Meanwhile, 3/4 plywood for attic floor is the recommended dimension regardless of the joist centre measurements and weight requirements. While 1/2 plywood is cheap, the support of 3/4 plywood floors gives long-term cost savings by preventing premature damage.
But if you plan to convert the attic space into a full bedroom or child's play area, you need thicker ¾-inch plywood sheets to withstand the weight of large furniture items and people.
The U-value is a measure of how quickly heat will travel through the floor. To achieve this standard, you will normally need at least 70mm of high-performance foam insulation, or 150mm of mineral wool, but this will vary depending on floor type, shape and size.
Thick plywood sheets are durable, but they're also heavy, and it may be safer to use 1/2-inch plywood -- which is actually 15/32 inch thick -- to avoid loading the ceiling joists with extra weight. Two considerations will help you choose between the only two viable options for your attic: 3/4- and 1/2-inch plywood.
While 1/2 inch plywood can be used for flooring, it's generally recommended to use thicker plywood, such as 3/4 inch, for better structural support and durability. Thicker plywood reduces the risk of sagging or flexing, providing a more stable and long-lasting floor.
Subfloor and Structural Plywood
For traditional plywood flooring installations, where the plywood is directly attached to the subfloor, the recommended thickness typically ranges from 5/8-inch (15mm) to 3/4-inch (19mm) plywood.
Vinyl: Vinyl flooring installations can often utilize a thinner subfloor, especially when installing luxury vinyl tiles or planks that aren't as susceptible to bending or breaking. A minimum thickness of 1/2 inch is generally adequate, but the subfloor must be very smooth and level.
Softwood plywood is a good option for light storage, while structural or hardwood plywood is ideal for attics that will bear heavy loads or serve as living spaces. For attics prone to moisture, marine plywood is the top choice due to its exceptional water resistance, ensuring long-term durability in damp environments.
For that reason, building codes in more humid locations will often require them, in which case you might not have much say about whether to install one or not. In drier climates, however, attic vapor barriers can be more of an optional add-on than they would be elsewhere.
Plywood is actually engineered to support weight and provide strength. Weight of 1 2 plywood can hold up to 35 pounds per square foot. 1/2-inch plywood can hold up to 35 pounds per square foot.
If you live in the Southern part of the U.S., the recommended insulation level is a minimum of R-38 or about 13-14 inches of insulation. If you live in the Northern part of the U.S., the recommended insulation level is a minimum of R-49 or about 16-18 inches of insulation.
It provides an additional layer of insulation by trapping air and helps to prevent moisture buildup by allowing for ventilation. So, it's always recommended to leave an air gap when installing insulation, whether it's in your walls, roof, or floors.
If looking to use mineral wool batts between joists in a pitched roof, you will need to install around 200mm of rock wool or fibreglass to reach the desired U-value. If opting for sprayed foam insulation in your roof, a recommended depth of 120mm will help your building adhere to the recommended U-value of 0.2 W/m2k.
Both plywood and OSB are effective choices for your subfloor needs, but OSB may be a better option for a garage than plywood. Plywood is a better option for projects that require a lot of cutting and molding, while OSB is a good option for those who need to cover areas where moisture exposure may be an issue.
For storage, distribute weight evenly and use sturdy containers. Uninhabitable attics without storage can typically support 10 pounds per square foot, while those with storage can handle around 20 pounds per square foot.
A finished attic should be insulated much like the rest of the house, with insulation in the walls, ceiling and floor. If the attic is unfinished, putting proper insulation on the attic floor is one of the simplest ways to keep heating bills down and keep cooling needs in check.
Even if the attic space is unheated, it's typically warmer than the outside air in winter. If you have chosen unfaced batting insulation for your rafters, you should staple sheets of plastic over the batting to accomplish a moisture barrier.
Faced Insulation: If the attic doesn't have any existing insulation, use faced insulation with the paper facing toward the heated living space. Unfaced Insulation: When adding more insulation to an attic that already has insulation, use unfaced insulation.
You should install two layers of insulation in your attic; wood joists must be covered to allow the air to move. The first layer will sit between the joists, and the second layer will run perpendicular over the joists. The first layer should have the facing against the drywall to act as a vapor barrier.
This is considering that not much weight will be placed on the floors. This is the choice for attics used solely for light storage. Meanwhile, 3/4 plywood for attic floor is the recommended dimension regardless of the joist centre measurements and weight requirements.
On average, 3/4-inch plywood can support a distributed load of approximately 50-75 pounds per square foot (PSF) when properly installed and supported.
Plywood or Oriented Strand Board (OSB) Panels: For attics that you will use for storage only, installing plywood or OSB panels over the top of your attic's joists should add enough strength to the joists to support the weight of stored items. This option is not strong enough to support more than light storage.
For traditional plywood flooring installations, where the plywood is directly attached to the subfloor, the recommended plywood flooring thickness typically ranges from 5/8-inch (15mm) to 3/4-inch (19mm). While 3/4-inch plywood is standard for most residential subfloors, certain conditions may require thicker plywood.
The code requires 1 1/4" floor thickness (overall) unless it is tongue and groove plywood in which case 3/4" is adequate. Will 1/4” plywood over 1x10 plank subfloor be thick enough t ...
The minimum thickness of plywood for subflooring is about 5/8 inch. Since it does not hold fasteners as well as plywood, OSB must be a little thicker, or at least 23/32 inch.