Expansion & Contraction: Understanding Building Movement
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Posted by on January 10, 2019 in Contractor Focus

Did you know that buildings move? I’m not talking about earthquakes or houses or sheds relocated by building movers. If architects, engineers, and contractors don’t take building movement through expansion and contraction into consideration throughout the entire building process, it can cause serious consequences down the road. Let’s look at some ways buildings move and how to resolve those problems.

 

Here in Wisconsin, if we build a single-story detached garage, we would typically build it on a floating slab. This would include a 5-inch concrete slab with a thickened edge (bond beam) around the perimeter where the outside walls sit. This would be considered the foundation for the garage. It is known as a floating slab because the slab floats up and down—sometimes several inches—as the frost comes and goes. If a garage is attached to a house that has foundation walls and footings that go below the frost line, the attached garage would need to be built with a foundation wall and footing rather than a floating slab.

 

Control joints are used to control building movement caused by expansion and contraction of building materials due to weather changes. For example, if a construction project includes a 600-foot-long straight wall of brick veneer, the engineer may specify a control joint somewhere around every 40 feet that runs from the top to bottom of the wall to absorb the expansion. This type of control joint can consist of a 1/2-inch gap in the brick from top to bottom, filled with a backer rod and a flexible urethane sealant in a color to match the brick. Expansion joints are also installed over windows and doors in this type of wall. 

 

Drywall walls can also have expansion joints. This type of expansion joint will consist of a 1/2-inch gap in the drywall with a special metal drywall expansion bead covering that gap. This bead is then taped in with the rest of the drywall and caulked with a flexible, paintable caulk.

 

Concrete also has expansion joints. A  1/2-inch thick expansion material would be placed against an existing wall when pouring a floor or sidewalk against it, against another existing slab, or around structural steel columns. Control joints in a concrete floor can also consist of a simple saw cut 3/16-inch wide by 1 1/8-inch deep to control cracks that will occur in the floor.

 

Building movement is considered when building interior metal stud walls when the height of those walls run from floor to the roof deck or bottom of the bar joist due to the roof movement. Engineers may not allow the top of the stud to be screwed to the top track to allow movement. Today, they have top tracks with longer down legs and slots in the top track, so the studs can be fastened yet will slide up and down.

 

Interior moisture can have an effect on wood. The last home my wife and I built had a lot of custom woodwork. The custom two-panel interior doors were 1 3/4-inch thick hickory. My cabinetmaker friend and I decided to get the moisture content down to 6% before building the door slabs and jamb stock. This moisture content had to be maintained when building the jambs and hanging those doors from scratch in the home. Keeping and maintaining an 1/8-inch reveal gap between the door and jamb when the door is closed can only be done by controlling the temperature and humidity in the home. Moisture moves wood through swelling, which can affect wood floors as well. Controlling the temperature and humidity in a home is important with woodwork. 

 

I recall as a child in the kitchen at my grandma’s house, she would be cooking at the stove, and I would hear her say, “A watched pot never boils.” Likewise, a watched building never moves—but eventually it does.


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