Roof Sheathing

By the Orillia Home Inspector

Certified Building Code Official


Roof Sheathing


Roof sheathing is a lot more than just flat sheets onto which shingles are attached. The roof's sheathing helps to keep the roof trusses or rafters properly spaced, and is the strength that holds the entire roof together. As such, roof sheathing has to be structurally sound and properly spaced to allow for expansion and contraction due to seasonal weather fluctuations. While carpenters have attached sheathing to roof trusses for years with a hammer and nails, a framing nailer makes the job go much faster.

Plywood, OSB board an Common Boards are the most common types of sheathing used on most home inspected in the Orillia area.Traditional plywood is the most expensive sheathing material for roof construction. Oriented strand board (OSB) has replaced plywood use in the United States for the majority of roof applications. It is more affordable and much more uniform, though it must be protected from water and moisture. 

An important part of the home inspection is to ensure that H clips are used on 24 inch centers when sheathing less than 5/8 inches is used. H clips are installed at each horizonal joint in each rafter bay. Because H-clips are not load rated, code approval is not required. Based on gravity loading requirements, building codes often require that H-clips or other means such as tongue-and-groove edges or lumber blocking be used to support panel edges. H-clips are an alternative to solid lumber blocking and tongue-and-groove panel edges

Always check with your local building department before installing any product to ensure that it meets the minimum code requirement and is properly installed.




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Inspection Definitions

1. Chimney - vent flue gases from fireplaces or heating equipment.
2.  Chimney flue top or chimney cap (if present)
3.  Chimney crown or chimney top seal
4.  Chimney Flashing seals the roof penetration to avoid leaks into the structure.
5. Masonry fireplace
6. Fireplace ash pit door. 
7.  Fireplace ash pit cleanout door.
8.  Fireplace mantel - horizontal trim attached to wall above fireplace opening.
9. Hearth - flat surface in front of the fireplace, protects flooring from fire.
10. Ridge cap or ridge vent (if present)
11. Ridge board
12. Cripple rafters or Jack rafters (between chimney and house eaves - rafters that do not extend the full distance between house eaves and the roof ridge board)
13. Rafter blocking or cross bridging, also found on floor joists and in some wall framing
14. Soffit or lookout or house eaves. The soffit is the enclosed portion of the roof that overhangs the house walls at the roof lower edges.
15. Roof sheathing or roof decking.
16. Roof shingles (asphalt shingles, clay tiles, slates, wood shingles, or shakes, similar materials)
17. Drip edge (used at lower roof edges or eaves). The drip edge is special metal flashing intended to divert water off of the roof lower edges into the roof gutter system. Drip edges should spill into the gutter, not behind it. 
18. Gutter (attached over or to fascia board) to collect roof drainage and prevent it from spilling down and along the building walls (leaks) and basement (wet basements
19. Downspouts (conduct roof drainage from the gutters to a destination away from the building or into a storm drain system).
20.  Downspout leader or downspout extension (hard to see, behind that front right entry porch column)
21. Gable end and gable-end attic vent. The gable end the house wall on a conventional simple gable roof such as shown in our sketch is the triangular end wall
22. Gable end fascia. The gable end fascia is the trim board attached to the roof edges, extending from ridge to lower roof edge, and where a rake overhang is present, covering the outermost rake rafter or barge rafter.
23. Gable end vent or attic vent at gable end