My neighbor had this problem. I'm about to have similar install, would like to avoid. . .

He's a cabinet maker--wise enough to hire a pro for the install of 3/4 solid walnut over 15lb felt over 1x6 sub perp to joists over dirt crawl space (1930's home).

Cupping noticed in living room after a few months. Installer replaced much of the damaged wood. Cupping again.

No water in crawl space. No over irrigation. No roof leak. No window leak. No leak around chimney. All per pro leak-detection-type guys. Yet when wood strips removed, there was beads of moisture laying on the felt under the flooring, and white fungus happily growing.

With no other idea, he put down plastic over the crawl space. During that time he discovered the fungus "stem" system climbing the foundation and up to the subfloor (pyorah fungus, or some name like that). It was living in the dirt, using his walnut for food source.

Scary enough--but I want to know how the water got on the felt. From high room humidity? He has no A/C. His old oak in the bedrooms is nailed to 1x6's without felt or paper--no cupping after ages.

Is it sometimes best to omit the paper because it may trap, rather than block, moisture?

15 lb. asphalt saturated felt paper (as suggested by NOFMA) neither blocks nor traps moisture. It is considered a vapor diffuser/retarder by NOFMA and the NWFA. The moisture was brought to the wood and was on top of the felt by the fungus. The installer should have measured the subfloor moisture content prior to installing the flooring. Also, the plastic vapor retarder should have been installed on the earth in the crawl space prior to the install. One need not have standing water to have excessive humidity in a crawl space.

Allow me to add to Gary's Comments.

We do not know why he has so much moisture in the crawl space and each location would be different. San Diego has high RH areas and moderate RH areas.
Maybe the home is on a hill with occasional water coming under the house?

At any rate, we also do not know the structure of the air flow under the home. Lowe's has a Sub-floor system fan that may be of help.

There are many opportunities to promote high moisture under a home, but exactly why it is on TOP of the Felt is not known by me... The fungi may have brought it or it was there when the wood floor was installed??

Yes, the plastic sheeting was put down onto the dirt in the (dry) crawl space in an effort to block the transmission of vapor from the dirt up to the floor framing. This was done after the second install also cupped.

I assume the idea of the felt between subfloor and strip flooring is to retard vapor transmission into the strip flooring moving from the direction of the crawl space, right? But what happens when there is greater moisture on the house side? Won't the house vapor condense againt the retarder (if the dew point is reached)? Putting wood flooring against something that may be damp (or wet) from time to time seems not-right.

Better to let it breathe? (in a temperate climate like ours, at least)?

-Brad

You may be right...... The humidity in the home may be the source of the moisture causing cupping..

I'm a Flooring Veteran of 45 years. Never seen water on top of felt other than water damage so this case is a mystery to me and makes little or no sense.

Dew points can easily be reached in crawl spaces.

Take 80º@ 70% and allow that air into a crawl space that is only 10 degrees cooler, and you have reached dew point and a 100% humidity under the home... Cupping floor.

Correct me if I'm wrong, but this case seems to involve moisture on the house-side of the vapor retarder, not the the crawl space side.

Seems to me that if the crawl space side is wettest, then the joists and subfloor get the brunt of the humidity, not the solid wood fooring, which is above the fray.

Remember that my friend's home is on top of a hill, dry as a bone under the crawl space, been there for 80 years without a problem until the new flooring contractor installed 3/4 solid walnut over felt. Portions of the original house (bedrooms, kitchen) remain un-affected by moisture, it seems.

It appears that the felt (and species--walnut vs. oak) is the only difference between rooms, but with vastly different performances.

-Brad

Same concept. What happens to a cool glass of water on a hot humid day???

You have your water(the high humidity in the crawl space)
You have your glass(the subfloor and felt)
You have a hot & humid summer day, and you don't close windows and keep the interior conditioned.

Sounds like you need to move some air under the home, with additional vents or even power vents.

The physical water seen tells me total saturation What is that? About 24% MC

Ya, I bet the floor was cupped badly!!

Floorguy,
In all your years;;; have you seen water ON TOP of the felt?

This could be Dew Point, but something tells me there is something else going on....

No air conditioning in the home, but San Diego is a place that heat/air is not needed.......... Wonderful place to live.

Could it be the ground side of the home is so cool that vapor is condensing?

Gotta be more to the story..

Actually, we had a thorough discussion about it here, but it was sheet vinyl not felt, and it was the exact senerio I described above. Remember???

Yes, I remember the statement you made, but the resilient was covered by the laminate. It did not make sense then, and it makes no sense now.
Vapor Condensation going through the Wood to the Felt?
Vapor Condensation moving UPWARD through the felt to the top of the felt paper?
No... just don't see it.

