Breaking down Part L

How new dwellings will be affected

1: Obtaining compliance is now a five-step procedure

Designers will need to:

• Show a home’s predicted CO2 emission rate will not be greater than the target emission rate
• Ensure the performance of the building’s fabric, heating, hot water and lighting meets the minimum values set out in the document
• Introduce passive measures to prevent homes overheating
• Ensure construction is consistent with the design
• Provide the occupier with information in order to allow the building to be operated as efficiently as possible

2: Dwellings will have to be pressure tested

The air permeability of the envelope should be no greater than 10m3/h/m2.

3: Flats will have to produce 18% less CO2, and houses 22% less C02, than they do under the existing regulations

A carbon comparison must be produced to show how a home’s predicted CO2 emission rate compares to a target emission rating based on a notional dwelling, compliant with the 2002 regulations. A fuel factor can be applied to the rating if LPG, oil, mains electricity or solid fuel is used, making it easier to comply when using these fuels than their carbon content would otherwise allow. So, with careful design, electric heating can still be used in apartment blocks.

4: There are two routes to compliance for apartments

A penthouse does not have to comply with the carbon emission rate provided the remaining dwellings can compensate, since the compliance for apartment blocks can be demonstrated either as individual SAP calculations for each dwelling or as an area-weighted average for all dwellings in the building.

5: A report should be provided to Building Control

This will identify the features that deliver the CO2 reduction. At completion, additional schedules covering lighting, robust details and non-accredited details are required, together with evidence that air permeability standards have been achieved, systems have been commissioned and operating instructions issued.

Issues to look out for on existing dwellings

1: More work is subject to the regulations

The rules will apply to: an extension, a change of use or alteration, provision of a controlled fitting or service and provision of a thermal element.

2: The route to compliance for an extension has not changed

The elemental route to compliance remains for extensions and cases where the use of a building has changed

3: Individual elements must meet specific standards

Provisions apply to acceptable performance standards for windows, heating and hot water systems, lighting, insulation of pipes, ducts and mechanical cooling systems, commissioning and the provision of information.

4: Entire elements may need to be upgraded

When 25% of a thermal element, such as a roof is upgraded, the entire element should be upgraded to the latest elemental standards if payback for the work can be achieved within 15 years. If not, it should be upgraded to a standard that does achieve payback within that time.

5: Historic buildings

Energy efficiency measures should be incorporated where they will not prejudice the character of the building.

Key changes for non-domestic new buildings

1: Obtaining compliance is now a five step procedure

• The predicted building CO2 emission rate should be no greater than the target rate
• The performance of the building fabric, heating and hot water and lighting should comply with the minimum limits in the document
• Passive measures should be included to prevent overheating for areas without cooling
• The building should be built as designed
• Provision should be made to enable energy efficient operation

2: Air permeability

Tests are required for every building that incorporates a floor area greater than 500 m2.

3: Overheating

Designers must demonstrate that the combined solar and casual heat gains do not exceed 35 W/m2 or that the temperature does not exceed 28°C for more than 20 hours a year for spaces with no comfort cooling.

4: Fully glazed buildings will comply

A typical mechanically cooled and ventilated building, 40% glazed and built to 2002 standards can comply through a combination of omission of roof lights, improvement in double glazing specification and lighting controls. An equivalent building with 100% glazed facade could comply with a similar improvement strategy, but with an additional improvement in the chiller seasonal efficiency.

5: Calculating energy consumption

Two calculations are required: a preliminary one, as part of the design commission, and a final calculation demonstrating compliance based on ‘as constructed’ information, incorporating any performance changes made during construction.

How existing non-domestic buildings will be affected

1: More work carried out to existing buildings is subject to the regulations

An extension, material change of use, material alteration, the provision or extension of a controlled service or fitting and the renovation of a thermal element are all now subject to the regulations.

2: Consequential improvements

Work to existing heating or cooling systems, windows or walls below the elemental standards must be upgraded, provided it is technically, functionally and economically feasible.

3: The 10% rule

The requirement for consequential work is limited to 10% of the value of the principle works. The following elements are all subject to the 10% rule: any heating, cooling or air handling system older than

15 years should be replaced by new plant and improved controls; any inefficient lighting system serving more than 100 m2 should be upgraded; energy metering should be installed; and if the renewable energy contribution is less than 10%, the system upgraded provided payback is less than seven years.

4: Extensions

Elemental standards are given for the building fabric and windows in extensions. There is some flexibility allowed, provided the heat loss for area weighted U-values is no greater than the equivalent compliant extension. Extensions over 100 m2 and greater than 25% of the floor area of the existing part of the building come under Approved Document L2A.

5: Controlled fittings or services

Compliance is largely elemental, with specific minimum standards to be achieved. There are additional requirements governing commissioning, the provision of sub-meters and log books.

Thanks to Hoare Lea for helping to prepare this article.

What if my building has already been designed?

If building work has already started before the regulations come into force on 6 April then the revisions to Part L will not apply.

The government will accept that building work has already started if:

• A building notice, or full plans and a commencement notice, has been given to the local authority
• A plans certificate has been given by an approved inspector and accepted by a local authority before 6 April
• Full plans have been deposited with a local authority before that date – and the local authority has stated that any conditions the plans were subject to have been met

Otherwise, evidence of work started on site can include almost anything related to the construction of foundations including:

• Excavation work for strip or trench foundations or for pad footings
• Preparation of the ground for raft foundations

Boring for piles or pile driving.However, if the works simply involve the removal of vegetation or topsoil; the treatment of contaminated soil; the excavation of trial holes;ground compaction or the construction of site services including roads and drainage then, according to the government – the scheme is not yet on site.