# Replacing subfloor



## BrandonBoss (Mar 4, 2017)

I am starting to look into replacing all subfloor in my 1000 square foot house that is closing in on 100 years old. I have hardwoods underneath the carpet and then it appears as though I have 2 layers of subfloor. I know I have atleast one layer of 1x6 diagonal subfloor. I wasn't expecting two but regardless its old. When I bought the house 6 years ago they redid all the floor joists by sistering in new joists that are notched and land on the stem wall and cut the ends off the old original joists and sistered them. They did a pretty bad job sistering them. They didn't clamp or glue them but it appears like they just used a nail every few feet. Since the repair my floors are getting creakier every month and I can't live with it anymore. I plan on opening up the floors and replacing the 3 layers with 1 layer of 1 inch tongue and groove plywood. I will use adhesive as well. My question is when I am dealing with walls that run parrelel with the joists do I just block the joists underneath them to support them? I do NOT want to replace all the subfloor under existing walls or around the rim of the house although it appears that I may have to do some rot repair in those areas regardless.  Any suggestions are welcome. I just planned on blocking all the joists that run underneath the parallel walls. The ones perpendicular should be ok from what I read. Thanks in advance.


----------



## zannej (Mar 5, 2017)

Have you also posted this question on our sister forum http://flooringforum.com/ ?
If you don't get an answer here, they might be able to help you over there.

I'm no flooring expert, but if the squeaking started after the joists were sistered and they only used a nail to sister, I wonder if that is what is making the squeak. But I will defer to the experts in that area. I could have sworn that you needed more than just nails for sistering(thought they used some sort of metal ties on the bottom as well as glue between) but I could be wrong.


----------



## slownsteady (Mar 5, 2017)

I would start with the joists before getting into the subfloor. One of the pros will be along to give you details, but I think you will solve some of the problem by adding some nails or screws to the sisters. Get a couple of heavy c-clamps and pull each pair of the joists tight together and run some 3 inch screws in. Then move on tho the next pair.etc. if there are no blocks in between, add them. You may need to shim or use new blocks after the joists are tightened up.


----------



## BrandonBoss (Mar 5, 2017)

Pulling up the edge of the carpet in my living room their is a gap between the hardwoods and first layer of subfloor. The 2nd layer has rot on it for sure. Not sure about the bottom (3rd layer) one. I really just want to fix it right and I know its going to not only be time consuming but expensive. Another thing is that the old joists were notched and were 2x10s. The new 2x10's were also notched at the ends to fit beneath the subfloor and stem wall. If the guy who did the work didn't notch them all around the same ( I seen one where it was notched less) then the tops of the new joists aren't going to be even. That was another reason I wanted to open it up so I could somewhat level the joists so their aren't any high or low spots when redoing the subfloor.


----------



## BrandonBoss (Mar 5, 2017)

Not sure why but I don't think my response posted. Ideally I wouldn't want to have to replace the whole subfloor in the areas that I walk. Underneath walls are areas I don't really want to mess with if I don't have to so I plan on blocking the areas underneath walls that are parallel to my floor joists. The walls that are perpendicular to my floor joists I just planned on sending screws in at an angle to attach the new joists that were sistered in to the subfloor under the walls. Then the outer walls that are parallel do the same thing by somehow blocking and connecting the closest joist to the rim joist or build something underneath the walls to support them since the subfloor won't be hitting a joist to support it. Another thing I am worried about is that when they sistered in the joists 6 years ago (these are now the main support joists as they cut the ends off the old joists that were rotten) they notched the ends to fit them underneath the walls and on top of the concrete stem wall. I know they didn't notch them all the same so I probably have some uneven joist tops so regardless I would like to even them out the best I can. I figured if I put down some 1'' tongue and groove plywood subfloor I would never have to deal with it again while I live here and it would be sturdy enough for any type of finished flooring.


----------



## Snoonyb (Mar 5, 2017)

After you have the sistering and blocking straightened out, you'll be better served to nail or screw the existing diagonal sheating, walking the floor and addressing and squeaking as you go.


