Roofing plywood allows to settle roof effectively and cost-effectively. Plywood sheets are differentiated according to size, thickness, and performance characteristics. To know how many sheets for the roof sheathing is required it`s enough to make simple calculations. An instance of similar calculations is given below. We are also going to consider, why laminated plywood is a better roofing material than the OSB.

Advantages of the roofing plywood

Roofing material, whether it is a tile or a profiled flooring it is attached to the so-called sheathing. One of the main requirements for the material is to be moisture-proof. Giving the fact that the rain can start even during the construction works. An ideal material for the sheathing is water-proof laminated plywood. It`s made of veneer layers which are covered with the laminate. Under the moisture impact veneer is extended equally without causing deformations on the discrete parts. Oriented strand board, as opposed, doesn`t have significant moisture proofness and swells at the edges resulting in emerge of the cracks in the middle of the plate.


Types of the plywood

A plywood sheet may have diverse properties. There are following types of plywood:

  • A type: it`s the best laminated veneer, without any disadvantages, but the most expensive one at the same time. It can be used like a sheathing material. Although there are cheaper options.
  • C type: quality of this veneer plate is still high enough but some defects can be found on it`s surface. They still don`t impede the attachment of a tile or a profiled flooring to this material.
  • D type: Surface of the laminated veneer of this type of plywood is further and further from the ideal, but still appropriate for settling the roof.
  • CDX type: is a speсial type of plywood. "С" characterizes front side of the sheet, "D" - the back one, "X" indicates glue, which is used to attach layers to the veneer. This type is the most popular one because it`s more durable and moisture-proof, these characteristics stand as a key factor to make roof reliable. Half inch CDX plywood is used with 24 spacing inch rafter.
  • Zip wood type: it`s durable and long-lived, moisture-proof material. Despite high moisture proofness it keeps drying properly. Thus, there is no necessity to use roofing felt. In case one needs to protect the house from the adverse weather conditions this option is most suitable.

Zip wood is used as a roofing covering what significantly simplifies laying process. It`s enough to lay plywood sheets on the specially designated for them place and conduct seam sealing to finish works. And expenses on its installation significantly reduce.

  • FRT type: Sometimes construction standards prescribe to use fire-resistant plywood at the villa communities.

Thickness and size of roofing plywood

Plywood sheets of at least 3/8 are required for roof sheathing. But this is not the standard but the minimum thickness, which can only withstand overload if the rafters are set 16 inches apart at most and the roof is made from light weighted material. The boards of this thickness are not recommended to be used for a flat roof. It's preferable to use higher thickness. The sheets that are one-half inch or 5/8 inch thick meant there.

Internet stores offer plywood sheets of a thickness from 5/16 inch to ¾ inch. The following factors are to be considered when choosing a necessary thickness: · The design of the roof; · The spacing of the rafter; · The expected load;

A half inch thickness remains to be the gold standard, but for those who want to get reinsured it is recommended to choose a thickness of 5/8 inch or even ¾ inch, though in most cases such choice is not reasonable.

As far as the size is concerned, the standard sheet length is 8 feet, the width is 4 feet.

How many plywood sheets do you need to sheath your roof? This important question needs an accurate answer for extra sheets will become a waste of money and the lack of them will turn into a waste of time. The latter means you'll have to purchase the missing material.

So, how many square feet are there in a standard plywood sheet of 4x8? To get the answer, you just need to multiply the length by the width. Thus, a sheet of laminated veneer is 32 square feet. Knowing this number, you can proceed to calculations. To do that, measure your roof using a tape measure, get the width and length of every slope. If you have a normal gable roof, the task gets simpler as all that it takes is to measure one side of the roof.

Both sides are usually identical in dimensions.

By multiplying the width and length of a slope, we get the square footage of that slope. If you have a gable roof, multiply the resulting figures by 2. The total square footage of your roof is determined in this way.

Example: your roof has a total of 1,500 square feet. Divide that by 32 square feets (the square footage of each 4×8 plywood sheet). You'll get the number of sheets that you need for sheathing. In this case, you need 47 sheets. It is recommended to order a few sheets more than that. They will be useful in case there are mistakes and flaws.

If you have a gable roof, use the following formula:

Measure the floor area covered by the roof. For instance, the ground floor area is 10 by 20 feet and the wing floor area is 10 by 15 feet. Multiply the figures and add the resulting figures: 600 + 150 = 750 sq.feets. Add 20% for roof slope, that is 150 sq. feets. You''ll get 900 sq. feets, then divide that by 32. You need to buy 29 sheets for roof sheathing. Just in case don't forget to add two sheets to that amount.

Plywood or OSB

Which plate is better, OSB or plywood? This question has long been a subject for intense debates. From the point of durability and longevity both materials are considered as of the same value. Everyone of them has its pros and cons.

Professional associations recommend to use both materials without making emphasize on their differences. Nevertheless, most builders are tend to use plywood.  OSB plate swells from the moisture and doesn`t restore even after drying.

But it also has pros. It's surface is less slippery and it`s edges have markings of 16 and 24 inches what simplifies attachment. In addition OSB is cheaper what makes this material cost-effective and the construction process more practicable. There are a lot of OSB adherents, first and foremost because of its affordability. But true professionals who prefer quality to cheapness choose plywood.