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Theme: insulation and energy management

Mandatory insulation standards are being made tougher with every revision of the Building Regulations. Yet there is still plenty of scope for improvement, with housebuilders reluctant to do more than the bare minimum and competing building systems and cost considerations further complicating the issue

Everybody pays lip service to the global virtues of insulation: sustainability, CO 2emissions, the ozone layer, alternative end-uses for waste materials such as wool and newspapers. And practically everybody in real life installs the minimum they can get away with. Happily for most of the above - and the £150 million-plus UK insulation-manufacturing industry - the minimum is steadily improving as, every couple of years, insulation rules in the Building Regulations get tougher.

Currently they stand at a minimum Uvalue of 0.35 W/m 2K in England and Wales.

They are more stringent in Scotland, at 0.3, and tougher still in Northern Ireland, at 0.27.

It is widely thought that the latter figure represents the minimum that will be set for England and Wales in the next changes to Part L. It is possible that the mandatory figures will eventually bottom out at 0.15 and 0.1, which are the current figures in Sweden for, respectively, roofs and walls.

That at least is the hope of EURIMA (the European Insulation Manufacturers Association), which points out that adopting these Swedish figures Europe-wide would result in a 50 per cent energy saving.

This is not a straightforward business because, oddly enough, Sweden turns out to be a bigger CO 2polluter than even Greece. * This does not let the UK off the hook. It has the fifth-highest annual energy loss from dwellings in Europe.

The most recent thermal regulations have dealt with a serious anomaly and now address the thermal performance of the whole of the building's skin including, crucially, air-tightness. And there are now three alternative permissible calculation methods.

These are further moves in a holistic and, it is to be hoped, architecturally more flexible direction.

Reluctant housebuilders Insulation materials are not themselves all that expensive so that, if you did not know how housebuilders squeeze the pips, you might be puzzled by the reluctance of builders to do more than the minimum. But it is said to be all to do with space: that is, the additional space taken up on a notional floor plan by extra insulation in the wall. On an estate of a thousand dwellings, runs this argument, the total extra area is significant - maybe as much as the area of a house or two.

So anything that keeps wall insulation at its current thickness has to be virtuous. Maybe manufacturers could produce more efficient insulation, so that a given thickness provides a better U-value. But if they did, wouldn't it be more expensive?

Bryan Woodley, chief executive of the UK Timber Frame Association, explains that although maximising site acreage is an essential for house builders everywhere, in the South East it is particularly acute. Land is at such a premium that when volume housebuilders use timber frames, they use the least thickness of insulation stuffed between the narrowest studs possible - 89mm deep. They then deploy the Target U-value method of calculation allowed by the current rules.

This involves factoring in more efficient boilers and more efficient (though more expensive) insulation.

When you hear this about - and sometimes from - volume housebuilders, you wonder if other things, such as a deep aversion to change or a perception about the hidden additional cost of bigger studding sections and thicker insulation bats, might not all be substitutes for hard cost analysis.

Woodley thinks that if the regulators continue to reduce the target U-value, timber-frame housebuilders will have to move to the use of a 195mm deep I-beam stud which, when it is used currently, allows space for a services zone behind the inner plasterboard face. When fully filled with insulation, typical U-values of about 0.20 for such wall construction would be well below the most stringent UK U-value - but still significantly higher than current Swedish values.


Southern England housebuilder Swan Hill dabbled briefly in steel frame with built-in insulation when the speed of construction and access to its site were issues. But however technically successful this was, the company normally deploys standard masonry-cavity construction. It is, however, more relaxed about maximising acreage than volume builders claim to be.

Howard White, regional technical manager at Swan Hill, explains: 'A couple of changes ago in Part L we increased the thickness of the external wall in our houses to around 300mm - 125mm internal block work, 75mm cavity and 102mm face brick.

