Drying Out A Building During Construction

• Phil Wheeler
• Senior Superintendent
• Rafn Company

Wood is one of nature’s best building materials; sustainable, renewable, strong, and it grows on trees! But wood-framed structures, especially here in the Pacific Northwest, will invariably encounter rain before the building has its roof, windows, and siding on. To continue construction inside the building, it must first be dried out to remove excess water. Continuing construction with wood that has been dried will greatly reduce shrinking and twisting of the walls which would crack the drywall. Properly drying the wood helps ensure a high quality finished product.

Planning

For our Green Lake Apartment project we are using a desiccant dehumidifier system because it is highly reliable, fast, and is an efficient way to dry out building materials. We work with a technician at Polygon to design our dehumidification system based on the size of the building and the architectural layout. We also work with the electrician and the electrical engineer to design temporary electrical service long before the start of the job to ensure that there is adequate power to operate the building drying system.

To determine the size of the dehumidification system we take into consideration the water content of the various materials in the building as well as the size of the building (see image 1). We also consider how much time is available on the construction schedule. And finally, consideration must be given to keeping the air exchange low to avoid humid air entering the building.

Execution

At our current project we began preparing for the drying process early by installing sheetrock as we built the building’s trash chute during framing. This shaft allows the dehumidification system’s air tubes to reach all of the buildings floors without using the traditional means of the stairwell and getting in the way of workers. We also have a great place for the system’s machinery in the corner of the building’s future retail space which is close to temporary power and the trash chute, and will be an easy and convenient place to get the machinery out of the building once the process is complete (see image 2).

When the system is turned on it actually does not blow hot air throughout the building, rather, its air has zero percent relative humidity (see image 3) though during cold weather spells heat can be added to the dried air. The drying process shows results quickly as the water content is highest at the beginning and reduces throughout the process. Dehumidification capacity will decrease as the water content value decreases. Generally speaking, we like to see measurements down below the 10% to 14% range before we begin to cover the wood framing with drywall materials.

Documentation

As the contractor, it is our goal to seek out the wettest locations and make sure they get dried out properly before they get covered up with other building materials. We take measurements at multiple locations (see image 4) throughout the building and document them on a plan drawing sheet for easy reference. This is a systematic process that ensures complete coverage and no possibility of missed areas. This documentation then becomes part of the Quality Control section of the owner’s Operation and Maintenance manual.

Other Uses

After the wood framing has been dried, wall cover materials can then be installed. We keep the dehumidification system in place and running to combat moisture that drywall mud, painting, and gypcrete applications reintroduce to the building.

Rain is a fact of life in construction in the Pacific Northwest, but with a proactive, thorough, and documented dehumidification process, we are able to construct long-lasting, high-quality buildings out of one of nature's best building materials.

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