View Full Version : purlin size and spacing spacing for floor

01-23-2006, 06:04 PM
I built a steel building that is tall and I am wanting to add a second floor in it for a sort of office for me. It is going to be 10 feet wide by 30 feet long. Nothing fancy just a desk, and a warm clean space to work on stuff. Maybe a small table on one end for poker night with the buddies.

Anyway right now I have 10" C purlins ran across the length of the shop that I am going to build the floor on. The purlins are parallel and 10 feet apart. I am needing to weld some more purlins in there to span this 10' gap and to attach the floor to. I am thinking of using 3/4" plywood for the floor and spacing the purlins 2' apart. Is this sufficient? What size of purlins are required to span this 10'? 3", 4" ?

I figure the maximum weight up there spread over the whole area will be 2000 lbs. That would be 6 guys at 200lbs plus 800 lbs of desk, furniture, etc. I have been welding for about 15 years and am confident in my welding ability, I am just not really sure what size material I need for this. Obviously I don't want it to collapse, but I also don't want to spend more on materials than I need to.

Pile Buck
01-23-2006, 06:38 PM
I donít have any information on purlins, but here are a couple charts for I-beams ;) .

01-23-2006, 06:46 PM
I have never used purlins for a floor, but have built many thousands of SF of steel stud floors. The smallest we would use were 10". Most were 12" at 24" OC. The tens were 16"OC, IIRC. They were also capped with 3" of lightweight concrete instead of plywood. If it were mine, I'd stick with 10" on 2' centers to be safe. You will beed to brace then laterally at mid span or on 4' centers. On 10' long, mid point would work. Also, any point where a purlin will rest on a wall or frame member below will need a stiffener. You put it across the open side and weld top and bottom. It keeps the purlin from curling under load. My two cents, anyway. :D

01-25-2006, 03:23 PM
http://www.flexospan.com/products_cees1.htm has a load table for cee and zee channel purlins

01-25-2006, 04:11 PM
i don't know much about the steel but tongue and groove plywood subfloor deck generally goes on joists spaced 16 inch centers minimum as far as the wood framing end of it it'd tend to sag on 2 ft centers


01-25-2006, 04:25 PM
Ok, 16" centers. That is no problem. 3/4" plywood? USMCPOP, those tables are exactly what I was looking for, but I am not sure I am reading them correct. For example if I were to use 6" purlin, with 2.5" flange, 14 gauge, on a 10 foot bay the chart says 331. What does this 331 mean? Total weight it can carry evenly distributed over the 10', weight per foot?

01-25-2006, 11:17 PM
Yeah, I had the same reaction. No units given whatsoever! I expect it's total weight in pounds evenly distributed over the span, but no way to know offhand. However, it does at least give you a way to judge relative strength from one size to another. It also made me wonder how your 30 ft. span of 10" channel was supported.

Wish I had my engineering resource with me now. My older son was studying mechanical engineering, but went off to Iraq with the Marines. Lost him a year ago tomorrow.

01-25-2006, 11:44 PM
Sorry to hear of your loss. If he was anything like you he must have been a fine young man. You must be very proud.

Semper Fi


01-26-2006, 09:56 AM
you're both in my prayers semper -fi

01-26-2006, 09:40 PM
don't wing it get a structual eng. won't be too expensive