Levelling the Floor: Part I

Drop a marble to the floor of an old house and it’ll probably roll a bit until it gets stuck in a cupped floorboard or a valley where a whole section of floor has sunk. The reasons for this are legion. The joists that the floor and subfloor rest on can twist, bow, and shrink. The beams supporting the joists, the posts under the beams, and the foundations anchoring the posts can settle. What’s even worse is that electricians and plumbers, amateur and pro, seem to have little compunction about chopping away at beams and joists, notching them at the edges, and drilling

Holeslarge holes to accommodate the passage of small wires. Then there’s water, probably the most destructive substance a house ordinarily encounters. Leaking radiators and loose toilet gaskets (a $7 ring of wax that can produce tens of thousands of dollars in damage if it’s not kept in good shape) keep subfloors and joists wet, introducing rot and, sometimes, the insects that rotten wood beckons to.

Our old house suffers from all these things except insects. Its original finish floor (birch or maple planks painted red) was a rolling field of little hills and valleys, high near the front of the house and 2 ½” lower in the centre (near the leaky bathroom toilet, of course). We want, eventually, to install solid or engineered wood flooring but, as with all renovation, “want” is preceded by “must.”

The must in this case is making the floor flat so the new flooring won’t look wavy, particularly considering that we’re changing the floor plan to produce longer sight lines and a feeling of openness. A distinction has to be made between level and flat, though. The flooring material you put down doesn’t give a damn about level. You can put a perfect floor on a surface that slopes 15 degrees; what matters is that it’s flat. Lay a long straightedge on it, peer under the straightedge, and see no light. That’s flat. Put a level on it and watch the bubble settle in the middle. That’s level.

Since we had to tear up the floor and subfloor, (the progress of that “peeling” shown below) we thought we might as well go for broke and make the whole thing flat and level. But how to do that, considering the joists, beams, and all the rest were anything but flat and level?

Front_room1

Front_room2

Front_room4

FloorWide

We consulted our great structural engineer, Jimmy Vathis, about the floor and he hemmed and hawed for a minute because he wanted to save us money and grief. At which point, Patricia asked him, flat out, “What would you do if it were your house?”

“Sister the joists,” he said, without hesitation.

Sisterhood, in this case, really is powerful. Sistering usually involves taking a new piece of lumber the same size as the original joist and gluing and screwing the old and new together. The new, sistered joist may also be levelled and placed in careful relation to the other sisters so their tops form a plane that’s both level and flat, a democratic sorority of infrastructure for a new floor.

What about floor levelling compound? No. It’s very heavy, the subfloor in many old houses is in bad shape with large gaps between boards, and you can’t drive nails into levelling compound when you install the finish floor. Shimming? Well, I suppose, but the thought of cutting dozens of 16-foot wood strips to bring each joist up to the proper height at the proper angle is a recipe for madness.

Sistering the joists was the answer I was sure we’d hear from Jimmy, and the one I most dreaded hearing. It meant that, working alone, I would have to glue and screw 16-foot 2”x 8”s to the old joists while making sure they were level and all positioned at exactly the same height to produce a flat plane. There was a modest saving grace, though. Since the original joists were all strong and in good condition, the new, sistered joists only had to contact them for 4 inches. That meant I could do the sistering with smaller, and less expensive, dimensional lumber.

Sisters_below

The first one took me four hours to put in. But before we got to the point of gluin’ it up, I had to do some careful measuring. I bought a DeWalt laser level and set it up in the middle of the floor, attached to a post. It projected a red line around the walls about two feet above the joists. Then I taped an ordinary bubble level to a yardstick so I could hold the yardstick perfectly plumb as it sat on a joist and measure its height. From there, it was a matter of hopping from joist to joist and finding the highest spot in the entire floor. Why? So the new, sistered joists could be set to exactly the same height. Flat and level? Easy.

Laser

Not. It’s still a 120-year-old house, and those joists are twisted and tilted, when means that attaching new 2”x8”s and expecting them to sit square to the face of the old joists is just not going to happen. I did the best I could, using lots of nails, lots of screws, and sometimes filling gaps with shims. I also discovered that the space between joists is anything but the modern standard of 16”. The spacing varies from 21” to 26”. That’s important because the OSB subfloor I’m putting down over them is rated 24” OC. Which is to say that it’s only acceptable to my engineer and to building codes if the maximum space from the centre of one joist to the next is no more than 24”. So, I sometimes had to sister on both sides of the original joist to decrease the distant between them. And before I’m done, I’ll have to hang some entirely new joists using steel joist hangers that can be nailed into the beams that cross the joists at right angles every 12 to 16 feet.

Double_sistered-2

One of the worst problems of working alone in this situation is just that, working alone. I made a jig to hold the new joist in place (from under the floor) while I ran upstairs to make small adjustments in the height and slope of the joist. It was inefficient, tiring, time consuming, and generally crazy-making. Finally, I decided to rip a flat edge, using a Makita track saw and guide (though the factory edge of a 4 foot or longer panel and a regular circular saw would also do a good job) on a 12-foot 2”x 8” and use that as a guide.

