Part L 2010 in practice: a worked example

CO2

emissions is achieved or bettered. This approach to target setting has

been adopted because the level of improvement that can reasonably be expected varies significantly from sector to sector, so a blanket improvement factor would be inequitable. The specification instead delivers an overall 25% reduction in CO2

emissions across the entire new-

build non-dwellings sector (the so-called “aggregate approach”). As a result, some building types will be required to improve by more than 25%, some by less (Table 4). This will put more pressure on certain

projects, particularly those with shallow plan mechanical air-conditioning.

Thermal bridging Another issue for small contractors is that guidance on avoiding thermal bridging at construction joints has been revised. Approved Document L2A states that the design must be calculated in accordance with BR 497 (Thermal Performance of Buildings). Perhaps more important, developers must demonstrate how specific details will perform when assessed to BRE IP 1/06 (Assessing the Effects of Thermal Bridging at Junctions and Around Openings). In particular, builders will need to show

they have factory-tested accreditation for the detail and that they operate quality- assured site inspection systems. If either of these criteria is not met, a 25% penalty will be applied to the design assumptions in the building energy rating (BER). If there is no accredited detail at all (likely to be the norm) a 50% penalty must be applied. The small contractor who doesn’t have an ISO quality assurance system will be operating at a significant disadvantage.

Other changes Guidance on shell and core development has also been revised, and it will now be necessary to specify at the design stage how the shell and services will meet the requirements. It will not be possible to simply design the shell to base levels and leave it to the fit-out contractor to install efficient services to compensate. On practical completion, it will be

In her blog “Elemental”, energy assessor Mel Starrs of architect PRP looks at the example of a one-storey research building, with a 2m² solar thermal array to provide a 10% renewables obligation as shown in Table 5 (below). When modelled using

SBEM 2010 it gives the results shown in Table 6. As you can see, the baseline construction fails the 2010 TER by a

significant margin (and due to the changes in modelling even fails to beat the 2006 TER). In order to pass it was

necessary in provide 10m2 PV and improve lighting and cooling. Interestingly, the previous silver bullet of adding biomass still resulted in a fail, and the addition of PV is still required to pass. When I spoke to Starrs

about her experiments with early modelling

Table 5 Base values: one-storey research building cONSTRUCTION

DESCRIPTION

External solid brick wall Internal partition wall Office roof

Ground floor Double glazed door Double glazed windows Skylight

Plant room doors Industrial door

Cavity wall full fill Timber frame wall

Flat roof; (lightweight) 2006 regs

Solid ground floor, 2006 regs 4-16-4, coated, argon-filled

frame — wood frame, thermally improved spacer

4-12-4, coated, argon-filled

frame — wood frame, thermally improved spacer

Skylight with twin skin,

softwood frame, aluminum spacer

Insulated personnel door

Vehicle access door, 2002/06 Part L

1.61 1.5

3.12 1.82

under the new system, she said “achieving a 25% improvement over 2006 does not automatically mean your building will pass under 2010”. Even more bizarrely,

she also pointed out that it is now possible to reach BREEAM “excellent” rating and still fail to meet the 2010 standards as the BREEAM standards have not been revised in line with the new notional building.

U-VALUE 0.26 0.30 0.16

0.22 1.74

Table 6 Modelling the research building using SBEM 2010 2006

1 Baseline

2 Change 2m² solar thermal to 10² PV

3 Improve lighting 40W/m²

to 12W/m², fully automated controls reduce parasitic power on controls

4 Improve cooling efficiency from 2.2 to 4.0

5 Biomass, with all

improvements, no additional renewables or PV

6 Biomass as above + 20m² PV 24 23.8 (pass)

30.9 24

29.5 (pass) 24.9 (fail)

TER 48.1

2006 BER

42.7 (pass)

2010 TER 30.9 30.9

30.9

2010 BER

48.7 (fail) 48.2 (fail)

32.8 (fail)

> CONSTRUCTION MANAGER | OCTOBER 2010 | 37