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    Rockwool Part L 2010 Guide


    Rockwool have produced comprehensive guidance as to the main changes to Part L 2010. Download the brochure "An Introduction to Part L 2010" (and it’s supporting documents) which covers information on new build and existing residential and non-residential buildings plus the party wall bypass effect. 


    •  ‘Design’ submissions are now part of the Regulation – submitting a design stage calculation and specification list to Building Control Bodies will be mandatory before building starts. Previously only the As-built calculation was a requirement.
    • Party walls – Plus their associated thermal bypass heat losses will be included for the first time in the calculations. You will need to insulate and seal your party wall cavity or use solid walls just to match the notional building.
    •  Thermal bridges – ‘Accredited Details’ scheme aimed at ensuring that developers only claim enhanced benefits in their SAP modelling by using approved accredited construction details which have actually been used (0.08 for accredited construction details is no longer an option).
    • Swimming Pools – New Indoor swimming pools will require a U-value for the basin walls and floor which should be no worse than 0.25W/m²K
    •  Air Permeability – Further improvements on air tightness. Part L 2010 now requires double the number of pressure tests to meet compliance. Generally a value between 5.0 & 7.0 m3/(hm2) will need to be achieved. 15.0m3/(hm2) can still be used in small developments but will tend to require improving further the performance of thermal envelope.
    • Thermal Mass – The heat capacity of the external and internal building fabric will be used in the calculation of TER & DER results. You will now have to define the internal walls, floors and ceilings along with any party walls. Increasing the effective thermal mass reduces the need for heating and cooling. However the rules or calculating heat capacity mean that items such as internal drylining, thermal lining and lightweight constructions will reduce your effective thermal mass.
    •  Fabric limits – Maximum area weighted U-values have been improved from the 2006 standards. The area weighted U-values are maximum values and unlikely to be low enough to comply with CO2 emissions requirements.


    Brochures available for download here are:

    •  An introduction to Part L
    •  An introduction to Part L – U-values
    •  An introduction to Part L – Insulating Pipes and Ducts.