In new construction, the primary source of moisture entering the building is most likely from the newly poured concrete slab.

The National Ready Mixed Concrete Association (NRMCA) describes the ‘What’ and ‘How’ of concrete slab moisture in their 2004 Concrete in Practice publication CIP 28-Concrete Slab Moisture. Potential sources of concrete slab moisture include:

  • The floor slab is in contact with saturated ground. Moisture moves to the slab surface via capillary action or wicking.
  • Water vapor from damp soil will diffuse and condense on a concrete slab surface that is cooler and at a lower relative humidity due to a vapor pressure gradient.
  • Residual moisture in the slab from the original concrete mixing water will move towards the surface.
  • It may take anywhere from six weeks to one year or longer for a concrete slab to dry out to an acceptable level under normal conditions. Reference: Bruce Suprenant,  Concrete Construction, November, 1997.

The topic is also dealt with in depth by the U.S. Environmental Protection Agency in their publication EPA 402-F-13053. Moisture Control Guidance for Building Design, Construction and Maintenance. December, 2013. Topics include: moisture control in buildings, basics of water behavior, designing for moisture control, constructing to prevent moisture problems, and operating and maintaining moisture-controlled environments.

As manufacturers of HVAC equipment, Cambridge Air Solutions has no input regarding the numerous factors involved in concrete work that affect the moisture in the slab. However, when moisture problems arise, we are often involved in looking for remedies to deal with the moisture. Some of our contractors refer to the procedure “IAQA flush-out, REQEQ2,2r1”, required by LEED and published by the U.S. Green Building Council. https://www.usgbc.org/credits/reqeq22r1-0. This flush-out, as required by LEED, is intended to rid the building of moisture as well as “off gassing” of building materials.

Requirements

Select one of the following two options, to be implemented after construction ends and the building has been completely cleaned. All interior finishes, such as millwork, doors, paint, carpet, acoustic tiles, and movable furnishings (e.g., workstations, partitions), must be installed, and major volatile organic compound (VOC) punch list items must be finished. The options cannot be combined.

Option 1. Flush-out (1 point)

Path 1. Before occupancy

Install new filtration media and perform a building flush-out by supplying a total air volume of 14,000 cubic feet of outdoor air per square foot (4 267 140 liters of outdoor air per square meter) of gross floor area while maintaining an internal temperature of at least 60°F (15°C) and no higher than 80°F (27°C) and relative humidity no higher than 60%. OR

Path 2. During occupancy

If occupancy is desired before the flush-out is completed, the space may be occupied only after delivery of a minimum of 3,500 cubic feet of outdoor air per square foot (1 066 260 liters of outdoor air per square meter) of gross floor area while maintaining an internal temperature of at least 60°F (15°C) and no higher than 80°F (27°C) and relative humidity no higher than 60%. Once the space is occupied, it must be ventilated at a minimum rate of 0.30 cubic foot per minute (cfm) per square foot of outdoor air (1.5 liters per second per square meter of outdoor air) or the design minimum outdoor air rate determined in EQ Prerequisite Minimum Indoor Air Quality Performance, whichever is greater. During each day of the flush-out period, ventilation must begin at least three hours before occupancy and continue during occupancy. These conditions must be maintained until a total of 14,000 cubic feet per square foot of outdoor air (4 267 140 liters of outdoor air per square meter) has been delivered to the space.

Written by Bill Meyer, Cambridge Applications Engineer

For years we have worked with an industrial retrofit contractor. He often installed vertical S-Series heaters in locations where space was at a premium, both indoors and outdoors. Since Cambridge did not provide a stand for vertical units, he had a structural engineer design a four-legged stand made from 2” x 2” square tubing. The legs would be cut to length in the field and a base plate welded to the leg.

This system worked alright but did cause occasional difficulties.

  • Depending upon requirements at the plant where he was installing the heaters, he may have to obtain a burn permit each day, which could result in a delay of an hour or more until the inspector could arrive.
  • He also had to ensure a qualified welder was on the crew, with the appropriate equipment.
  • When possible, he would set up a welding area within the plant so he only had to set up his equipment once. This simplified the burn permit process, but often resulted in double handling the stands when transporting them to and from the location.

The contractor looked to Cambridge to provide a vertical stand that did not require field welding. Cambridge responded with designing the vertical adjustable stand, which provides vertical adjustment while not requiring any field welding.

Due to this success, Cambridge has since added the vertical stand, structural inlet elbow, structural filter section, 3’, 4’ & 5’ vertical duct extensions, adjustable elbow, and 24”, 38” & 50” wall sleeves to our standard product offering.

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Cambridge has been actively supporting our contractor partners with industrial retrofit heating/ventilating projects for over 40 years. Projects include: aluminum rolling mills, automotive/farming/construction/mining equipment manufacturers, tire plants, electrical appliance & motor manufacturing, corrugators, insulation product manufacturing, steel processing plants, bottling & canning plants, warehousing & distribution centers.