replacing entire subfloor

Discussion in 'Remodel Forum & Blog' started by number1hag, Sep 24, 2007.

  1. number1hag

    number1hag New Member

    mountain home, ar.
    my house was built in the 70's so the subfloor is partical board and in some places if it were not for the carpet you would fall through. at some point someone covered some of the partical board with 1/2" ply (not much help). the only up side is without the bad floors i would not have been able to afford this 2000 sq. ft. house where it is.

    i am planning to tear up all flooring down to the joist and replacing it with 3/4toung and groove subfloor.

    i have 15 yrs. expeirience as a remodel carpenter in AZ. but there every house i ever worked on was on a slab so subflooring is not my fortee.

    i know i can do this but i do have a few concerns.

    1st. what subfloor is going to work better 3/4" osb or 3/4" ply? price is less than 2 dollars a sheet diference. i am planning to put 2 3/4" X3/4" oak hardwood over it. my joist are 16" apart.

    2nd. anything special i should watch out for when lifting the interior walls enough to slide the new subfloor under them? (all electrical comes down from the attic)

    3rd.where the water pipes come up through the floor, should i cut and notch the new subfloor or just cut the pipes and replumb? i am thinking replumbing would be best.

    i know there is going to be plenty of drywall repairs to do when this project is over.

    anyone who has ever taken on a project of this magnitude and lived through it without getting a divorce please give me any advice you can no matter how simple or mind numming you may think it is. you never know, that little tidbit you throw out there could be the one that makes my job that much eazier.

    thanks in advance for all your helpful comments, Kevin
  2. Livin4Real

    Livin4Real New Member

    Indianapolis, IN
    I fell your pain. We're in the middle of a complete gut and remodel right now, though I didn't go all the way down to the joist on the subfloor. I have however removed everything in between the rafters and floor aside from studs, we've been living in it during the process as well and there have been times I thought I'd go insane.

    1.) My vote is for plywood, here's a great article on the debate as well.

    2.) I think your going to run into major problems trying to lift the interior walls, especially if you don't plan on replacing ALL the drywall. You would be better off just cutting along all the walls and leaving the sub under the walls, unless it's just completely trashed. That's a huge undertaking involving structural engineers, etc.

    3.) Leaving the sub under the walls would take care of this problem, along with alot of electrical wiring having to be moved as well.

    Like I said, I'm living through a big remodel right now, next up is a complete plumbing replacement in a house with only one bathroom! Luckily we have a full basement so most of the houses contents are crammed in it right now. Our kitchen at the moment consists of the kitchen sink (that's it,lol) with 2x4 legs so I could cut out the rest of the counters/cabinets and redo the drywall, wiring, etc. Our future bathroom is setup in the living room so I can preplan on all the measurements, plumbing, wiring etc. So I can have everything ready to go right back in since we only have the one bathroom, we'll be using a boat toilet while the ceramic is getting put down. So yes it will be rough and yes you'll find days where you want to severely hurt anyone within 5 ft. but it'll be worth it in the end (at least that's what my wife keeps saying, lol)

    Good luck,

  3. leejosepho

    leejosepho DIY scratch-pad engineer

    I would likely use t-g plywood at least 3/4" thick to go under the hardwood, and I would not try to lift either the interior or exterior walls. Unless you have balloon framing, the flooring is likely under both, you know, and the exterior would be the more crucial anyway. So after cutting the floor along the walls, I would assess the overall situation as far as the walls sitting on something solid and possibly, if necessary, chisel the old flooring out over one joist at a time and insert planed-if-necessary blocks of SYP (not SPF) 2x4. Then to get a solid edge for the new flooring, I would add nailer blocks between the joists along the walls.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    #2. You are kidding, right, about lifting the interior walls? You would have to lift the roof and everything to do that.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    I replaced all of the subflooring in my place partly for the same reasons, but also to flatten the floor. I cut it flush with the walls, and where they would have been hanging, I put in enough cross blocking to support them well or sistered a joist when necessary. I personally like Advantec - it lays flatter than ply and works well. While applying the subflooring will help flatten the floor a little, take the time, if you can, to take a littel crown off the high ones. Laying down any flooring on top is SO much easier if the subflooring is flat. use construction adhesive on the joists and ringshank or screws to hold it down and it is substantially stronger than without the glue.
  6. Old Dog

    Old Dog G.C. 22+ years(in 3 states)

    subfloor replacement...

