Mold in new homes


Is it possible to have mold in a brand newly constructed home? Well, let’s put it this way, do you know of any builders that have construction materials inspected for mold BEFORE the materials are used in the construction? Builders do not typically like to employ environmental controls during new home construction.

The major issue with construction lumber is moisture content. Moisture content, or MC, is defined as the weight of water in wood as a percentage of the weight of the wood’s fibrous material. The moisture content of wood can be measured by using a pin-type or pinless moisture meter, which can be found at most big-box home improvement stores. At or less than 15% is considered dry. A MC of 15-17% is considered an indication of the wood reaching its saturation point. Mold growth can be supported at this level of moisture content. At 20% MC, wood has reached a point that not only will it support mold growth, but dry rot may begin which will destroy the wood’s structural integrity. But what is interesting is that at 20% MC, the wood may not appear to be wet. Wood does not appear wet until it reaches 30% moisture content, which for wood is its saturation point.

Lumber is classified as heartwood, wood from near the center of the tree, and sapwood, which is the wood nearer to the tree’s bark. Most construction lumber is sapwood. Sapwood is less dense and more apt to absorb water quicker than heartwood.

mold in new homes

Common Causes of Mold In Newly Constructed Homes

  1. After the delivery of the construction lumber, the lumber gets rained on. A 2x4 may just have surface water on it, wet to the touch, or it could have absorbed enough water to elevate its MC above 15%. You can’t tell just by looking or feeling.
  2. The exterior walls are up but the roof isn’t on and it rains. This would affect all aspects of the rough construction; studs, floor joists, and subfloors.
  3. The plywood roof sheeting is on but the shingles or finish roofing isn’t installed, and it rains some more.
  4. The roof is complete but there has been venting access cut out of the roof to accommodate HVAC and plumbing systems.
  5. Interior concrete was poured and not allowed to completely cure before further construction was continued. Concrete contains 85% water, which can be absorbed by any wood coming into contact with it. Nature is an equilibrium; wet will always go to dry if it can.
  6. Until the yard is finish graded, the ground may slope towards the building’s foundation allowing excess moisture to build up in the concrete or block walls.
  7. Today’s tightly constructed homes do not allow the building to “breathe”. This restricts the exchange of moisture from inside to outside.
  8. The construction material contained what is known as lumberyard mold. This is mold that was already in place on the lumber while it sat in a warehouse waiting to be sold. There could be several reasons for the mold to be there already. One reason could be the result of improper drying at the mill. Or it could have been exposed to moisture while it was being shipped to the warehouse.

High MC Lumber: What Can Be Done

If you are having a new home constructed you could ask the builder to verify that all construction materials are at or below 15% moisture content before being used. A second option would be to have a restoration company set up drying equipment after the rough-in construction is completed to lower moisture content to acceptable levels. By rough-in I mean when all exterior sheeting and siding is installed, the interior stud walls are up, the roofing is on, and all windows and doors have been installed. This would allow the restoration company to control the interior environment of the building.

Most builders are hesitant to do this. It delays their schedules and adds to their construction costs. But at what price and to whom?

An Actual Case

Not so very long ago, a builder in our area contacted my company with concerns about mold showing up in a basement that was being finished on a new construction home. Our inspection found mold down low at the floor level as well as on the walls near the ceiling. At the time it was a very slight amount of mold but the humidity levels in the basement were above what is considered normal, in the 40-45% range.

We recommended that affected drywall and baseboards be removed and the installation of our dehumidifiers and air movers to lower the basement’s humidity levels. Instead we were asked to use some type of chemical and just wipe the mold off the walls and base so that finish work could be completed. We refused to accept the responsibility for doing things incorrectly and did no further work for the builder at that time.

Apparently the builder, in an effort to lessen overall construction costs, and against our advice, cleaned and then covered up the mold with a sealer and then completed the finished basement. A few months later, after the new owner was forced to file a lawsuit, our company was contracted to return and remediate a mold problem that had gotten much worse and much more expensive for the builder. The owner’s children both suffered from a type of immune deficiency and reacted negatively to being exposed to mold in their basement playroom.

In summary, it is entirely possible to find mold in new construction housing. My advice to you is before you sign on the dotted line it would be smart to have your new home tested for the presence of mold. If you have already purchased your home and are concerned there may be mold present, you can follow this link to get a list of local mold specialists who will give you a free home inspection. If they do find mold, they will provide a free estimate for removal. There is no obligation on your part.



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Written by Mark Huey.



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