Expert: Dan Griffin - 3/22/2009

Question
I am currently turning an attic space into a home theater room.  I was able to find some chairs from a commercial theater, and I would like to build a step-up platform in the new room to place the chairs.  My concern is the weight load that this platform, chairs, and people will exert on the floor system.  The platform will be made from 2x6 lumber and plywood creating 3 levels that step-up in 6" increments.  The platform will be 6' wide and 10' long.  I estimate its weight at approx. 400 lbs.  With the theater chairs loaded with people, the total weight could reach approx. 3200 lbs.  The platform would lay across (perpendicular to) the floor joists and would be supported by approx 7 joists.  The floor system consists of 2 x 10 Southern Yellow Pine set on 16" centers with Advantek T&G underlayment.  The floor joists span approx. 14' with one end resting on the exterior wall (2x6) and the other on a laminated beam (approx 15" X 5" X 23.5'.  The platform will rest approx. in the center of the floor joists.  Is there a potential to overload my floor system?

Answer
Greg, I think you are all right.   I like to use this span calculator:
http://www.awc.org/calculators/span/reversecalc/reversecalc.asp

it indicates that 50#live, 10#dead, 14' span, 16" c, southern yelow pine should work with #2-2x10.  These figures should meet your estimates.