    I prefer to use 3/4"plywood sub flooring.Definitely use subfloor adhesive
    (Like liquidnails brand).I personally use screws on my subflooring.Nails are more prone to leave a "squeak" behind.
    I take a circular saw at the right depth and use the guide up against the bottom plate to cut out bad subflooring.I finish up the inside corners with a sawzall.It leaves a straight cut to butt the new subfloor to.It can be a little tricky in the corners and expect to hit a couple of nails along the way...
    I normally don't cut the sub floor up to the bottom plate unless it's damaged.
    I would install nailing blocks at the walls.Also a good time to make sure all the simpson strong ties are in for the joists.
    Don't forget to stagger your sub floor panel joints...
    BTW,the only reason to lift a wall like you proposed is if there is sagging due to wood damage of the joists,beams,etc where you have windows and doors not opening or shutting because of it.
    Last edited: Sep 25, 2007
  7. number1hag

    number1hag New Member

    mountain home, ar.

    thanks for all the info. i never thought of just putting blocking between the joist under the floor wher the walls run in line with the joist. this will make my job a whole lot easier and less stressful. trust me, my wife thanks you all.
  8. statjunk

    statjunk DIY Senior Member

    Use lots of glue when puttin down your subfloor. It will stop the floor from creaking. You'll also need less screws to hold the floor down.

    While you have the joists exposed you may want to consider adding additional strength to some areas. For example if you plan on installing tile in the bathrooms you may want to beef up the floors in those areas incase you end up going with a natural stone or something like that. There may be some other things that you'll want to do.

    I'd vote for plywood and redoing the plumbing. I'd also vote for cutting the floors out from around the walls.

    One last note. If a wall bears weight you'll have to support that wieght while you install blocking to hold up the wall.

    Good Luck

  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    If you get a good glue and coverage (I like PL brand urethane stuff), the anchors are only there to hold things until the glue set up and a quality ring shank nail is fine. Screws can really help if the joists are not straight, though, since snugging the subflooring up to them can be a pain if it is not already sitting flat on it. You could remove the screws or nails after it sets, and not compromise the install if your glue coverage, contact, and quality is good. Sweep off the top of the joists to remove dust and crud before applying the glue.
  10. LiamM

    LiamM New Member


    i just did basically the same job. it was on a second floor, and i demo'd the interior framing as well since it was non load-bearing. i got rid of all the old subfloor from one gable end to the other, and replaced it with 3/4" T&G OSB (although in hindsight, i prob would've spring for the 3/4" T&G ACX or BCX particular reason, i guess just a gut feeling). i'm putting down 1/2" BCX plywood underlayment on top, prior to the finish flooring.

    to get rid of the subfloor, i rented a toe-kick saw to cut flush with the sole plate of the exterior walls. in the corners where the toe-kick wouldn't fit, i used a sawzall to finish the cuts. those corner cuts came out a little jagged, but i just notched the corner of the new subfloor before i put it down.

    where the outside wall is parallel to the floor joists, i installed full-height blocking every 12" between the rim joist and adjacent joist (make sure that you have blocking in this joist bay underneath the subfloor may need a coupla additional pieces since 12" may not fall exactly under a seam). i then used a 3" deck screw, screwed through the outside wall sole plate into every piece of blocking. i also screwed the new subfloor into all the blocking.

