Civil Engineering Reference
In-Depth Information
5.3.2 Roofs
Except for Zams-Schönwies and some parts of Schwanensdtadt, most roofs of the
cases are new structures and are also now highly insulated. Added external
insulated layers provide effective means of eliminating thermal bridges, and for all
four schools, the mean U-value of the walls and the roof is = 0.1 W/(m
2
.K); the
range for this value was between 0.08 and 0.17 W/(m
2
.K).
5.3.3 Ground
Insulation under the ground of existing buildings is a complicated task and a
challenge to confront while achieving the passive house standard. Most existing
buildings either do not have any insulation under the ground, or have some cen-
timetres of EPS. Walls under the ground can sometimes get accessed from outside,
which is especially opportune if drainage work is done, and allows for installation
of additional insulation. This was not the case for the schools studied. For Sch-
wanenstadt, a unique solution was provided for the ground slab allowing a mean
U-value towards the ground of 0.16 W/(m
2
.K).
5.3.4 Thermal Bridges
For Schwanenstadt, an interesting analysis shows the comparison between two
thermal bridge mitigation approaches (Lang et al.
2006
). An initially proposed
approach could have kept the same placement of windows, on the inner side of the
columns, and packed the columns with insulation to reduce the thermal bridge.
However, such a cumbersome and costly job would not have made achievement of
the same thermal resistance possible compared with the prefabricated façade
elements designed to be placed on the outside of the columns. The thermal bridge
is limited to the outside of the column and insulation is placed in a continuous
plan, limiting the angles that imply complicated handwork to avoid thermal
bridges. The continuous plan also simplifies the air tightness and cladding work.
This improved approach brings the walls' mean U-Value from 0.37 to 0.08
W/(m
2
.K) (Lang et al.
2006
). A similar approach was taken with the other schools,
with a complete redesign of the façades (Fig.
12
).
Shown above is the first proposal for thermal bridge mitigation. Shown below is
the final strategy which provides a much better insulation and a straightforward
construction. Drawing by Xavier Dequaire from an original by LANG consulting,
Vienna.
