I'd use caulk. put backer rods into the gaps to reduce the size of the gap,

then caulk both sides of the backer rod to the sides of the gap.

once caulk has dried completely, go back & caulk any areas

where caulk has shrunk.

use a good quality caulk with a long life.

short of foam insulating the floors, caulk & backer rods are the

next choice.

both caulk & backer rods will move with expansion/contraction

of wood.this would be an excellent guide for you, as La. & Fla climates

are similar. but you have to pay LSU agcenter a big ol dollar

for the guide. worth every penny & then some.

http://www.lsuagcenter.com/en/communications/publications/Publications+Catalog/Home+Improvement/construction/Insulating-Raised-Floors-in-Hot-Humid-Climates.htm

best of luck

The American Plywood Associationrecommends the spacing you're trying to fill. Abandon this idea please.

I don't know whether I agree with energy rater's comments or with Joseph Corlett's...it depends on the size of the gaps. I assumed you were talking about really big gaps that indicated a structural defect, rather than small gaps that are intentional to the construction technique, as well as gaps where they shouldn't be. More details or photos would be helpful.

In addition, I am concerned about your comments regarding a mildew smell. I don't know that spraying it once will be a longterm fix for something that might generate more mildew and perhaps mold over time. I'm not real familiar with details of CBS construction beyond what it is, but you should consider talking with a consultant to see if there is a way to do some type of moisture control underneath. My concern may turn out to be trivial, but it is worth asking the question.

Thank you all, havent looked at links yet, but wanted to comment to clear up some details. The plywood is tight but being wood and being florida there is expansion and contraction. In dry conditions the edges pull away not gaping holes but were not sealed either. The neighborhood flooded really bad years ago and the city installed drains and that has helped. We had an unusual week of rain and then more rain...the property was flooded but the house and suounding was high and dry. So i think before the drains were installed the water was under the house. Durring clean up i found evidence of mold under the carpet, more evidence moisture was comming up. I agree there needs to be ventilation added under the house once i do the clean up. Somewhere i read not to do that but after seeing what happens without it cant see it being worse. I need something besides caulk...the house is 3800 sq feet. Way too much to cover...i need something approved for interiors that i can spread into joints like grout. But stays flexible. The floors were all painted with a microbial paint after mold was cleaned up. We will probably end up double plying the floor but we dont have the money for that now. I cound look into caulk and squeegy it in but it seems there must be something better.

Why not add a sheet membrane before installing the finished floor ? Back in the day it was tar paper for hardwoods.... Why not use spray foam insulation under the house once all the renovations are complete? Even a thin layer will work nicely and allow for the needed expansion and contraction.

Jean Bo:

Before doing another thing, you need to determine whether or not you are subject to the state of Florida's 50% rule.

Cabot & Rowe yes, we definitely have talked about the spray foam, and want to do it. But like you said, do it after renovations. We do have plans to do a complete renovation. But I got to keep this air and smell filtrating up now. I was looking for a cheap cap that I could roll on smear around the edges. We really wanted tile but due to the structure when I ran the numbers on the defection meter on John Brige site we are not approved. After speaking to the pros they didn't feel double plying and ditra (a water proofing un cupling membrane) would prevent cracking. I had a contractor out to talk about shoring up the flooring to remove deflection. He didn't feel it was really needed unless we laid marble. But whatever I lay down it will be laid tight, or I might have to settle for tightish. So you are left with no solid answer and what do you do? roll the dice lay tile on 3000 sq feet and it all starts crumbling...So I know I am getting off topic but as with any house project there are many factors to consider. And you have to look ahead. So right now I just want to seal me from the space below, got to find something....

http://www.greenbuildingadvisor.com/blogs/dept/musings/air-sealing-sprayable-caulk

I've read about this product, but never seen it/used it/ tested it with blower door. you should test for moisture content of wood before spraying.

you don't want moisture trapped in the floor that has to evaporate to the

inside of the house.

you should look at the lsu agcenter info when it is time to insulate floors fully. and make sure that spray foam installer tests wood for moisture before spraying foam.

what type of flooring will be/is already installed?

best of luck

Tear it down and start over. It will be cheaper than any ''extensive'' remodel of a home with so many issues that are moisture related.

After speaking to the pros they didn't feel double plying and ditra (a water proofing un coupling membrane) would prevent cracking. I had a contractor out to talk about shoring up the flooring to remove deflection. He didn't feel it was really needed unless we laid marble.

You need to find new installers.

1-Double ply doesn't do squat for the deflection we're concerned about. There are 2 types of deflection- generally when we speak of deflection, we are speaking of the joist deflection. This is stiffened by adding joists, sistering joists or reducing the joist span. Adding plywood to the surface, or blocking between the joists does nothing to help. There is also between joist deflection. If your joists are 16" on center, 5/8" BC plywood would be the bare minimum when laid with the face grain perpendicular to the joists. 3/4" is better.

2- Natural stone requires two layers of plywood installed in a specific manner we can cover later. This is to decrease the between joist deflection. You still need to meet the L720 joist deflection for natural stone.

Sounds like the guys you talked to are confusing the two, or at least don't explain things well enough.

Cabot and Rowe thank you for clearing that up for me as I was thinking of the floor as one unit and the joist don't move it is the ply where two meet that we just found out today move a lot! The house has 3/4" ply and the joist are what we believe to be Dade county pine I don't know if you are familiar with that. But is solid stuff and you can't get it anymore. Some rooms are 12" oc (they had a game room with pool table) and some are 16" oc. all with 3/4" ply. We found today that the ply (stood over a crack and leaned right and left) is deflecting but the joists don't so we are going to double ply. This should firm up the floor in-between as you stated and deal with all the I can see light down there issues. Tomorrow we will do a true measurement of the joist but we believe that they are 2x12 it is in really good shape and beefy.. more details to come and I can't thank you enough for your expert advice.

Energy Rater thanks I looked at that site. I like it..... will consider it for that end of the project.

Sophie... really?

You could use ZIP tape on the plywood seams. I'd be looking at insulation/ventilation options though.

KSC 36 where do you get zip tape it might be something I can use around the perimeter?

Joseph it would help if you included more information then that? I don't know what you are talking about.

Joseph I dug a little deeper and found what you are talking about and it doesn't apply. Thank you...

Every lumber yard in my area carries it. Even HD and Lowes...

http://www.huberwood.com/zipsystem/home-zip-system

Thanks ksc36.. Well we decided after we found so much ply movement in areas unsupported by the joist, to just glue and screw another layer of 3/4 ply down and with that we are caulking around the edges wher the wall plaster stop and floor meet. The feeling in the room now is incredibly different, and more solid. So there is a lot of work ahead. We are also underneath doing a treatment for what is mildew there. So fresh times ahead... We will look into a push pull ventilation system for under neath moving forward.

i need something approved for interiors that i can spread into joints like grout. But stays flexible

aka caulk

Anywhooo.... you could put an underlay with a vapor barrier. They typically seal to each other with a tape edge. But really caulking is not that hard or expensive, put caulk down, spread with putty knife. Shouldn't really interfere with expansion and contraction.

Ventilate the crawlspace to get rid of the musty smell, sounds like you knew that already.

Thanks Vith....yes we had planned to use ditra which is an uncoupler and vapor seal but was worried about the movement..now that we are double plying we have a good seal between us and the underworld. We will make further flooring choices