Installation Guide

Figure 17: Specialty Roof Deck-Strapping Over Insulation
Figure 18: Specialty Roof Deck-Vented Roof
Wood decks form an ideal base over which to
apply Certi-label shakes or shingles, since they
can be attached in the conventional manner.
Rigid insulation raises the issue of how to
fasten Certi-label shakes or shingles. The use
of abnormally long nails driven through the
Certigrade shingles, the insulation and into the
deck below is generally unsatisfactory.
Horizontal strapping will be required to
overcome the fastening difficulties (Figure 17).
When strapping is used, fewer nails penetrate
through the insulation to the deck, and greater
thermal efficiency is achieved by reducing the
number of conductors. In addition, the lengths
of the nails may be chosen to prevent the
points from protruding through the deck
where they may mar the inside face.
If ice-damming is a potential problem or if
reverse condensation is likely to occur, such as
may be encountered in an ice arena, a cold
roof system should be used in conjunction
with horizontal strapping, and ventilation must
be provided at the eaves and at the peak. In
buildings such as ski cabins that may be
subjected to heavy snow loads, it is usually
necessary to fasten wood members (typically
2 x 4 on edge) from ridge to eave on the roof
deck and place the rigid insulation between.
Strapping is then applied across the top of
these members, giving a ventilated air space
and avoiding compression of insulation
(Figure 18). For additional details on cold roof
systems please see page 17.
The need for strapping can often be
completely eliminated by the use of a false
plywood deck, immediately over the
insulation, to which the Certi-label shakes or
shingles are directly fastened (Figure 19).
Exterior-grade sheathing panels are ideal for
this purpose, since they provide a strong,
smooth surface. However, under certain
conditions of slope and loading, there may be
a tendency for the entire roof above the
decking to creep downwards, bending the nail
fastenings and compressing the insulation,
thereby reducing its efficiency. In such cases, it
is often desirable to install the vertical
members as previously described.
Wood Deck
SPECIALTY ROOF DECK DETAILS
Rigid insulation
Wooden deck
Certi-label shakes or shingles
(applied per specification)
Boards
Joist
Nails
If the Certi-label shakes or shingles are nailed
directly through rigid insulation, a number of
problems may be encountered. For instance,
the longer nails have thicker shanks which
tend to split the Certi-label shakes or shingles.
Product movement may cause a reduction in
insulation efficiency. For this reason, the use
of strapping or a false plywood deck is again
recommended.
15
Vertical lumber member
Rigid insulation
Certi-label shakes or shingles
(applied as per specification)
Boards
Wooden deck
Joist
Air space