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Structural Plywood Roof: Sheathing, Span, Thickness, Fastener
A structural plywood roof carries the shingle and the snow load through the seasons, and the sheet that the mill glues and stamps with the span rating gives the deck the stiffness that the rafter needs. The panel that nails to the rafter braces the frame and carries the weight that the weather sends. The right roof panel gives the house its cover and the finish its base.
Structural Plywood Roof: the Deck That Carries the Shingle
The roof deck that the plywood forms carries the shingle and the snow through the seasons, and the sheet that spans the rafter carries the load that the weather delivers. The builder who spaces the rafter on the span rating reaches the stiff deck that the shingle trusts. The roof deck gives the house its cover and the interior its line.
The glue that the mill uses on the structural panel also resists the moisture that the roof sends, because the exterior bond that holds the plies together resists the damp that the open build delivers. The builder who reaches for the exterior panel reaches the sheet that survives the site. The waterproof glue gives the roof its service.
The core that stays void-free and the face that the mill grades also shape the roof panel, because the sheet that holds the fastener and the load carries the weight through the span.
Sheathing the Roof
The sheathing that the builder nails to the rafter covers the roof in one pass, and the four-by-eight sheet that carries the strength and the flatness saves the time that the smaller panels would take. The builder who lays the sheet on the rafter and drives the nail reaches the deck that the shingle trusts. The sheathed roof gives the house its cover.
The clipped corner that the maker cuts on the groove panel lets the sheets seat without the interference at the corner, and the builder who starts the run square reaches the deck that stays true. The clipped sheet gives the roof the clean joint that the trim hides.
The gable and the overhang that the builder covers with the sheet also reach the base that the siding and the trim trust, and the covered roof gives the house its exterior.
The Ventilation and the Eave
The ventilation that the builder runs through the eave keeps the roof dry and the deck sound, because the air that moves under the panel carries the moisture that the shingle sends. The builder who leaves the vent gap at the eave reaches the roof that the frame trusts. The ventilated deck gives the roof the service that the weather asks for.
The soffit that the builder covers with the plywood panel also gives the eave the flat base that the trim needs, and the covered soffit gives the roof its line.
Span Rating and the Rafter Spacing
The span rating that the mill prints on the panel sets the rafter spacing that the sheet allows, so the builder who reads the number spaces the frame to the panel. The sheet that carries the twenty-four over sixteen rating serves the roof on the twenty-four inch center and the floor on the sixteen. The builder who matches the spacing to the rating meets the code.
The thickness that pairs with the rating also matters, because the thin panel that carries the rating at the short span serves the roof while the thick panel serves the floor. The builder who pairs the thickness and the span reaches the deck that stays flat.
The deflection that the load sends through the deck also follows the thickness, and the builder who checks the deflection limit on the span table picks the sheet that keeps the roof quiet.
The Ice and Water Shield
The ice and the water shield that the builder lays over the deck before the shingle carries the moisture that the melt sends through the winter, and the membrane that the builder rolls over the plywood keeps the water out of the core. The builder who laps the shield at the eave reaches the roof that the ice dam cannot damage. The shielded deck gives the roof the service that the freeze asks for.
The drip edge that the builder installs at the eave also carries the water off the deck, because the metal that the builder bends over the edge sheds the melt before it reaches the plywood. The builder who runs the drip edge under the shield reaches the eave that stays dry. The drip edge gives the roof the line that the shingle needs.
The flashing that the builder installs at the valley and the chimney also protects the deck, because the metal that covers the joint carries the water past the seam. The builder who lapped the flashing reaches the roof that the storm tests.
Thickness and the Snow Load
The snow load that the roof carries through the winter asks for the thickness that the span table lists, and the builder who matches the panel to the snow load reaches the deck that stays flat. The thicker sheet that carries more plies spreads the load across the rafter without the sag. The right thickness gives the roof the stiffness that the winter demands.
The ice and the water that sit on the deck also test the panel, because the sheet that carries the span resists the load that the freeze sends. The builder who matches the span to the snow load reaches the roof that stays true.
The plywood that the builder uses on the roof also resists the moisture that the melt sends, and the sealed edge that the builder coats keeps the core dry through the season.
Installation and the Fastener
The nail and the screw that the builder drives follow the schedule that the engineer sets, because the panel that carries the shear needs the fastener spacing that the plan lists. The builder who follows the edge and the field spacing reaches the roof that the storm tests. The fastened deck gives the frame its strength.
The gap that the builder leaves between the panels lets the sheet move with the season, and the builder who leaves the eighth-inch gap reaches the deck that stays flat. The gapped panel gives the shingle the seam that the trim hides.
The glue that the builder adds to the joint strengthens the roof, because the panel that bonds to the rafter shares the load with the nail. The builder who spreads the adhesive and screws the sheet reaches the deck that stays quiet.
The Roof and the Weather
The weather that the roof carries through the seasons tests the panel, and the builder who uses the exterior glue and the sealed edge reaches the deck that survives the rain and the sun. The panel that carries the waterproof bond resists the moisture that the open build delivers, and the sealed edge that the builder coats keeps the core dry through the season. The weathered deck gives the house its cover across the years.
The wind that the storm sends through the roof also tests the fastener, because the panel that carries the nail on the schedule resists the uplift that the gust delivers. The builder who follows the nailing pattern reaches the roof that the storm tests.
The roof that the builder covers with the structural plywood panel gives the house the strength and the stiffness that the weather demands, and the rated sheet that the builder orders gives the frame the proof that the code reads from the first rafter to the final shingle.
The plywood roof panel gives the house the cover and the budget the value across the seasons.
The rated deck that carries the shingle and the snow gives the roof the strength that the frame and the weather demand.
Frequently Asked Questions
Builders ask these questions about the plywood roof.
What plywood is used for a roof deck?
The CDX or the exterior-rated sheathing on the span rating serves the roof, and the thickness follows the rafter spacing.
What thickness for a plywood roof?
The half-inch or the five-eighths serves the roof on the rated spacing, and the span table sets the limit.
Can I use plywood for a flat roof?
Yes with the exterior glue and the sealed edge, and the builder covers the panel with the membrane and the trim.
How do I prevent plywood roof sag?
Match the thickness to the span, space the rafter to the rating, and seal the edge to keep the core dry.
For the panel that carries the roof and the deck, compare the stock at HYY, which runs Commercial Plywood for the frame and Film Faced Plywood for the formwork.