Q: For our new sunroom, the plywood subfloor was laid and primed with a latex primer. The walls were then erected during a rainstorm and a few days later the contractor put down luan panels. A moisture meter showed the wetness level in the subfloor at 28% or greater. Before laying vinyl tile, the contractor thinks we can dry out the subfloor, through ventilation, with the luan in place. I think we should pull up the luan first. What is the correct approach?

A: There is good news and bad. Let us start with the good news.

Your concern about the possible moisture content in the plywood shows that you were thinking ahead. It's especially important that you have a moisture meter that can show you relative moisture levels. Twenty-eight percent moisture is much more than you should see in this material. In fact, you might want to check some newly bundled plywood pallets to see what the unaffected plywood moisture levels are. This will give you a goal on what to expect in your sunroom flooring.

I think that if the contractor had waited before installing the luan panels, the wood subfloor may have dried out. He could certainly have rented a dehumidifier unit - the kind used in many water-damage projects - contained the wet floor using a Visqueen or plastic sheeting, and pulled the moisture out of the subfloor before it became an issue. As it is, however, he laid the luan panels over the subfloor and that is going to inhibit the drying process.

The bad news is that you are going to have to insist that the luan panels be removed and the use of a construction adhesive is going to make that much more difficult. It may even wind up destroying the subflooring material. But let's examine what could happen if you don't follow this process.

The moisture is going to attempt to move out of the exterior plywood. Right now, that moisture is trying to go into the luan. As long as the luan is installed, it is going to take a very long time for the plywood to dry. In the meantime, the potential for mold to grow on either the plywood or luan exists. Let us also consider the structural damage that can occur to the plywood from being wet for an extended period of time. Exterior plywood is designed to get wet. But designers assume that it will dry in a reasonable period of time. When that does not happen, it can delaminate. Now you have a squeaky subfloor that is turning to mush, and may be growing mold.

The luan has got to come up first. If the contractor can remove it without damaging the plywood then you can certainly save the plywood. The plywood has to be dried properly and then inspected for delamination. If all of this is done, and you are satisfied that the subfloor is as good as new, or as good as you need it to be, then you can proceed with building the sunroom.

Travis West

Travis West is the president of Building Air Quality Inc., a Houston-based indoor air quality consulting firm. He can be reached at twest@baq1.com, or toll-free at 866-367-1177. )

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