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EDUCATION & SOLUTIONS
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14. What are compression/ expansion
joints? What are their purposes?
What are their weaknesses?
Compression joints are necessary and must be installed on a two-storey or more building….on each floor joist at the top of the joist. This allows for the compression that happens as a building dries out and shrinks. It also allows for the compression of the air spaces and the vibration of the movement of the floor…during occupancy. Usually a wall will compress at least ¼ inch in 20 years…most of it in the first 5-10 years. If the compression is greater than ¼ inch then the wall will begin to compress…and this will put a stress on the stucco and eventually cause extra cracking and buckling at the floor level. Using dry wood and allowing some time before totally finishing is done will allow a bit of natural drying and shrinking to happen before the stucco goes on.
These joints are also places where water can enter the envelope. They are like a mini gutter….they are sealed along their length but open at the ends….or at joints. In this way they intersect water coming down the wall…and run it along their length where it runs out or if the tar paper is ripped….as it often is, on inside corners of walls, then it gets behind the concealed barrier and causes damage to the wooden substrate. Usually inside corners are the more protected corners by the roof line….so damage is minimal…especially on conventional stucco, however, on acrylic stucco it will accumulate over time and cause rot. On the outside corner of the wall is where we most often find damage associated with the compression/ expansion joint….it is almost always open to the air…since there is no provision for a proper connection between pieces of compression joint. Especially on acrylic stucco this is an area to be concerned about…if it is on a weather wall and the joint looks a bit open…it will probably have damage.