External Walls
The greatest
proportion of heat loss from a typical house is through the walls,
mainly because of their large area. Installing external wall
insulation slows down the rate of heat loss thereby giving
immediate savings on fuel bills.
An efficient building envelope is an obligatory step towards the
higher code ratings of the Code for Sustainable Homes in
conjunction with National Building Regulations. This is now the key
benchmark by which the thermal performance of external walls will
be assessed and is likely to have a major influence on the
evolution of external wall constructions. Partial cavity fill and
insulated dry linings, for example are likely to become less
popular as thermal insulation values rise.
Full fill insulation and timber frame construction are able to
achieve improved U-values at the expense of wider cavities and
deeper timber studs. There is likely to be greater innovation in
other forms of construction, especially where rainscreen cladding
is used to protect the insulation layer.
The tightening of thermal regulations will also place a greater
emphasis on avoiding thermal bridging and ensuring an airtight
external envelope. As a result, detailing at junctions is likely to
become more complex and sophisticated. In the following section we
explore a number of innovative constructions which maximise thermal
and acoustic performance while ensuring compliance with the
increasingly stringent regulations.
New build
The 2006 edition of Approved Document L1A in England and Wales and
Technical Bulletins F1 in Northern Ireland and the 2007 revised
edition of Section 6 of the Technical Handbook in Scotland no
longer specify Elemental U-values that will automatically show
compliance. All new buildings must use the ‘whole building’
approach to show compliance. However, the table below shows typical
U-values that would need to be achieved to comply with the
Regulations.
The whole building calculation methods used to show compliance
with Building Regulations require the performance of the building
element to be no worse than the values indicated in Table 11.
However, this will have to be compensated for by improved
performance in other building elements or building services.
All UK Regulations include a maximum area weighted average
U-value for all walls in the building and a maximum permissible
U-value that cannot be exceeded for the avoidance of technical
risk. These values are laid out in Table 10.
|
Table 10:Typical U-values standards for
external walls
|
|
Maximum U-value
(W/m2K)
|
| England &
Wales |
0.27 |
| Northern
Ireland |
0.27 |
| Scotland |
0.25 |
| Republic
of Ireland |
0.27 |
|
Table 11:Limiting U-values standards for
walls
|
|
Area Weighted
average U-value
|
Limiting U-Value
|
| England &
Wales |
0.35 |
0.70 |
| Northern
Ireland |
0.30 |
0.70 |
| Scotland |
0.35 |
0.70 |
| Republic
of Ireland |
0.37 |
n/a |
|
a) Masonry Cavity Walls
Masonry cavity walls have been popular in the UK since the
1920’s. This method of external wall construction is simple and
traditional, whilst allowing great scope for flexibility in design
and later adaptation or extension.
The adaptability of cavity walls has led to a significant
evolution from their beginnings as two skins of masonry and an
empty cavity, a form of construction offering minimal thermal
performance. In contrast, the full and part fill systems used today
provide exceptional thermal performance.
This section includes solutions for all three types of cavity
wall insulation shown below. The introduction of higher performance
products, such as Crown DriTherm Cavity Slab 32, means that
U-values can be improved by approximately 10% compared to standard
Crown DriTherm Cavity Slab, with no increase in cavity width.
b) Pitched Roofs - Rafter Level Insulation
Timber frame construction is the developed world’s most widely
used residential building method. It fulfils a 21st century agenda,
offering a method of construction which is engineered, energy
efficient, sustainable and quality assured. With a huge supply of
plantation timber readily available in the UK and Ireland this form
of construction is sustainable and environmentally friendly.
External wall insulation solutions:
