software they use makes this up for them, using the date of construction. So my 19th-century cottage goes down as having uninsulated suspended timber floors, despite the fact that it has well-insulated brick ones.

On top of these errors, one assessor measured the fibreglass loft insulation to be 100mm; the other measured it at 50mm. One noticed my electric night-storage heaters are fan-assisted, with automatic charge control; the other didn’t, and recommended I upgrade, to the very type of heaters I already have …

I have discussed these mistakes with the heads of the assessors’ accreditation schemes – BRE and SAVA – and both agreed a spot of extra training might be in order. The only trouble is, one of the pair who made such a dog’s dinner of assessing my house is actually a SAVA trainer.

Jeff Howell is a bricklayer and chartered surveyor. He writes The Sunday Telegraph’s “On the level” column