The roof of a building functions to protect the occupants from snow and rain. It
also functions as the plane where heat tries hardest to escape. In a design
sense, it functions as a symbol of shelter and protection. A roof not only needs
to function, it needs to play a role in completing and enclosing a space. When
the roof is too low, the occupants become stressed. When the roof is very high
(like a church) the occupants become more calm.
Roof Edge Details
Quickly sketch the roof edge to scale by
showing wall, roof slope and overhang. The approximate distances for these
pieces can be obtained by measuring from elevations or building sections
already drawn or started. With this sketch complete, another drawing can be
started with a better idea of how the pieces of a roof edge assembly will come
together. The aesthetic considerations of this detail are also important and
the geometry or ‘proportioning’ of the elements is key to creating a roof edge
that does not look too heavy or ill proportioned.
Figure 1 Roof Edge detail studies
Figure 2 Roof Edge Detail
With a sketch completed, the next drawing
can begin to resolve and indicate portions of the assembly with a little more
clarity. The scale of the drawing is important. The level of detail that will
show on a detail at a scale of 1:5 (3” = 1’-0”) is very different than the
level of detail that will show at a scale of 1:50
(1/4” = 1’-0”). Detail sections such as the one shown above are usually drawn
at a scale of 1:10 or 1:5 in order that the design assemblies can be understood
in a clear and legible fashion on a piece of paper.
Figure 3 Roof Edge Detail being
resolved
If the interior ceiling is flat with an
attic above, the insulation can be placed directly above the horizontal roof
plane.
Figure 4 Roof edge detail being
resolved with quick notations
During the process of sketching a detail,
add notes and questions and comments. These can be helpful to make
determinations about the work and to bring clarity to the reader in terms of
design intent. Placing notes and dimensions on initial sketches also helps to
organize and edit the text for the final drawing. Line weights and hatching
should also be considered at this stage in order to emphasize portions of the
detail.
Figure 5 Roof edge detail with
various pieces proportioned to scale
Draw the pieces to scale and pretend you
are in the act of building the detail. What would be built first? Think about
that question as you draw and the detail will become more meaningful as a
process.
Figure 6 Roof edge detail
Add dimensions were necessary to clearly
describe the intent. If a dimension is not useful to someone putting the detail
together, then don’t show it. There will be some discretion involved in this kind
of decision making process and the author of the drawing should ensure that the
information provided is clear and easily understood.
Figure 7 Roof edge detail
In the detail above, the top of the window
frame (head) is showing too close to steel lintel (beneath the brick). The
bottom of steel lintel might be better aligned with the underside of the rough
opening.
A 3/8” (10 mm) or 1/2” (12 mm) space will
be required between the window frame and adjacent substrate in order to provide
for backer rod and sealant. See figures 2,3,4.
Figure 8 Roof edge detail studies
for roof overhang with cathedral ceiling
If the interior space adjacent to the roof
edge is vaulted or raised (also referred to as cathedral ceiling), the
conditions of the roof edge and roof assembly will change. Without an attic
space to ventilate the roof, it is still necessary to provide venting in the
roof cavity in order to ensure that any trapped moisture is allowed to
evaporate. With cathedral ceilings, this is accomplished by way of adding
‘purlins’ or cross pieces perpendicular to the rafters. The 1/2” exterior
plywood sheathing is then place upon the purlins and the resulting detail is a
roof plane that will satisfy the requirement for cross ventilation.