How to Level a Plywood or OSB Subfloor Using Asphalt Shingles & Construction Felt. December 1. 0, 2. Fred (email) | This article is part of our series on How to Install Hardwood Floors. While preparing to lay 1. OSB subfloor that will serve as the nailing surface for the hardwoods. At Wickes we're serious about tool hire, which is why we've teamed up with Travis Perkins to offer you a comprehensive range of tools and equipment to hire. - Our Marine Carpet Styles - (Good) Standard 16oz. Marine Carpet: Our economy line of 16oz. Marine Grade Boat Carpet may be used on any boat or indoor/outdoor. ![]() Finished tile floor installed over a plywood and cement backer board subfloor. Installing tile over a wood subfloor is a lot easier today than it was when I started. This article provides detailed instructions for leveling a subfloor based on our project. Project Overview: Uneven OSB Subfloor. The subfloor beneath our first floor is 5/8″ oriented strand board (OSB) laid over 2 x 1. The joists run from the front of the house to a steel I- beam in the middle of the house, and then from that I- beam to the back wall. Each span is approximately 1. Before we pulled up the previous flooring surfaces (carpet and vinyl), we knew there were some spots on the subfloor with significant peaks and valleys. Our kitchen, for instance, had a noticeable dip around a cabinet peninsula. We think the house was built with ‘green’ lumber that may have been exposed to moisture before it was installed. When it dried, the bowing became very noticeable. Also, every piece of dimensional lumber has a natural crown to it (the direction it bows along the long edge of the wood). The joists should have been laid such that all the wood was “crown up,” but we suspect that several of the joists were incorrectly installed “crown down.” When this happens between two joists that are “crown up,” the depression can be significant. on this page. The depth error in the worst spots on the floor was as much as 3/4″ over about 4 feet.This is well outside the tolerance for hardwood flooring, which should be no more than 3/1. You can see the dramatic slope on just one part of the floor in this picture. The level is sitting on the crown peaks, with the same measure in a depression between them. What is surprising about this floor is that the actual OSB is in very good shape. Sometimes, you’ll find OSB swelling at the joists where moisture contacted the subfloor. This wasn’t the case in this house. We did have to replace one piece of OSB due to wood rot where a persistent leak existed, but the rest of the floor was in pristine condition. If you’re dealing with a swelled OSB situation, we think the best course of action is to use a belt sander to grind down the swelled edge. ![]() ![]() Just make sure this doesn’t cause any structural instability.If the piece is rotted or just beyond reasonable repair, the best course of action is replacement. . The Solution for Leveling a Subfloor. Searching around the internet for solutions, we eventually landed on this article from Ask the Builder that suggests using construction felt and asphalt roofing shingles to level an uneven plywood or OSB floor for hardwood installation. This was a novel idea to us, but it made sense. Both roofing shingles and construction felt are dense, not prone to compression (a key element for leveling), and sufficiently thin that they can be used as incremental steps to get to a flat surface. Since we have such dramatic slopes on the floor, we decided to use the shingles and construction felt solution along with a new layer of 3/8″ plywood. We chose 3/8″ plywood because it is rigid enough to absorb very minor depressions underneath it, and not so heavy as to be unwieldy. We are planning to lay 3/4″ exotic hardwoods on top of the plywood, so what we’re looking for from the new plywood isn’t an “ultra- rigid” surface, it simply needs to bond to the layer beneath it, absorb very small gaps where the leveling provided by the construction felt and shingles isn’t perfect, and allow sufficient “grab” by subfloor screws to get a tight bond with the 5/8″ OSB below. To fasten the plywood to the OSB, we considered using a combination of 2″ subfloor screws and construction adhesive (i. Liquid Nails for Subfloors). This is generally referred to as “gluing and screwing,” and you’ll see it suggested on some ceramic tiling sites as a method to increase the rigidity of a floor for tile installation. Since we’re going to be laying the 3/4″ hardwoods on top, which itself will entail 1. Our primary motivation was speed and less mess, and so far after walking on the floor, we’re happy with the result. For the subfloor screws, we used a Senco Screwgun (reviewed at that link) to fasten the 3/8″ plywood to the OSB. The screwgun is an absolutemust for this job. We put a screw in approximately every one foot square, which means approximately 1. Driving with a drill- driver is simply not an efficient option. Alternatives to Shingles and Plywood for Leveling. Before getting into all the details of the leveling job, I should say there are other options for leveling a floor. For instance, we could have pulled up the OSB, shimmed the joists underneath, and refastened the OSB to the shimmed joists. This would have the advantage of not putting any additional load on the subfloor, and addressing the cause of the problem directly at the root. In our situation, however, we believed that this effort would be much more significant than a new layer of 3/8″ plywood, because the problem was pervasive throughout the floor in varying degrees, and as you’ll see from the pictures below, the shingles give a lot of options for how to address a slope over a wide range of floor. If we were dealing with a single, significant depression in one or two parts of the floor caused by joists being incorrectly crowned, we probably would have opted for this solution since it is much less expensive. There’s also self leveling concrete as an option for leveling a subfloor. We used self leveler to level the concrete slab in our basement with great success. We opted against this solution on the first floor because most self levelers aren’t rated for installation over OSB, and because they are expensive and messy. Plus, we figured we would need to install 3/8″ plywood over the self leveler to prepare for hardwoods (this may have been overkill, but we weren’t comfortable with the solution of driving staples directly through the leveler). Effectively, the asphalt shingles in our solution are a rigid leveler that we think works as well as any liquid self leveler would have, and they are easier to control. If you’ve never worked with self leveler, it is a miracle product, but it has its drawbacks, including short work times. Tools Required for Leveling a Floor with Plywood and Shingles. String and nails – for pulling a string above the floor both before and after the installation to get floor- wide perspective on the problem.Utility knife with roofing blade (2 knives are nice if you’re working with two people). . Tape measure. Circular saw (recommended) and/or table saw for cutting plywood. Screwgun (we like this Senco Screwgun with square head driving bit). Materials Required for Leveling a Floor. Asphalt roofing shingles – the 3- tab kind that are about 1/1. You can find these at Home Depot, Lowes, roofing supply stores, and other home stores. You will need a sufficient amount to cover the subfloor. Steps for Leveling a Subfloor. Preparation: Ensure the subfloor is clear, clean, and free of debris, with plenty of space to work. Remove molding and baseboard at the edges so you can get the plywood close to the walls. Step 1: Determine and mark high and low spots across the floor. We did this two ways, first by dragging our 8 foot level across the floor to try to determine where the high and low spots were in local areas, and then by stretching a string across the whole floor, secured by a nail on each end. The string does a better job of showing high and low areas across the whole floor. We marked high and low spots using a non- scientific method, sharpie marker on the floor with the words “high” and “low” and sometimes “very low” in the worst spots. Step 2: Set a strategy for filling in low spots to “even out” the floor. The floor doesn’t have to be level, it has to be flat. Also, it doesn’t have to be perfectly flat – 3/1. We decided to start at one end of the floor near the fireplace that had a significant low area and a nearby high area. Near the front of this fireplace, the depression is almost 3/4″, so we’ll have to stack the shingles over one another. Step 3: Fill in low spots with shingles and construction felt. For our efforts, we decided to use shingles exclusively under the 3/8″ plywood, with the possibility of using the construction felt between the 3/8″ plywood and the hardwoods if necessary. This can be hard to get perfect, and we found ourselves frequently going back and forth between our 8 foot and 4 foot levels.
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