----------



## BrandonBoss (Mar 5, 2017)

Any tips on if I do replace the subfloor? I have a feeling its going to be a gut job and want to be prepared for the worst of it.


----------



## zannej (Mar 5, 2017)

Do you have any photos of the joists and how they are notched? That could be a structural issue.


----------



## BrandonBoss (Mar 5, 2017)

They are all notched like this. I would say they are notched anywhere from 1'' - 2''. They are 2x10's. I don't think its a structural issue although one of them is is starting to show signs of getting crushed by excessive weight from above (I have a safe over the one that is) so I plan on strengthening that one this summer. Not sure if it matters but they are all pressure treated. 
	

	
	
		
		

		
			





http://[/IMG]


----------



## slownsteady (Mar 5, 2017)

Okay, so we can safely assume you have access to the joists from below. Is it a crawlspace or a basement?


----------



## BrandonBoss (Mar 5, 2017)

Crawlspace. I probably have around 30'' or so give or take from the bottom of the floor joists to the ground.


----------



## nealtw (Mar 5, 2017)

Engineers don't like to see notches what so ever but unless you are seeing cracking starting at the notch you are fine.
If you are seeing crush factor at a joist you want more blocking below the floor along side the floor joist to spread the load to a larger area, may want to lift it to get it back to straight and level.

Run a new floor joist to support an interior wall that is only supported by the sub floor.
Remove old flooring leaving the angled floor, might be able to fix that with screws.
If you do remove the last one, cut the old floor 1 1/2 inches from wall, (width of skill saw table).
Glue and screw joiners under the floor, something like 2x4 half under old floor, half under new floor.

T and G plywood, thickness to match old floor glue and screw.


----------



## BrandonBoss (Mar 6, 2017)

I was looking into buying a toe kick saw so I can flush cut against a wall. That way I can put in the thicker subfloor. If I blocked underneath the wall between the closest joists and then cut would it be ok? Not sure if I will be able to run a new joist underneath the wall but we could try. What about supporting the exterior walls running parallel with the joists? Thank you for your time. I appreciate it.


----------



## nealtw (Mar 6, 2017)

Your biggest fear is things moving when you remove the floor. If you can't get a floor joist in under and interior wall some blocks between to joists below the wall and the same for the exterior wall blocks between the first joist and rim. Block every 2 or 3 ft  joist material.
A sawzall with a long blade will be quicker for cutting flush to the wall


----------



## BrandonBoss (Mar 6, 2017)

What would I use to hold in the blocking? Would I use joist hangers and just mount them to the interior sides of the joists or use 3'' screws on the outside of the joists? Any suggestions on screws or lag bolts? I may have to sister in some joists to level the floor since the joists are notched at the ends and they probably aren't all level. I planned on buying a cheap planer just in case to plane down any high ones. Thanks again.


----------



## nealtw (Mar 6, 2017)

BrandonBoss said:


> What would I use to hold in the blocking? Would I use joist hangers and just mount them to the interior sides of the joists or use 3'' screws on the outside of the joists? Any suggestions on screws or lag bolts? I may have to sister in some joists to level the floor since the joists are notched at the ends and they probably aren't all level. I planned on buying a cheap planer just in case to plane down any high ones. Thanks again.



If you are already doubled up a 3" screw won't reach 
I would just use hangers, you not holding that much weight for the interior wall and the exterior wall you block will have full support on the sill plate and that would be enough to stop the bending factor.

Any high joists will bend down to true if you screw down 1" plywood.


----------



## BrandonBoss (Mar 6, 2017)

I know I don't have a sill plate on the 2 sides of the house that the joists land on the stem wall. I know they did it wrong but I have to live with it now. They notched and landed them on the concrete with a roofing shingle between the two layers. Now the other 2 sides of the house where the joists run parallel I have no idea what is going on their yet. I can't get to it right now because I have a sunken crawl space and it has water in it all winter/spring. Only about 6'' is above ground and the rest is underground. I was planning on getting rid of the sister joists when I opened up the floor so thats why I said 3'' screws. May be hard hammering in hangers between joists so maybe I can just use smaller screws to hold them in? I don't need to level the joist tops before laying the 1'' ply? Thanks again for your time. Its a great help.


