Moisture barrier for cupping over crawl space

puttster

Our home was built last fall and has 3 1/4" heavy grained hardwoods all over. The foundation looks to be cinder block, dirt crawl space with lattice all around. The house is well insulated, including between the floor joists. Now, a year later, there is a lot of cupping on the ground floor flooring. Upstairs is ok. The house in is Houston.

The dirt under there is sandy and seems to be moist pretty much of the time. However, our old house, built in 1934 with skinner, select red oak boards, had a crawl space that flooded and puddled all the time but nary a warped board.

The builder's rep is coming over tomorrow to check it out. I gather from searching here there should have been a barrier between the flooring and sub floor. How would it be possible for us to check if that was properly done?

As for a fix, I'm wondering if the best next step would be to nail a moisture barrier up to the joists. Sealing up the whole crawl space does not appeal to me, don't know why.

Thanks

Puttster

joecaption

No vaper barrier layed on the ground if you have a crawl space when you have a hardwood floor = cupped floors.
No vaper barrer between the subflooring and the hardwood floors = cuped floors.
Flooring 101.

puttster

Of course. Looking for some answers here.

joecaption

The moisture barrier needs to be laying on the ground.
If one was added in the floor joist bays it would be right under the subfloor,
not to the bottom of the joist.
If it's that wet under there, I'd be taking a look at why.
No gutters, grade not running away from the foundation, mulch piled up againt the foundation, flower beds forming ponds for water to collect, condinsate drain for the A/C not run to the outside of the foundation, dryer vent not run outside, grade needs to be raised under the house.

puttster

How/where can one check if there is a moisture barrier under the floorboards?

Will a moisture barrier attached to the bottom of the joists be as effective, or nearly so, as a barrier on the ground?

thx

Elkypro

Can you remove the base trim and then maybe you can hope to see a bit of vapor barrier (if it is there) poking out past the flooring? And the you would also be able to look at if there is an expansion gap too.

joecaption

If there's floor registers you may get lucky and be able to pull one out and take a look.

puttster

No registers but there is a trap door. The edges are trimmed tyhough. I was thinking of using a hole saw in it from the underside.

But just to be straight - failure to install *something* between the sub and the flooring, in a house in Houston built last year over a dirt crawl space - that would be a failure of code or something like that, so when I confronted the builder he would be required to provide a solution?

putts

joecaption

Going to have to check with your local building dept.
I would at least check with the company that made the flooring, if they did not follow the directions on laying it then there responsable for it.
Laying hardwood with a vaper barrier under them has been the norm for at least 30 years that I know of.

Jim Decker

First you need to get a hygrometer, Walmart 9.00 and record relative humidity readings if over 55% you need to get it lower. NWFA Instructions
6. Basements and crawl spaces must be dry. If power washing is required in the basement, do so before
wood flooring is installed and allow subfloor and basement to dry before installing wood flooring.
7. Crawl space should be a minimum of 18” (457mm) from ground to underside of joists.
8. Crawl space earth (or thin concrete slab) should be covered 100 percent by a vapor retarder of black
polyethylene (minimum 6 mil) or any recommended puncture‐resistant membrane, such as Class C,
meeting ASTM D1745. See Figure 1‐1. Check local codes.
9. Crawl Space Conditions
a. Where a proper ground covering is in place and
when venting is required by local building codes,
the crawl space should have perimeter venting
equal to a minimum of 1.5 square feet per 100
square feet of crawl space square footage,
unless local building codes differ from this
specification. Note: Local building codes may
differ. Follow local building codes.
b. For crawl spaces without ventilation openings,
vapor retarder joints must overlap a minimum
of 6 inches and be sealed or taped. The vapor
retarder should also extend at least 6 inches up
the stem wall and be attached and sealed to the
stem wall. Continuously operated mechanical
exhaust and perimeter wall insulation or
conditioned air supply and insulation must be
provided.


a. Where a proper ground covering is in place and
when venting is required by local building codes,
the crawl space should have perimeter venting
equal to a minimum of 1.5 square feet per 100
square feet of crawl space square footage,
unless local building codes differ from this
specification. Note: Local building codes may
differ. Follow local building codes.
b. For crawl spaces without ventilation openings,
vapor retarder joints must overlap a minimum
of 6 inches and be sealed or taped. The vapor
retarder should also extend at least 6 inches up
the stem wall and be attached and sealed to the
stem wall. Continuously operated mechanical
exhaust and perimeter wall insulation or
conditioned air supply and insulation must be
provided.

Houston is an area of high humidity and if, I could not discern solid or engineered wood, solid most assuredly you had better follow these instructions. Heat and the dryness of winter may allow this to be sand and finished BUT do not do so until the moisture content is low enough so that when it drys out you won't have a crowning look to the wood.