1. www.swingacat.info

2. Alan W. Evans and Oliver Marc Hartwich, Unaffordable Housing: Fables and Myths, London, Policy Exchange, 2005, Figure 5: Comparison of Dwelling Sizes, p 24, based on Housing Statistics in the EU, European Union, 2002

3. BedZED, posted on www.bioregional.com

Not enough room to "Swing a Cat"

It is not easy when talking to North Americans, Australians, or New Zealanders to get them to realise that while 200m2 homes may be considered "small" where they come from, in Britain the vast majority of households are really living in much smaller homes. David Birkbeck of Design for Homes produces the excellent Swing a Cat website, (1) and makes the point very clearly with a European comparison:

Source: Alan W. Evans and Oliver Marc Hartwich, Unaffordable Housing: Fables and Myths, London, Policy Exchange, 2005 (2)

If a new British home is 76m2 on average, and it is two storey, that is 38m2 a floor. We can further assume this is typically a simple rectangular plan of say 8.1 x 4.7 m. That is a perimeter around the inside of the external walls of 25.6m. Ignore partition walls and stairs.

Most house builders were happy with brick and block cavity wall thicknesses of 300mm, with a 50mm air cavity and 50mm of some kind of fibrous or foam insulation. Some insulants can be used to fully fill the 100mm space between the outer brick and the inner block leaf of the wall. As the Building Regulations are revised for higher thermal performance in 2010 more insulation is needed, and wall thicknesses are likely to increase to 350mm. Insulation can be either doubled to 100mm thick with a 50mm air cavity, or trebled to 150mm thickness if the wall is fully filled. The insulation must be suitable for "full fill".

Assuming it is a detached home, a 300mm wall, wrapped around the 25.6m plan perimeter of the notional average new British house, occupies 8.04m2 in area, including the corners. That makes the total external area 46.04m2. Compare that to the total external area of 47.45m2 for a 350mm wall, wrapped around the 25.6m plan perimeter, occupying 9.45m2. The area has increased by 1.41m2, which over the two storey structure is an additional 2.82m2.

That does not sound like much, adding £2,256 to the construction cost if budgeted at £800/m2 overall, which can be achieved in brick and block cavity wall, or £3,384 if budgeted at £1,200/m2 as many architects tend to do. The greater wall thickness has used up a bit more site too, of course. But this might not seem too much to pay for meeting the higher thermal insulation standards of the 2010 Building Regulations. By building semi-detatached, terraced, or row houses the impact of greater external wall thicknesses can be reduced while shared or "party" walls between homes may be uninsulated and thinner.

However a point has been reached, where the 350mm wall of the detached home of 76m2 occupies an additional 18.9m2 over two simple storeys. That is a total of 94.9m2. The wall is 19.9% of the total area of the home. Add the wet plaster or dry plasterboard internal finishes and 20% of the home cannot be lived in. It is wall, not useable space.

Smaller than average homes are worse in their proportion, of course, and in Britain's housing there is not enough room to swing a cat. Behind the averages in sizes it is necessary to look at occupation. A 100m2 British house is considered a "large" family home, and the limited stock of 200m2 housing is at the luxury end of the inflated British market.

The Building Regulations are going to be further revised in 2013 and 2016, requiring greater improvements in thermal performance. As insulation thickness increase to meet those regulatory changes the wall thickness must increase. More than 20% of the total area of the home will be the construction of the insulated wall.

House builders might try to solve their math by reducing the internal space provided below the average of 76m2, and may even be able to sell these diminutive homes as house price inflation returns to the British housing market. But the best builders will not want to do that.

As the Building Regulations approach 2016 masonry wall thicknesses will have reached up to 500mm, with up to 300mm of full fill fibre in the space between commodity bricks and blocks. A thick approach promoted by architect Bill Dunster, notably at BedZED in Sutton, claimed as the "best known eco-village" in Britain. (3) Then the space taken up around a 38m2 ground plan will be 13.8m2, if the 76m2 home is detached. That is 26.6% of the home that cannot be lived in because it is wall, not space. Not calculating for partitions and stairs, as a further reduction.

Building homes in rows will soften that problem, but not everyone wants to live in a terrace house. However the up to half metre thick external wall will still look "clunky" at window and door openings. Where does the window and door go in a 500mm reveal? What are windows and doors fixed to at the opening? Where can you buy wall ties and lintels that will span the 300mm gap inside the wall stuffed full of insulation that doesn't work sufficiently well to meet the ambition of the Building Regulations.

