March 2014

ENTER

A BDA Study
Into Brick
Skin Thermal
Performance

Brick Development Association www.brick.org.uk

A BDA Study Into Brick Skin Thermal Performance CONTENTS 2

Contents Page

introduction 3

case study The Britten Pears Archive 4-5

decrement delay 6

case study Hanson EcoHouse TM 7

Conclusion 8
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INTRODUCTION
The envelope of any modern building must fulfill a number of, sometimes contradictory, requirements. It needs
to turn the weather, provide comfortable internal conditions, resist fire, be flood resilient, etc. This means
being dense for acoustic reasons but lightweight for thermal reasons. Consequently most wall structures
consist of layered constructions, with each layer fulfilling one or more functions. Specifically there is usually
one layer of lightweight material providing thermal insulation.
The concept of Thermal Mass whereby some relatively heavy materials are used to fulfill functions within the
insulating layer are well understood eg the inner leaves of cavity walls. These materials, as well as providing
structure, moderate temperature changes by absorbing heat from the internal atmosphere and subsequently
re-radiating it to warm the atmosphere as it naturally cools.

Housing in the south of England will receive significant benefit through using thermal
mass combined with shading to mitigate the effect of summer time peak temperatures.
(Tuohy et al)

Until relatively recently the role of heavyweight materials outside the insulated envelope has been largely
unconsidered. This is somewhat surprising as the effect of massive construction in historic buildings, for
example our cathedrals, is well established.

In 2012 Altherman began to discuss the potential for moderating the thermal behavior of a building interior by
utilizing the thermal resistance of various other building elements.

It is clear that a more representative parameter than U Value is required to fully capture
the dynamic thermal behavior of a walling system. A relatively simple metric which
encapsulates the contribution of all physical parameters influencing the thermal
performance is required.
(Altherman)

What Altherman is exploring in the case of walls is the concept of Thermal Shielding. The provision of materials
outside the insulating layer that have a high thermal capacity is extremely beneficial as they absorb considerable
amounts of heat as the external temperature rises before significant temperature gradients exist in them to
drive heat to the interior. This attribute of brickwork adds to those of weather resistance, fire resistance,
structural and acoustic performance, together with a warm, attractive appearance.

The Britten Pears Archive by Stanton Williams, as seen overleaf, is a great example of a ‘fully breathable’
structure, which uses well insulated walls of solid load-bearing facing brickwork to help moderate the
temperature and relative humidity between the outside environment and the material within. Therefore, the
building protects the world class and fragile collection of Benjamin Britten’s work without the aid of mechanical
temperature control.

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CASE STUDY THE BRITTEN PEARS ARCHIVE

The Britten Pears Archive by Stanton Williams is a red brick archive building which compliments the site
of The Red House in Aldeburgh, Suffolk, the Grade II listed former home of Britten. The building is designed
firmly within context and uses pioneering low-energy methods to provide an optimum passive environment
to preserve the Britten collection.

The Britten Pears Archive ©PhilipVile

Stanton Williams worked with engineers, Max Fordham, on this project to investigate and test ideas in order
to create a passive archive where the internal environment is controlled with minimal energy input. As the
structure required good thermal shielding, brick provided the ideal solution.

A recent Australian study, conducted by The University of Newcastle, measures how well the internal surface
responds to the external surface temperature. The performance of various external walling systems, exposed
to dynamic weather variables (influenced by ambient temperature, solar radiation and wind speed) have been
recorded. The study looks at and includes the interactions of all of the wall components under all weather
parameters giving an accurate view of wall thermal performance.

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CASE STUDY THE BRITTEN PEARS ARCHIVE

Over the testing period, across 4 seasons, a range of walling systems were used to test Altherman’s theory.
The performance of each module was observed with the interior space being either in a ‘free-floating’ state
(directly influenced by real weather conditions), or with the interior heated or cooled to a pre-set temperature.

