Installation Guide

13
Air flow
Insulation
Figure 15c: Shed Roof
Figures 15a-15c: Ventilation Details
Certi-label shakes or shingles
(applied per specification)
Roof rafter
Air flow
1-2" diameter screened
vents each roof
rafter space
Figure 15a: Gable Roof With Attic
Figure 15b: Cathedral Ceiling With Partial Attic
The importance of good attic ventilation beneath
the roof cannot be overemphasized. Such
movement of air will prevent or inhibit
condensation of moisture on the undersurface of
the Certi-label shakes or shingles, or on the roof
decks. Vents should be provided at the soffits
(eaves) as well as at gable ends (screened to
prevent ingress of insects), on roof by using attic
roof ventilation or preferably the ridge lines with
cross-ventilation desirable. A rule of thumb for
adequate ventilation is that the ratio of total net
free ventilation area to the area of the attic should
be not less than 1:150, with compensation made
for screens over vent apertures. In the case of a
balanced system a 1 square foot per 300 square
feet of floor area may be adequate ventilation.
Check with your local building department. Attic
fans may be beneficial by supplying additional
movement of air in attic spaces. Several roof
ventilation construction techniques are shown in
Figures 15a-15c.
Any modification to the vapor barrier system or
addition of a vapor barrier system should only be
done after consulting with your local building
official or a building envelope specialist. In some
areas, building envelope specialists are regulated
by government. Please check with local building
officials to see if there are professional
requirements in your area.
Ventilation Guidelines
VENTILATION DETAILS
Continuous
screened vent
Louvered
vent at each
end of attic
Insulation
Air flow
Roof rafter or truss
Certi-label shakes or shingles
(applied per specification)
Air flow
Certi-label shakes or shingles
(applied per specification)
Air flow
Roof rafter
Louvered vent
at each end
of attic
Insulation
Continuous
screened vent
Ridge ventilation
product
Ridge ventilation product