What thickness plywood should I use for shed roof?
Roof and Floor. If you want the shed to be waterproof, its roof must be constructed just like any other roof -- a plywood decking covered with shingles or with composite or metal roofing. Most builders use 15/32 CDX for the roof; it is an exterior-grade plywood with a thickness just under 1/2 inch.
Most Common Thickness. For rafters spaced 20 or more inches apart, 1/2- or 5/8-inch plywood is recommended. The most common rafter spacing is 24 inches, and 5/8-inch plywood is recommended for that. It will support roof loads for most situations and is the standard for most roof applications.
- Use these two tables for roof rafters with a slope of 3" in 12" or less.
Nominal Size Spacing (o.c.) Species and Grade of Lumber ( 20# Live Load - No Finished Ceiling) 2" x 8" 16 19-6 24 16-8 2" x 10" 12 27-6 16 24-8
- the subfloors need to be thicker. For joist spacing of more than 16 inches up to 19.2 inches on center, the minimum thickness for both plywood and OSB is 3/4 inch. For joists spaced more than 19.2 inches on center, the minimum thickness for plywood is 7/8 inch and for OSB, 1 inch.
- The letter "X" in CDX refers to the type of glue used in the factory to bond the plywood veneers. Some mistakenly think the "X" stands for "exterior"—which is not true, exactly. The letter stands for exposure, which means the plywood is tough enough to withstand a little moisture—but for only a short time.
Standard Thicknesses. Before lumber companies began selling OSB, the standard choice for sheathing a roof with a 24-inch rafter spacing was 1/2-inch CDX plywood - the letters CDX indicate that it is construction-grade material intended for exterior applications.
- Particle board – also known as particleboard, low-density fibreboard (LDF), and chipboard – is an engineered wood product manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded.
- MDF consists of thin panels made from wood fiber, resin and wax. When it comes to engineered wood, MDF is often considered a level above plywood. It is denser, stronger and more durable. But as we mentioned in the beginning both solid wood and MDF have their good and bad points.
- Invented in the United States, it is a compound of wood dust and scrap bonded together by a resin containing formaldehyde - a recognised carcinogen. When MDF is cut, sanded, shaped or machined in any way, it releases clouds of dust particles coated with formaldehyde.
Wood fiber is used more efficiently in osb. Osb is stronger than plywood in shear. Shear values, through its thickness, are about 2 times greater than plywood.This is one of the reasons osb is used for webs of wooden I-joists. However, nail-holding ability controls performance in shear wall applications.
- A simple trip to the average lumberyard or home supply store is all it takes to realize that OSB is almost always cheaper than plywood. “For a typical 2,400 square foot home, OSB will save about $700 if used as the subfloor, sheathing, and roof decking instead of plywood."
- SMARTPLY OSB3 is a strong, versatile board suitable for structural use in humid conditions (service Class 1 and 2), ideal for applications as diverse as roofing, flooring, hoarding and wall sheathing etc..
- When a roofless, partially built structure takes on water, the plywood or OSB used for floor decking can absorb water, swell, delaminate, and require sanding or replacement before finish flooring can be installed.
Updated: 21st November 2019