----------



## nealtw (Mar 6, 2017)

When you level joists, you just make sure the top of the ends are level, so shims under the ends is the usual trick. High crown is not usually a problem but a sag in the center of a joist is.
So that is the concern you have before you lay plywood.
Water laying under the house is a major problem, are you looking at drainage for that?


----------



## BrandonBoss (Mar 6, 2017)

No idea what to do about the drainage issue. The house has been dealing with this for almost 100 years so I figured if it was going to cause an issue it would have by now.The problem is that I am at sea level and when it rains hard we even get standing water in our yards where I live. So since the house foundation is dug out 2 feet their really isn't any way that I can think of to keep it from getting underneath unless I concreted the floor down below. I have a sump pump at the back of the house in a pit but it doesn't keep up with the water. All the joists are pressure treated and their are blocks underneath the house supporting the central cross beams.The blocks then have a 6x6 on top that is also pressure treated supporting the beams.  The water gets up onto the wood at times though. I could see that being an issue. I may try to find a way to get a pump under the house to pump the water out.


----------



## nealtw (Mar 6, 2017)

Hmm. A perimeter drain below the level of the inside is the recipe or raising the level to above the water line.

Have you thought about changing the floor to concrete slab?


----------



## BrandonBoss (Mar 6, 2017)

Thanks for the suggestions. What would be the best bet for raising the 2 walls that run parallel to the joists? I was thinking about putting  in  9'' tall 4x6 posts on the stem wall every 12''to support that wall or blocking underneath that wall to support it when I do the subfloor. It is more then likely going to be rotten whatever is currently their. Their may not be a sill plate their either. I think that those 2 walls will be the hardest part of the job. The interior walls I can attempt to put another joist under or just block them. I just don't know how much room I will have between the last joists that runs next to the stem wall and the space where the sill/rim joist should be.


----------



## nealtw (Mar 6, 2017)

Explain what you think a stem wall is.
It is not a term we use up here but I have heard a few different meanings.

Footing with wood wall below floor
footing and concrete wall below floor
footing concrete wall and wood would wall below floor.
Footing and piers below beams.

100 year old house most times the floor joist are just nailed and hung from the wall studs as they were balloon framed rather than platform framed as we see today.
So you might be looking at a mix of old and new systems.


----------



## BrandonBoss (Mar 6, 2017)

I was just referring to the concrete foundation. The gap between the top of the concrete and the bottom of the old subfloor is the area I was referring to when I said I wanted to block it or put in some kind of 4x6 that is the same height as the gap to support it.


----------



## nealtw (Mar 6, 2017)

BrandonBoss said:


> I was just referring to the concrete foundation. The gap between the top of the concrete and the bottom of the old subfloor is the area I was referring to when I said I wanted to block it or put in some kind of 4x6 that is the same height as the gap to support it.



Yes you can do that even with short pieces  but then you have to figure how to join the new floor sheeting.


----------



## BrandonBoss (Mar 6, 2017)

If I am able to block it that should work to hold up the new sheeting between the wall and the nearest joist. I plan on cutting the subfloor flush with the wall so I can install the larger 1'' subfloor. I will try to make sure to have a block underneath the joints of the subfloor too. Any tips on jacking up the outer walls in case I have to?


----------



## slownsteady (Mar 7, 2017)

In an effort to make us all stop & think for a second, is it possible that correcting the issues with the joists will prevent the need to do major surgery on the subfloor?

Side question: Is a 2x10 with a 1.5 inch notch any stronger than a 2x8 when it comes to joists?


----------



## nealtw (Mar 7, 2017)

slownsteady said:


> In an effort to make us all stop & think for a second, is it possible that correcting the issues with the joists will prevent the need to do major surgery on the subfloor?
> 
> Side question: Is a 2x10 with a 1.5 inch notch any stronger than a 2x8 when it comes to joists?



