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However, in the case of a weak subfloor that flexes up and down when walked on, an additional layer of 3/8-inch or 1/2-inch-thick plywood underlayment, glued and screwed down over the weaker subfloor, will add … By adding all the screws through the extra layer of ply directly, I only have to contend with the more limited number of screws put in by the builder. I'm looking for some advice on adding a second layer of OSB to a 3/4" T&G subfloor. Vinyl flooring is usually not installed directly over the subfloor in residential applications. Stone floors need the extra stiffness and decoupling of a 2 layer subfloor because the stone may have natural flaws that are unseen until the stone is installed and only then when it fails. I-joists are 16" oc. For hardwood floors, use some felt layer over the plywood underlayment for better results. I just started a kitchen demo today, and once the old cabinets were out I got to take a look at the subfloor. Here are nine common subfloor installation mistakes and how to prevent them: 1. Avoid screwing the second layer into the joists (but make sure the first layer is solidly attached before adding the second). Ultimate Hardwood LTD, Derek - I have a fact pattern similar to Derek's, i.e., wooden subfloor needs to be raised two inches in the entryway (previously had mortar and stone), so I'm planning to screw 2x4's on top of the 3/4" subfloor, directly over the floor joists, adding a layer of plywood, and then installing hardwood. The subfloor is the first layer of flooring material installed on top of the floor joists. I have a second story floor that was carpet over plywood subfloor. With the plywood in place, install the backer board as you normally would. If you are thinking of laminate, use a pad to cover the underlayment. The joints between pieces of plywood on the subfloor might require reinforcing with 2-by-6 blocking if the plywood used did not have tongue-and-groove edges. If you have really solid hardwood floors, then bridging small gaps won’t be an issue. This is new construction. Mobile home subfloor thickness may be of some concern, and installing plywood over this subfloor can give you a stronger base for your hardwood, laminate or carpeting. I used a lot of nails as I wanted it to be solidly affixed and I did not want to have to wait for the glue to dry to lay down more sheets. Because of the seamed plywood sheets, there are rare perfect subflooring process possible. Only now is the subfloor ready for cement board underlayment. We are looking at a rather expensive hardwood so I want the installation to be ideal so I'm going to add a 2nd layer of plywood underlayment over the existing subfloor. How to Lay Subfloor on an Uneven Floor. Seems like the extra layer could cause issues if not installed carefully. Improper spacing. I have removed the carpet and 5/8 particle board. I will be installing 3/4 prefinished oak naildown flooring in our bedrooms. Parke, Star, JBowers, this 2 layer not-glued subfloor system is very counter-intuitive, but has passed both laboratory testing and field experience. First I nailed down the corners and placed a nail in the middle.Then I placed the nails in columns that ran down the lenght of the sheet, each collumn of nails abound 4-6 in from the next. It was a mess. The subfloor is 3/4" T&G Avantech on … A beautiful floor starts with a stable subfloor. If you add a layer of plywood or cementboard, however, you could raise the floor by as much as 3/4 inch, not including the extra height added by the tiles themselves. It can’t be removed easily. In most situations, the easiest way to firm up the floor is to install a layer of 1/4" plywood over the subfloor (nailed or screwed and glued) in such a way that the new plywood seams do not lay over the old seams. I believe that 2 layers of 5/8" ply is one subfoor recommendation. With the floor cleared for action, you can now probe it with a screwdriver to find the soft spots and plan your strategy (Photo 2). If there is any "flexing" or movement at the seams, the tiles will eventually crack across these seams. Re: Screwing Plywood Over Subflooring If your joists are 2x10, you can eliminate the extra layer of plywood and the water proofing membrane, by using Ditra Matting as your underlay. Make sure your 3/4" plywood subfloor is attached solid to the joists. Plywood and engineered flooring is made stronger by alternating the directions of the grains, between layers. The customer's complaint was the dark, rusty spots coming through the wood but it wasn't until HD ripped it out that it was discovered they had a much larger problem. I'd probably be better off investing in thicker, quality hardwood that sheathing my entire first floor in another layer of plywood. I proceeded to remove all the particle board to find the 5/8" (19/32" really) CDX Subfloor over 16" OC Joists. try this: www.schluter.com Still, the top layer has the grain running lengthwise, so installing it perpendicular to the floor joists will make it slightly stronger. If you have a concrete slab floor, the slab may be considered the subfloor. Just screws, no glue is necessary. Engineered or Solid Wood Flooring that is less than 1/2" thick can be installed over a plywood subfloor. Avoid having a plywood seam on the second layer lining up with the subfloor plywood seams. We shared the day with a dozen volunteers, working primarily on structural components of the house, including installing floor joists, installing a 3/4 inch plywood […] Installation over concrete with a calcium carbide reading of greater than 2.5 percent. A layer of 3/4-in. It looks like the cabinets were installed