Conductivity, λ

Used to measure how much a type of material conducts heat. For insulation, the lower the better.  For example:

Conventional rigid foam insulation (PIR) has a conductivity of 0.022
Woodfibre natural insulation boards 0.042

So PIR is almost twice as insulating as woodfibre.

This means that 100mm of woodfibre will provide the same level of insulation as 50mm of PIR.

The units are: watts, per meter, per degree, W/mK



Compact Fluorescent Lamp. The old type of ‘energy efficient’ light bulb, about 80% efficient, now surpassed by LED bulbs.




Carbon dioxide, a greenhouse gas. The average UK household is responsible for emitting around 5 tonnes (5,000kg) of CO2 a year, contributing to our carbon footprint.


Daily Mail

A national newspaper that hates Britain.


Green Deal

The Green Deal, farcical from the start, was the government’s flagship scheme to help you make energy saving improvements.

Improving efficiency is so desperately needed on so many UK houses; a genuine, relatively simple, long term answer to fuel poverty whilst giving immediate comfort and health benefits (and therefore also big NHS savings).  It can also have a major impact in tackling climate change, the most severe planetary emergency humanity has ever faced.

The Green Deal gave some grants for External Wall Insulation for example, otherwise too expensive for most people (us included), which is why the Green Deal grant was so essential.

The conservative government, which cynically promised to be the greenest government ever, axed the Green Deal in summer 2015.  It has not been replaced with anything.

The Green Deal Home Improvement Fund closes on 30th September 2015, possibly sooner if it runs out of money again.  Good luck.



Polyisocyanurate, a rigid, plastic foam. Used to make insulation boards such as Celotex.

Ten Foot

Local vernacular. The Hull name for the alley accessing the rear of a row of terraced houses.



A U-Value is a measure of how quickly a building element looses heat. Basically, the lower the better. Here are some examples:

single glazing 5.0
old double glazing 2.5
brick wall 2.0
high performance triple glazing 1.0
current building regs for a wall 0.3
super insulated, Passivhaus, the bees knees 0.14

These numbers show us that old double glazing (2.5) is twice as good as single glazing (5.0).

I’ve generally missed off the units for simplicity, which would no doubt have annoyed my old science teachers, so they are: watts, per square meter, per degree, W/m2K.

U-Value Example

Let’s take a section of brick wall 1m by 1m, with a 1˚ temperature difference between inside and outside. We see from the table above that a solid brick wall has a U-Value of 2.0, which means this section will loose heat at a rate of 2W.

The U-value is used to calculate the heat demand for a building.

Let’s say you have a lounge wall 5m long x 2m high = 10m2. Your thermostat is set to 20˚C and it’s 0˚C outside, so there’s a 20˚ temperature difference across the wall.

U-value    x    area    x    temp difference    =    heat loss

2.0W/m2K    x    10m2    x    20K    =    400W

So on this winter’s day we know how much heat must be supplied to the room to replace the heat being lost through this one wall. That heat might be supplied by the sun shining through the windows, or a 400W heater.