Are you guys oversizing joists for shops?

[Tom Rick]

I am building a small freestanding shop of 20'x24'.
The floor is supported by three beams with posts on 7'.

So the maximum floor joist is 9' and beams of 7'.

If I use the residential tables with 50 psf live and 10 psf dead load I am within tables using 2x8 joists and doubled 2x8 beams.

Are you guys sizing up for machinery loads?

Typical shop... 700 lb jointer/planer, 700 lb bandsaw, 400 lb bandsaw, table saw, 200 lb sander, 200 lb scroll saw, etc etc...

Go with 2x10 joists and double 2x8 beams or...?

Thanks all

[Thom Sturgill]

As I read it, 9'-5" 2x8 @ 19.2 c/c would be good for 75psf. I plan on using 2x6 @12' <8'0 span which would be good for 100psf. (assuming #2 syp). Not sure about beams though. I am building 12 x 16 (turning shop - lathe, dp, bs, and sander and sharpening station - other tools will be in the basement) and beams will be supported at 6' between block piers which gives a span of less than 5'.

[Tom Wassack]

Greetings from NC!
Not necessarily over sizing - but reducing the spacing from 16 OC to 12 OC!

When I built my 20X32 shop in 2000, I used a pier and curtain wall foundation with 2X2 piers down the center, spaced every 6 feet. I tripled the center 2X8 SYP beam resting on the piers and used treated 2X8's on the flat under the beam for a joist ledger. The floor joists are 2X8 SYP spaced on 1 foot centers. The floor joists rest on a treated 2X8 mud-sill on the pier and curtain wall foundation with a double outer band. OSB underlayment was glued and screwed to the joists with a pine tounge and groove finished flooring. This yielded a substantial and sturdy floor system, showing no signs of sag after 10 years - even with vintage WW machinery occupying most available floor space. On caveat - running under-floor duct work for the DC was challenging with 1 foot joist spacing.

Regards,
Tom Wassack
Asheboro, NC

[Alan Schaffter]

I am building a small freestanding shop of 20'x24'.
The floor is supported by three beams with posts on 7'.

So the maximum floor joist is 9' and beams of 7'.

If I use the residential tables with 50 psf live and 10 psf dead load I am within tables using 2x8 joists and doubled 2x8 beams.

Are you guys sizing up for machinery loads?

Typical shop... 700 lb jointer/planer, 700 lb bandsaw, 400 lb bandsaw, table saw, 200 lb sander, 200 lb scroll saw, etc etc...

Go with 2x10 joists and double 2x8 beams or...?

Thanks all

My entire shop is above my 3 car garage, so I had my builder beef up the whole floor structure because I didn't want a machine sitting on the roof of one of my cars and I wanted an open bay garage without lolly columns. He ran big 14" (or larger?) microlams front to back between the three garage bays and 2X10 or 2x12's cross-wise on the resulting 12'6" spans. It is really sturdy and firm.



My heaviest machine is my old Delta RC-51 20" planer which weighs 1300# and has an approx footprint of 2' X 2' which yields 325PSF but not sure if you include a wider area than the actual footprint.

My subfloor is Advantech which is harder and tougher than OSB and waterproof. That has been my ONLY floor for 6 years, has worked great, and will likely be the only floor until my ship comes in and I can afford hardwood.

[Kent A Bathurst]

....... running under-floor duct work for the DC was challenging with 1 foot joist spacing........

When I have the opportunity to build a shop, I would use floor trusses (not I-joists - actual plated trusses) or exactly this reason. The open-web design would make it trivial to run DC + elec power.

The downside - definitely more $$, would require proper engrg to get them sized properly, and consume more vertical space than solid-sawn joists. But - that's what I would do - AND - clear-spanning your entire area is NBD when using them. Relatively uncommon in single-family residential (except at the high-end), but very common in multi-family and light commercial applications.

[Alan Schaffter]

When I have the opportunity to build a shop, I would use floor trusses (not I-joists - actual plated trusses) for exactly this reason. The open-web design would make it trivial to run DC + elec power.

The downside - definitely more $$, would require proper engrg to get them sized properly, and consume more vertical space than solid-sawn joists. But - that's what I would do - AND - clear-spanning your entire area is NBD when using them. Relatively uncommon in single-family residential (except at the high-end), but very common in multi-family and light commercial applications.

I would rethink that. By running your duct in the joist bays you are really limiting your runs which also tend to be orthogonal- at right angles to each other and hence require 90 deg. fittings which is the worst for static pressure resistance . You want the shortest, most direct DC ducting with fewest changes in direction from the machine to the DC and that often means if you have the headroom make the runs diagonal. This is more easily accomplished below the joists. My shop floor structure uses microlams (boxed below the ceiling) and dimension lumber joists between them.)

