How thick should roof decking be?
Roof decking is an important structural component that goes on top of the trusses and joists and before the insulation and weatherproofing layers. Roof decking and roof sheathing are the same thing, both are made from strong, thick materials and is another layer of protection for your home.
Typically, roof decking is 7/16-inch, but it may be thicker or thinner based on building codes for each jurisdiction. In some areas, 3/8-inch plywood is acceptable and when installed on rafters spaced twenty-four inch centers, it is as strong.
Can you use OSB for roof decking?
Yes, and there are several types of materials used for roof decking:
- OSB Sheathing is the most common material used for roof decking. It comes in sheets that are sixteen feet long or longer, and is made by bonding interweaved wood strands together, creating uniform boards. It is a moisture-resistant, rigid material, ideal for roof decking purposes.
- Tongue & Groove is typically 2×6 boards that have a “tongue” on one edge and fits into the “groove” the next board, sliding them together for strength. It is often used for an architectural element to the rafters in home where there isn’t a ceiling.
- Plank Sheathing are spaced about 18” apart and usually used with wood shingles that re installed in layers. This roof decking material is found in homes built before 1970.
- Step Sheathing are boards that run perpendicular and have a space separating them so that air can circulate under the shingles. The space created is dependent on the type of roofing shingle to be used, frequently paired with cedar shingles.
- Plywood Sheathing usually comes in 4’x8’ sheets. Made form mature trees, creates a moisture- resistant, strong base for roof decking.
Is roof decking treated?
Roofing contractors typically will use a treated plywood because of the possibility of rot that can happen due to moisture building up on roof decking. Pressure-treated lumber is improved untreated plywood to create an insect resistant, water resistant material.
What is roof decking code?
Every jurisdiction will have its own building code requirements, including the roof decking code that builders must adhere to when constructing new structures. Manufacturers of roofing materials also have their own recommended roof decking code, and while that may not be adhered to as strictly as the codes in each jurisdiction, it can affect the warranty of the product.
An example of a manufacturer’s roof decking detail code is Owens Corning as follows:
- Owens Corning requires the following roofing manner be followed for all asphalt shingles to be installed in the following manner on solidly-sheathed roof decks:
- Use minimum 3/8-inch plywood sheathing
- 1 – Minimum 7/16-inch OSB
- Installed with 1/8-inch spacing at all panel edges and end joints
Should roofing nails go through the sheathing?
Roofing nails should penetrate the chosen roofing material (asphalt shingles) and go 19 mm into roof decking. The thickness of the shingles, flashing, underlayment should be considered when determining the nail length.
Does roof sheathing go over fascia?
The order of how soffit, roof decking and fascia should be installed is confusing for most people that are not in the house construction industry. The soffit is the board that lays horizontal between the outer part of the house and the edge of the roof decking. The fascia is even with the roof decking and on the most outer side of the soffit.
On Roof Decking with Insulation
It is a dilemma: Does insulation go on the roof decking? Or does it go on the floor of the attic? Or does it go in both places? The answer to these questions is yes, but no. It is all dependent upon how the attic space is to be used.
Today, homeowners are all about conserving energy and that would mean to protect the volume of any area by making it as small as possible, in regard to the parts of a home you want cooled and heated. The less volume there is to cool and heat, the less energy it requires. So, ask yourself these questions:
- Are you planning to use the attic as a room that comfort of cold or hot is important? If keeping it cool or warm with the weather doesn’t matter, then you do not need to keep it protected from the outside temperature, so insulate only the attic floor. This will keep warm air in the winter and cool air in the summer down below in the main living space of your home.
- Are you planning to finish out the attic to use as a room? Then insulate the pitched roof with insulation on the roof decking.
Another option is to insulate both, the attic floor, and the roof decking. This gives you both scenarios above, but it is an extra expense of insulation, but that is extra insulation that keeps the outside temperature outside and inside of the living space cool or warm as needed. This should only be done through when adequate and proper attic ventilation is installed to make sure any moisture build-up is evaporated thoroughly so as not to mildew and grow mold under the insulation. Need help with your roof decking? Call (651) 796-2341 today for your expert service needs.