Time was that for many, the answer to the increasingly stringent performance targets set by each subsequent revision to the Building Regulations, appeared to be simple and obvious: deeper cavities, filled with more insulation will deliver better thermal performance. Problem solved.

Except that it isn’t.

The 2006 revisions to Approved Document L2 require the use of ‘whole building method’ when measuring the thermal performance of a building. This method stipulates projects deliver an overall building thermal performance increase of 23.5% over the base build given in the 2002 regulations.

Politicians are charged to reduce CO₂ emissions and we are virtually at the point where increasing insulation has a diminishing return. In fact, increasing the weight and thickness of the roof and wall components sees an increase in the embodied energy, which is likely to significantly increase the build costs by anything up to 20% of the overall cost of the building as footings, columns, rafters, purlins, rails, spacers and panels all need to be increased to cater for the additional weight. Many other options are able to deliver far greater reductions in CO₂ at a much lower cost. Industry has to be motivated to continue innovation for the elimination of CO₂ emissions from the operation of the building.

The question architects, designers and specifiers need to be asking is, has the point at which increasing insulation alone, to improve thermal performance, reached diminishing returns?

When conducting whole building calculations with iSBEM, improving the roof and wall cladding U-values from 0.25 and 0.35W/m²K to 0.16 and 0.25W/m²K respectively, would be equal to an increase in building performance (or asset rating) of approximately 3-4%. The cost of doing so, however, would be increased by up to 25% for the external envelope and steel frame due to the increased construction depth and additional weight.

The most cost effective methods to improve thermal performance include:

Rooflights

Reducing rooflight U-values to less than the minimum weighted average U-value of 2.20W/m²K, for example C A Building Products’ GRP rooflights can achieve 1.80W/m²K, at no extra cost, equating to 2% improvement on the building envelope. We can also offer a 1.40W/m²K U-value rooflight system at no extra cost, which equates to 3% on the building envelope.

Thermally Efficient Details

By using the ‘robust’ details and MCRMA recommended details, the performance enhancement of the asset rating is approximately 7-8%, without affecting cost. When incorporating the recommended standard roof and wall cladding details from C A Building Products, however, the enhancement is 15-16%.

Air Permeability

Enhancing the air permeability for the building from 10.00 to 5.00m³/hr/m² will achieve an improvement on the iSBEM the asset rating of 2%. CA Building Products feel, however, that an air permeability of 3.00m³/hr/m² is achievable, which equates to approximately 3% enhancement on the asset rating. When seeking a high asset rating, low levels of air leakage are vital. To find out more click here to visit our Air Permeability section.

In summary, there are zero cost actions that can deliver extremely high proven CO₂ savings. A 58% building envelope performance enhancement can be achieved, at no extra cost, by specifying systems with rooflight improvements, reduced thermal bridging and by ‘robust’ design, all of which are proven to consistently achieve high levels of air tightness.

All of this, through careful design and modelling, helped contribute to the ‘A-rated’ Energy Performance Certificate (EPC) at ProLogis 360, Crewe. To view the certificate, click here.