Now we generally insulate cavities using either blown fibre or cavity bats or mineral fibre, which go in as the work proceeds. With blown insulation, the openings around doors and window openings are sealed off with insulation closers, holes are drilled in the brickwork and mineral fibres are pumped in. For the floor we use Durox aerated blocks sitting between concrete inverted T-beams at 600mm centres. On top of this is a layer of polyurethane insulation of maybe 50mm, with a screed over the top ready for housebuyers' carpets or flooring.

For the roof we used to use a 150mm quilt.

Under the new rules we now use a double layer of 100mm quilts.'

But Swan Hill is happy to innovate. At a small development outside Abergavenny, the company's builder, George Wimpey, is using Springvale expanded polystyrene Platinum Wallshield boards in the cavity and the same manufacturer's BEAMShield T-beam floor insulation. Here the Durox blocks are replaced by similarly shaped EPS blocks topped by a reinforced structural screed.

Inside, outside and in the middle There is not a lot of choice about where you locate insulation: it is either inside, in the cavity, or outside. Until 2000, when there was a temporary cessation of funding for installation of domestic insulation, nearly four fifths, by value, of all insulation installed in the UK was cavity fill. External insulation accounted for 13 per cent and internal wall insulation for eight per cent.

Currently the insulation people are calling for the government to calm demand so that the 4.5m homes its February White Paper envisages can have their cavities filled in an orderly way in the five years after 2005.

If choices are limited as to where insulation is positioned, there is a lot of choice in insulation materials. Ignoring such local US variants as insulation made from cotton waste, there are perhaps 30 materials available, among them blown glass and mineral wool, cellulose, the expanded, extruded and foamed polys:

polyurethane, polystyrene, polyethylene and polyisocyanurate. There is exfoliated vermiculite, expanded perlite, reflective foil, mineral and slag wool, sheep's wool, blown cellulose and straw bales. These can come as, variously, small spheres and fibres for blowing, rigid slabs, quilts, sandwiches, and in some cases, especially in the US, as liquids which are applied foaming on site. For all that diversity, just six companies in the UK make about 65 per cent of its insulation.

The alternatives

Alternative and recycled insulation materials such as waste newsprint, wool and straw have a fashionable currency among the sustainable community. There is no doubt about their long-term performance or that they work. But they will miss out on the cost advantages engendered by economies of scale until they are widely used and until manufacturers can demonstrate a long-term supply of raw material. Housebuilders are carefully courteous about their use - and would never dare think of using them on the grounds that housebuyers would recoil from their supposed eccentricity. But for sheer weirdness, the idea of insulation made from fine hairs of liquid rock is something you might expect to read about in Lord of the Rings - not the Rockwool catalogue.

Meat in the sandwich If promised government support for raising insulation standards in existing housing comes to anything, it will mostly be for cavity fill. That means that existing cavities will be filled. Yet cavity fill is also the most common method of insulating houses.

Companies such as Knauf and Kingspan, Rockwool, Vencel Resil and Celotex all produce rigid or semi-rigid boards which are fixed in the cavities of conventional two-leaf masonry walls as they are built up. So far, it is still possible to insulate only part of the cavity but already we are seeing wider, filled cavities. As the regulations tighten up the functioning cavity will disappear.

If cavities are being filled then they are not cavities any more - certainly not providing a water-controlling gap between the wet outer wall and the dry inner wall. So you ask whether they really are worth thinking of as cavities any more, and whether in the future we should not just use the term composite walls. Blockmakers and makers of timber frames may not like the idea but, under the influence of increasingly stringent thermal rules, there seems to be a convergence in which the wall and floor and even roof insulation are no longer simply something added to the essential structure. Instead they become the core element around which the structure develops - or, as in the case of hollow expanded-foam building blocks, the core element into which the concrete and reinforcement are inserted. It is also a sign of the times that some housebuilders are comfortable with the idea of floors whose structure is largely rigid plastic foam.

The tea cosy effect

The idea of insulating the external face of a building is relatively recent. One of the UK pioneers was Permarock, which based its reinforced skin on a substrate of Rockwool slabs. Originally it was mostly used, as were Sto and Alsecco, at about the same time in Germany, to retro-insulate local authority homes where decanting and dislocation were likely to cause problems. The point these companies make is that the exterior is the technically correct position for insulation if it is to minimise successfully the effects of condensation, mould growth, cold bridging and water penetration.

