I'm looking for some advice on adding a second layer of OSB to a 3/4" T&G subfloor. If you are thinking of laminate, use a pad to cover the underlayment. The existing sub floor is one layer of 1/2" (15/16") plywood over 2x8s 16" on center. I-joists are 16" oc. Just screws, no glue is necessary. Conclusion Make sure your 3/4" plywood subfloor is attached solid to the joists. For this fix to work well, the upper edges of the joists must be solidly fastened to the subfloor above. Add a layer of 1/2-in. The subfloor is the bottom-most layer and it rests on the joists. Re: attaching 1/2" plywood to existing subfloor 19.2" provide a 16" span between joists allowing sheet goods with a 16' rating. The second layer of plywood should be bc grade or better exposure 1(exterior glue)plywood. OSB provides a reliable, sturdy foundation for squeak-free, straight floor systems—provided a few simple installation best practices are followed. 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 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. nally laid 1x planks instead of plywood or OSB (oriented strand board). The subfloor is the first layer of flooring material installed on top of the floor joists. When nailed through the old subfloor and into the joists, the new subfloor can help to reduce floor bounce. Once glued set the plywood on the subfloor and nail it down. 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. The subfloor usually runs in a continuous sheet under all the walls. I have been told to lay the new plywood in the oposite direction to the bottom layer and put it down with screws. 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. try this: www.schluter.com 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. If you have a concrete slab floor, the slab may be considered the subfloor. Is the purpose of the 3/8 subfloor rated plywood over the Sturd-i-floor to make the floor stiffer for the tile ? I'd probably be better off investing in thicker, quality hardwood that sheathing my entire first floor in another layer of plywood. Laminate Flooring on Two Layers of Plywood Subfloor? I have removed the carpet and 5/8 particle board. 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). It can’t be removed easily. I just started a kitchen demo today, and once the old cabinets were out I got to take a look at the subfloor. Improper spacing. Once the plywood is securely fitted, use some wood filler to get rid of rough spots. 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, … If you have really solid hardwood floors, then bridging small gaps won’t be an issue. 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? Keep the plywood running across the joists to provide the max stiffness. A beautiful floor starts with a stable subfloor. 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. 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. And it should be ready for the next flooring installment. To install a floated subfloor system, first place a layer of plywood subfloor panels with the edges parallel to the wall. 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 … 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 […] I proceeded to remove all the particle board to find the 5/8" (19/32" really) CDX Subfloor over 16" OC Joists. Avoid having a plywood seam on the second layer lining up with the subfloor plywood seams. Over a toilet works best. Parke, Star, JBowers, this 2 layer not-glued subfloor system is very counter-intuitive, but has passed both laboratory testing and field experience. 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. 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. Vinyl flooring is usually not installed directly over the subfloor in residential applications. 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. Engineered or solid wood flooring less than 1/2 inch thick can be installed over a plywood subfloor. If there is any "flexing" or movement at the seams, the tiles will eventually crack across these seams. If you’re planning to remodel or just add new flooring to a room, consider adding a layer of 3⁄ 4-in. I have been considering tile on my new construction floor and was wondering if I could put the tile board directly over the subfloor. Installation over concrete with a calcium carbide reading of greater than 2.5 percent. Add screws/nails if needed. For hardwood floors, use some felt layer over the plywood underlayment for better results. It’s rare that the subfloor turns out to be absolutely flat and perfect. Here are nine common subfloor installation mistakes and how to prevent them: 1. 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 will be installing 3/4 prefinished oak naildown flooring in our bedrooms. plywood firmly fastened to the undersides of joists helps prevent this side-to-side bending and stiffens the floor. I have a second story floor that was carpet over plywood subfloor. Because of the seamed plywood sheets, there are rare perfect subflooring process possible. Seems like the extra layer could cause issues if not installed carefully. Once you’ve installed a vapor retarder, install your subfloor. The floor joists run lengthwise to the room, and we want to install a floating laminate floor. If you add a second layer of plywood, locate the seams where the two sheets meet and offset them from each other. How to Lay Subfloor on an Uneven Floor. Do not line up joints - overlap them about 4-6" or so. This will add extra strength while also helping prevent flexing. plywood subfloor sheathing over the lumber decking. 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 understand that I should install a plywood layer over the original lay in order to enable the planks to be installed lengthwise. There could be minor imperfections such as pinholes, gaps, grooves, pits, and splinters. If your home has particleboard subfloors instead of plywood subfloors, you may want the added durability plywood has to offer. It was a mess. Avoid screwing the second layer into the joists (but make sure the first layer is solidly attached before adding the second). 3/4" T&G is glued and nailed. Subfloor, underlayment, and flooring is perfectly normal. I believe that 2 layers of 5/8" ply is one subfoor recommendation. 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. 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. I am going to add another layer of 1/2 plywood over the existing 1/2 subfloor. In addition to a flat surface, your subfloor must also be at least 1 ½ inch thick. This is the standard size for tiling. The subfloor is 3/4" T&G Avantech on … 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. Still, the top layer has the grain running lengthwise, so installing it perpendicular to the floor joists will make it slightly stronger. 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. 3/4" T&G was rained on several times. This is new construction. But the real concern is the length of the seams along the sides of the individual planks of flooring. Only now is the subfloor ready for cement board underlayment. 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. Using Kerdi band on the seams will make the floor water proof. 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). 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. Might be perfectly acceptable. Just need to mull over that 3/4" threshold I'd have if I use 3/4" flooring. Engineered or Solid Wood Flooring that is less than 1/2" thick can be installed over a plywood subfloor. Tongue-and-groove edges on plywood make the subfloor strong, as if a single piece of plywood was fit over the entire floor. A layer of 3/4-in. Plywood and engineered flooring is made stronger by alternating the directions of the grains, between layers. Most floors have two layers of wood: an underlayment over a subfloor. Thanks for the info. 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. 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. With the plywood in place, install the backer board as you normally would. Laying Plywood Over Particleboard. 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.