Mold growth during structural framing

I have just completed the framing of a very large residential structure, and found mold growing within the framing members. The framing had been delayed during the late summer and fall, and we were forced to start the framing of the structure in December, in Connecticut. Because the project is located in New England, meant that the framing occurred during the cold and snowy winter, and extended into the early spring, which was exceptionally wet. The structure is a 100,000 square foot residential building, housing 90 separate residential apartments. To make the situation worse, the structure is located on the shoreline, where the wind and winter storms are most intense. In addition, the new code requires the structure be built to withstand winds of over 145 miles per hour. This code requirement obligated the structural engineer to design multiple shear walls, that are made of oriented strand board, ( OSB ) , or more popularly called, particle board.

The entire structure is a wood framed structure, with the only steel being erected in the center of the building to allow the openness needed for common spaces, elevator shafts and mechanical spaces. The entire surface of the shear walls is constructed of oriented strand board, secured to the wood studs forming the interior walls of the hallways, as well as constructed at a designed spacing within the structure. The second and third floors are all sheathed in oriented strand board, as well as the roof.

Although the popular belief is that standard plywood panels are better than oriented strand board, this is not necessarily the case. Oriented strand board is considered the same as plywood by the majority of building officials and codes. Oriented strand board is made up of smaller strands of wood that are oriented in layers perpendicular to each other and glued. In most strand board assemblies, the strand board consists of at least 50 layers of material. Plywood is made in a similar manner, however is made of full laminates or plys that are laid at perpendicular direction and glued. Plywood has a tendency to be smoother than the strand board but can have small voids within the center of the sheet, whereas the strand board will not have any voids.

Which of the two materials is better withstanding water infiltration, is a matter of discussion and disagreement? The plywood faithful will indicate that plywood will dry out much faster than the strand board, however, the strand board proponents will indicate that the plywood will swell more than the strand board.

Unfortunately, it is my experience that both types of material will deteriorate, swell and retain moisture, if they are subjected to the countless rain and snow storms of a New England winter.

After watching countless wood structures built, in the rain and snow of New England, are there techniques that could be used to reduce the amount of water that infiltrates the wood framing of your structure, as the building is built? Listed below are some techniques that can be used, to try and minimize the amount of inherent moisture absorption within the framing lumber and sheathing, as the project is constructed.

  • The most effective method of minimizing moisture absorption and accumulation with the wood framing members and sheathing is to build modular. I completely understand the resistance to the modular method of construction; however, this article is about a discussion of minimizing moisture within a wood framed building. If the structure is built within an enclosed and controlled environment, such as a modular builder’s factory, the amount of water that infiltrates the framing and sheathing is normally zero. You can’t obtain a drier or more controlled environment than under the roof of a modular factory.
  • The second best alternative, if the structure is not to be built with modular units, is to use any technique that will more efficiently construct the building. These techniques can be the panelization of portions of the structure, roof panels to allow the roof to be more quickly constructed over the building, pre-assembled headers, studs framing, or any other pre-built portion of the structure that will allow a quicker means of assembly. If the structure can be built in less time, the occurrence of wet weather will be minimized.


  • Cover the materials at the jobsite. The majority of time, lumber and sheathing is delivered to the site, and these materials are simply placed around the jobsite, uncovered from the elements. The standard attitude of the framers is that they are not responsible for the covering of the materials, and will not be responsible for any damage or deterioration of the material due to the storage on the site. This attitude will promote the infiltration of water, and will accelerate the deterioration of the product, prior to even being assembled within the structure. The covering requirement should be purchased within the framers contract. Even if the material is being purchased as a separate entity, the actual covering and protection should be within the scope of work of the framer. In this manner, the superintendent on the project, can obligate the framer to cover the material or simply have a “ labor ready “ person hired, to cover the material, and back-charge the individual framer that failed to perform their scope of work.


  • Make your superintendent or foreman understand the importance of covering the framing material and sheathing, both on the ground and once it is assembled within the structure. Although it is difficult, the application of large tarps over the structure is a possibility, if water infiltration is truly an issue. This step in protecting the wood from water, requires the full “ buy in “ of the superintendent on the project, and is not an easy task. I have had many superintendents simply laugh at me, when I suggest that some attempt be made to keep the framing dry.


  • Once the first deck is sheathed, cover the entire deck with either a house wrap or plastic. This suggestion, although somewhat radical, will keep the water from soaking into the horizontal framing and sheathing. Although there will be resistance by the framers to this technique, if the focus is on keeping the structure dry, this technique will work. As the structure is built, the continued application of either house wrap or plastic, on each succeeding floor, will stop the water from penetrating the structure. The wall plates for the interior framing and the exterior walls is simply applied over the plastic or the house wrap. In this manner the watertight integrity of the structure is maintained as the building is constructed.
  • Once the roof elevation is achieved, the roof sheathing should be coordinated to allow the application of ice and water shield, or a self-adhesive roof membrane be applied to the roof as it is constructed. Do not allow the framer to sheath the entire roof prior to the application of the water resistant membrane. Apply the membrane on the roof sheathing as it is installed.
  • Attempt to apply the building wrap on the exterior walls, as the wall sheathing is installed. Do not allow the entire structures envelop to be completed prior to applying the building wrap. This material will reduce the amount of water that will infiltrate the structure. This waterproof material should be applied as the sheathing is installed.


  • Attempt to install the windows as the framing and sheathing are installed. Again, do not wait for the entire structure to be built, prior to installing the doors and windows. This will be met with resistance from your framers; however, if this technique is purchased within the initial contract, its compliance becomes a contract issue and is more easily maintained.


  • Once the structure is covered and the windows and doors installed, humidity control is mandatory. Rent de-humidifiers that can be operated to remove the water that is accumulating within the interior of the structure as the lumber and sheathing dries out. The removal of the moisture within the saturated air will reduce any mold build up and growth. Do not cheat the system and minimize the de-humidification until the so-called finishes are ready to be installed. By this time, mold will have the opportunity to establish itself within the structure and the moisture will have already taken its toll on the structure. De-humidification is essential for proper maintenance of the interior environment to properly perform all of the finish work.


Construction is an industry that has been indoctrinated by customs, habits, intimidation and aggressive behavior, which was founded on years of doing it the same way. In addition, the industry resists any real type of change, or any different technique. Although probably true of all industries, construction workers think they have all the answers and they are the only ones to understand how to frame a structure.

This is incorrect, and the superintendent on the project must be strong enough to insist on any technique that they feel is beneficial to the project. If water infiltration is important, and its prevention is the ultimate goal, then the typical framing techniques will not work.

The growth of mold within a structure is an important issue, and must not be minimized. My structure is basically full of mold, and I am in the middle of determining what the best alternative to alleviating this issue is. I am not sure at this point, however, I will fully report on how this issue is finally resolved, once I determine how that will occur.

In the meantime, think about the negative issues that can occur, if your wood structure is continually subjected to water infiltration. Research the effects of mold on the inhabitants of residential structures and you will immediately realize the potential of severe negative issues, which can result from a structure that is contaminated with mold.

Once you realize the negative effects of any mold within your structure, it becomes mandatory that its prevention be maintained, as your structure is built. This is the reason that I oppose the use of wood framing and sheathing on large residential structures. The advancement of light metal framing and the use of synthetic sheathing products will eliminate the negative effects of water absorption and accumulation within a wood structure.   However, due to the importance of cost, and the efficiencies and inexpensive nature of wood, the use of this structural element will continue.

There must be better and more advanced creative methods to keep the water out, and minimize the mold growth within these structures. This is a new issue and will become more important as the negative effects of mold are more clearly understood.


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