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Building Regulations Part L2 2010 - A Review

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On the 1st October 2010, the latest version of Part L Conservation of Fuel and Power of the Building Regulation came into effect.
Part L2 deals with building other than dwellings, there are two parts, part A for new buildings and Part B for existing buildings.
Part A - New Buildings
The main principle is that the energy performance of the building shall not exceed that of a notional building of the same size and shape as the actual building. Unlike the 2002 regulation there are no specified U values for the roofing and cladding systems.
The form of measurement of energy performance of the notional building is the target carbon dioxide Emission Rate (TER). The TER is calculated using approved software, one being the Simplified Building Energy Model (SBEM).
In terms of roofing and cladding the information required for the model is
  1. U values of the systems
  2. Linear thermal transmission value Ψ (psi value) of junctions
  3. Air permeability of the building
The values for the U values for the notional building are specified in the National Calculation Methodology (NCM) modelling guide (for buildings other than dwellings in England and Wales) 2010 Edition.
Element U-values (W/m2 K)
Roof 0.18
Walls 0.26
Windows, roof windows and rooflights 1.8
Vehicle access and similar large doors 1.5
Pedestrian doors 2.2
The air permeability of the Notional building must be 5m/h per m envelope at 50 Pa.
Values for the actual building the Building carbon dioxide Emission Rate (BER) needs to be calculated.  The U values should be specified by the design team but must not be greater than.
Element U-values (W/m2 K)
Roof 0.25
Walls 0.35
Windows, roof windows, rooflights, curtain walling and pedestrian doors 2.2
Vehicle access and similar large doors 1.5
Roof ventilators 3.5
The air permeability of the actual building must not exceed 10m/h per m envelope at 50 Pa.
Part B - Existing Buildings
Renovation of Thermal Elements
Where more than 50% of an individual roof is to be re-roofed then the new roof shall comply with the regulations.  The U values that should be achieved are:
Element U-values (W/m2 K)
Pitched roof - insulation at ceiling level 0.16
Pitched roof - insulation at rafter level 0.18
Flat roof or roof with integral insulation 0.18
Walls 0.3
However the Regulation does say that these values should only be achieved where it is technically functionally and economically feasible.
Where it is not feasible, then the the element should be upgraded to the best standard that is technically and functionally  feasible and which meets a simply payback criterion of 15 years or less.
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