I think it depends on who you talk to.
The notch gives the timber a place to break or start to crack, but sistered to the smaller joist will aid with the bend or sag. 
So really the same advantage should be obtainable with the sister cut short of the bearing walls.


----------



## BrandonBoss (Mar 7, 2017)

The notch was to be level with the previous joists. 2x8's were a little to short so they used 2x10's and notched them enough to be level with where the house was before. It wasn't to provide extra strength.


----------



## BrandonBoss (Mar 7, 2017)

I don't want to do this major surgery but at the same time when I am done with this fix I don't want to mess with it again ever while living here. I plan on ripping up the carpet, hardwoods, and underlayment to expose the subfloor first and see if it is salvageable. If it looks decent I will probably go underneath the house with one of the guys I use for construction work and clamp the two joists together and use a palm nailer on them. I may use bolts on them as well. The other thing though is underneath areas like kitchen cabinets / bathtub how would I connect the subfloor to the newer joists? Would I just try to toe nail some nails through the new joist into the old subfloor from the bottom? Or use screws?


----------



## nealtw (Mar 7, 2017)

When you install the new joist use a lot of floor glue between the joists and on the top edge of the new one.
Your first nails want to be sucker nails. Nailed near the bottom edge of the new joist on a 45*, once nailed all the way in, a few heavy swings with the hammer will suck the new joist up against the floor.
After that then nail 3 nails every 16"


----------



## BrandonBoss (Mar 7, 2017)

I don't plan on installing new joists though because they were all replaced 6 years ago with pressure treated ones that were sistered to the old joists. So would I just try to get glue on the top of the joists that are already their and then try to send in screws at a 45 degree angle to suck the subfloor down onto them? I appreciate you taking the time and walking me through all this.


----------



## nealtw (Mar 7, 2017)

45* screws will not pull a gap closed, actually it will lock the gap in place.

Better would be to pre drill a 2x2 in two direction apply glue to top and side, screw it to the top of the joist first and the screw it to the floor. Pre drilling is important so the threads don't grab the 2x2 . Both screws straight in and straight up.


----------



## BrandonBoss (Mar 7, 2017)

So I was planning on screwing down the 1x6 planks to the new joists. Will that not pull the joists and 1x6 together?


----------



## nealtw (Mar 8, 2017)

yes it will.


----------



## BrandonBoss (Mar 9, 2017)

One more set of questions that I am wondering about. Which kind of screws/nails do you think I should use for connecting the old subfloor to the new joists and what kind of glue or adhesive do I use for the sistered joists that I plan on clamping together and screwing together? I was going to use the subfloor adhesive for on top of the 1x6's under the new layer of plywood. Wanting to know what kind to use for those 2x2's you recommended and also what to use in between the sistered joists that I am going to try to clamp together. Thanks again.


----------



## nealtw (Mar 9, 2017)

Galvanized deck screws because you have treated lumber, anything metal should be galvanized.

Any of the construction floor glues that come in the large tube


----------



## mabloodhound (Mar 16, 2017)

A few items to consider:
Hangers....use that palm nailer to drive the nails or you can also use screws.
Glue.....Any construction adhesive sold for sub-floors, roof decking, etc. will work.  Both for use between the 2 joists or for the new sub floor.
Flooring......3/4" tongue & groove plywood is sufficient as a sub-floor.
Fasteners......screws are less likely to "squeak" later on.  Nails loosen and that causes the noise when the board moves against the loose nail.
Screws........The coated exterior screws will work in PT lumber as well as galvanized screws.
You could also look into the Timberlock screws for use in pulling the 2 joists together.  They have a hex washer head and will not pull through the wood as easy.
Planing/leveling......do not try and make everything perfectly "level".  Just get the bumps and dips out of the joists and live with a minor slope if necessary.

If you pull the entire sub floor up, it will be much easier working on the joists.  You can also do it in sections.  And for the parallel wall, you could add a joist to catch the new flooring along that edge.


----------