[Tom Wassack]

When I have the opportunity to build a shop, I would use floor trusses (not I-joists - actual plated trusses) or exactly this reason. The open-web design would make it trivial to run DC + elec power.

The downside - definitely more $$, would require proper engrg to get them sized properly, and consume more vertical space than solid-sawn joists. But - that's what I would do - AND - clear-spanning your entire area is NBD when using them. Relatively uncommon in single-family residential (except at the high-end), but very common in multi-family and light commercial applications.

Kent,
It wasn't so much the solid vs web-designed joists, but coming through the floor (12 OC joists), with 6 inch pipe did not leave much room for error when cutting in DC runs. My clear span below the joists leaves room for the DC pipe and egress for me to reach any portion of the crawl space. I do see your point about running electricals, etc., through an open web truss.

Regards,
Tom Wassack
Asheboro, NC

[Andrew Joiner]

If I use the residential tables with 50 psf live and 10 psf dead load I am within tables using 2x8 joists and doubled 2x8 beams.



Thanks all

The residential tables are based on maximum safe loads, but safe for what?
I asked my engineer " so with the floor packed with people shoulder to shoulder and those people dancing for hours is it safe?" The engineer said " yes" . I'm not an engineer, but dead weight seems less likely to cause a failure than live "dancing".

To be safe,I overbuilt my shop floor a little just in case I had it packed with vibrating machines and they all started to dance !

[Don Alexander]

i tend to build things to hold alot more load than i ever intend to put on it


this has the benefit of never ever feeling like it isn't adequate no matter what i put in it/on it i like the floor to feel rock solid if 2x8 16" OC with 5/8 OSB is "sufficient" according to the engineers a bit beefier than that
isn't going to be a bad thing IMO

[Kent A Bathurst]

.........I would rethink that. By running your duct in the joist bays you are really limiting your runs which also tend to be orthogonal- at right angles to each other and hence require 90 deg. fittings which is the worst for static pressure resistance....

Alan - thanks for the primer - I'm fairly well up-to-speed on DC piping concepts, although I don't recall ever using big words like "orthogonal" to describe a right-hand turn . Smallest install I've been involved with is my shop; biggest fell a bit short of $1.5 million - a fella can flat-out move some dust with a handful of 250hp motors . 'Course, there might be some height issues in the typical garage for the cyclones and the open-top trailer live-loading system.

There may be some semantics issues here - when I say "plated floor trusses" I mean critters like the ones shown in the photo below. The open-web design offers a lot of paths through the system - not just in the joist bays, and not just 90* turns. Not shown in the photo are duct chases - rectangular openings designed into the truss web system for HVAC ducting runs. These are not off-the-shelf items, so a guy could have more than one duct chase run designed in as required to accomodate the DC plumbing, and not necessarily lined up @ 90* to the trusses.

You have plenty of headroom in your garage photos - that's great!! I'd hazard a guess that the TOTAL rise from the bottom of your DC pipe to the top of your (hidden) joists is greater than an equivalent floor truss system that clear-spans the garage - truss height depends, tho, on span + loading. Loading specs are given to the design firm, so the upstairs toy room gear is taken into account.

Your flooring system was no doubt cheaper - which is definitely a consideration as I noted. There are other trade-offs as well, and I'd doubt many people would take my approach. But, cats are skinned in a variety of ways - just tossed in my comments as an alternative.

[Alan Schaffter]

With modern truss design software, you can just about accomodate anything running through the web of the truss. The big problem, at least for someone like me, is that it requires a lot of prior planning to figure out where to put the machines, mains, and drops. Then how do you allow for long runs that have a bend mid-run. You might need to install the duct runs during construction- the framers will be happy about that. And getting back to the prior planning, if you want to change the location of the drop you are almost SOL.

One problem I encountered running drops is that due to the depth of the joists it was a little tight if I had to run my angled drops perpendicular to the joist bay. The height of the joists almost prevented this for my 6" PVC. I avoided this problem by terminating the drop below the level of the floor. That ended up working just fine since I didn't want the drop sticking up above the floor anyway and had planned to put hatches over the openings.





I eventually removed the blast gates from all machines and moved them below the floor (or behind the knee wall) when I converted them to autogates.

[Kent A Bathurst]

......... it requires a lot of prior planning to figure out where to put the machines, mains, and drops.......You might need to install the duct runs during construction.....if you want to change the location of the drop..........

(A) - