Changes to the thermal, environmental and acoustic regulations will affect the way walls are constructed. Alex Smith examines changes in Part L and E of the Building Regulations and new European standards
The EU has implemented a progressive ban on ozone-destroying HCFCs (hydrochloroflourocarbons) as blowing agents. From 1 January 2002 manufacture of extruded polyester using HCFCs was banned. The use of HCFCs in polyurethane sandwich panels will be forbidden from 1 January 2003, and for all other foams (phenolic, polyisocyanurate, and polyethylene) from 1 January 2004.

Avoiding thermal bridging
Part L demands that there is no significant thermal bridges or gaps in the insulation layer(s) at the junctions of floors, walls or roofs and at the edges of elements such as window and door openings. Specifiers can comply with the requirements by adopting the recommendations in the robust construction details. If they want something less standard, specifiers should turn to BRE Information Paper IP 17/01. Robust details are only suitable for walls with U values in the range 0.3 to 0.47W/m2°C. Elements constructed with U values higher than these will need to be checked for compliance using the criteria described in IP 17/01.

Method of calculation
The calculation of U values for walls will have to be carried out to a new standard (BS EN ISO 6946:1997) as a requirement of the new Part L regulations. This method of calculation takes greater account of the effect of air circulation within structures and cold bridges such as wall ties and mortar joints. Specifiers should ensure manufacturers' figures are based on this latest standard.

Weight of blocks

Specifiers using denser masonry to meet proposed changes to Part E of the building regulations may inadvertently contravene HSE's manual handling recommendations when the project goes on site. The HSE states that the maximum block one person can repeatedly lift should be no more than 20 kg. If denser blocks are used, two people will be required to lay each block, adding to the cost of labour on site. The maximum thickness of a standard face size dense block that can be lifted under these regulations is 100 mm. For a medium density block it's 140 mm and for an aircrete block, 215 mm.

Insulation performance
The way the performance of insulation is measured is changing between April 2002 and March 2003. New European standards require that manufacturers declare an aged performance for their material so any loss of performance over time must be taken into account when declaring it. Specifiers should check with manufacturers to find out whether they are describing the physical properties of their materials according to the old or new standards.

Unheated spaces
Under the elemental U value approach, wall elements next to unheated spaces must also meet the minimum U value requirements of 0.35 W/m2°C.