Meeting the New Energy Standards

Monique and Laurence Steijger’s super-insulated new eco-friendly timber frame house cost less than £200,000 to build and requires no central heating. Read more about this project.

Partial fill insulation is still the standard choice for brick and block self-builders but the choice of insulation material is going to become crucial as building regulations tighten.

Insulation is one of the few areas that sees the self-builder and the Government in complete harmony. That which will make your new home warmer in the winter, cooler in the summer and more comfortable all year round is the very thing that will lower your fuel bills, protect the environment and help the UK to meet a commitment to reduce CO² emissions.

The wise self-builder will quickly realise the financial and lifestyle benefits of making sure their home is energy efficient. The Government is more concerned with slashing energy consumption and thus reducing the amount of global warming and ozone depleting gases pumped into the skies over Britain but they are both aiming for the same thing.

In the UK, emissions from buildings account for at least 40% of all energy use. This is slightly higher than the global average and reflects the effects of our climate and the age profile of our building stock. The Government is so concerned about global warming that it has scheduled no fewer than three major revisions of the Energy Efficiency Requirements of the Building Regulations in the next five years and they will all impact on self-builders and those creating a new dwelling by changing the use of an existing building.

Why should you be bothered by all these revisions to the minimum standards of energy efficiency when it makes sense to voluntarily incorporate the highest standards of insulation into your new home anyway? It's economically viable: life-cycle costing ie, the time it takes to recover the cost of better insulation through reduced fuel bills is acknowledged as the best way to evaluate insulation and the payback period of superior insulation is relatively short. There is a further incentive to insulate well: should you ever consider selling up, you may in the future find that you have added value and appeal to the property. Germany has traditionally been one of the most forward looking nations on this subject and it's now the norm there for home sellers to include an energy consumption audit in their Vendor's Pack. It is likely to be only a matter of time before this is commonplace in the UK.

The New Building Regs:

The current review of the Building Regulations is looking at Approved Document L (Conservation of Fuel & Power) and consultation documents presently circulating the insulation industry suggest that the revisions will take place in 2001, 2003 and 2008, with each revision superseding the previous one.

How will this affect the self-builder? Undoubtedly it will involve the reduction of elemental U-values ie, an increase in the minimum level of insulation acceptable in the various building elements, walls, floors, roofs and windows. The U-value is simply a measurement that provides an easy method of assessing the amount of heat lost through the building structure, the lower the U-value the better. Low U-values mean lower fuel bills, less environmental pollution and greater comfort for the occupier. It is worth noting, however, that the minimum performance quoted in the building regulations assumes the use of a high performance boiler. If a lower performing boiler is used, the required elemental U-values are more stringent.

Under the current Regulations, acceptable levels of heat loss are defined as minimum U-values for roofs, walls and floors. The present values set for these are as follows: roof 0.25 (W/m²K), walls 0.45 (W/m²K) and floor 0.45 (W/m²K). W means Watts, m² means square metre and K means Kelvin.

The values proposed for 2001 are likely to be pitched roof 0.25 or 0.20 (for insulation between joists), walls 0.35 and floor 0.30. Obviously, values for 2003 and 2008 will be lower. These are the targets so how do we meet, or better still exceed, them?

Cavity Wall Construction:

Still the most popular form of construction with self-builders is cavity wall construction. The choice is either 'full fill' insulation, which fills the whole cavity, or 'partial fill' insulation, which preserves the integrity of the cavity.

The 'partial fill' route helps to overcome some of the potential problems of poor workmanship where inexperienced bricklayers can allow mortar to 'bridge' the cavity providing a route for water penetration into the building. Whilst full fill construction is acceptable under the Building Regulations and Standards of the National House-Building Council (NHBC) with the exception of high exposure areas such as parts of Scotland and is widely used, some experts believe that there is a higher risk of water getting into a building than with a partially filled cavity. Without a clear void, there is no drainage channel to allow water to escape down the cavity and away. Consequently there is an increased chance that some non-waterproof insulation materials will become waterlogged, possibly to the extent that the material no longer performs to the required standard.

One benefit of full fill cavity walls is that there is plenty of room within a standard 100mm cavity to contain enough insulation to meet and exceed the new revisions expected in 2003 and 2008. With partial fill, however, consideration needs to be given to the width of the cavity necessary to incorporate sufficient insulation whilst still leaving the minimum 50mm residual cavity required by organisations such as the NHBC.