The same sort of predicament faces timber and steel framed systems, concrete "sandwich" panel manufacturers, or the makers of timber Structurally Insulated Panels. Render systems cannot be applied over ever increasing thicknesses of externally applied insulation, and rainscreen cladding systems become ridiculous when the insulation zone is widened. It is not a good idea to lose 300mm of floor area to insulation apllied internally, when that could be useable space if the insulation were better performing. The only winners in pushing the thermal performance requirements of the Building Regulations to extremes in three steps to 2016 are the manufacturers of fibrous and foam insulation, who have the ear of regulators at the Communities and Local Government ministry.

John Healey has been made Housing Minister just as house price inflation returns. The government needs an inflating housing market, which a limitation of development to 10% of Britain, the frustrating planning system, inadequate levels of housing supply to meet household growth, and low interest rates certainly ensure. The "volume" of house building achieved in 2007 was 200,000 homes a year, while Britain needed at least 500,000. In 2008 house building is likely to have been about 100,000 homes. Healey will find, perhaps to his satisfaction, that house builders have shifted from attempting volume to addressing a smaller luxury "eco" market. That may mean healthy profits for house builders in planning, but it will mean a permanently reduced size of market for most of the construction products and materials manufacturing "supply chain".

These "eco-homes" will display increasing wall thicknesses unless Healey, and the rest of the CLG regulators, put pressure on insulation manufacturers to improve the performance of insulation beyond the present use of fibres and foams. The CLG cannot do that after providing a means for the established insulation manufacturers to double and treble the thickness of the products they hope to sell. For the established manufacturers the new "eco-home" market will still be bigger if they can sell treble thicknesses for 100,000 homes in 2010, compared to sales of single thicknesses of the same material for 200,000 homes in 2007.

To it's great credit the brick and block industry has started to confront this predicament, and has supported the International Vacuum Insulation Symposium, to be held this year at the Royal Institution. Without a penny of CLG or other government department funding, an alternative insulation technology must be found to reduce wall thicknesses below 300mm. This is an effort that might unite the construction and materials manufacturers who find that their interests in "volume" are being undermined by the interests of the existing insulation manufacturers in "eco-thickness".

If wall thicknesses could be reduced to 225mm, which is equivalent to the longitudinal work size of a brick, they would represent 13.6% of a home with an internal area of 76m2. If 250mm, the wall would be 14.9% of the home. At 300mm the wall would be 17.5%. Clearly a range of practical solutions are sought, but below a wall thickness of 300mm. For that better insulation is needed, to supercede the familiar use of "cut to fit" fibre and foam at ambient air pressure. Any "made to fit" vacuum insulation technology is, in my present view, unlikely to be made widely available by established fibre and foam manufacturers.

The vacuum insulation could cost more than ambient fibres and foams for a given thermal performance. A 500mm ambient air pressure insulated wall adds 27.6m2 to the base 76m2 plan, while a 300mm cavity construction insulated with a protected Vacuum Insulation Panel of no more than 50mm adds 16.1m2. That is a difference of 11.5m2, which at £800/m2 is worth £9,200, and at £1,200/m2 is worth £13,800 on the budget of a two storey house. If the 50mm VIP is "full fill", so that the 50mm air cavity is designed out, the wall is 250mm, the area saved is 14.3m2, which is worth between £11,440 and £17,160 on the budget. If a masonry solution were available at a wall thickness of 225mm the area saved against the 500mm ambient air pressure insulated wall would be 15.6m2, worth between £12,480 and £18,720. This matters, particularly if the housing is architect designed at £1,200/m2, rather than priced more practically at £800/m2. The choice with VIPs is a lower overall budget based on external area, or more useable area in the home.

These figures all assume a detached house type, and are all before the internal finishes are applied, of course. However they show that the development issue is not an isolated one of the cost of the insulation itself. The pricing of VIPs are an issue, and prices are falling as VIP manufacturers move into the construction sector from the refigeration sector. The robustness, longevity, and modularity of VIPs are all technical issues that have to be proven, and are being resolved internationally.

If the house is to stay around the British average of 76m2, why spend more money on insulation thickness? If the budget is fixed it is possible to spend more on VIPs and have more useable space in the home. Adding square metres of space to the 76m2 new house average makes a difference when trying to swing a cat. However the CLG seems to care little about reduced space standards or money wasted on the use of poorly performing but cheaply available ambient air pressure insulation.

The stupidity of the CLG in regulating around "eco-homes", without having undertaken the Research and Development needed to sensibly meet the Building Regulations in practice, must be confronted.

Ian Abley 24.06.2009

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