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Mon, Feb 2nd - 1:14PM

Moisture - The Hidden Enemy In Your House

Every week I receive calls from people asking for advice of information about wall movement, drywall cracks and humps in floors. Usually I try and answer these questions on the phone although some people are quite insistent that I visit their home to see for myself.

Most builders and contractors are professional and will take responsibility for their workmanship, others are quick to point the finger at somebody else, usually any other trade will do as long as it is not them. Tarion allows your house to settle for one year before they will look at or discuss any drywall cracking issues.

First problem is, your load of lumber used to build your home. Un-like myself when buying lumber, choosing the straight lumber takes up most of that time. On the other hand, your home package is dumped off in one large skid at the construction site. So your framer has just the right amount of lumber to build your home. Most framers won’t bother checking moisture content and straightness of the lumber, he will make do with what he has. A good framer will use most of the warped pieces as fillers etc where they won’t matter as much.

Most homes in the Barrie, Alliston, Orillia area have 2X8 floor joists. If it is raining when your package is delivered these joists will be exposed to extreme moisture until the roof is completed. This is a recipe for high moisture content and eventual shrinkage and possible warping etc.

As the lumber gives up this moisture, the change in size can be dramatic. But it is important to know that a standard piece of lumber does not shrink the same amount along all of its dimensions. The greatest amount of shrinkage occurs across the face of the grain.

Let us assume that a standard 2×4 that is 8 feet long will be exactly 96 inches long, 1.5 inches thick and 3.5 inches wide. Once this 2×4 has been in your house for 6 months and had a chance to acclimate and dry out if it was wet, it will still be nearly 96 inches long. There is very little shrinkage along the length of the lumber.

The thickness of the 2×4 will change slightly, but not by much. But the width of the 2×4 will experience the greatest shrinkage. It may only measure 3 and 3/8 inches in width. Imagine how much shrinkage might happen with a large 2 x 12

Wood shrinks only when moisture content falls below about 30%. A 6-in. wide treated southern pine deck board should shrink by about 3/16 in. if it reaches 12% EMC, so laying wet decking boards tightly against each other should result in a 3/16-in. gap when the boards dry (photo top right). For redwood or cedar purchased at 20% MC, a nominal 6-in. decking board will shrink only about 1/10 in. when a 12% EMC is reached. If the lumber installed is drier than the local EMC, and if the boards are laid tight, there’s potential for the wood to pick up moisture. swell and buckle.

Truss uplift is a condition where the bottom chord of a truss lifts or cambers in the winter and then lowers again in the spring. The movement of the truss is caused when there is a temperature and moisture difference between the top chord and the bottom chord. The wood in the top chord expands with the absorbed moisture from the attic space. The bottom chord remains stable with the heat from the space below. Structurally this is not a problem but it can produce cracks in the tape joint at the ceiling and wall junction on partitions near the center of the truss span. If the truss is connected rigidly to the to the top plate of the partition wall it can even lift the wall revealing a gap under the baseboards.

truss-uplift


Two items need to be addressed during construction to prevent problems caused by truss uplift. First the partitions should be connected to the truss bottom chord with a slotted ‘L’ bracket to allow vertical movement of the truss. Secondly the ceiling drywall should not be connected to the truss within 18″ of the partitions. The simple use of 2×6 blocking on top of the 2×4 wall plate will provide a fastening point for the drywall which will stay with the wall. The ceiling drywall will flex from the blocking to the first fastener to the truss.

After two years all your lumber has settled and your house should not be moving either. Some houses will settle more than others. New homes are required to be built on un-disturbed soil but when building sub-divisions, who is there to ensure the ground level was not altered exactly where your house was built?

If you are not willing to have possible humps in your floors I would recommend upgrading to the engineered floor systems. Some builders offer Silent Floors as one of many upgrades thrown in when the real estate market tightens up a bit.

When the builder does come in after your one year period is over to repair those drywall cracks, pay attention to what he is doing. Some builders will want to trim your door rather than re-level your frame. This is totally up to you but I would rather have a square door than one which has been trimmed to fit a jamb that is no longer square.

Written by Roger Frost
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