How to deal with uneven porch floor joists?
So I ripped out my 104 year old front porch and steps. I replaced the steps and they are nice and leveled and attached to the leveled rim joist (not sure if that’s what it’s really called). However when it comes to replacing the floor of the porch with 3/4″ T&G fir I’m in a quandry. Those old joists, almost 14′ long, meander up and down. I didn’t expect them to be dead flat and I never noticed the old floor being full of dips or hills but some dip down as much as 1/2″ in places while others are near perfect. I plan on pneumatic nailing the fir directly to the joists with 2″ galvanized nails at an angle through the tongue side. Since the joists are a lot stronger that the fir I’m sure the joists will win the battle. Do I try to make long shims to lay on top of the joists to make them even? If so do I need to make them from pressure treated lumber? Perhaps I should sister 2″ x 4″ on the sides of each joist to nail the fir to? If so do I need to use PT? I’ve never met a straight piece of pressure treated lumber. I suppose I could use a power hand planner to get any humps out.
Is there a better way to go about this?
An additional related question: When laying the fir do I start at the center and work to one side then put a loose strip tennon in the first groove back where I started and lay to the other side or start at one edge and go all the way to the other. The latter seems more likely to be out of square by the time I get all the way over to the other side (14′). It’s hard to tell if the porch is really square because there are 30″ x 30″ hollow stuccoed columns on each front corner. I can’t get under there to do a accurate diagional corner to corner measuement.
Thanks,
Roy
Replies
Sister Act?
I'd sister new to the old.
You can string the existing joists to see where, how much, how often, etc, the existing ones rise and fall. You might not have to sister every joist, just the wild and crazy ones. If you use PT, PT lumber can affect your choice of fastner, so be aware of that.
KD PT is usually in better shape than green PT. But PT can usually be coerced into shape, especially 2x6 and smaller.
You could also consider protecting the top edges of your joists by laying down strips of something like Vycor prior to installing the new fir.
In Wi joists in deck or floor over 10' must have solid bridging of equal size. Placed through the center of the span they can go a long way for strength and may even pull themselves into a much better plane .where onlyb small adjustments or sistering will be needed
If there already is bridging they may just need to tightened up or adjusting with more nailing or heavy screws. They may come together easy or be very difficult. Just depends on locked into shape they are or how cupped etc. Just be sure to make sure they stay straight and you don't let the bridging push them out of shape. you may have to both nail and screw and use levers to push them into shape.
I should also add that when nailed well the t&g flooring will also help to pull the floor flat. keep an eye on the nailing so the boards are pulling tight to the joists.
I second the sistering, will be much easier to get close to a true flat surface for the new floor. and yes pt.
Square
I'd go with sistering as in the other posts. It doesn't matter if it's square. With T & G all that matters are that the sides are parallel. Start at one edge.