I'll start off by saying my carpentry skills are fairly basic, but I want to learn to tackle more myself. I'm more mechanically oriented, but I generally enjoy DIY projects. I'm also a bit of a perfectionist, so doing my own work usually takes time, but I end up with a better result than when I pay people. Anyway after getting some quotes to install hard wood flooring in a section of our house I decided to attempt it myself. What most of the videos I've seen online don't prepare you for is the unlevel subfloors that I found under the carpet. It seems like quality wasn't a concern when they framed the house. I had a friend that is a custom home builder come by and help me with a few small tasks to get me started. He told me to get Mapei Self Leveler Plus and put it down in the low spots on the floor. I started this process and did several spots, but I'm really having concerns. One section has it almost the length of the room near the wall. I have another client that is also a builder and after telling him about it, he seemed really nervous about me using that under flooring that will be nailed down, rather than floating floors. His concern is it breaking away when you shoot a staple or cleat through it, but he's never done it and is curious to hear how it goes. This lead to further Google searching with some people saying they shot staples through it and it's fine, while many others are saying you can't nail through it as it'll crack it and lead to it crumbling over time. I've seen suggestions on everything from putting shingles over the low spots, using multiple layers of roofing felt in the low spots, using cedar shims, etc. I talked about this more with the guy who originally recommended it and he didn't seem concerned and seemed to think it didn't really matter if it cracked under there since it was just holding the flooring up and the staple was going into the actual subfloor and joist. Now I'm kind of at a loss on where to proceed. I just don't want to end up with a huge issue 5-10 years down the road where I'm having to redo all of this, as it's been a ton of work and I haven't even gotten to the point of laying the floor down.

So my options now are to attempt to chip this stuff away from the plywood and go with either many layers of felt, or a shingle, or similar. Or to cut the subfloor up in these spots and use a shingle or layers of felt to level it from there. Or option #3 is to leave this stuff and staple through it. What are your opinions? Am I going to have issues down the road from this stuff? It'll be a pain to remove/replace what I've put down, but I've only done one room and it'll be much easier to do it now rather than after I lay the flooring if using this stuff is a bad option.

How much deflection are you talking about,

Hard wood staples are usually not long enough to reach the joist.

What will be directly under the new flooring, plywood, mdf, t & g. These would determine how I approached the issue.

I’ve used the self leveler on concrete floors before tile. It is a skill in itself to get it level. When stapling or nailing any material such as flooring. It is common when you hit something hard , the staple can curl and come to the surface of your floor. I would think a leveler that was like acrylic mastic might work better. Hope you don’t have low spots over 1/2 inch. You might try going to a hardwood flooring supplier and ask what the floor guys are using. Most pros do not buy at the box stores. You need a straight edge , longer the better, and go over your floor. Get good with a trowel! You might think about screwing your old subfloor down to eliminate squeaks. Make sure you store the flooring in the house to acclimate. Leave enough space for expansion.

You have several issues going on at once. First why is the floor so unlevel? Does it need structural support? The best flooring job in the world won't be worth much if the floor isn't stable over time.

Next how much of a gap needs shimming? I might would lay an extra layer or two of felt here and there, but you can't shim out something that's way off.

https://www.homedepot.com/p/DEWALT-...-Gauge-Flooring-Tool-DWFP12569/204334521

Yep, stxhunter (aka Ron Jeremy).

Typically the flooring guys are knocking down high spots even on a brand new house. Is that big low spot between joists or?

Some good advice here, This is a birch floor at our cabin. We used a Portnailer.

Never seen a wood subfloor bad enough to not be able to take nail down wood floor. If anything some sanding on the high spots, should be all you might needs. Floor leveler like that is typical for putting in vinyl products. Not nail down hardwood. Have you acclimated the wood floor for the range of moisture content in you area? Post pictures of the subfloor in the house and the product you’re using, It will speak volumes on your situation.

I will admit it is indeed rare, but the OP has yet to inform us the degree of diflection

The portanailer uses barbed wedges.

It doesn't matter if it cracks or not once it's under there. Use it! I use it all the time in my home improvement business. Anyone who mentions it cracking is not a flooring "expert".
Heck, you could even use play sand as a leveler if you wanted to, though definitely not recommended.