    where the outside wall is perpendicular to the floor joists, i didn't use any blocking, although i did screw through the outside wall sole plate into every floor joist. again in hindsight, i probably would've laid at least a 2x4 flat in every joist bay, with 1/2 under the sole plate, and the other 1/2 acting as a nailer for the subfloor edge, and then screwed both the sole plate and new subfloor into every piece of blocking.

    to actually install the floor, i used 2 1/4" screws, plus a bead of liquid nails (subfloor type) on every joist. make sure your first row of subfloor is straight; it'll make the rest of the job easier. and you only have 1.5" where 2 panels meet, so it's easy to accidentally cut a panel too short (so it doesn't end in the middle of a joist). if so, just screw a 2x4 or bigger so it's flush with the top of the joist; that'll double your space.

    good luck with this job...take your time, and you shouldn't have a problem. i'm a homeowner and had never done any rehab work before this DIY job, but so far, i've gutted everything, put down 850 sq ft of new subfloor, installed all the insulation, done all the partition framing (2 bedrooms and a bathroom), hung and taped 2500 sq ft of drywall, and am now putting up window trim and doors. these online forums have really helped me out...
  11. always leave an air gap -- others will tell you more about how much.

    cutting the existing subfloor at the walls and installing another subfloor there helps isolate acoustically, preventing sound transfer through floors and ghrough walls at the floor. Heavy steps, loud subwoofer sounds, these things will stop at the wall-floor junction if you leave an air gap.

    high quality OSB will be as good as plywood, from what i hear and read. Not to contradict anything said above. I might use the product mentioned that is one level of quality higher than plywood. When remodeling, often the cost of materials is not the big factor. Whatever works, is available, etc.

  12. G8KeaPoR

    G8KeaPoR New Member

    F'burg VA
    My floor

    Ok I bought my house 5 years ago and at the time replaced the carpet back then there were no water damage spots on my floor. recently My cats started to "attack" one area of the carpet in the master bedroom where the batthroom and bedroom meet along the exterior wall. When I removed the carpet I found rot on the floor. fortunately it was only the Subflooring. I have been reading alot in this thread about different tactics to fixing and thought I would throw in my way that I fixed mine. My house has single layer 3/4 particle board and I dont have floor joists my house uses tressles so it doesnt have the I beam or any metal supports through the house. Being that it was the exterior load bearing wall that had the floor damage and the floor was rotten under the bottom plate I did have to "Jack" my wall's. It doesnt involve lifting the entire roof as someone mentioned earlier. I was able to get by with cutting the bottom foot of drywall the lenght of the area off. Next I used 3 people and 3 BIG prybars (by big I mean 4'+ bars) to lift the wall just enough to get a sawsall blade in there to cut the nails. (we jacked it in sections not all at once either.)
    I worked in just over 2 foot sections or the span of 3 tressles. cutting the nails and from the exterior of the house I had removed one strip of sideing to apply a brace every 2 feet from the house to my deck to keep the wall from kicking out.
    as each section was finished and the wood removed I would slide in small maybee 1 inch by a little over 3/4" shims underneath where the tressles and bottom plate met to keep the wall from sagging anywhere. once I was done I took and cut notches in the subfloor board so I could slide the new flooring in and then with the lower foot of drywall removed I put new nails through the bottom plate etc. (note this was the second level of my home.) I did have some minor drywall cracks in other parts of the house but nothing big enough to require a major taking probably the worst one I had was on the opposite eng of the house in the cathedral ceiling. but it was only bad because I had to get a ladder to get up to it. all in all it took me a half hour to fix the cracks. I can't guarantee you wont run into problems and depending on house constructions and ages etc you should probably consult someone that knows structural stuff as you could end up with colapsed walls and a roof in your lap. luckily for me my neighbors brother was a structural engineer so we came up with a cheap alternative to having a contractor come out and apply scaffolding etc to "jack" the wall.
    Sorry for the poor punctuation etc im used to typing in Unix or SQL not in english!!!
    Last edited: Apr 1, 2008
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