Framing a floor

Framing the floor of your future house is a very important step.
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1. Erect steel supporting posts
2. Prepare the floor
3. Install the sill plate and the ribbon joist
4. Mark the location of the joists and beams
5. Install the beams and floor joists
6. Stabilize open-work joists with tie beams
7. Subfloor

1. Erect steel supporting posts

The first step in the construction of the frame is to erect steel supporting posts in the basement to support the beams which, in turn, support the lower one end of the floor joists on the ground floor as well a as the load from the upper floors which gets transmitted down the walls and studs. You should get a structural engineer to calculate exactly what you require in the way of posts, based on your house plan.

1.1 

Centre the supporting posts on plates that are designed for that purpose. Lay black construction paper around the plates to provide an isolation joint between the post and the basement concrete floor. Adjustable cylindrical steel posts (jack posts), able to meet load-bearing requirements, are commonly used as beam supports. They are fitted with steel plates at both ends. The upper plate must be at least as wide as the beam it has to support and must be bolted onto a steel post, or nailed to a wood post, as the case may be. You can also use a 6 × 6 in. (140 × 140 cm) wood post. Whatever your choice, you must base it on the calculations of a structural engineer.

2. Prepare the floor

Your next step is to prepare the floor, starting with the sill plate, the joists and the beams. Be sure everything is level, as you would in foundation work so as to avoid unpleasant surprises. Use dry structural lumber (19% humidity or less, rated S-Dry) as recommended by the Canada Mortgage and Housing Corporation (CMHC). Be sure to protect your lumber against the effects of weather so it won't warp or crack.

3. Install the sill plate and the ribbon joist

The sill plate is a piece of 2 × 4 in. or 2 by 6 in. pressure treated wood (38 × 89 mm or 30 × 140 mm) that supports the box-end joist or rim joist . The box-end/ribbon joist is a piece of 2 by the same depth as the floor joist that supports the floor joists which in turn support the subfloor.

3.1 

Begin by installing sill gasket on top of the foundation wall to avoid the transference of moisture from the concrete to the wooden sill plate.

3.2 

Then install the sill plate over the foam. It's imperative that your sill plate be level because it will have bearing on the straightness and levelness of the house. It must lay on top of the foundation over its entire length. Nail it in place using concrete nails as well as bolted into place using achour bolts which are embedded into the concrete foundation wall.

3.3 

Nail the box-end/ribbon joist perpendicular to the sill plate every 2 in. (51 mm).

4. Mark the location of the joists and beams

Start at one side and work towards the other use a measuring tape and a pencil to mark the location of the floor joists and beams on the sill plate and the box-end joists. Make a mark on the beam and the sill plate in keeping with the engineers required joist spacing as per the structural plan, or National Building Code or the manufacturer's specifications.
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