THis man is seeing WATER on top of the felt...

Also;; San Diego is mild weather wise and RH wise year-round. The climate is nothing like we are used to in the South.

I'll have to give my neighbor a visit and see how it's going since the plastic install on the crawl space dirt.

By the way, no A/C. We are a couple of miles from the coast--very temporate year-round. Few homes have A/C, we keep windows open nearly all the time. The vented crawl space conditions cannot be too different than our fully vented homes! --I would guess.

Just seems to me that fully ventillating the floor (top and bottom) would be the thing to do in this locale. In fact, that's what they did decades ago on these old homes, and I suppose that's why the floors are still in service--without damage, for the most part.

Anyhow, I'll get an update from him Sunday.

-Brad

Found some information on the net:
Current theory on vapor retarders indicates that both air infiltration and direct diffusion play significant roles in the transfer of moisture vapor and, therefore, both must be accounted for. Effective vapor retarders must have a water vapor permeability not exceeding 1.0 grains per hour per square foot per inch of mercury vapor pressure difference (referred to as 1.0 perms), and must be installed in such a manner as to prevent air leaks at joints and laps.
Although the issue of what makes a vapor retarder effective is generally settled, controversy still remains as to where to install it, if at all. From this standpoint, the authority on the subject is the 1997 ASHRAE Handbook of Fundamentals, which has more to say on the topic than any of the model codes. In what is defined as heating climates (4,000 heating degree days, base 65F, or more), vapor retarders belong on the interior side of the insulation. In warm, humid, cooling climates (Florida and Gulf Coast) where moisture vapor transfer conditions are effectively reversed, vapor retarders are best placed close to the exterior.

In mixed climates (not fitting either of the above definitions), the vapor retarder should be placed to protect against the more serious condensation condition, summer or winter. If in a mixed climate the winter indoor relative humidity is kept below 35 percent, a vapor retarder at the interior side of the insulation is usually not required, and an exterior vapor retarder strategy is most effective. Where winter interior humidity is not controlled or if a humidifier is used, an interior vapor retarder is most useful. Vapor retarders should never be placed on both sides of a wall. Where a vapor retarder is employed, the opposite wall surface must provide a permeable surface to allow drying to occur. Thus, in hot, humid, cooling climates, where a vapor retarder is employed at the exterior, the interior wall surfaces should be permeable. No vapor retarder paints, kraft-faced insulation, or vinyl wall coverings should be used. Conversely, in northern heating climates, with interior vapor retarders, the exterior wall coverings should be vapor permeable.

Slightly more in initial cost than building felt. Availability of some products may be limited. Inferior performance as a weather barrier compared with building felt. Nail penetrations in housewrap are not self-sealing, as they tend to be in felts. Housewraps are not selective vapor permeable membranes: moisture vapor will pass through in both directions. As water-absorptive siding materials such as wood and brick veneer dry, moisture in vapor form can be forced through housewrap into sheathing and insulation. Less vapor-permeable building felt can better withstand reverse vapor migration.

Some recent studies appear to indicate that surfactants, a class of substances found in wood, stucco, soap and detergents, can decrease the natural surface tension of water and allow it to pass through housewraps wetting the underlying materials. According to anectdotal field observations, this process is most likely to occur in regions with heavy rainfall and when unprimed wood siding is placed in direct contact with the housewrap.


http://www.oldhouseweb.com/stories/Detailed/10362.shtml

Good info, Ray, but here in San Diego at least, it would be most unusual to find an insulated floor. His old old house exterior 3-coat plaster (stucco) on redwood studs with no insulation. The interior walls, where original, are cement plaster on redwood strip lath. The attic does have a couple of inches of blown-in insulation.

If you look at the weather averages chart for San Diego the year-round average is min 65 max 75, with the odd cold day (never freezing) and 100+ day here and there.

Vapor retarders are not the norm in wall design here and are rarely installed as such. Foil-faced glass fiber batt insulation is a rarity, too-- Kraft-faced or non-faced is typical.

I find it hard to believe that dew point could ever be reached in San Diego at the bottom side of wood flooring, but maybe. Without heating and cooling, the indoor environment is (I suppose) fairly similar to outdoors. This makes this whole wet felt thing even odder to explain! Yes, I saw it myself.

Like I said, I'll follow-up with him tomorrow.

-Brad

Dew point condensation, is not vapor passing through the moisture barrier. It is a surface temperature cooler then the dew point of the surrounding ambient conditions.


Looks to me, like SanDiego, is much like it is here in my area.

San Diego rH average year around...

http://www.cityrating.com/cityhumidity. ... =San+Diego


right now the temp in San Diego is 66º with a dew point of 61º