directly on top of the plywood subfloor, and then there was another layer of plywood added below the laminate. Be aware that installing plywood over a subfloor will leave you with an unfinished surface that is exposed; you will almost certainly want to add another layer of flooring before you've completed the job. If you’re planning to remodel or just add new flooring to a room, consider adding a layer of 3⁄ 4-in. Once the plywood is securely fitted, use some wood filler to get rid of rough spots. I have been considering tile on my new construction floor and was wondering if I could put the tile board directly over the subfloor. Re: attaching 1/2" plywood to existing subfloor 19.2" provide a 16" span between joists allowing sheet goods with a 16' rating. It’s rare that the subfloor turns out to be absolutely flat and perfect. The second layer of plywood should be bc grade or better exposure 1(exterior glue)plywood. Over a toilet works best. This will add extra strength while also helping prevent flexing. From a basic sectional properties point of view, if adding the first layer of subfloor increases the strength of the joist (composite joist/subfloor section now) by 10%, then adding an additional layer of subfloor should increase the strength by an additional 10% if not more since the additional layer is further away (larger moment arm). Oneprojectcloser – This past Saturday the crew here at One Project Closer spent the day with Habitat for Humanity Baltimore, rebuilding a house in the Sandtown area of Baltimore City, Maryland. 3/4" T&G was rained on several times. Typically made of plywood or OSB and ranging in thickness from 19/32" to 1 1/8" thick, the subfloor is truly structural, second only to joists in this respect. The subfloor usually runs in a continuous sheet under all the walls. plywood subfloor sheathing over the lumber decking. Most floors have two layers of wood: an underlayment over a subfloor. I have been told to lay the new plywood in the oposite direction to the bottom layer and put it down with screws. The subfloor is the bottom-most layer and it rests on the joists. Add a layer of 1/2-in. Just need to mull over that 3/4" threshold I'd have if I use 3/4" flooring. The existing sub floor is one layer of 1/2" (15/16") plywood over 2x8s 16" on center. But the real concern is the length of the seams along the sides of the individual planks of flooring. But if you have a weak subfloor that flexes up and down when walked on I would recommend adding an additional layer of 3/8" or 1/2" thick plywood underlayment, glued and screwed down over the weaker subfloor will add stability. Laminate Flooring on Two Layers of Plywood Subfloor? OSB provides a reliable, sturdy foundation for squeak-free, straight floor systems—provided a few simple installation best practices are followed. Add screws/nails if needed. If you add a second layer of plywood, locate the seams where the two sheets meet and offset them from each other. Once glued set the plywood on the subfloor and nail it down. Subfloor, underlayment, and flooring is perfectly normal. Tongue-and-groove edges on plywood make the subfloor strong, as if a single piece of plywood was fit over the entire floor. Once you’ve installed a vapor retarder, install your subfloor. plywood firmly fastened to the undersides of joists helps prevent this side-to-side bending and stiffens the floor. This is the standard size for tiling. In addition to a flat surface, your subfloor must also be at least 1 ½ inch thick. Using Kerdi band on the seams will make the floor water proof. And it should be ready for the next flooring installment. 3/4" T&G is glued and nailed. Laying Plywood Over Particleboard. nally laid 1x planks instead of plywood or OSB (oriented strand board). Because it was an elevated subfloor they didn't realize there was water under it that had pooled and the screws from the extra layer of sub the HD installed under the hardwood rusted. 35 years ago we used 1/2" CDX subfooring, 1/2" or 3/4" [depending on the circumstances] and underlayment which might be [again depending on what the finish flooring was going to be] plywood, … Is the purpose of the 3/8 subfloor rated plywood over the Sturd-i-floor to make the floor stiffer for the tile ? I'm thinking of adding a layer of 1/2' or 5/8" OSB on top of the 3/4" T&G after the roof is on, which should be mid-next week. The floor joists run lengthwise to the room, and we want to install a floating laminate floor. Do not line up joints - overlap them about 4-6" or so. There could be minor imperfections such as pinholes, gaps, grooves, pits, and splinters. I would use a good epoxy filled with wood flour between the layers of plywood with screws to hold the plywood until the epoxy sets. I am going to add another layer of 1/2 plywood over the existing 1/2 subfloor. Engineered or solid wood flooring less than 1/2 inch thick can be installed over a plywood subfloor. I understand that I should install a plywood layer over the original lay in order to enable the planks to be installed lengthwise. Conclusion Might be perfectly acceptable. To install a floated subfloor system, first place a layer of plywood subfloor panels with the edges parallel to the wall. Increasing the floor height can create problems in a room with cabinets or a toilet, and it may cause headaches at transitions to other rooms with different flooring. Some flaking. Thanks for the info. Keep the plywood running across the joists to provide the max stiffness. If I add screws to the existing subfloor and then add the plywood I will have a much higher chance of hitting the screws I just put in, wouldn't I? 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