The building industry will inevitably focus on finding the cheapest way for developers to meet the new regulations. Calculations will balance any additional cost of building with wider cavities, designed to accommodate a greater thickness of the standard and least expensive insulants, such as mineral wool or expanded polystyrene, against the additional cost of superior insulants that can achieve or exceed the required standards with little or no increase in the cavity width you generally need only half the thickness of insulants such as phenolic and rigid urethane than you would of mineral fibre/wool to achieve the same U-value. Unlike developers, however, self-builders are interested in their homes running costs and not just raw building costs, so should also take into account the lifetime cost of their choice of insulation ie, the likely saving on fuel bills achieved through reduced energy consumption. If you plan to live in your self-build home for several years, it probably makes sense to invest in the best insulation you can afford, rather than the least and cheapest you can get away with.

Industry research suggests that increasing the width of the standard cavity to 110mm is unlikely to have any impact on construction costs. However, some experts believe that increasing the overall size of the walls by much more than 110mm will add to costs because longer ties will be required to span the cavity, along with wider lintels, cills and deeper door and window reveals. Also, Part A of the Building Regulations, governing structure, currently requires an engineer to prepare calculations for any construction where the cavity is wider than 110mm, which will have a cost implication.

Another implication of wider walls is an overall increase in the size of the footprint required to achieve the same internal living space. In some instances, where plot size is restricted, this could have serious implications if there isnt the room on site to increase the footprint size, or if the planners have placed a restriction on the size of the dwelling that can be built, then the only way to increase wall thickness would be to reduce the size of the internal living space. In this instance using the highest performing insulation available will always make instant economic sense.

Timber Frame Construction:

Timber frame houses are probably going to be affected most by the new Building Regulations, as existing standard construction techniques will not enable the new Regulations to be met.

ABOVE: Improving the thermal performance of solid brick or stone walls, typical of many conversion projects, is best achieved by adding insulation on the inside. Insulation/plasterboard composites are ideal for the job.

Standard timber frame walls are currently constructed using 89mm studs filled with 90mm mineral fibre quilt/batts. This construction achieves a U-value of 0.411 W/m²K, which complies with the current requirement of 0.45 W/m²K. However, to meet a U-value of 0.30 W/m²K (the standard which will be required in 2003), over 100mm of mineral fibre quilt/batts would be required. This would mean increasing the minimum stud depth to 140mm in order to accommodate the increased thickness and consequently the cost of construction. Industry estimates suggest that increasing the standard width of timber frame walls from 100mm to 140mm will add around 2.65/m² to costs.

There is an alternative to widening the walls, however. The slimness of high performance insulation boards, such as phenolic or rigid urethane, means that the higher thermal efficiency can be achieved whilst maintaining the standard thickness of the timber frame, without compromising the depth of the insulation layer in any way. In fact, by the time the 2003 Regulations come into effect phenolic and rigid urethane insulants are going to be the only products that can achieve the required U-values using an 89mm stud construction (see table on page 103), although by 2008 even these high performance insulants cannot achieve the minimum elemental U-value for walls (0.25 W/m²K) without an increase in the wall thickness.

Solid Wall Construction:

When improving the thermal performance of solid brick or stone walls, often a feature of refurbishment and conversion projects, the solution to the problem of achieving acceptable levels of insulation is to use an insulation/plasterboard composite to 'dryline' the internal walls. This will provide excellent levels of insulation, comply with Building Regulations and simultaneously provide a first class surface for plastering or decorating. This method of wall insulation also has the added advantage of combining insulation, dry lining and a vapour control in one board.

When you adopt this method of wall insulation, one of the most important considerations is to minimise the loss of internal space but at the same time insulate to the highest standards. By 2008 you would need to use 105mm of rock mineral fibre compared to 56mm of rigid urethane or extruded polystyrene or only 54mm of phenolic insulation. A point also worth noting is that these figures are for the insulation thickness only and do not take into account the thickness of the plasterboard, which usually adds 12.5mm to the overall board thickness.

Further Reading:

• Acheiving the New Energy Standards (November 2008)
• 6 Steps to an Energy Efficient Home
• A Few Facts About The Code For Sustainable Homes

Further contacts:

• Energy Price Comparison from Confused.com