Roofs
The roof comprises
a large percentage of the external shell of most dwellings and is a
key interface between interior and exterior environments. It must
not only be weather-tight and waterproof, but also adequately
insulated to minimise heat loss. Without loft insulation as much as
15% of a house’s heating costs could be lost through the roof*.
Loft insulation acts as a blanket, trapping heat rising from the
house below.
*Source: Energy Saving
Trust
New build pitched roofs
Insulation for new build pitched roofs
can be placed either in the plane of the rafters, creating a warm
roof space, or between the joists at ceiling level of the upper
storey creating a cold attic or loft.
The insulation of a pitched roof at
ceiling level is a relatively straightforward matter with
insulation being placed between and over the joists. The insulation
thickness is largely unrestricted by construction considerations
and therefore low cost lightweight insulation solutions that
achieve very low U-values can be adopted. It is necessary to
carefully detail the installation of the insulation at the eaves
where ventilation may be necessary.
When insulation is placed in the plane of the
rafters, creating a warm roof space the installation of the
insulation provides greater challenges. However creating a warm
roof space can provide attractive living spaces with sloping
ceilings and rooflights, enhancing the value and desirability of
the dwelling without significantly altering the building envelope.
This can make the dwelling more shape efficient in terms of the
ratio of total internal floor area to exposed surface heat loss
area.
With the whole building methods that
must be used to show compliance with building regulations it may
therefore not be necessary to achieve the same low U-values in a
roof with insulation in the plane of the rafters as it is with
ceiling level insulation.
Table 4: Typical U-values for new
build pitched roofs
| |
Ceiling Level
(W/m2K) |
Rafter Level
(W/m2K) |
| England & Wales |
0.13 |
0.20 |
| Scotland |
0.13 |
0.16 |
| Northern Ireland |
0.13 |
0.20 |
| Republic of Ireland |
0.16 |
0.20 |
a) Pitched Roofs - Ceiling Level Insulation
Insulation placed at horizontal ceiling level creates a cold
roof space. This is the lowest cost option for insulating a roof
and uses low cost readily available glass mineral wool quilt
insulation. Very high levels of thermal insulation can be achieved
because there is virtually no restriction on the thickness of
insulation that can be installed.
b) Pitched Roofs - Rafter Level Insulation
Recent changes to planning policies requiring higher density
residential developments have led to dramatic growth in the
utilisation of the roof space as a living area. When this is
coupled with the improved thermal efficiency required by the latest
Building Regulations, the specification of insulation for this
application is becoming a matter of increased complexity and
importance.
These types of construction require the installation of
insulation at rafter level, following the pitch of the roof. Knauf
insulation products provide a number of insulation options for this
type of construction, maximising both space and thermal
efficiency.
Roof insulation solutions:
