Removing Entire Subfloor

[farmhouse]

Hello Everyone! First post here, but long time lurker.

I am starting a major first floor renovation of my house. The house was built ~1910. I am about to replace all of the flooring on the main floor, and would first like to rip out all of the flooring, including the subfloor.

My question is this: Is it ok to remove the entire subfloor from the first level of my home before replacing any of it? My plan is to remove everything, down to the floor joists, find the "high spot" and then level all of the subfloor to the high spot.

The flooring that is in the house right now is not in too bad of shape, and is fairly level. I would build over it, but it already has a couple layers on it, and I would rather just put in the extra effort and "start from scratch" to make sure everything is flat and level.

Is there any problem I should be concerned about if I remove all of the subfloor before replacing any of it?

Thanks!

[HayZee518]

use a crowbar and a nail remover on the boards. a house that old might use cut nails to hold the boards down. sight along each joist to see which way the joist is cupped. what that means is each joist bends either up or down along its length. the cupped or up side should go up. if you have the opportunity to see a flat bed truck trailer, you'll see that the middle bends up, so that when a load is applied, the bed springs downward a little to support the load. same concept in a floor joist. the springy-ness is what gives the joist the property of holding a load.

[mrcaptainbob]

I had the same issue in my house (c:1860's). I did two rooms so far. What I did after removing everything to the floor joists was to set up a horizontal laser. I made a map of sorts of the floor joists. Taking spot checks along each joists at about 12" intervals and noted them at their locations on that 'map'. I then zeroed the dimensions, that is to find the highest/ lowest and find the difference. Then subtracted that diff from all the other dimensions. Cut the blocks to size and glued them at their respective locations. They ranged from 1/16 to almost 1 3/4". I chose 12" spacing as it was just easier to deal with. I figured the joist dimension was 16", so the 12" in the other direction was at least as good. Over this I set a layer of 3/4 ply and glued it to the spacer blocks, while screwing it to the joists. The second layer of 3/4 ply was layed perpendicular to the first and also glued and screwed. That was about six years ago. Solid as a rock and still as level as the day it was done. That laser was the key for me.

[Nestor]

I've never done this kind of work, but I can't help wondering if an easier method than Mr. Captain Bob describes couldn't be had by sistering each of your existing joists.

What I'm thinking is that if you could use a water level or laser level to find the high point of your floor, and then use that same water level or laser level to get the sisters at each end of your row of floor joists level with that high point, you could then tie a mason's line between those two end sisters to set the elevation of all the intermediary sisters in between.

That is, instead of gluing spacers on top of each joists, buy straight lumber (and anything larger than a 2X4 is usually pretty straight) and just set the ends of each intermediate sister level with the string.

And, if it wuz me, I would borrow a trick used by people who build fences. That trick is to cut a short piece of 2X4 into three pieces of approximately equal length. Fasten one such piece to the same side of each of the two END fence posts of the fence you're building. (When building fences, you set the end posts first.) Then, attach a string to the outside of the 2X4 fastened to each end post, pull tight and fasten the string down (by tightening a screw the string is wrapped around, for example). NOW, when you set each intermediate post, use the third piece of 2X4 as a gauge to measure the distance from that string. If your intermediate fence posts are all the thickness of your 2X4 gauge away from the string, and vertical according to your spirit level, the fencing God "Picket" will smile on you and make sure that your fence ends up perfectly straight.

The idea here is that by measuring the distance of each intermediate post from the string, no intermediate post will actually be touching the string and thereby potentially changing the string's position. Cuz, if that were to happen, all subsequent posts would be out of line.

By setting each sister the thickness of a piece of 2X2 under the string, each sister should be level with all the other sisters as well as the end sisters. Now, just fasten your new subfloor to your sisters instead of your original joists.

In fact, you probably don't even need to sister the joists. Gluing and screwing 2X6's to the sides of your existing joists should be sufficient. I'd use LePage's PL Premium as your glue because it cures to a bond strength three times that of other construction adhesives within 24 hours.

PS: You definitely don't need to read the rest of this post. In fact, you might even regret reading further, but I think it's interesting...

Speaking of LePage's PL Premium, which the LePage's Company claims is a moisture cure polyurethane construction adhesive...

... it was actually Otto Bayer, the founder of the company that makes Aspirin, that patented the very first "polyurethane" back in 1956, and Otto's "urethane modified alkyd" quickly became the clear coat of choice over wood because it dried to a harder, more durable and clearer film than real varnish.

And, the way Otto cooked up his first batch of "polyurethane" is actually quite straight forward (although it was cutting edge chemistry at the time):

An "alcohol" is a "hydroxyl group" (like this: -OH) bonded to a carbon atom, and
a "polyol" is a chemical that has more than one of those.

Glycerine, for example, has three alcohol groups in it:



An "isocyanate" is anything with an -N=C=O group in it, and
a "polyisocyanate" has more than one of them, like this:




When you cook an alcohol and an isocyanate in the same pot, they react to form a "urethane" linkage between the former alcohol and the former isocyanate, like this:



and that ugly yellow mess between R and R' is a urethane group or urethane "linkage".

Well, an "alkyd resin" (which you find in modern "oil based" paints) is made by cooking two chemicals, namely phthalic anhydride and glycerine in the same pot. And remember, glycerine has three alcohol groups in it.

So, what Otto did was add polyisocyanates to the pot when making alkyd resins.

The result was that the isocyanate groups in the polyisocyanates he added reacted with the alcohol groups on the glycerine molecules to form urethane linkages INSIDE the alkyd resins.

The result was an alkyd resin that was built like a race car. The urethane linkages within the alkyd resin acted very much like the roll cage in a modern Nascar car, making the alkyd resin harder (if you could squeeze one) and stronger (if you could stretch one) than a normal alkyd resin. This is the reason why polyurethane hardwood floor finish, or even polyurethane "varnish" is harder and more durable than modern alkyd "oil based" paint. It's because the tiny particles of plastic that make up polyurethane are harder than the tiny particles of plastic that make up an alkyd paint.

The way those alkyd and polyurethane resins bond together to transform into a solid plastic film remains exactly the same, tho, cuz that involves a different chemical reaction that the urethane linkages don't play any part in. This is why polyurethane "varnishes" and alkyd paints are similar in so many respects; they both rely on the same chemical reaction to transform into a solid film. It's just that one kind of resin is harder and stronger than the other kind cuz it has a roll cage made of urethane linkages.

But, Otto Bayer's kind of "polyurethane" is a completely different animal than a "moisture cure polyurethane", which is what LePage's claims that PL Premium is. There are lots of different kinds of "polyurethanes" depending on what R and R' you use to make them, but there is only one kind of urethane linkage; namely -NH-(C=O)-O-, and any plastic that has lots and lots and lots of those, is a "polyurethane". That's why you can have a clear, hard polyurethane coating on your hardwood floor, a strong polyurethane bumper on your car and polyurethane foam in your sofa's seat cushions. Completely different kinds of materials that are all "polyurethanes" simply because they all have lots and lots and lots of -NH-(C=O)-O- linkages in them.

[mrcaptainbob]

I wish it were that simple, Nestor. Hopefully it is for the op. The situation I have is, as mentioned, a house from the 1860's. The floor joists in the one room were severely ant eaten from years ago and had to be more than sistered. I sistered all the joists anyway. In fact, the main beam that spanned the access staircase was also eaten away. Did not want to replace that 10 x 10 with another. Instead I used a 4 x 4 x 20' I-beam next to the rock wall for a new support. All sisters rested on that and the opposing natural rock wall. As for the new lumber being perfectly straight, well, these weren't. But I did lay them so the curve (though minor) was to the top. Glued, temp nailed, then through bolted all sisters. After the laying of the sheet wood over those admittedly complicated spacers, it did make for a very level and very solid floor. As a side not, the second floor had to be jacked up with posts resting on the basement floor. That 10 x 10 I mentioned was holding up (barely!) what was the original brick outside of the house. That brick was removed and replaced with a stud wall resting on those new sisters. It was more than an interesting job. Lots of challenges with rewiring, plumbing (waste and dw) as well as the heating system.
Although your note segued a bit from the op, it was still an interesting and informative read. Thanks for sharing.

[Nestor]

I'm just thinking that there may be an easier way to level an old floor by sistering the joists instead of installing spacers.

[pushkins]

The first question one needs ask is "what is the floor doing ? is it a high spot due to a crowned joist, other joists that have sagged, or a foundation issue where one side is or has at some point settled.
The second question would be "by how much" ? often you will find one or two joists sag and this can throw out an entire room. If this is the case then sistering is the best option.

Make sure if you do sister joists in place that they get "glued and screwed" to the existing joists and if possible sit them on the same bearing points. Whatever you do do not try to straighten the sagged joists by pulling them up to the new joists.
While you have it all open add in some blocking of the same size lumber between the joists, this will help stiffen the floor.