Insulate Magazine Issue 11

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The report is being revised to reflect new and
updated practice, but at the time of writing the
2006 edition remains current.
BR 443 is also listed as a ‘source of data’ by the
BBA, along with a couple of other standards,
current BBA certificates, and recognised declarations
by manufacturers.
If specific material data is missing from a particular
specification, these data sources can provide
appropriate assumptions to maintain a level of
accuracy in the calculation.
ISO 13370
Here is the standard that complements ISO 6946
and provides the means of calculating heat loss
through ground floors, or what is described in
the standard as the “three-dimensional nature”
of heat flow in the ground. It applies to slab-onground
constructions and ventilated suspended
floors.
Heat transfer into the ground is affected by the
thermal properties of the ground itself, the area
of the floor, and the perimeter of the floor including
thermal bridging at its edge. If you request
a ground floor calculation you will be asked for
measurements of the floor’s area and length of
exposed perimeter for this reason.
BRE Digest 465
This Digest, developed jointly by the BRE and the
Steel Construction Institute, provides a methodology
for calculating the thermal transmittance for
warm, cold and hybrid steel frame constructions
that otherwise fall outside the scope of ISO 6946.
Validated by detailed calculations to ISO 10211,
it allows a simplified method to be incorporated
into common software tools and provides a
means of assessing steel frame constructions
more widely.
SCI Information Sheet P312
This information paper also adapts the procedure
in ISO 6946; in this case, to provide a relatively
simple means for calculating built-up metal roof
and wall cladding constructions featuring rail and
bracket spacers. The differences in calculation
method account for a compressed insulation
layer, as well as the impact of linear and point
thermal bridging due to metal components and
fixings, all validated by calculation to ISO 10211.
BRE Information Paper IP 10/02
Another document dealing with the effect of
metal components on insulation layers, this paper
offers a method for determining the thermal
performance of insulated double skin metal roof
and wall systems that incorporate ‘z’ spacers.
It accounts for the thermal bridging of the metal
connectors between the inner liner and outer
sheet.
In Conclusion
For all the talk of ‘simplified methods’, calculating
U-values remains a largely specialist activity. If a
calculation says a certain result will be achieved
then the majority of readers will assume it to be
correct. The quality of a calculation depends as
much on the information provided at the outset,
and the ability of the person doing the calculation,
as it does on the standard used to perform
the calculation. Which is why, next month, we will
look at some typical calculations to illustrate how
they display their data.
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