Expert: Bruce E. Johnson - 4/9/2009

Question
QUESTION: Last year I purchased a split level home in southwesten PA.  It was built in 1965.  When we purchased, we renovated and added a second story.  Orig dimensions were 28x44 and the house now is 2 stories, 28x44.  When renovating, the entire process was inspected by certified inspectors.  The question is when I am downstairs in the basement (not split since we added a porch and raised the front door), I have noticed cupping in the floor joists (some feel like they are curved vertically like a C).  The unusal thing is I notice these where there is technically no significant load bearing, meaning under the front door, or under a window as well as sporatically throughout the first floor.  The floor joists are 2x10s and are on 16 inch centers.  I should add that in 1985, the house was in a flood with approximately 2 feet of water covering the first floor.  I was wondering if I should be concerned with structural integrity or if the joists are natually settling?  I cannot recall what the joist were like pre-renovations.  Any advice would be greatly appreciated.

ANSWER: HI Matt, I was just in Southern PA looking at old Victorians to refurbish. A beautiful area.  Anyhow, it could be related to the flooding that your joists are cupping.  It could be that your joists are not properly "bridged".  Bridging is a solid block of joist material that is installed between joists every eight feet or  so.  Sometimes X bracing is used in the older homes but generally it is solid blocking.  Bridging helps keep the joist from vertical bending, i.e. cupping, and it also stabilizes the joists from up and down movement.  The grain of the joist has a lot to do with this problem.  If you look at the end of a joist you can see where that joist was in the tree prior to being sawn from the log.  The more cross grains that are arced or curved the more that joist will have a tendency to cup over time.  Newer lumber is noted for this because as the trees are smaller and smaller the joists cut from them have smaller and smaller rings.  Bridging helps keep the joists from cupping like this because it creates a solid barrier between the joists and holds the lumber in place.  Let me know if you have had bridging installed and how often.  If you have access you can always install bridging after the fact to try and minimize any further damage.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: Bruce, thanks so much for the response.  I was hoping that everything was just the natural tendencies of the wood and not the extra weight of the upstairs causing the cupping.  Since I only noticed the joists after the addition was on, I had nothing to compare to.  There is in fact bridging in the joists.  They consist of 2x4s "X" braced between each joist.  Some bays do not have any as to allow heating ducts/plumbing to pass through.  Most of the runs are about 14 feet and there is 1 section of bridging down the center of the span.  If I were to add more, is it ok to force them back into alignment (vertically)?  Would this possibly stiffen up the floor?  When I am sitting at the dining room table and someone walks past, I notice their footsteps.  (The flooring is 1/2 inch plywood with 3/4 oak hardwood over and laminate on top of that-could not refinsh the wood b/c we moved the walls around in the remodel).

Answer
Hi again Matt, yes you can add the bridging and use it to force your joists back into shape if possible.   That's why I like the solid bridging because it holds the entire joist firm and vertical..And yes, adding bridging will also help take some of the bounce out of the floor.  The general rule for bridging is over support beams and midspan  between bearing points.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com