hardwood floor install - getting the base right

[Andrew Thuswaldner]

I will be installing 3/4" ash hardwood flooring on the main floor of a townhouse (circa 1976). The subfloor is 5/8" plywood and was nailed to the 2x8" 16" O.S. joists. The floor is a bit bouncy and squeaking in some places. I plan to put in some sister joists and blocking in the basement below but aside from that what else would your recommend I do before laying down the hardwood? I would like the floor to be stiffer and without squeaks. I could screw down the existing plywood. I could add another later of plywood (1/2" or 5/8") and glue and screw that down (about 450 square feet). I welcome your suggestions.
thanks,
Andrew

[Jason Roehl]

What distance are the floor joists spanning? A 2"x8" isn't very big, and you'd be adding substantial weight with 3/4" ash. Ultimately, what you may need to do is install a beam and posts mid-span in the basement. Which may require some footers cut and poured into the floor...

[Andrew Thuswaldner]

Jason,
This townhouse has a full basement that is poured concrete with the individual homes (6 in a row) separated with concrete block walls.The foot print of the house is approximately 18 feet wide by 26 feet deep. There are two I-beams with joists sitting on top. See attached picture.
Andrew

[Andrew Thuswaldner]

3895B Floor Joist and Beam Layout.pdf


Jason,
Here is he picture.

[Mike Cutler]

The 5/8" plywood is marginal (at least it's not OSB), and depending on the actual unsupported span,( If the span is 9' of unsupported, your pic didn't post), you're on the edge of the limits for a 2X8, I don't care what the load deflection charts show for 2x8. I have 2x8's on 10' and 14' unsupported spans and it's not enough.
If you plan to sister to the existing joists that will certainley increase the load rating of the floor. Make sure to sister full width joists and follow the correct nailing pattern for a sistered joist. No stich nailing.
If you really want to increase the stiffness you're going to need to either redo the subfloor, or add a layer of ply. If you add another layer of ply you have two options. Nail through and into the joists which will compromise the ability of the subfloor to expand and contract, or screw and glue to the first layer and avoid having the second layer physically attached to the joists.
An "out of the box" solution would be to put the flooring down on top of Elastilon, and bypass mucking about with the subfloor.
Elasitlon is an 1/8" thick self adhesive pad that the floor is adhered to. It will definitely get rid of the squeaking as the floor has an 1/8" layer of a close cell neoprene between the new floor and the subfloor. Elastilon also allows the entire floor to float and expand/contract with seasonal changes in humidity. There are no nails.
If you're worried about seperation of the elastilon from the flooring, don't. Once the elasitlon is adhered to the flooring it will tear out wood to seperate it from the flooring. At least it did with the 3/4" brazillian ebony flooring I put down.

[Peter Kelly]

A second layer of 5/8" or 3/4" plywood will make a huge difference if the floor is bouncy but it'll create a good sized step at the doorways. I'm assuming the existing space is carpeted? 3/4" blind nailed T&G hardwood strip flooring will also make a big difference on it's own provided that it is installed perpendicular to the floor joists.

[Andrew Thuswaldner]

.........If you really want to increase the stiffness you're going to need to either redo the subfloor, or add a layer of ply. If you add another layer of ply you have two options. Nail through and into the joists which will compromise the ability of the subfloor to expand and contract, or screw and glue to the first layer and avoid having the second layer physically attached to the joists.
An "out of the box" solution would be to put the flooring down on top of Elastilon, and bypass mucking about with the subfloor.
Elasitlon is an 1/8" thick self adhesive pad that the floor is adhered to. It will definitely get rid of the squeaking as the floor has an 1/8" layer of a close cell neoprene between the new floor and the subfloor. Elastilon also allows the entire floor to float and expand/contract with seasonal changes in humidity. There are no nails.

I don't see the 'compromise' in adding a second layer of sub-floor, gluing that second layer to the first and then screwing through both layers into the joists. In fact that is the recommendation I get from the articles I've read and the experienced people I've talked to. I also don't see how a layer of neoprene is going to help stiffen my floor. It might help to deaden the sound, but stiffen the floor and get rid of bounce, not so much. The picture of my joists and house footprint did post, right above your post.
Thanks for the dialog,
Andrew

[Mike Cutler]

Andrew

Geographically each area is different with respects to seasonal humidity changes, so techniques may vary. I only offered my input based on the inspection criteria I was subjected too, for a very similar, almost identical, job.

According the The APA, Georgia Pacific, and Weyerhauser, the second layer of substrate material in a floor is recommended to be screwed, and or glued to the first layer avoiding the joists. This "supposedly" allows each layer to "float" and react to seasonal humidity changes independent of the other. The pattern for screwing the 2nd layer to the first is also subjective. I had to screw the second layer to the first so that no screw was more than 6" from another screw, basically a 4" pattern. The first layer had to be screwed and glued to the floor joists.
I'm still knee deep in this process and have another 15'x30' area to tear up and redo from the floor joists up. Once that's done the second story floor has to be done also.
I's a lot of work.

You are correct, the Neoprene material won't stiffen the subfloor. It will make the floor itself one large connected surface though. Sorry for the bad lead there.

[Andrew Thuswaldner]

Thanks for providing the quote. That sounds like a pretty good source so I don't know what I am going to do. How much did you pay for Elastilon?
thanks, Andrew

[Mike Cutler]

Andrew
My house was built in 1921, on a dry stacked stone foundation. The actual materials are rough cut 2x8's of various species of wood. Some soft pine, some oak, some who knows what it is. The 2x8's are sitting on 14' spans for the most part, and they have bowed across the length.
The dry stacked foundation has caused the entire floor to bow across the joists. Compounding the issue for me is that the flooring is two layers of tongue groove on top of each other, running the same direction, across the joists. There is no Ply substrate. I also heat with a woodstove which has to be accounted for.
I mixed 5500lbs of mortar by hand and mortared the dry stones. A layer of hardware mesh and rebar was shot into the stones and mortar and then concrete, followed by Redguard was applied to hopefully arrest the settling of the stone foundation prior to starting to level and redo floors.
Your home is much newer than mine and is certainley built to more "exacting codes" than my original construction. If the experienced folks you've talked with in your area recommend attaching the second layer to the joists, and it doesn't violate your building codes. I'd probably be inclined to listen to them, as they are closer to the source than I am.

I think I ended up paying about $210.00 (US) per roll for Elastilon.
Lately I've been seeing it come up from time to time on Craiglist for about 1/2 that price, and I've been tempted to just buy the rolls and store them until I need them.

In retrospect, I know that I would have nailed that second layer with a pneumatic nailer and ring shanked nails rather than screw it down every 4". That was a ton of work, and took a long time.