Civil Engineering Reference
In-Depth Information
Thermal efficiency
All new buildings, extensions and alterations
must comply with Part L of current Building
Regulations. This covers many aspects of
the building, including design to reduce
heat loss, provide airtightness and conserve
fuel and power. The usual way we do this
is by designing for solar thermal efficiency,
to utilise the natural energy of the sun to
provide heat that can be stored in some
materials (thermal mass) and prevented
from leaving the building by insulation and
good design details. Additional heat could
be provided by an energy-efficient heating
system, such as an air-source heat pump
with under-floor heating.
In brick or block walls, this often takes the
form of expanded polystyrene or foam (high
in embodied energy, and using pollution-
intensive production methods) stuck to the
back of the blocks inside the cavity of the
wall. Other types of eco-construction may
use timber and sheepswool or Warmcel as
insulation. With strawbale walls, the insula-
tion (straw) can also be the building block
- and the surface for plaster - so reducing
the need for extra materials. The amount of
insulation of a material is measured by its
U-value.
The Regulations cover all aspects of building,
but for our purposes, although the whole
building is built predominantly of sustainable,
natural materials, the only areas that are
substantially different from other building
techniques are the walls and foundation
design. So the areas of concern for Building
Regulations are:
The U-value, or thermal transmittance, of a
material is the amount of heat transmitted
per unit area of the material per unit temp-
erature difference between inside and
outside environments.
It is measured in units of Watts per square
metre per degree of temperature difference
(usually measured in Kelvin): W/m
2
K. Put
simply, the U-value is a measure of how
much heat a material allows to pass
through it.
•
thermal efficiency (insulation)
•
acoustic efficiency (sound insulation)
• fire resistance
The lower the U-value, the greater the
insulation of the material.
• structural performance
Part L of the Regulations (2006) states that
the following elements of a new extension
or new build must have a U-value no
greater than those shown in the table
opposite (top).
•
durability (including degradation due to
moisture)
• airtightness
•
log book, energy ratings etc.
