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L1A Compliance ...I enclose my information sheet to help make some sense of the requirements. I also enclose a checklist.  All the information is based on my own perception of the requirements
Revised 28-12-10

Designing Dwellings to Part L1A 2010 (New-Build)

This note is a personal interpretation of requirements based on experience as a Code for Sustainable Homes assessor. … J C Beachey
 

From October 2010, there has been a further reduction in designed Carbon Dioxide emissions of 25% in dwelling design.

This is further complicated by changes in SAP, for which some of the fuel parameters are altered.

For economy, future designs should concentrate first and foremost on getting the basic structural design right.

It is a mandatory requirement to provide a detailed SAP rating and Building Regulation checklist (including full U-value calculations to BR443) before construction commences. The SAP assessor will be responsible for accurately calculating the U-values or providing and checking third party accredited calculations.

The actual extent of low energy lighting fittings is now be considered by SAP (minimum 75% of fittings ... see below for clarification)

Choice of Structure Type: EXTERNAL WALLS

Traditional masonry structure can achieve good results, as can timber framed structures. Additional layers of highly efficient un-bridged insulation can make all the difference. Personally, I would be wary of using some of the multifoil insulants … If you do, insist on a make that has a BBA Certificate.

Care must be taken in specifying these highly insulated structures. A condensation risk analysis must be undertaken for any unorthodox structure, in terms of insulation placement and thickness.

Remember also that the outer layer of a highly insulated wall can freeze in winter. Porous materials can spall . Care must be taken with brickwork to avoid surface saturation. Recessed pointing should be avoided.

With dry-lined finishes, the blockwork must be parged. There are practical difficulties with some light-weight blocks due to suction. I can only suggest spraying the wall surface with dilute PVA prior to rendering. Strong cement /sand mixes must be avoided … they should be weakened with the addition of lime or pfa.

Choice of Structure Type: GROUND FLOORS

For solid floors or beam & block floors, it is best to detail the insulation on top of the slab/beams, with either screed or floating floor finish. The insulation thickness can be up to (say) 200mm for beam and block or 150mm for slabs (Celotex/Kinspan or similar). 

Suspended timber ground floors should be insulated above the floor joists to reduce thermal bridging (inter joist insulation can also be provided).

Choice of Structure Type: ROOFS

Insulation above ceilings can be 300mm or more. The specification using Enhanced Construction Details for roofs, requires a layer of rigid insulation below the ceiling joists. Sloping ceilings can be insulated inter-rafter and beneath. A battened cavity below the insulation decreases the U-value if a foil faced insulation board is used. Otherwise consider 400mm or even 450mm total thickness. Rockwool, although an excellent product for sound insulation, is not as good as glass fibre in providing thermal insulation.

Choice of Structure Type: PARTY WALLS

Party walls with a cavity (masonry or timber) will be penalised if there is any risk of air convection within the cavity reaching an area outside the heated envelope. These walls must be fully specified at the outset. A party cavity that is neither fully filled or sealed at the thermal perimeter, will not comply.

Accredited Construction Details:

It will be essential to use Accredited Construction Details. It seems likely that an accreditation companies may be set up to register and monitor these details … perhaps similar to Robust Details Ltd. It is likely that the EST Enhanced Construction Details will be embraced within the ACDs.

Thermal Mass: 

The new SAP (2009) indicates increased CO₂ emissions if structures of low thermal mass are used. In future, the wall finishes (external and partition walls) should be established at design stage. The use of masonry or stud partition walls should be clearly shown, together with their finishes.

Air Infiltration/Ventilation: 

Reduction in air infiltration levels is important. Air changes by unregulated natural infiltration can use far more heating energy than is lost through the structural envelope. I would advise aiming for an infiltration rate of 3m³/m²(envelope area)/hr. The reduced air changes pose a problem of condensation/air quality risk. This would be overcome by the use of whole-house mechanical ventilation systems, preferably with heat recovery (see the requirements of the new Part F). Duct runs can pose a problem, but the use of webbed joist systems (Eco joist or similar) is to be recommended. Download the information on the latest Vectaire product

Alternatively, an infiltration rate of greater than 5 can be specified, with individual extract fans. This approach may also require solar water heating panels or PV panels to reduced the DER

New rules are now in force regarding the pressure testing of single house-types in a development. Previously, the pressure test result of a sample house built of the same or virtually the same size and structure as the others, in the same phase, could be applied to the remainder of that house-type. Now, the remaining houses will have 2m³/m²/hr (confidence factor) added to the primary result. This may cause non-compliance, dependant on the designed air infiltration rate … and will probably lower the EPC rating.

Windows:

One should aim to specify highly insulated windows, preferably with Argon filled low-E glazing, insulated spacers etc.. Ideally, the U-value should be 1.6W/m²K or better. All replacement windows to existing dwellings must be 1.6 or lower. This has prompted manufacturers to economically produce windows to lower U-values. 

At build completion, it is now a requirement to provide certified U-value results to Building Control. Purpose made timber windows can also be certified, albeit at a cost. The calculated U-value includes the glazing and the frame (centre-pane U-values are not acceptable). The calculation can be based on a GGF standard domestic glazing configuration (a window 1480 x 1230mm)

External Doors: Similarly, well insulated doors should be specified. It will not be possible to use un-insulated doors

Orientation: Solar gain through windows (offsetting heating requirements), can be useful, but also cause problems in respect of the Summertime overheating risk assessment. The requirement for compliance in this respect is strengthened in SAP 2009. It is also possible that solar water heating/PV will be required, that ideally should face within 30deg of South.

To gain overall DER/TER compliance, “add-on” renewable energy features will often be required such as solar water heating or solar PV. These usually require an orientation within 30 deg of South to be most effective.

Lighting: 75% of light fittings will have to be low energy (now 45 lumen/Watt or more ... previously 40 ... specifications should be amended). Standard fittings can now be used as long as the lamps are low energy. TUNGSTEN HALOGEN LAMPS DO NOT COMPLY. LED lighting of 5W or less is not counted.

Heating: The Building Regulation TER (Target Emission Rate) is based on mains gas heating. It is much more difficult to comply using oil, LPG or resistance electrical heating. Heat pumps can be considered a viable option.

Enhanced heating controls should be considered such as delayed start thermostats. Use this link to view control types.

Secondary heating (room heaters) such as wood burning stoves, can assist compliance, but can conflict with balanced mechanical ventilation systems.

Typical Scenario:

A house designed to be heated by mains gas

• Design to Accredited Construction Details
• Design to a target infiltration rate of 3m³/m²/hr
• Boiler … Band A condensing boiler (SEDBUK/SAP2009 of 89% or more)
• Heating Controls … Add weather / load compensation, delayed start etc.
• Walls … Aim for U-value of 0.25 or better
• Roof … U-value of 0.13 or better
• Ground Floor … U-value of 0.15 or better
• Windows … Ideally U-value of 1.6 or less
• External Doors … U-value of 1.00
• Lighting … min. 75% low energy fittings
• Ventilation … Whole house mechanical ventilation with heat recovery
• Secondary heating … Carefully consider.

• There is no guarantee that this scenario will comply. Solar water heating or solar PV may have to be added. For heating by oil, LPG or electricity, compliance can be much more difficult.

Design Checklist

In many instances, it is going to be difficult to comply under Part L1A 2010.
This list is a basic checklist covering the vital points of consideration

I can provide paper copies if required

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