Here are the first steps to achieving flat and level:

• Once the high point of the floor is determined, attach sisters at the proper height to joists separated by a distance equal to the length of the straightedge

• Clamp the straight edge across the ends of the newly sistered joists

Straightedge

• Install new sisters between them by pushing the new lumber firmly to the bottom of the straight edge. That way, you don’t have to measure (thereby introducing errors) to have the sisters all at the same height

• Move straight edges once new sisters are glued and screwed, and repeat.

This method has saved me a bunch of time and hassle. Carpenters avoid measuring when they can because it takes time and introduces error.

After doing that for a bunch of joists and laying down a couple of OSB 4 x 8s, I was worried about how wavy (not flat) the floor would be. It’s not dead flat, but the greatest error I could find was about 0.075” of light shining underneath my long straight edge. Good enough.

By the way, this long-delayed blog is flying under a WordPress search category I’m using for the first time: Construction. Long time comin’.

About Terence Byrnes

Terence Byrnes is a writer and photographer who teaches at Concordia University in Montreal. Visit www.terencebyrnes.com to see his photography.
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10 Responses to Levelling the Floor: Part I

  1. jerry rude says:

    terence, haven’t seen you lately in spfld…..
    you posted a picture of my father from your collection, thank you…
    …the elderly man sitting amid the demolition project…
    in case you don’t remember, i’m the guy at ‘tom’s auto sales’…
    “the biggest dealer west of the mississippi” LOL
    hope this finds you and yours happy and healthy…
    jerry

    • Jerry! Apologies for the ridiculously slow reply but I got sick. Am on the mend now. You haven’t seen me because I ran out of money. Hope things will be looking up this year and I’ll definitely be dropping by to visit. Great to hear from you.

  2. Bonnie-Carol Cooke says:

    Mr Byrnes:
    I love reading about your Reno/Restoration Project in the Point but you haven’t posted anything since Nov/13… when can we expect more stories??? My husband Eric Couture and I are involved in our dusty nightmare Reno not that far away from you on Sainte-Madeleine. If you need a list of people “not” to hire email me.. LOL!!! Looking forward to your next post.

  3. Kim George says:

    Excellent blog and great post. My partner and I are planning to reno our 1885 duplex on Rue de Liverpool. This is some really helpful information.

    Out of curiosity, I’ve been trying to identify the timber in the house. I’m assuming the houses in the Pointe from this vintage are all made from the same lumber. Do you know what the floor joists, wall infill timbers are?

  4. Paul Lohr says:

    Hello Terence,
    I have a similar issue and was thinking of building and installing sister beams. Where did you purchase your 2×6’s or 2×8’s? I was going to buy them from Home Depot but rarely are they straight. Often they are out by 1/4″.

    • That’s a sore point! Construction lumber is awful stuff. If I wanted to count on getting reasonably straight boards, I’d have two choices: go the lumber yard or Home Depot and choose them myself; order about 30% more than I need and dump the bad ones. It’s a “gotcha” both ways because I don’t have a car or truck. So what I do is order 15% more than I need and grit my teeth when I see all the boards that are as twisted as fusilli. The only way to make it work is with labour. I learned to choose the straightest sticks, making sure all the crowns faced up, use lots of PL construction glue, clamp the sisters (2 x 8s the smallest you should use) to counter some of the twisting and, after all that, be prepared to plane down the boards that are too high or twisted. It’s useful to have a long straight edge (milled from a 2 x 6) or a long level. It can also help to set up a laser line maybe a foot or so above the tops of the joists and use a story stick to make many spot checks on the heights of the sister joists you’re putting in. It’s definitely a two-person job. When I started, I was working alone and being as careful as I could. Despite that, there’s an area maybe 5′ x 7′ at the front of the house that’s clearly visible–maybe as much as 5/8″ high. It should have been planed down, but once you glue that sub-floor with PL, forget it, it’s not coming up. Ever.

  5. That’s a sore point! Construction lumber is awful stuff. If I wanted to count on getting reasonably straight boards, I’d have two choices: go the lumber yard or Home Depot and choose them myself; order about 30% more than I need and dump the bad ones. It’s a “gotcha” both ways because I don’t have a car or truck. So what I do is order 15% more than I need and grit my teeth when I see all the boards that are as twisted as fusilli. The only way to make it work is with labour. I learned to choose the straightest sticks, making sure all the crowns faced up, use lots of PL construction glue, clamp the sisters (2 x 8s the smallest you should use) to counter some of the twisting and, after all that, be prepared to plane down the boards that are too high or twisted. It’s useful to have a long straight edge (milled from a 2 x 6) or a long level. It can also help to set up a laser line maybe a foot or so above the tops of the joists and use a story stick to make many spot checks on the heights of the sister joists you’re putting in. It’s definitely a two-person job. When I started, I was working alone and being as careful as I could. Despite that, there’s an area maybe 5′ x 7′ at the front of the house that’s clearly visible–maybe as much as 5/8″ high. It should have been planed down, but once you glue that sub-floor with PL, forget it, it’s not coming up. Ever.

  6. Alex -UK says:

    We have similar problems in London – Most of which is built on clay left millions of years ago. I’m currently topping out Victorian joists, but they slope down along their range, not their length. In this instance ‘packing’ is an easier option.

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