Technical Bulletins

Part L2 - The Technical Bit

New Part L2 regulations came into force on May 6th 2006 and apply to non-domestic buildings beginning construction after this date. The regulations requiring designers to demonstrate significant reductions in carbon emissions from building energy use relative to the standards set by the previous (2002) edition of the regulations. This is achieved by performing a detailed analysis of the carbon emissions of two buildings:

The actual building – the building as designed, but subject to standard patterns of occupancy and plant operation, and

The notional building – a version of the building that conforms to standards similar to those applying in the Part L2 (2002) Elemental Method. The notional building is subject to the same occupancy and plant operation patterns as the actual building.

The analysis must demonstrate that the actual building’s carbon emissions improve on those of the notional building by a specified margin – 28% for an air conditioned building. It is this improvement that constitutes the tightening of the regulations in the 2006 edition.

Requirements on the control of summertime solar gains apply to the actual, not the notional building, and only to rooms without mechanical cooling. In this respect the 2006 notional building sets a slightly less demanding performance target than the 2002 notional building.

Part L2 - The Layman's View

Newspan design & build ltd

Statement of Design Philosophy for Commercial Garden Centre Building

An anomaly currently exists between the needs of a garden centre to carry out its legitimate trade, and the need of new commercial build to comply with the energy conservation requirements of Building Regulations. It is in trying to square this circle that we recommend best practice throughout each of the design stages, in order that both parties might ultimately be satisfied with the result.

It is obviously the case that garden centres need to sell plants, and that seasonally the area of floor space required to do so will expand and contract. To do this the garden centre must have plenty of light, the right quality of light and plenty of free air movement. Seasonally this space also needs to be heated, and it is here that the anomaly exists – how do you provide flexibility throughout a garden centre, when a properly heated glazed structure is at odds with the needs of Approved Document L2, commonly known as Part L2.

The practical response is to accept that you cannot satisfy both sides fully, but that a lot can be done to create the right space without being overtly detrimental to the environment.

This can be achieved by starting with a building envelope that is insulated as described in Part L2, and then inserting rack and pinion operated ridge vents, glazed with multiwall polycarbonate, to one or both sides of the ridge of each span of building. This will provide air movement and light for the plants, and when coupled with the right polycarbonate type (based on location and orientation of building), the right sort of light level. This should be coupled with areas of glazed elevation in order to supplement light levels, and doorways that can be ‘held’ open during the warmer months to aid air flow.

The vent control system should be one selected from a wide range available from the commercial horticultural sector. These systems intelligently ‘measure’ the rate of change of temperature and send an instruction to the motor to operate for a period of time which varies with the rate of change of temperature.

The heating system employed within the space should be based on a mean temperature lift of 17⁰C; being a minimum requirement for both bedding and house plants, with additional capacity to allow for a maximum wind chill factor of -15⁰C.

This design criteria puts compliance (for these elements of the build) at no greater than 4% below that of the requirements of Part L2. This reduced (for the average existing garden centre) level of light will enable seasonal plant sales to be continued throughout the building area.

Larger, slower (in turnover terms), plant sales activity will need greater light levels than the above solution, and where this is necessary the whole of the roof area in question should be glazed with multiwall polycarbonate and fitted with an automatically operated ridge vent. In this instance it would be necessary to seek a greater relaxation of the rules.