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General Panel

Perma R Products

Roof Panel specification

Panels manufactured by General Panel should be installed as follows:

General specification- The primary concerns in using panels is adequate fastening to maintain a stabile roof deck and minimize uplift, and adequate sealing between panels to reduce infiltration/exfiltration and moisture migration.

Nailbase panels- Nailbase panels are to be used only over a fully structural deck (typically T&G pine, spruce or fir or metal decking).

Panel fasteners should be used at 12" on center at all crossing support points (up to one fastener per two square feet for all "field" (non-perimeter) panels and all perimeter (including ridge, rake and eave) panels shall be fastened at 6" to 12" on center at all perimeter fastening points.

Panels should be gapped sufficiently to allow osb expansion (minimum 1/8" per 8' or less) with the gap between panels sealed (not necessary to fill) with low expanding urethane foam. If splines are used, the keyway should be sealed.  If no splines are used, the gap between panels should be sealed.  Roofing felt or synthetic underlayment is necessary prior to roofing with metal or shingles. It is recommended that roofing underlayment  be used over a wood structural deck prior to installation of the nailbase panels. No additional moisture barrier is recommended at either surface.

Shingle venting is not necessary or recommended due to condensation buildup. No attic ventilation is required since the attic becomes conditioned space. Panels are warranted to provide an adequate roofing deck for shingles or metal as follows: over two bye (nominal) T&G up to 8' o.c., over one bye (nominal) T&G up to 4' .o.c. This warranty assumes combined loads (live and dead) not to exceed 40#/sq ft. with a roof pitch of 6/12 or greater.

SIP- Fully structural panels (osb/osb, osb/Arauco, and osb/osb/gyp) are designed to span full length (in most circumstances) which limits the fastening opportunities. 6" on center is recommended at the panel ends and all perimeter opportunities. If any cross beams (rafters or purlins) present the opportunity to fasten, panel fasteners should be used at 12" on center.

For spans up to 8' on center osb splines may be used to align and secure the panels. These splines should be glued and screwed (12" on center).  A keyway is used to foam the gap between panels to seal them from moisture incursion and air infiltration/exfiltration. Foam may be used prior to installation (hard) or subsequent to panel installation through drill holes through the spline every 12". If foamed after installation start at the bottom and work upwards to allow gravity to help fill the gap.

For spans exceeding 8', dimensional lumber splines should be used to stiffen the panel. In some cases double two-byes may be necessary to limit deflection. All wood to wood contact points should be glued. Dimension lumber splines should be attached using adequate fasteners (nails or screws) at 12" on center (alternating). Low expanding foam is recommended- avoid over foaming. As with nailbase panels ventilation for shingles, metal or attic are not recommended. SIPs are warranted to provide adequate structure per our span tables as adjusted for load rotation.

OSB/GYP- OSB/Gyp panels may be used (subject to higher snow or wind loads) for spans of up to 4' on center ( at combined roof load of 40#/sqft) and may be used along supports or across them. Fasteners should be used at 6" on center and top osb splines should be used. Foam should be used in the same manner as in the SIP panels using osb splines. Dimensional lumber splines are not recommended because they tend to twist over time and create crackes at seams.

Ventilation- In general, ventilation is detrimental to closed panel systems. Ventilation within the panel is never a good idea.

We do not manufacture ventilated panels. Ventilation under the panel is in conflict with energy efficiency guidelines and is unnecessary. Ventilation above the panel to ventilate the roofing material is not recommended, but may be necessary to maintain shingle warranties. Our research has indicated that most roof/panel moisture problems occur in ventilated roofs due to condensation in the evenings.

Independent research on shingle venting suggests that ventilation is unlikely to improve shingle life. The same research indicates that shingle color and mass play a much more important role in shingle life than ventilation does. Some manufacturers do not warrant over a ventilated deck. Given the unlikely advantage and the likely disadvantage of shingle ventilation, we do not recommend shingle ventilation. If the ventilation is improperly installed it may void our warranty. Metal roof ventilation is also problematic, but we recommend that you follow your metal roof manufacturer recommendations in all regards.

Roof ridge tapes- Various companies are developing adhesive roofing tapes for use on panel roof seams to seal moisture leaks. When testing is complete it is likely that we will recommend the use of these tapes, but until testing is complete on the long range use of the tapes, we discourage their use.  Other panel companies have reported excellent results using roof ice dam shield "peel and stick" products and window wrap tape.