Thermal considerations
Thermal
fabric
The primary purpose of insulation is to limit
either heat loss or heat gain though the external structure and
fabric of a building.
All building materials used in a wall, roof or
floor, increase the thermal resistance to some degree, however
insulation materials are the most efficient at adding thermal
resistance because of their low thermal conductivity. Heat loss
through a building element can occur through conduction, convection
or radiation.
The Law
In England and Wales, Part L Building
Regulations set out the statutory requirements for the thermal
design of new and refurbished buildings, for which the thermal
performance of building fabric is a fundamental component. The
standards outlined in Part L Building Regulations will become more
demanding in terms of thermal performance and are scheduled to be
upgraded again in 2010 and then 2013. In Scotland, Technical
Handbook, section 6 and in Northern Ireland Technical Booklet F
cover thermal regulations.
Key guidance
For domestic new build, the Code for
Sustainable Homes is now a critical influencing factor. The Code
sets out criteria for creating ever-more carbon and environmentally
efficient housing with the objective of all new-build housing being
carbon neutral by 2016.
Thermal
airtightness and ventilation
Airtightness and thermal bridging at junctions
of building elements are key design considerations for all
buildings.
Uncontrolled air exchange with the external
environment is a major cause of heat loss within a building.
However, there are differences between air leakage and ventilation.
Nearly half of all heat lost from the average home is a result of
uncontrolled air leakage through gaps in the structure. This is
distinct from controlled ventilation resulting from intentionally
designed vents – such as windows and fans.
With air leakage, heat energy in the air is
lost, while the moisture vapour condenses on cold surfaces within
cavities. The way to eliminate uncontrolled air leakage is to form
a sealed external envelope, through which internal moisture can
escape, but wind and water cannot excessively penetrate.
Constructions with high levels of air leakage
have been exposed as wasteful of energy and are major contributors
to CO2 emissions. Further ventilation systems with heat
recovery require buildings with high levels of airtightness to
operate at maximum efficiency.
Key guidance
Accredited Construction Details have been
specifically designed in order to minimise heat loss from dwellings
due to air leakage and infiltration. They can be considered to be
the industry best practice details and can be downloaded free of
charge from:
www.planningportal.gov.uk/england/professionals/en/1115314255826.html
Guidance on the ventilation of buildings can be found in BS
5250: 2002, Code of Practice for Control of Condensation in
Buildings.