Insulate Magazine Issue 11

The only independent insulation industry trade magazine
Insulate Magazine
Working to the
Right Standard(s)
U-values are an integral part of everyday life for the construction industry. Sometimes the
success of a project can hinge entirely on hitting the thermal targets for the building’s
envelope. By extension, that magnifies the importance of proving a specification’s ability
to meet its target - and being able to trust in the answer provided. By Insulate Magazine.
Which is where U-value calculations come in: all-important pieces of paper providing the required proof.
There are many and various standards relating to calculations, so for the purposes of providing an overview
we’ve used those listed by the British Board of Agrément (BBA) as applicable to their ‘Scheme for
U-value Calculation Competency’ as a framework.
ISO 6946
For all that this international standard might be
seen as defining how the majority of U-value
calculations are done, it is actually surprisingly
narrow in its scope. The document’s own text
limits itself to walls and roofs!
Nevertheless, it forms the basis for many of
the calculations that insulation manufacturers
and energy assessment professionals produce,
supplemented by a variety of other guidance
that we’ll come to shortly. Known as the ‘combined
method’, ISO 6946 describes a simplified
tool capable of establishing the performance of
constructions for the purposes of comparison,
or helping determine compliance with thermal
regulation targets.
A detailed calculation method is also referred to,
defined in ISO 10211. Numerical modelling carried
out to that standard uses specialist software
and tends not to be a widely-offered service, so
we’re not going to cover it in detail here. However,
when the majority of calculations are done
the ‘simplified’ way, it is easy to forget there are
alternative, more complex methods which provide
additional data such as minimum surface
temperatures. Obtaining a calculation done using
the combined method is relatively straightforward
- but that isn’t to say it is always the most
appropriate method.
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