I disagree , when you shoot it with floor staples it will crack and as the flexing of the subfloor lossens those cracked spots it will begin to crack and pop when you walk on it. the real concern should be why its so uneven .first then you have to install a product that will work with the situation. just because you want a nail down product dose not mean thats the right product for the situation. OH and I have been doing floors for 36 years doing all kinds of flooring products. I would not call myself an expert , but I have worked in many ALOT of multi million dollar homes and offices. But I will tell you IT WILL MAKE NOISES.

Thanks for the replies so far. It's about a 1/4" variance in the worst spots. I'm trying to keep everything within 1/8th of an inch. The worst spots are actually around the edges rather than in between the joists. It's like the boards around the outside on one wall are all about 1/2" lower.


The subfloor is plywood. I've already had to screw some pieces down to fix squeaks, and one section wanted to sag in between the joists. So I cut that up and braced in between the joists to give it some support. It really tightened that up.

There's multiple issues going on in my unprofessional opinion. There is some slight sagging in the middle between joists on a few spots, but that's relatively minor. Less than 1/8". The joists are 24" on center which seems too far apart. This is why I've had to cut the floor up and brace the worst.

The next issue is that there are two spots where the joists seem to be slightly higher which is creating a crown in each. They are joists that have walls under them on the floor below. I'm not exactly sure what went on here during the framing.

The 3rd is the issue I mentioned above. Along one wall it seems like the edge sheets are slightly lower. It's like that joist is lower underneath. Its the biggest variance and is about 1/4" +/- lower.

Neither of the contractors I know are flooring guys, but they are both telling me I need to address anything over 1/8" or it's going to be hard to install and I'm going to see and feel it in the floor. So that's what I've been aiming for.

I have been letting the flooring sit in the house to get acclimated to the moisture level here.

If the floor joists are lower under the walls, and joists are 24" apart , the walls are carrying too much weight for the 24" joists can support. I am not sure , it is hard to tell with a post . I dont do all that many hardwood floors anymore , since the laminated stuff became the craze. There are some things you need to make sure of.. If the joists can support the weight that the wall is bearing, it may be settled after all those years. It is very hard to prop a joist up from underneath if it is low and holding weight. That would mean you would have to raise the joist, the wall , the ceiling joist
and rafters.. If the floor is lower just around the walls, it seems they settled. If they are done settling, you can just put a 4" strip of plywood around the where the subfloor is low , screw and glue it and you should be good. Again, i am not sure exactly what the problem is so I am guessing a little. If it helps, it is rare to take out carpet to install hardwood floor and not have repairs. We always have a few low and high joists. If it is only 1/8", we dont care, but 1/2" is not good. Pictures might help.

were no building codes required or permits when the house was built? Post some pictures of it. Sounds like the floor may need to be sheeted first. Before tung and grove osb they used plywood then 3/8 partical over that to help the floor not sag between joists and where there was 2 pieces of plywood butting up.

I'll have to take some pictures. The house was built in a county with both building codes and permits were issued. It's in a large subdivision and it seems like the majority of the houses in the neighborhood are all built the same way. I'll have to take some pictures tomorrow to post.

The majority of wood I've done has been glued down engineered wood. I'm sure cumminscowboy has more knowledge on this type of installation than I do.

Lots of questions. I will say a T&G floor is not typically a DIY project. However I get that you want it done right and are willing to learn.

I will also say that a real T&G floor is not practical in every home as a retrofit project.

Subfloor is plywood, good, T&G? How thick?
Size of the joists? 24"O.C. is ok if the joists are sized properly, the subfloor should be 3/4" T&G.

How big is the area? 1/2" out of level is not a big deal in a large room, different story in a bedroom

Realistically forget level, the goal is to make it flat.

Is the new floor to be laid parallel or perpendicular to the joists?

Is the floor end matched in random lengths?

I would make sure the subfloor is screwed down.
I would be concerned with fasteners holding in plywood.

Do you have many transitions to deal with?

Any stairs?

Sorry, I made a mistake. It's about 1/4" variance instead of 1/2". I went back and corrected my post. It's late and I wasn't thinking through what I was typing. Not that it's great, but it's not quite as bad as 1/2".

