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Fremont Dave 12-23-2005 12:28 AM

Subflooring Question
My house is undergoing substantial remodeling. The floor plan has been opened to include a great room, dining area and kitchen; all contiguous. Engineered hardwood flooring will eventually cover all of these areas and more.
Currently, there is 1 1/8" plywood subflooring atop a support system that mainly consists of girders supported by posts and piers. The girders are 5' apart, with the posts/piers supporting them at 4' intervals.
To eliminate the bounciness of the floors, our contractor has proposed the addition of 2x6 floor joists on hangers between the girders at 24" OC. These are to be installed from beneath the subfloor via the crawlspace. The coverage is approximately 1,200 square feet. They have estimated four to five days to complete the work.
My questions to the forum are these:
Will this method produce a more solid floor?
Should the subfloor be further fastened to the new joists?
Could there be less expensive solutions?
Fremont Dave

K2eoj 12-23-2005 09:12 AM

So your subfloor is supported on 5' centers?? That would be very unconventional but if true than the idea of 2x6's should take all the bounce out. yes secure the plywood to the new joists. Sounds like that might be the least expensive way to correct your framing. HS.

Fremont Dave 12-23-2005 04:45 PM

Correction and New Information
Thanks Hammerslammer,

Here's an update:

The girders (4x6) run the width of the house, are attached to the foundation on each end and are supported by post/piers at 60" intervals. Each girder is spread 48" (OC) from its neighbor. Currently, there are no joists running between the girders. The first proposal from the contractor is to hang joists each 24", midway between the location of the post/piers.

Now, that said, I discussed an alternative approach with our construction foreman. Instead of installing the extra joists under the subflooring, we talked about installing a new layer of plywood (5/8 T&G) on top of the existing 1 1/8'. These sheets would be fastened with screws and liquid nails. This new layer would then serve as an improved underlayment for the 5/8' Owens unfinished engineered hardwood we are contemplating using. We discussed running these materials perpendicular to the girders to achieve greater stability. We also discussed evening-out some of the dips and unlevel portions of the current subfloor as part of the installation of the new plywood.
So, would this appear to be a sensible and cost-effective solution? It makes logical sense to me. However, I'm prepared to hear any sound advice in agreement or to the contrary.
Fremont Dave

K2eoj 12-23-2005 05:50 PM

I'm thinking that 4' centers is to much span for 1-1/8 plywood and you must feel the same because you are asking. My guess is that 3/4 over the existing will not improve your plywood deflection by much. Of course I don't have much experience with your situation because what you have is not the industry standard but you could try a small area and see if you get the results you want. I personally would like to see another framing member in between the 4' centers existing making it 2' centers. Hopefully some other guys will be along here with other ideas. Good luck and let us know how you resolve this. HS.

jproffer 12-23-2005 09:12 PM

I'm picturing a sheet of plywood, each edge nailed to one of your existing joists, and nothing in the middle. Then my mind goes to a vision of a trampoline for some reason:D . Now, seriously, I'm guessing that the plywood runs with it's 8ft. direction crossing the joists (or I hope so), but even still I agree with Hammer, add more lumber to cut the centers down to 24" (if you didn't already have 1-1/8" plywood I would probably even say go with 16" centers, but I don't think that's necessary in this case)

Bonus 12-23-2005 10:13 PM

I'd go with more joists, too. Not convinced you'd get what you're after simply adding thickness. With someone cutting and carrying, and someone on their back with the hangers and a palm nailer, it should go pretty fast, not much fun but you'd end up with something you could trust. With just a layer of plywood, you could never put down tile, for instance, and I think the placement of the girders would telegraph through to whatever flooring you put down.

3-4-5 12-24-2005 02:30 AM

If in fact it were me I would not only place a 2x6 every 24"o.c, I would also place a row of 1x4 cross bridging every 4'-6'o.c.
In my mind depending on the load factor of this particular space, girders at 5' would not provide much support for a 2x6 floor joist system.As time passes what may have started out as a bounce or squeak may end up as dips not only on the plywood but also in your 2x6 especially with this span between girders.First of all I would have used 2x8 floor joists spaced at 24" girder spacing 4' as well as 4x6or 4x8 blocking only because 1 1/8 ply weighs so much

KAdams4458 01-29-2006 12:27 PM


Originally Posted by Fremont Dave
Thanks Hammerslammer,

Here's an update:

The girders (4x6) run the width of the house, are attached to the foundation on each end and are supported by post/piers at 60" intervals. Each girder is spread 48" (OC) from its neighbor. Currently, there are no joists running between the girders.

Amazingly, my house is built in nearly the same fashion with the exception that the beams in my house are 4X12. This can't possibly be any form of standard construction, especially for a house built in late 1970, such as mine.

I have a three substantial dips in the subfloor between beams as of now. The worst offender is a 1.5" drop in the floor directly beneath the water heater. In my case, I'm planning to replace a piece of water damaged 1-1/8" subfloor directly beneath the water heater with an identical 1-1/8 patch supported from beneath by 2X6 joists spanning the 4' OC distance between beams.

Did I mention that I have no idea what I'm doing? Would you believe that this project started out last month as an attempt to replace an old Federal Pacific load center that had caught on fire? This home repair stuff snowballs entirely too well, doesn't it?

Anyway... I was thinking that adding in the 2X6 joists was the right way to go about fixing existing half-witted construction. While I'm at it, I could even insulate the floor. What a concept!

Someone feel free to steer me in the right direction if I'm going about this all wrong.

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