in the long term: The main use/purpose of a
building often changes during its
lifespan and thus the design and materials must
be adaptable for this without great disruption or cost.
The simpler the house design and its services and the greater
the thermal and moisture capacity of the building the easier
this will be. In particular vapour open constructions with
simple insulation and air tightness layers are easy to adapt
and traditional building materials such as timber, blocks,
renders etc. and products traditionally made out of it have
been time proven to suit these requirements. Building in
thermal capacity and moisture buffering assists the success
of internal and service alterations.
changes per hour (ACH): The ACH (also air change
value) is like the air
permeability a measure of infiltration
(unplanned air changes) used for energy calculations to
indicate the performance of a building in terms of both
energy use and fabric integrity. It indicates how often
the entire air quantity in a building is renewed within
one hour without any ventilation in place1
[m3 m-3 h-1], also [h-1].
It is calculated by creating a particular pressure difference
between the outside and inside of the building when all
intentional openings and ventilation systems are closed
and by then measuring the amount of air that leaks through
the external structure. The standard2
pressure difference is 50 Pascal. For EnEV3 buildings
without MVHR an AHC of 3 m3/m3/h (c.p.
footnote4) and for Passivhaus an AHC of 0.6 m3/m3/h
is accepted as the maximum.
Permeability: The air permeability is like
the ACH a measure of infiltration
(unplanned air changes) to indicate the performance of a
building in terms of both energy use and fabric integrity.
It indicates the cubic metres of air leakage per square
metre of external area of the building per hour - [m3
m-2 h-1]. It is calculated by creating
a particular pressure difference between the outside and
inside of the building when all intentional openings and
ventilation systems are closed and by then measuring the
amount of air that leaks through the external structure.
pressure difference is 50 Pascal. In Part L Building Regulations
an air permeability of 10 m3/m2/h,
for EST best practice for CSH level 3 an air permeability
of 3 m3/m2/h, for higher CSH levels
an air permeability of 1 m3/m2/h is
accepted as the maximum.
tightness test: Also called Blower-Door-Test.
Measurement of air
changes per hour or air
permeability. During this test areas of air leakage
can be identified by using smoke guns and other means.
tightness: Through statutory air tightness
requirements for the building shell, i.e. in Building Regulations,
Code for Sustainable Homes, DIN5 4108, EnEV3
or SIA6 180, energy losses in the form of
of warm air is prevented. See also air
changes per hour, air
dew point and air
Building Regulations set the standards which have to be
met. The approvals are ways of showing compliance. This
can be done by providing data and evidence of a specific
type for a specific project, so that for instance, a building
company would get approvals contract by contract for non
standard ways of building (including traditional timber
construction with wattle and daub infill, wychert construction,
shallow flexible lime mortared footings etc). The company
has to produced evidence from laboratories, suppliers and
engineers. More easy is to get a generic approval. The basic
ways are BBA, BRE certification (similar to BBA), LANTAC
(which applies to all local authorities in England and Wales)
or the use of European certifications7.
Only BBA and BRE are accepted by NHBC and some other insurance
and mortgage companies.