# Concerned about a 5/8 thick subfloor



## ctbuilder (Apr 10, 2007)

*Neolitic -*

You have described sub-floor in another post:

I'm with you, Sub floor goes on the joist, underlayment goes _over _the subfloor and _underlays_ the finished floor.:thumbsup:

Using your definition, the 5/8 decking I am referring to is the first layer over the joists in my case. I wanted to add an additional underlayment of 1/2 on top of the 5/8 for strenght. The inspector wants the vapor barrier underneath the 5/8s sub floor.


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## neolitic (Apr 20, 2006)

ctbuilder said:


> You have described sub-floor in another post:.....
> The inspector wants the vapor barrier underneath the 5/8s sub floor....
> I know there is a moister issue as when they metered the current subfloor, the moister content was too high to install floors.


Same page,* beneath* the sub-floor.
Also, beneath the* joist *and *duct work* and* everything else in the crawl space!*
On the *crawl floor*!



ctbuilder said:


> If I drap 6 or more mil poly down the sides of the concrete walls, which are about 4 feet in lenght, how do you attach the foam boards to the walls with poly in the way? I thought the foamboards were glued with foam board adhesive to the cement wall. Do you use the type of foam boards where one side has foil? Some of the foam boards are T&G, I believe DOWs blue are not.
> Does mold form behind the poly and foam boards? Does moisture drip down behind the foam boards into the basement?


I use 20' 6 mil, tape any seams with any good tape other than cloth backed duct/duck tape.
Run it up the walls 12" - 16", and tack it with tape or adhesive.
Tack Styrofoam® (blue foam) to the mud sill, and over the 6 mil, with 16d's to hold while foam adhesive sets.
Styrofoam® comes in 2' and 4' X 8' sheets.
It should extend at least 2' below grade -- more if you want -- all the way to the crawl floor if you want.



ctbuilder said:


> Why is putting sprayed foam, which makes a complete seal to the underside of the decking so bad? The inspector said to put the fiberglass paper against the underside of the decking, not the top of the floor, so I don't know why you keep saying he said to put it on top of the subfloor. A guy who installs wooden floors in Canada for 30 years said he coats the bottom of his oak floors with polyurethan and never has a problem.


I think that we've covered this.



ctbuilder said:


> I fiqured sealing underneath the decking couldn't hurt to get any rising moisture from entering the flooring. I have 98 inches from the current decking layer to the 2nd floor joist, so I though it won't hurt to put down another 1/2 inch, glued and screwed to give more strenght, and nail holding for the aok floors instead of just 5/8.


I think, and seems that the floor guys agree, you need to let the sub-floor dry out.
Then if it's sound and the oak is perpendicular to and nailed on the joist...do whatever you want.



ctbuilder said:


> I understand your solution, I was just wondering if there was another one as mice love to live in the fiberglass in the joists, no matter how well the crawlspace is sealed.


If mice worry you so much fill the joist pockets and rim joist with cut foam or spray foam or ....
If your duct work is down there and you're heating the house, it should be warm enough to foam it.

I surrender.


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## ctbuilder (Apr 10, 2007)

*Neolitic*

I notice you help many of the viewers and want to thank-you for the feedback.

It sounds like if I drape the 6-8 mil poly accross the crawspace cement floor and up the walls from the floor 12-16 inches, then glue the DOW foam boards to the walls over lapping the 12-16 inch poly, I should be good to go to stop moisture in the crawl space. 

I just hate the smell poly leaves. Thanks for your help.


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## Pavola (Nov 12, 2007)

Whether you add 1/2 or not, I'd replace any soft plywood as a sound precaution. Solve the mice infiltration problem so as not to worry about what type of insulation would be most suitable. Is this crawl vented? There's still speculation if this is a +/-, but it still will be a factor in what's the best solution in your case.


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## ctbuilder (Apr 10, 2007)

*Pavola*

The crawlspace has a 40x48 openning that will be a closed door. It has 5 basement windows with screens that can be opened for ventilation.

My only thought is by adding the 1/2 in 4x8 plywood (will need 40 of them) is it will create a 1 1/8 inch base above the joist to nail the 3/4 oak floors to.
I'm not sure when floor installers if the take the time to make sure the joists with 16 on center are nailed.


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## Pavola (Nov 12, 2007)

You *have to* figure out the insulation/vapor barrier method that's going to be best, otherwise no matter what you do to the subfloor to strengthen it, that hardwood is going to turn out like crap over time. 
With that many windows and that big of an opening, are you planning for storage use or something? If so, installing your vapor barrier takes another turn.


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## ctbuilder (Apr 10, 2007)

*Pavola - any thoughts apprecited*

No storage (but would be nice to still be able to put something down there) and no mechanicals in crawdpace. 

Our town inspector sugguested fiberglass insulation, paperside faced up to the decking, stuff between the joist and to cover with a poduct like Tyvek allowing to breath and moisture out. At first I was going to do this and put rigid 2 inch T&G foam board under the joists.

Architec said to spray Iceynne which is a sponge type foam between the floor joists. 

Any ideas or thoughts are appreciated.

i'm thinking of polyurethan to bottom on new 1/2 plywood so I can continue constriction and have the floors put in and deal with the moisture in the spring as the brushed on polyurethan should protect the oak until then. What am I missing?


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## neolitic (Apr 20, 2006)

ctbuilder said:


> i'm thinking of polyurethan to bottom on new 1/2 plywood so I can continue constriction and have the floors put in and deal with the moisture in the spring as the brushed on polyurethan should protect the oak until then. What am I missing?


You are still missing the *whole point!*
Address the *structural *problems* first*.
(The already/soon to be rotting joist and sub-floor)
Then deal with *cosmetics*(the oak).
Ever hear of putting lip stick on a pig?
(Hint---It's still a pig!)
BTW...the 5 or so windows that you didn't mention until #25,
need to be dealt with as well.
I'd block them up (lay concrete block, or just frame and fill).
Good luck.


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## ctbuilder (Apr 10, 2007)

*Neolitic - Dude your being kind of rough*

Not sure why you come down on posters - it good of you to answer, but answer the whole question instead of parts. Who's talking about making it pretty. I'm installing a subfloor of 1/2 for strenght - do they put Polyurethane on boats and is it still a boat? 

The joists have been there for 20 plus years in this older section of the home and they are not rotting and falling in. This was originally a full basement that had a sub-pump and a lot of moisture, where it smelled bad in the summer. Fema rules required the basement be filled in inorder to build. The windows can't be filled in because they also act as flood vents as the crawl space is pitched to allow water to flow thru in case of the big one.

All I asked was which started this post was since the subfloor, deckling, what ever you want to call the plywood above the joists being 5/8 thick, should I add a layer and make it 1 1/8 thick so when I do put down the oak floors, there is more to grab onto. I don't think floor installers land on every joist when nailing. 

I would need to insulated the floors so I was just asking if foam between the joists was an option. Seems insulating and sealing underneath the joists is the answer, was just asking for ideas. The walls of the crawl space, which are about 2 feet under grade, is not an option.


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## ctbuilder (Apr 10, 2007)

*the more I think of it*

Polyurethane brushed in the bottom of the sub-floor and joists would be like a boat and no vapor could enter the wood or the floor above. Maybe I just created a new industry. I could still get into the bays if I want to put in radiant heat if the insulation doesn't hold the warmth. :clap::clap::clap::clap:arty:arty:arty:


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