# How do I use 'surface shims' to level out a sloping floor?

Asked a question about leveling my floor here earlier this week, and one of the options suggested sounded appealing, but didn't contain enough detail for me (a not-too-handy, not-very-experienced-with-home-repair guy) to move forward on:

Assuming jacking is not an option, the next easiest way would be to install "pearlings" or surface shim boards every 12 to 16 inches on center across the floor in decreasing thickness and install a new 3/4 inch subfloor over these, screwing it down all the way into the old floor.

Is there another word or phrase than 'pearlings' that is used for this process? Searching specifically on pearlings has gotten me nowhere. Can anyone walk me through the steps of the outlined procedure in more detail, or point me to a walkthrough of the procedure somewhere else on the internet?

I think the word is actually spelled "purlin," and normally refers to framing members bridging laterally across roof trusses, rafters, or wall posts or studs.

You say (in the other question) that the slope is consistent, i.e. the floor is still planar, just not a level plane. This means the method suggested by shirlock homes in your other question shouldn't be too difficult; certainly a lot easier than the other options you mentioned.

If the slope is across 10 feet, and the outer edge is 1" lower than the inner edge, you'd start by ripping a 1" strip off the edge of a piece of 2-by lumber, so you'll have a strip that's 1" x 1.5". Attach that to the existing subfloor at the outer edge. Now say you've decided to put these shims every 12", that means you'll end up with 10 of them across the 10' dimension of your room, and each one will need to be 1/10" shorter than the last one so that you end up at zero right where the room meets the house. So rip your next one to 0.9" thick, or about 29/32", and attach it parallel to the first one, 12" away from it. Next one will be 0.8" or 13/16", and you'll attach it 24" away from the first one. Then just keep going until your last shim is 0.1" or 3/32" thick, and it will be about 12" from the inner wall of the room.

Once you've installed these shims, their top surfaces will form a flat level plane onto which you can attach your new subfloor. Your finished floor will be higher with this method (at the threshold it'll be equal to the thickness of your new subfloor plus the thickness of your new flooring material, and at the outer wall it'll be one inch thicker than that), but if that works in your situation I think this is a great solution.

• good explanation, and thanks for the spelling correction. Spelling was never my strong suit. + – shirlock homes Jan 27 '11 at 7:49
• It's funny, when I saw your spelling I actually thought it looked more correct! "Purlin" just looks like it's spelled wrong. – Mike Powell Jan 27 '11 at 15:29
• that's cause I'm from Maine. we got an accent. lol – shirlock homes Jan 29 '11 at 21:59

Sorry for the delay. Mike gave you a good explanation on how to use purlins.

As a practical matter, once you have calculated the drop at the far end of your floor, rip the first purlin and install it against the lowest wall. (1X3 stock and/or 2X4'stock should work well) I would then use a very straight edged piece of board, cut to the length of the highest level to the lowest level and set it on the floor bridging the entire space. Now you can easily measure the gap to the existing floor at 12 to 16 inch increments in order to give you the thickness of each successive piece of purlin.

You will also want to install a perpendicular nailing strip between the purlins at 8 foot on center, alternating as you would when installing the plywood. This is just a little extra support for the butt ends of your new subfloor. Cut these to the smaller purlin dimension, that will be fine. So what you will have created is a grid to lay your underlayment on.

Speaking of underlayment, I would highly suggest you use a tongue and grove style 3/4 inch underlayment. Do not leave gaps in this underlayment. Snug them together well. This will make the absolute best, stable platform for your new hardwood.

Also, to assure a nice solid quiet floor, lay a bead of construction adhesive on each purlin before you install the underlayment. Secure the purlins and underlayment with 2 1/2 to 3 inch ring nails or decking screws.

When you install your floating floor, be sure to use a foam backing layer, unless the product you have selected has a backing preinstalled.

If you need specific questions answered, see my profile for my e-mail address. This process is actually quite easy and doesn't require any advanced skills. As long as you have a decent table saw and a feather board, you can rip out purlins in a snap.

What he is describing is to lay shims over your existing floor. You would set shims such that when you level across those shims the tops of all the shims are level. You do want them fairly close together, so yes 12 to 16 inches apart. "On Center" means you measure center to center, not strictly between the shims. 3/4 subfloor is usually just 3/4 inch plywood. You'll need to secure your shims and make sure they are all level before you try to lay plywood over them. Generally you'll want to lay the subfloor with just a bit of gap between each panel of plywood such that any expansion doesn't cause your subfloor to buckle or warp.

That being said, this does not sound at all like something I would try with very little skill. Leveling individual points across a large area is not something that is easy to do.

Many years ago we had the same exact problem. A 1920's porch that had been enclosed with windows and a shore wall below. Our contractor installed shims on top of each 2X6 sloped rafter with the thickest part at the lowest and it was cut at an angle to match the splope thus making it level. Then plywood and tile on top. It's been great for 20 years.

• Welcome to the site. I edited out the extra question in your post; please use the Ask Question button at the top of the page if you have a question that is not addressed by the information on this page. DIY Stack Exchange is a Q&A site, not a forum, so we expect answers to address the original question. – Niall C. Aug 27 '14 at 16:38

if there's a consistent slope across your floor you may want to examine the members supporting the floor joists, perhaps they are rotting, cracked or otherwise causing the slope to occur. shimming then later discovering and repairing the broken member could result in a new slope in the opposing direction.