Creative solutions, energy efficiency and aesthetics: how Part L is affecting historic buildings
One of the key changes to Part L, which came into effect last month, was a move to amend exemptions for listed buildings and to encourage architects to consider upgrades.
The Approved Documents now make it clear that it is no longer acceptable to create a blanket exemption for listed buildings and that a reasonable attempt to meet energy efficiency targets must always be made. At the same time it is acknowledged that there is a fine balance that needs to be achieved between building conservation and measures to improve energy efficiency to avoid lasting damage.
In an attempt to reach this balance, Part L retains some specific exemptions and references to circumstances where ‘special considerations’ apply for historic buildings and those of traditional construction. In each case the appropriate balance should be discussed early in the design process through dialogue with the Building Control Body (BCB) and the conservation officer. As there is a choice between BCBs, architects working on such schemes would be well advised to check the relevant sector experience of alternative providers before making an application.
It is very important that the BCB has an understanding of what constitutes the special interest or significance of a historic building. Very often technical, philosophical and aesthetic conflicts will need to be resolved and on occasion highly creative solutions to problems will be necessary.
To aid those in this field, English Heritage has this month revised its ‘Guide to the application of Part L of the Building Regulations to historic and traditionally-constructed buildings’. The guide sets out a process for designers and BCBs to follow when upgrading traditional buildings.
Step 1.Consider repairing the building, using compatible materials and techniques to reinstate its optimum original performance. This should extend to removing any damaging alterations and additions that compromise the building’s permeability.
Step 2. Look at benign enhancement through improving heating strategies, controls and equipment. For example, condensing boilers are highly efficient and, combined with effective controls and programming, can make substantial reductions in energy use, with negligible impact on the character of the building.
Step 3. Control draught and air infiltration throughout the building. Large amounts of energy can be lost through gaps in construction, and will reduce the effectiveness of any upgrading work which might have been carried out elsewhere on a building. Start by repairing any cracks and holes in the construction, and incorporating draught proofing and/or secondary glazing.
Step 4. Incorporate insulation options once these steps have been completed, starting with those that utilise existing voids and reversible techniques. Insulation can be installed at ceiling level, between the rafters or between the floor joists, though careful detailing of ventilation is required to control condensation. Again, secondary glazing is cited in Part L as an effective way to meet the target U-value and can be discreet and reversible.
Step 5. Assess intrusive insulation options of the external envelope, such as recladding. The guide acknowledges that these techniques can be highly effective and in some cases match the performance of new construction. However, such techniques will have obvious effects on the character and appeal of older buildings and are less likely to be acceptable.
Step 6. Don’t forget carbon-neutral energy supply from micro-generation where practically possible. The most common options such as solar panels and wind turbines are unlikely to be visually acceptable. However, small-scale hydro-power schemes and combined heat and power systems can be viable options. Another option is to incorporate a ground or air-source heat pump, which provides constant low-level heating and is beneficial in traditional buildings as they typically have a high thermal mass which allows heat to be constantly ‘topped-up’ to the benefit of both the building and its occupants.
Whenever any of these insulation techniques are being considered, they should be supported by dew point calculations, undertaken to ensure that the proposals do not create conditions that will lead to condensation forming, which could cause long term degradation.
Those who want to know more about best practice in this field can access a number of exemplar projects on www.rethinkinghousingrefurbishment.co.uk.
A free copy of English Heritage’s new guide to Part L can be downloaded from the news page of www.thebuildinginspector.org.