Literature Review on Building Envelope, Heating and ... - Beeshive.org

this case, a means of venting the roof space that minimizes snow infiltration is
recommended.
Stepped roofs and offsets are to be avoided to prevent the accumulation of snow
drifting that may cause excessive roof loading and wetting of walls and roof joints. If
two roof levels are required, a sloping roof section should connect them. Parapet
walls are to be avoided, because a parapet adds to snow drifting accumulation on the
roof.
A ventilated roof system performs satisfactorily in locations below the tree line.
Venting roof assemblies is problematic for locations above the tree line. It is difficult
to avoid snow infiltration through vents. Wetting of the insulation and roof assembly
occurs when conditions allow snow to melt. Drains should be used to drain melted
snow.
Minimum eave projections are 100 to 200 mm (4 to 8 in.) in regions above the tree
line, and 200 to 600 mm (8 to 24 in.) in regions below the tree line. Eavestroughs are
to be avoided. Ice buildup makes them ineffective and causes damage during spring
melt.
Skylights are not recommended unless shown to provide significant benefits and are
provided with a means to control condensation. Clerestory windows are alternatives
to skylights, but design should ensure they are clear of snow accumulation.
• Doors and windows: Door issues include heat loss, an RSI usually less than 1.8 (R
less than 10.2) and air leakage at door edges. Here, the weather seal loses its
flexibility in extreme cold, and doors are difficult to close properly due to the lack of
alignment of the door and frame as a result of higher than normal use or structural
strain on the walls caused by impact damage or foundation movement.
Doors should be insulated metal, with a minimum RSI-1.3 (R-7.4). A vestibule
between outer and inner doors is more practical than a storm door and saves energy.
Vestibules also help keep warm interior air indoors. A storm door is considered
impractical, because leaking warm air from the inner door could cause frost on the
colder storm door, affecting the weather seal. Residential grade storm doors also wear
out quickly from heavy use.
Window recommendations include double or triple glazed sealed units with low-e
coating. Insulated frame PVC, vinyl, or fibre reinforced plastic frames are preferred,
because they are easy to maintain and no potential for damage by condensation. Metal
windows with thermal break frames or wood windows are acceptable. The interior of
the window frame should be on the warm side of the insulation. Wide interior
window ledges should be avoided, because they reduce airflow over the glass, which
could allow condensation or frost buildup on the window. Also, the window frame
should straddle the plane of the air/vapour barrier.
PERD-079: Task 2 - <strong>Literature</strong> <strong>Review</strong> 31