BRICKS, BLOCKS & PAVERS
JULY 8 | BUILDING PRODUCTS
the wall that could potentially cause thermal
bridging must be considered in order to achieve
the optimum energy performance for the building
and comply with energy saving legislation and
The thermal performance of a building is
calculated by taking into account heat loss
through the fabric of the building itself, such
as walls, roof, floors, doors and windows, and
through linear thermal bridges found at junctions
between different elements of the building
including window heads, jambs and cills.
Heat loss through the building fabric is
expressed as a U-value and measured in W/
m2K, while heat loss via linear thermal bridges
is expressed as a psi value and measured in W/
mK. The total fabric heat loss is the sum of the
combined fabric U-value, multiplied by the total
area, plus the product of the psi value of junctions
and their total length.
The steel lintel
Due to their nature, enabling the structural span
between openings above doors and windows
across cavity walls, steel lintels have the potential
to form an effective, yet unwanted, thermal
bridge. For example, on a typical four-bedroom
house with a floor area of 57m2, the heat loss
through standard lintels can account for about 6%
of the total amount for the building, based on a
default lintel psi value of 0.5 W/mK.
Lintels are of course essential in us being able
to build structurally sound homes. However, the
legislative landscape of increasingly demanding
energy efficiency standards, combined with the
sophisticated measurement of energy wastage
through the building envelope, has highlighted a
need for improvements in their psi values.
Specifiers can derive lintel psi values from a
number of sources. It is possible to work from the
default values taken from BRE IP 1/06 or ACDs,
however they present the worst-case scenario,
so are best avoided. Alternatively, it can be
worthwhile looking to the lintel psi values that
the insulation and block manufacturers include
with their thermal data sheets. However, by far the
best option is to use the psi values provided by the
lintel manufacturer themselves.
It is possible to achieve improved lintel psi values
by using lintels without a base plate (removing
the potential for additional thermal bridging) or
separate lintels within the cavity wall construction.
However, a lintel that incorporates a complete
thermal break between the inner and outer leaf of
a cavity wall will deliver the best possible thermal
performance for a building; with thermally broken
lintels available that utilise the thermal insulating
properties of a high-density, fire retardant core
to achieve a transmittance Psi value of 0.02 to
0.05 W/mK – with no compromise to structural
performance and the same stable installation
benefits as traditional cavity wall lintels.
Specifiers should also consider the detailing
around a lintel. This needs to be kept as simple as
possible so that the reliance on site workmanship
is removed and ensures the actual performance
of the junction meets the design expectations.
For example, a lintel with a flat top proves a
consistent junction with the cavity wall insulation.
This maintains the thermal performance of the
junction. The specification of a lintel like this has
added cost, time and logistical benefits because it
can be installed in the same way as a traditional
steel cavity wall lintel.
The replacement of traditional lintels within
typical housing designs can result in significant
heat loss reductions for housing developments.
By utilising lintels with a thermal break, that
offer the same benefits of a traditional cavity
wall lintel, steel lintels can support a fabric
first approach to building design, with no
compromise to energy performance.
Steel lintels can support
a fabric first approach to