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Both plywood and OSB are suitable building materials for sheathing the underside of a new or replacement roof. However a choice has to be made between the two so here is our side by side comparison of these two roofing options. Please bare in mind that much of the information here will also be relevant if you are trying to choose between OSB and plywood for other home remodeling projects.
WHAT IS OSB FOR ROOFING?
OSB stands for oriented strand board, and this versatile building material has been around since the 1970s. It’s so popular and cost-effective that it has surpassed plywood as the most commonly used material for sheathing roofs.
How it is made: OSB is manufactured from fast-growing softwoods that are chipped into thin strands of wood. The strands can be mixed with glue and formed into sheets or with treated wax and resin and then heat treated with high pressure to melt the wax/resin to bond the strands.
Panel sizes: You can purchase OSB in a variety of thicknesses, starting at ¼” and going all the way up to 1 ¼”. The most commonly used thickness of OSB for roofing are 1/2″, 5/8” & 3/4″. Code for panel thickness varies based on potential snow loads for the area
One big draw to using OSB is that it comes in a variety of sizes for the panels. Most homeowners use 4’x8’ or 4’x10’ foot panels for roofing. Panels are manufactured as large as 4’x24’, but good luck finding that size – or getting the material to your project site.
Plywood is a traditional building material many seasoned builders prefer.
How it is made: This strong composite material is manufactured from thin “plies” of wood glued together, pressed and then heated to create a panel that is usually 4’x8’. The plies of wood are glued with the woodgrain of each layer crosswise to the layer beneath it. This gives the material greater strength and structural integrity – it keeps its shape.
Panel sizes: Plywood can come in three basic forms or plays: 3-ply, 5-ply, or multi-ply. The most common type of plywood for roofing use is 15/32” or 1/2” 3-ply or 3-layer panels. Roofing plywood is made by using conifers or softer woods, such as birch or poplar.
There aren’t many strong opinions among roofing contractors in the OSB vs plywood debate. Some prefer one or the other, but it often comes down to cost or availability – or the particular wishes of the homeowner who is paying the bill.
The materials install and perform about the same. However, plywood weighs about 9 pounds less per panel, a consideration if you’re hauling each piece up a ladder to a second floor.
Plus for plywood: Contractors have noted that plywood tends to hold nails better than OSB, and that’s important when nailing asphalt shingles to a roof in a high-wind zone.
Plus for OSB: If you can find longer OSB panels, they mean a little faster installation, and fewer seams, so less potential of swelled seams showing through the shingles.
The current retail price for OSB is $37 – $40 for a 1/2” 4’ x 8’ panel. A 1600 square foot roof will require about 50 total sheets, so the price to use OSB for sheathing your roof will cost approximately $1850 – $2,000
The current price for plywood is $40 – $50 for a 1/2” 4’ x 8’ panel. A 1600 square foot roof will require 50 total sheets, so the price to use plywood for sheathing your roof will cost approximately $2000 – $2,500.
OSB cost is roughly 10% to 15% lower than plywood cost. For a 1/2” 4’x8’ panel of OSB, you can expect to pay $37-$40 per sheet. In comparison, the same size of plywood will cost around $40-$50 per panel. These prices are definitely subject to change.
Note on Pricing – 2021/2022 is a tough period in which to be buying building materials! With material shortages, supply chain problems and inflation, lumber costs are quite high. It is common for framing packages on new construction to be 100% higher than for the same packages pre-COVID.
The best maintenance for either material is to keep the roofing above it in good condition!
OSB definitely needs to stay dry, and to that end, roofers sometimes seal its edges to prevent water absorption and swelling that will show through roofing materials.
While a problem for plywood too, moisture doesn’t absorb as quickly nor cause swelling. And plywood dries out faster.
Heat is the bugaboo for plywood. If it has been stored in a hot warehouse, especially a humid one, the plies are prone to delamination, a roofing turn for separating or falling apart. You don’t want plywood on your roof that shows signs of delamination.
There are three critical issues for the lifespan of both OSB and plywood – and for the roofing they support.
First, cover the roof deck quickly once installed – either with roofing material or with tarps if the roofing is delayed or heavy weather is approaching.
Secondly, keep roofing in good condition, and make repairs or replacements to the roof before leaks cause water damage to the roof deck.
Finally, make sure that the attic beneath the roof deck is well-ventilated. Moisture in a humid attic will slowly and surely destroy OSB and plywood from below.
Bottom line? Plywood handles water better. If it gets soaked, it is more likely to retain or return to its normal shape when it dries. OSB won’t. If you are concerned about wet wood, pay the extra cash for plywood.
Oriented strand board is produced more sustainably because fast-growing softwoods like Scotch pine and poplar are used. Plywood construction requires older, larger trees that are slower growing.
If eco-friendly construction is a high priority, choose OSB – but make sure no formaldehyde has been used in its construction.
Roofing contractors in the Pacific Northwest – think rain – and on the East Coast – think storms – tend to use plywood rather than OSB.
In hotter climates, OSB is preferred over plywood since plywood can come apart at the plies in extremely hot weather.
What to do in hot and stormy places like along the Gulf Coast? Both materials are popular, but the most experienced roofers use plywood when available.
Plywood offers better all-around performance. OSB is greener.