Environmental Engineering Reference
In-Depth Information
Table 5.2
Limit thermal transmittance values in some building components, from the Italian
Legislative Decree n. 311/06 (
2006
)
Climatic
zone
Vertical opaque
structures (U
limit
W/m
2
Horizontal and inclined
structures (U
limit
W/m
2
Openable windows
including frames
(U
limit
W/m
2
Glass (Ug
limit
W/m
2
K)
K)
K)
K)
Roof
Floors to unheated
rooms or to the
outside
A
0.62
0.38
0.65
4.6
3.7
B
0.48
0.38
0.49
3
2.7
C
0.40
0.38
0.42
2.6
2.1
D
0.36
0.32
0.36
2.4
1.9
E
0.34
0.30
0.33
2.2
1.7
F
0.33
0.29
0.32
2
1.3
repointing of external walls, of external plasters, of the roof and of the roofs
sealing), the opaque vertical structures bounding the coating must show values
of thermal transmittance (U) in accordance with the Table
5.2
(the values refer
to the current legislative framework in Italy), as a function of the climatic area.
Moreover for all categories of buildings except those for industrial, handicraft
and similar uses, for the same above cited cases, for the horizontal and inclined
opaque structures, openable shutters and similar elements and glasses bounding the
envelope, the values of thermal transmittance (U) reported in the following table
must be respected.
Such rules are mandatory except than for those buildings having social features:
historical buildings, buildings for industrial and tertiary use when the rooms are
heated for needs connected to the productive process or using the waste energy
deriving from the productive process and that would not be used elsewhere, iso-
lated buildings with floor area below 50 m
2
.
The values of U must be respected with thermal bridge solved,
19
when the
design of the coating does not require the correction of thermal bridging, the limit
19
One of the key aspect of making low-energy buildings is the care given to the thermal
insulation. That means using the right materials with the right thickness to provide the right
thermal coating. But this is not enough. The thermal insulation must not have holes where heat
would flow thus defeating the purpose of the thermal insulation. Fighting those thermal bridges is
essential in making excellent quality low-energy consumption buildings. Thermal bridges are
localized regions in a building which display increased thermal losses. They can be caused by
components whose geometry, such as balconies, or whose materials, such as aluminium window
frames without thermal break, have higher thermal conductivity. Thermal bridges are most often
created by the structure of the building, at the junction of walls and floors, at the junction of walls
and roof, in the corners or around windows if they are not properly installed. Interior thermal
insulation is well known to create many thermal bridges that could be completely avoided for
example by doing exterior thermal insulation (
http://beodom.com/en/education/entries/
