Expert: Dan Griffin - 2/12/2009

Question
QUESTION: we have a home built 1992. The upstairs bedroom was converted into a media room.  The upstairs room is 12x16.  It sits above a very large family room and kitchen that is all open and roughly a 23' x 35',  The upstairs room shares two corner load bearing walls along the left and entrance side and the rest of the room sits directly above the family room. A year ago I built a 9'x 8' 10" high platform out of 2X10 with 1/2 inch plywood on top.  I would guess it weighs about 300-350lbs but I built it to spread out over the floor for weight distribution.  We have four media chairs about 40 lbs each.  I then put in a window cabinent a large screen tv (160lbs) against the window that is also one of the load bearing walls.  A few months ago the downstairs family room ceiling started showing a seam and is now a crack the runs the length of the drywall joint on the ceiling.  I assume this is due to the weight settling.  The home is a custom home and I assume the open downstairs floor plan means it was designed to handle this kind of weight. The previous owner had a weight lifting multi-gym in the same room.  How worried should I be or is this just normal shifting after a year.

ANSWER: I'm sorry, my response disappeared, so this is a repeat.

If your kitchen ceiling is 23 x 35, then something is spanning probably the 23' dimension.  This is far beyond typical 2x12 joists so it must be something like LVL, truss joists, or Silent joists.  The original builder should have designed the joists for 40# per SF live load and 10# per SF dead load.  Any structural loads (roof or other bearing conditions) should have been dealt with in a different manner.

I don't know where your 12x16 room is in relation to the kitchen ceiling, but it sounds like your platform added another 10# of load somewhere on that ceiling.  There must be other room walls or something over the kitchen ceiling, or is it just attic?

Most building design loads allow an L/360 loading.  On your 23' span that would mean the ceiling joists will deflect .76666 inches at mid span = 3/4".  Drywall should typically deal with L/360 loading.  Are there any other loads that the kitchen ceiling is carrying?  I don't know why your ceiling joint opened.  There is obviously movement, but I don't know from what.  Repair the joint, but it will probably reoccur.  It may well be best to install an expansion joint in the drywall.  YOu may want to install several to create a pattern.  Look up Trim Tex - they make a plastic expansion joint that I prefer using.

---------- FOLLOW-UP ----------

QUESTION: Thanks, yes the 12x16 room is on the far back side of the family room kitchen span.  Next to the 12x16 room there is a game room with built in book shelf and tv that is essentially the rest of the 35' span.  If the whole upstairs was one big room it would have a 12x16 area and a 20x18 area next to it with an entertainment wall seperating them.  I put the platform in the far back corner so two sides were next to load bearing walls and not adding to dead load in the center of the spans.  So from your note it sounds like I within the load parameters with the weight added and in North Texas where the ground shifts all the time, I just had some shifting or settling that caused the drywall joint to open.  Appreciate the guidance and response.

Answer
Dave, I agree that it would seem to be a settlement issue if you have had some other shifting.  Again, if it does reoccur, you might look real hard at the expansion joint idea.  You have a huge expanse of drywall to ask it not to have issues.  I'm in Oklahoma City, the wind blows enough to crack sheetrock.  This stuff can be cut into an existing ceiling without removing or replacing any sheets.  Yes, there will be sanding dust, etc.  Here is their website:
http://www.trim-tex.com/
The expansion joints:
http://www.trim-tex.com/commercialproducts.htm