Weight on wood floors with floor joists

[John Bailey]

I'm building my shop. I've used 2x6 joists on 16" centers with the longest span of 5'. I've put 3/4" ply over the joists that will be covered with 7/8" pine boards. I gave the 230 lbs.(me) jumping test on an individual joist before I put the ply on the joists. It didn't budge. I'm trying to decide how heavy a machine I can put on this floor. Does anyone have any experience, or know where I can look for more information? Code tells me I can use 2x6 on 24" centers with a span of 7'. So, I'm well within those specs. I couldn't find any information specifically about shops. The heaviest machine I'm contemplating is 463 lbs. Having used only a radial arm saw and hand tools in the past, I don't have experience with heavy machines. I'm not sure what kind of weight a floor like this will be able to hold.

John

[Mark Singer]

John

How big is that machine 463 pounds? Floor area? What beams or walls are you resting on?

[Andy Haney]

I found this website when planning a shed recently. I've made some statements here I have no qualifications to make in hopes this response may trigger input from a structural engineer, architect, or someone with similar qualifications.

Based on this:

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Spruce-Pine-Fir&size=2x6&grade=No.+2&member=Floor+Joists&deflectionlimit=L%2F360&spacing=16&wet=No&incised=No&liveload=100&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span

a "standard white wood" 2x6 joist 6'8" long at 16" o.c. will support a 100 psf load. I made some assumptions about wood species, grade, etc. when "plugging in" the data that may well be inaccurate. You can open the page up and change variables as you see fit.

As I review these numbers, your heaviest machine should comfortably sit on your floor if it has a "footprint" in the neighborhood of 5 sq. ft. If the footprint is smaller than that, you could set in on a piece of 3/4" ply large enough to reach the next joist, and that should reduce the psf load (enlarge the footprint).

Hope I'm not too far off track, and that this website is as helpful to you as it was to me.

[Bob Worrel Jr.]

With that short of a span, you'll be just fine for 500 pounds, if not more.

[John Hemenway]

I am also an aquarium nut. Comparied to water in a box tools are light. My 180 gal. aquarium is about 2000 lbs. Footprint is 2x6 feet (12 sq. ft.). Most modern houses can support this!

You should be fine - especially using both 3/4 ply and 7/8 pine to spread the load.

[Rob Russell]

You're fine with that construction. You'd need to put some seriously heavy machinery in there to cause problems - like mongo metal working machinery.

[John Bailey]

Thanks to all your responses. It would appear that I've nothing to worry about. In fact, instead of that 463 lb. 18" bandsaw, maybe a 650 lb. 20", or maybe a 1000 lb. 24", or maybe a .....

[Bob Smalser]

Just make sure you use solid blocking between those joists before laying the floor.

[John Bailey]

Bob,

I'm not sure what you mean by "blocking." I put perpendicular 2x6's staggard every 4 ft. between the joists. Is this what you meant? BTW, how's the boat coming? One of my first projects will be to build a new sailboat tender.

John

[Rob Russell]

John,

I'm confused now.

Your initial post said that your floor is framed with "2x6 joists on 16" centers with the longest span of 5'" and now you say that you've got "perpendicular 2x6's staggard every 4 ft. between the joists".

Are the staggered perpendicular 2x6's just 14 1/2" sections of 2x6 that span from joist to joist, staggered so you could nail them in? If so, that's cross-bracing or blocking. They help transfer point loads from joist to joist and also keep the joists from twisting. Keeping the joist vertical is important because that's how it's strongest.

Now - back to your "longest span of 5'" statement. Do you have beams underneath your floor joists at 5'? Is this a standalone shop and you have concrete piers every 5' and that's how you have support in the middle of your floor? What is the overall construction of your shop floor?

Rob

[Bob Smalser]

I put perpendicular 2x6's staggard every 4 ft. between the joists. Is this what you meant?

No.

If your joists are on 24" centers, "blocking" is a 2X6, 24" long placed every 4' or so in each joist bay nailed in from the joist sides.

They are important to prevent the joists from splaying under load and are required by code....even if you have beams running beneath your joists. They also combine with the deck to make a stiff, monocoque structure...especially with some construction adhesive beneath the plywood underlayment.

Can also be done with crossed 1X3's but solid blocking is stronger and easier. Helps to have a palm nailer, tho, when working with 16" centers....which before palm nailers were common was one of the reasons buildwers often used cross bracing.

The McMaster-Carr brass arrived yesterday and I may begin the rudder layout today.

[John Bailey]

Rob,

Sorry for the confusion, but, the way you described the "blocking" is exactly the way I've got it. As far as the 5' spans, the shop is 20'x20' with 2' support walls built in the crawl space every 5'. So, I have a support wall that supports the joists at 5', 10' and 15' to support the joists. This seems to be plenty sturdy, but again, I haven't dealt with heavy equipment in the past.

[John Bailey]

Bob,

I think I've done what you have described, but I'm doing a lousy job explaining it. Thanks for the advice.

John

[Rob Russell]

John,

Thanks for the description of your shop's floor framing. You don't have anything to worry about. The live load capacity of your floor is more than 100 lbs/sq ft. That means that you could put a 600 lb bandsaw (who's footprint is about 2' wide x 3' long) in the middle of your floor span and the deflection of the floor will be no more than anything in your regular house floor.

If you want to get really heavy machinery, I'd simply put it on the floor so it's basically over one of the support walls. By heavy, I mean something like my combination jointer/planer. It weighs about 1500 pounds and has a footprint that's about 2' x 30", or an effective load of around 300 lbs/sq ft. You could put that machine dead center in the middle of the 5' span of your floor and the floor probably wouldn't fail (break) - it would just sag a bit. If you wanted to get something that heavy, just put it in your shop so the machine is centered over one of those walls. With a wall every 5', I'd think you could lay out the shop pretty much anyway you want and not worry about it

As a specific example, the Grizzly 27" bandsaw weighs about 1100 pounds "in place" and has a footprint of 18"x40", for a total load of 200 lbs/sq ft. You could put that in your shop, just over one of your 2' support walls and never worry a whit about the floor.

Hope this helps.

Rob

[Steve Wargo]

There is an excellent book called the Wood Handbook - Wood as an Engineering Masterial. That will have all the specs you've requested. It's a little pricey but is just as important to own as the architectural standards book IMO. Hope this helps.