The Britten Pears Archive ©Hufton & Crow

From the study it emerged that the Insulated Cavity Brick module performed the best due to the accurate
combination of thermal shielding and the insulation layers. The outer skin was proven to have a positive
contribution on the overall performance and as expected thermal mass located internally within a wall played
a significant role in appropriate moderation of internal temperature.

The key to all of this is thermal capacity which provides both Thermal Shielding and Thermal Mass depending
where heavyweight materials are located in the building. Both properties cause the difference between the
maximum and minimum external and internal temperatures to be reduced. The internal temperature reaches
a peak or trough after a time lag from either occurring externally. The time lag is known as a ‘decrement delay’
and is illustrated on the next page.

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DECREMENT DELAY

Decrement delay graph

Time lag (delay)
Maximum temperature

Te
Maximum temperature

Ti

Minimum temperature

Minimum temperature
Outside Wall Inside

Decrement delay
Different materials allow the passage of heat to travel at different rates. The period of
time it takes the peak temperature on the outside skin of a building (such as wall or a
roof) to make its way to a peak temperature on the inside face, is called the ‘time lag’
or, more scientifically, known as ‘Decrement Delay’.

By controlling the Decrement Delay it is often possible to control and prevent the overheating of a building.
Designing for a long Decrement Delay will ensure that during summer, peak heat gains from outside will not
get through until night, which is when the risk of overheating is moderate.
Medium and heavyweight walls insulated to current standards will slow the passage of heat by around 9 to 12
hours, which provdes an optimum level of Decrement Delay [The Concrete Centre].

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CASE STUDY Hanson EcoHouseTM

The construction of the Hanson EcoHouseTM

at the Building Research Establishment (BRE) in
Garston, Watford, provides an outstanding concept
dwelling. It brings together the latest developments
in off-site masonry construction, thermal mass and
natural ventilation. Constructed using masonry
panels manufactured off-site in a controlled factory
environment, it brings the benefits of high quality
and speed of construction with little or no site
wastage.

Thermal Mass
Masonry construction has high thermal mass.
This inherent feature enables the dwelling to store
heat and remain cooler for longer than lightweight
structures, meeting the needs of climate change
and keeping buildings cool in an energy efficient
environment. The house has high thermal mass
creating a structure to cope efficiently with
extremes of temperature in both summer and
winter. No matter how hot it gets outside during
the day or how much cooler it gets during the night
inside the house it’s always comfortable.

Natural Ventilation
A ventilating roof lantern is used to give light and to enhance natural air currents, so maximizing the energy
conservation potential.

Flexible Design
Masonry panels manufactured offsite in a controlled factory environment provide total flexibility in the design
of dwellings. The system has been designed to meet the needs of house builders and developers and is
applicable across a wide range of housing options.
Addressing the key issues of climate change, carbon efficiency and sustainable masonry construction, the
Hanson build process and systems ensure a flexible range of practical and environmental solutions.

Brick Development Association www.brick.org.uk

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CONCLUSION

The ability to control the internal temperature of buildings so that they do

not fluctuate too much is a contributory factor to human comfort. If this can
be achieved by passive means, especially by the selection of appropriate
materials for the construction of the fabric of the envelope, the energy usage
over the lifetime of the building will be reduced. For some time it has been
acknowledged that Thermal Mass is a property of heavyweight materials
that is effective in restricting temperature fluctuation internally and limiting
overheating in a climate of generally increasing temperature. Recently an
extensive study in Australia has demonstrated the effect of Thermal Shielding
which is the provision of thermal capacity in the fabric of the envelope outside
of the insulating layer. This provision, which can of course be by the use
of clay brickwork, helps to delay the occurrence of maximum and minimum
temperature internally from their occurrence externally. Consequently the risk
of overheating is reduced, the maintenance of steady temperatures is easier
and energy usage is reduced. These effects are major gains in human comfort
and environmental performance.

GJE/JB
14/7/14

Brick Development Association www.brick.org.uk

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