Leveling an OSB subfloor/floor on sloped concrete

I want to make a garage a more hospitable workplace. I plan to cover it (~300sqft) with DMX I step underlayment first, then t&g OSB. I’ll paint the OSB, and that will be the floor. The concrete slopes to the drain in the center (I’ll preserve access). Haven’t measured yet, but the slope looks like maybe 3-5 inches. I’m looking for a low-cost, low-effort solution to level it. Not expecting perfection at all, just improvement. I’ve found some clever ideas online, but wanted to tap into this great resource. Ideas? Thanks!

workisfun

in General Discussion 1 year and 5 months ago

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workisfun | 1 year and 5 months ago

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Thanks all!

justinromeu26 | 1 year and 5 months ago

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doing what china town red suggested means you can use 2×4 on side. just plane a taper in to meat the level floor. it will be a long taper, like 25 degrees or something. i do not know, i eye this stuff.

then shim and block under it. also, at the far end you can start by laying a treated 2×4 on side the entire length. with the addition of the 2×4 tapered spans, you already have 3″. so you can decide what and where to add from there. keep a lot of shims handy. in fact, do not buy those little packs. buy a starter course bundle.

workisfun | 1 year and 5 months ago

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I have an electric hand plane

justinromeu26 | 1 year and 5 months ago

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plane the face side as it approaches the level floor. but you will have to plane it as cutting even a 2×4 on that side will be hard. an electric plane makes child’s play out of a lot of this but not everyone has one and will really help op clean a lot of these up no matter what way they do it.

kassie319 | 1 year and 5 months ago

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Can you frame with 2x material flat on their face side and use cleats or blocking down to the concrete? Save all that ripping.

workisfun | 1 year and 5 months ago

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Thanks for that. I saw a YouTube video that does much the same thing. It’s good to know that you more or less endorse that method. Now I just have to make some kind of jig for the tablesaw or circular saw to make the long and slender cutting easier. Much appreciated.

justinromeu26 | 1 year and 5 months ago

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ok, the first time i had to do this it seemed like a lot.

get some 2×6’s and cut tapers. in the old days i would have layed a very straight one down across the slop and measured. mark the start of it on the 2×6 or an inch or so back. then from that point run a chalk line to the end and mark it at say 5″. now cut that taper. cut end so it will be plumb when the taper is on the ground. plan on 16″ apart but i am worried these will rock, so i would double them up. in the old days they would have be set on felt to get them off the concrete. maybe use treated even though they will be on that mat. so lay them all down and then run a string across. some might sit where they should, some might not. the ones that side high have to be ripped or if just a little use a plane. when you get the high ones down to where they are level, if you have low ones, you can lay shims on top of them, doubled up with the tapers working in a way that they run thinner to thicker if needed. lay shims underneath them where there may be voids to help stabilize them. when you have it all set up, put bridging down near the bottom at the far end so they do not want to shift. use 2×4 for bridging and use PL premium construction adhesive or if you have an air gun, nail them. 15 guage finish nails will hold the the bridging.

laser levels make this work easier today.

hey, anyone who wants, i have a 15 gauge porter cable finishing nail gun here that i used for one job 10 years ago. i put it away and took it out a year ago to use and it worked for a day but then something inside began to leak (probably a seal around the trigger valve). that gun is sitting here and i doubt at this point i am going to repair it. it is free to anyone who reaches out to me. it looks brand new.

Steve

workisfun | 1 year and 5 months ago

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I can do quite a bit.

justinromeu26 | 1 year and 5 months ago

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I imagine this is all pretty uneven any way from position to position along this 3-5″?

It is easy enough to do but if you have not done it before, it will seem like a monumental task.

Lmk the answer to above so i know how much detail to go into.