If you have access to the joists from below you can use Jack's to raise the low spots and sister another joist in , conversely you can cut a high one, stack your wood on it till its level and sister that one . Only had one floor that extremely out of whack but that did the trick. Less extreme ares you can just run shims between the joists and deck and re screw.

Subfloor is 3/4" plywood, but it's not T&G. I don't know what the size of the joists are. I didn't measure the joists under the floor. Possibly 2x10"s? Here's a picture.


I have the measurements of the rooms, but don't have them infront of me. It's two fairly large bedrooms and a hallway. I meant to say 1/4" variance, not 1/2" above.

The new floor is going to be laid perpendicular to the joists. I'm not sure what exactly you mean by the floor end matched in random lengths.

I did go through and ran a couple of screws in each sheet of subfloor. Some of them needed to be tightened up from the nails already. So I've fixed those and then put a couple of screws in the pieces that didn't need any help.

The stairs are already hardwood, as is the lower level. I'll just have to match this up to the top of the stairs, but I don't need to go up or down any stairs.

Knocking down the high spots with a sander helps a ton, especially when you are talking a 1/4" max.

A layer of tar paper, or two, helps more.

Self leveler is a problem with nailed in floors, unless it is mixed with latex or acrylic, as it cracks when nailed and sounds "crunchy" under the floor.


Prep work is what you pay professionals for, the installation is simple.

After seeing the photo, you are over reacting. That looks like good construction. The plywood joints need to be blocked to eliminate movement. There are foam type rolls you buy to put on the plywood before the flooring. This is a place not to go cheap. It will make your floor quiet and act as a moisture barrier. It’s about 1/8 thick. Watch some YouTube videos to build your confidence. It’s pretty easy! Just get your first row straight. Allowing for expansion against the walls are where people make mistakes. I’ve been in the construction trades for over 45 years. There are several here that have the knowledge based on what I’ve read.

One thing not covered here is baseboards. If this is a low budget job you put the baseboards over the floor once installed. The higher end job. Which I prefer, you put the base in first. Install your floor, then go over the base with shoe mounding. It looks nicer. If you ever want to take up the flooring , the base stays. I did a job a few years ago where the people had me put in 1x8 pre primed base. In the old days this was more common as the stacked wall treatments on top. Like bead board. Just think it through. One thing to remember, if you put the base over the flooring, the gaps between the floor really show. With shoe mounding, you can push the mounding tighter to the floor to eliminate gaps.

Sorry , I misspelled molding.

I use shoe mold unless the customer asks that the base be removed.

It’s hard to tell from the photo, but to me that does not look like 3/4 plywood, looks like 1/2.

You are going to want to get a jamb saw to cut your casings and the jamb.

https://www.homedepot.com/p/ROBERTS...in-Jamb-and-Undercut-Saw-10-56/205399057

Also make sure your exterior doors, if you have any, will operate properly with the increased height.

Sounds like Ryan home?!?!

For a smaller job, one of these multi-tools will do the casings and they're useful for many other things. There are lots of models, both corded and battery, to choose from. They're a lot cheaper than a dedicated casing saw, too. There are lots of different blades you can get to match the job.

Is that water line something you did as a repair, or is that throughout the house?

That is some unreliable schit.

Yep. I would replace as much of that as I could with PEX.

Yup, they work just as well, just quit a bit slower.

If this were my project, all the base would be removed, nails pulled and labeled . Less time and money involved than buying base shoe, priming base shoe, painting base shoe, installing base shoe .

This is my biggest concern at this point, so I really don't know what to do. I'm wondering if I should just cut the subfloor up and try to replace it in these spots, possibly shimming it.

Throughout the house. We had to have the pipes replaced 20+ years ago because it originally had Quest pipes. I didn't do that work.

My Wife, and I worked a month on a 12x16 ft floor in our cabin.

Double check that sub floor thickness, sagging between joists is not common with 3/4 plywood.

Like I said, looks like 1/2 inch to me

While not common 24" centers is a decent span, even for 3/4" plywood.

when you say decent span even for 3/4...I assume you mean its on the verge of to much span.....bob

I use these for door jams, I've got two right now both over 3 years old and I use them all the time, no need to spend big bucks.

https://www.harborfreight.com/2-amp-variable-speed-oscillating-multi-tool-57808.html

It's possible depending on how many plies.

