Continuing Professional Development Part L 2010

>

study by Zero Carbon Hub entitled Defining a Fabric Energy Efficiency Standard produced in November 2009 showed that increasing wall thickness from 320mm to 385mm reduced the U-value by 0.07W/m2

K, yet increasing

from 385mm to 425mm only reduced the U-value by 0.03W/m2

K. What is significant, however, is that

heat loss through party walls is now considered for the first time, with a limiting U-value of 0.2W/m2

K. An unfilled

and unsealed cavity wall would achieve 0.5W/m2

that insulation to party walls must be specified (see Table 2, right).

Pressure testing The increased requirements for air- pressure testing will concern many builders, with the testing requirement almost doubling. This means Building Control will now expect to see tests from up to three units of each dwelling type, or half the instances of that type (whichever is smaller). In addition, a “confidence factor” must

now be applied to dwellings that are not pressure tested. Where the contractor decides not to test a dwelling, a confidence factor of 2m3

/h/m2 /h/m2 to get the same

rating as a tested one designed to 10m3

/h/m2 K, and therefore fail, so it is clear

Table 1: Part L1A Comparison of limiting U-value 2006 v 2010 (W/m2

ELEMENT Roof Wall

Floor Party wall

Windows/pedestrian doors Table 2

Solid

Unfilled cavity with no effective edge sealing Unfilled cavity with effective sealing all around

exposed edges and in line with insulation layers in abutting elements Fully filled cavity with effective sealing at

all exposed edges and in line with insulation layers in abutting elements

Table 3: Part L2A Limiting U-values (W/m2 ELEMENT Roof Wall

Floor Party Wall Windows/Pedestrian doors 2.2

Table 4 CO2

@ 50 Pa is

applied, so an untested dwelling must be designed to 8m3

. Where a value of 15m3 /h/m2

adopted there is no requirement to test, however, it is very difficult to get a building designed at this rating through SAP in the first place. The use of a design value as low as , however, in turn risks the

8m3/h/m2

possibility of “accidental brilliance”, where a contractor unintentionally seals the building tighter than 5m3

/hr/m2 @

50 Pa, resulting in additional requirements for ventilation kicking in under both Parts F and L.

Approved Document L2A — Non-dwellings Part L2A is also based upon a 25% improvement over the 2006 standards, yet the limiting U-values for commercial

36 | OCTOBER 2010 | CONSTRUCTION MANAGER is 22%

SHALLOW PLAN

(HEATED) 40%

SHALLOW PLAN

(AIRCON)

26% DEEP

PLAN (AIRCON)

buildings are unchanged (Table 3). This is because the way in which the

25% improvement is being implemented is completely different to the approach in L1A. Here, the National Calculation Method (SBEM) doesn’t simply apply a 25% improvement to the previous model, but recasts the notional building. So the TER is no longer based on a

2002 notional building and an improvement factor. For 2010 it is based on a building of the same size and shape as the actual building, constructed to a concurrent specification. Developers are still given the freedom to vary the specification, if the same overall level of

34% WAREHOUSE

16% HOTEL

27% SCHOOL 21% RETAIL 26%

SUPER- MARKET

reductions by non-domestic building type K)

U-VALUE 2006/2010 0.25 0.35 0.25

Not Given

2010 0.20 0.30 0.25 0.20 2.0

U-values for party walls PARTY WALL CONSTRUCTION

2006 0.25 0.35 0.25

Not given 2.2

K)

U-VALUE (W/M2K) 0

0.5 0.2

0

“ The target emissions rate is no longer based on a 2002 notional building and an improvement factor. For 2010 it is based on a building of the same size and shape as the actual building.”