In the UK the argument behind the wall cavity (let the water in, control it and guide it out again) has held near-theological status since it became popular, much later than is commonly supposed, in the 1930s. Britain was initially quite cautious about adopting external insulation - although it grasped the virtues of the upside-down roof quite quickly - because although external insulation did not eliminate the cavity it worked quite successfully without one. And so England moved slowly in the '70s and Permarock made its name primarily in the local authority and housing association world, which still represents a large part of the market.

Permarock's Dr Jeremy Richings says:

'There comes a point where cavity construction has its limits and so you start thinking about structural insulated panels, that is composite wall panels which are heavily insulated, made pretty much off site so there is a great deal of quality control. We have done some fast-track schemes of this sort at the scale of supermarkets and schools and magistrates' courts. And we have achieved really low U-values - about 0.2. We reckon 0.35 is a bit of a cop-out because we can put on as much insulation as you could want.'

Permarock, with its new AI European classification, is a systems assembler not a manufacturer and has, says Richings, concentrated heavily on third party accreditation. It is the only company accredited (by BRE Wimlas) to use its system in conjunction with timber and metal frames. When Woodley's timber frame builders are faced with the next round of U-value changes, they have a readymade solution to hand.

In the past decade there has emerged an architectural fashion for rendered walls - made possible, people argue, by the concurrent development of Sto's through-colour expansion-joint-free render system. It needs to be said that its competitors such as Permarock and Alsecco offer the same specification. But Sto has run a brilliant marketing campaign and has responded to the market well by introducing a wide colour range. Despite its name, Alsecco is also a German company, owned by Alsecco AG. It has been here for seven or eight years and, although it doesn't sniff at social housing, this is not its mainstay. It is alert to current fashions and its Alwood system consists of larch boarding (the German fashion is for larch rather than western red cedar) over the insulation. The company's Paul Winwood says 'the big problems occur at the interfaces. We offer a single background insulation and you can apply different façade techniques as the primary face.' Alsecco has a steel variant but it is not overly popular. But more recently, and on a big social-housing scheme, the company has used EPS insulation with a skin, called for by the planners, of render and acrylic brick slips. Thin brick slips attached to an insulation substrate seems to offer a solution to the housebuilders' wall-space problem but it is unlikely to please architects.

So what, maybe a decade ago, was a fairly straightforward issue has now become complicated by such things as inexorably improving mandatory insulation standards which have begun to change our concepts of traditional construction, competing building systems which require different insulation solutions, the complications of the cost: thickness: effectiveness equations and an assessment of the true energy performance of materials which incorporates the energy costs of their extraction, production and shipping to site.

*Source is the European Insulation Manufacturers Association at www. which provides comparative insulation statistics across Europe Depends where you are The insulation rules are contained in Part L of the English-Welsh Building Regulations.

Northern Ireland's thermal rules are in Technical Booklet F of its regulations, and Scotland's in Part J of the Technical Standards of the Scottish regulations. The anomalies may be political but may also reflect differing climates, standards of building, building inspection and the like.

Do-it-yourself energy sums The UK Timber Frame Association recently commissioned BRE to devise an Excel spreadsheet for its members which takes all the relevant data about their buildings and produces a yes or no about conformity with the appropriate regulatory authority. It's available only to members - who will use it on behalf of their customers.

On the other hand, Yorkshire Building Services' YBS Insulation has developed an AutoCAD-based design/drawing program for architects which can be downloaded from www. yinsulation. com or from the YBS technical department on 01909 721 662.

Alsecco 1500 Celotex 1501 Durox 1502 Excel 1503 Inca 1504 Kingspan 1505 Knauf 1506 Permarock 1507 Rockwool 1508 Springvale 1509 Sto 1510 UK Timber Frame Association 1511 Vencel Resil 1512 YBS Insulation 1513 READER ENQUIRIES Enquire at www. ajplus. co. uk/ajdirect

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