If its not T&G subfloor then they likely used cdx and didn't see much glue in the one photo.

Blocking would be a solution, but not possible with a finished ceiling below.

Replacing the SF would not be something I would not be interested in.

Stairs, unless you have changed something, adding 3/4" to the top rise creates a awkward and potentially unacceptable variance in the rises. 3/8" is typically maximum acceptable variation. People base the rise by the first step.

I assume any staris leaving this area is going to a lower level? It really is the same deal if you are dealing with ascending stairs, the rise is less, however if someone trips they fall into the stairs not down.

PVC pipe would not be my choice, but certainly acceptable.

End matched refers to the ends of pieces of flooring also being T&G, pretty common and necessary if using random lenghts.

Why are you set on using a true hardwood floor?

Depending on where you live the joints can open/ close seasonally.

If I was looking at this job for a client I would be steering them to LVP floor, apply some good underlayment, replace the baseboard and move on.

He asked for experts

Even without the T&G, plywood rated for structural sub flooring is different than standard plywood.

It has layers that are not just altered 90*, but one or two that are at a 45*, we used to call it StrudyFloor


Regardless, his subfloor is neither T&G or subfloor rated.

I still have a hard time believing it is 3/4

He is better off sheeting the whole thing with a Sturdy floor sheathing and then applying click together or glue down

.
I don't like the "base shoe" look and would rather have base at full height above the floor.
I could see on a remodel where you might want to leave the existing base and then add base shoe.
It's all personal taste, I like the cleaner look of just the base and a cleaner interface with the door casings.

Glad someone mentioned using a Multi-Tool for cutting off the door casings. This tool was a boon to floor guys.

The stair mention was about the added height to your last riser with the new floor covering.
Unavoidable unless the entire stair is re-done....not practical in most cases.
There may be other new floor interfaces to deal with like existing thresholds, door bottoms and lower floor surfaces.

Use the roll underlayment....several brands like Quiet Floor.

"All edges supported" on your plywood subfloor....no plywood butt joints unsupported.

Get your fat guy buddy to walk around and identify any floor squeaks and soft spots that need to be taken care of.

Thoroughly think through which direction to run the new flooring.
Often one way makes the room look bigger and the other makes the room look smaller.
Some rooms like a corridor, look better "long way".
An entry area might look best with the flooring running away from the entry door instead of across it.
If you have to change directions, make the transition at the center of a door bottom or other natural break, if any.

Mark your joist locations.

Use random locations for your flooring butt joints.
A uniform "stair step" pattern does not look good at all.

Use (rent) a bona fide hardwood flooring pneumatic nail gun. This is a mallet-actuated gun.

I buy very few high-end hand tools or small electric tools for work, they have a way of disappearing between helpers and others on job sites.

There is only one way to run the flooring in this situation, perpendicular to the joists.

Seems to be an ass load of flooring experts.

Should change the name of this place. Hmmm, I never knew.

Go with Roger’s advice.

The thing about these is the guard around the blade can keep you from getting into tight corners so on the two I had years ago I removed the guards which makes them dangerous as hell. I wouldn't let anyone use them because I knew how easy it would be to lose fingers.

No surprise.

Almost as many experts as on the medical question threads.

Just buy real 2x4s and drink black coffee . Pray.

I do not claim to be an expert.

It’s a good thing

1/4 inch over how much span? Thats very little except if it's in a really small area.

Nobody is claiming to be an expert, not even Roger, just guys with some experience trying to help out.

But, hey, be a dick, it's just par for the course.

On something like this, I'm leery of giving advice without having actually looked at it, pictures don't tell you everything you need to know on something like this. I never quote a price for prep without seeing the job myself first, that chit can come back and bite you in the ass when it comes to collecting and you tell them prep was going to so and so, and then you tell them it's going to be a few hundred extra.

Another prep trick - if you have some low spots, lay down some pieces of asphalt shingles. They don't compress under weight. Often a shingle dealer will have some broken bundles in a scrap pile that you can get cheap or free. 3 tabs work best.