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