Figures have been released that show that the number of cavity wall and loft insulations in Great Britain is falling.
Cavity wall insulations in the last quarter fell from 128,000 to 95,000, a fall of 25%, and a staggering 45% below those installed in the same quarter last year.
Also, the number of professional loft installations fell by 32%, and is 38% below the number installed in the same quarter last year.
DECC has published the figures, which also show that at the start of July 2010:
• 12.3 million homes had loft insulation of at least 125mm
• 10.3 million homes had cavity wall insulation.
In Great Britain 23.2 million homes have lofts and 18.6 million have cavity walls. This means that 47% of eligible homes do not have sufficient loft insulation and 45% have no cavity wall insulation.
What the figures do not reveal is the level of effectiveness of the installations. Those which the author of this article has seen leave much to be required, i.e. gaps that mean that their ability to keep heat in is severely curtailed.
This implies that they cannot be relied upon to generate the carbon savings that will be assumed in government figures.
Moreover, the figure of 125mm for loft insulation is not sufficient. Current building regulations require a roof to have a thermal resistance U-value (a measure of their insulation value) of at least 0.13W/m2K, which would typically be achieved with 300mm of loft insulation.
DECC says that a threshold of 125mm is used in these statistics since homes with less than this would expect to see significant improvements in energy efficiency from a top-up.
It also says in its Departmental Business Plan 2011-15 that this measure will be one of its key impact indicators to track progress on insulating homes.
But if it really wants to show the scale of work required and monitor improvements, it should be using its own Building Regs figure of 300mm of loft insulation.
In addition, the width of cavities in walls varies considerably. Just because a wall has cavity insulation does not mean that it meets any building regulation requirements for thermal resistance of outer walls.
The figures are obtained via surveys from the English Housing Survey and equipment for Scotland, Wales and Northern Ireland.
Most of the statutory work has been carried out through the Carbon Emissions Reduction Target requirements. Only a small proportion has come from Warmfront, which targets the fuel poor. DIY loft insulation is currently done at around twice the rate of professional work.