After you have installed your floor joists the next step is installing the plywood decking that will be the base for your home’s floors.
Before you begin this part of your project it is important that you make sure your joists / rim joists are aligned so the home is square. Using a tape measure check the corners for square and double check the distances between the joists at 16 on center.
Decking comes in two types of wood product: either standard plywood which can be pine or spruce, or OSB plywood which is made up of pieces of wood layered and glued.
Decking comes in 4 foot x 8 foot pieces and is tongue and grooved on all its edges to provide a good connection between the sheets.
Which product is better is difficult to say but both products can not withstand direct water contact over a prolonged period. The plywood will react to water by delaminating its layers and curling and the OSB will loose adhesion between the wood chips and fall apart. The choice is really between you and your architect but for best results the decking should always be covered with an underlayment material like 1/8th inch luan before adding vinyl or other flooring.
When installing decking you should lay the pieces so the long dimension of the plywood extends across the joists and the short dimension runs up the joist length.
Laying your first piece in the outside corner of the floor you want the long dimension of the plywood to lay across six joists with the final edge ending up in the center of the 6th joist. If you were to run your plywood the opposite direction then the board would only connect 3 joists. The idea here is that for best stability if you can connect joist 1 to joist 6 then movement will be minimized during conditions that cause lateral shifting … earth quakes or high winds that can shift the structure or even a flood.
Prior to laying down the first piece you want to apply construction adhesive to your joists. Construction adhesive comes in caulk tube and you should cut the very end of the tip completely off so the adhesive will exit the gun quickly in a half inch wide pattern.
Construction adhesive will help reduce any voids between the plywood and the top of the joist. It will also reduce rubbing and popping noises when you walk on the floor which is a serious reason for call backs.
Install the first piece so that the grooves are pointed into the center of the house and the tongues are to the outside of the house. This will aid when you install your second piece and insert its tongue into the board that has been already nailed to the joists.
Nail the plywood to the outside rim joist first and then position the joists that are still loose 16 on center beneath the plywood. It is important that you line up the joists on this first outside row and also as you work. If you need to use a string line but many decking manufacturers mark the top side of the decking to help you line up the joists as you go.
Once you have the outside nailed and the joists lined up put one nail about an inch from the edge on the joist you just aligned. After all the joist are straight finish nailing down the length of the joist every 6 to 8 inches.
Eight Penny Ring shank nails are a good idea they will reduce lifting. If your Building Official requires a common nail then you may want to screw the decking in high traffic areas such as bathrooms, kitchens and hallways.
The second row of plywood should start with a half piece. Install the full 8 foot piece of decking on the joists with the edge resting on the third joist at the 48″ mark. You will cut the end off later and use it on the other side of the house if possible.
The idea of staggering every other row of decking is so the joints do not line up.
Once the first piece is in place continue to use full sheets until you reach the other side of the house.
If you can use the scrap piece that is ok but more then likely you will add another full sheet when you finish the row and end up with another half sheet to cut off. This is just the cost of building and those scraps can be saved for projects.
Cutting Stairway and Other Openings
You should mark your openings as you work and then cut them after you are done. Work safely and do not walk over the stairwells. Often you will find that you can work around most stairwells that are on the perimeter of the building and won’t end up with as much waste.
Other openings such as for duct work can be cut after your partition walls are installed.
After you have installed your decking you can begin to build your perimeter walls. Since your deck is probably the best place to build your walls it is a good idea to stack a wall section if needed so you will have area to work.
It is a good idea to use a red spray paint can and mark a 2 foot boarder line around the stairwell. This is important when you are walking your outside wall and can not predict when the stairwell will be coming up on you.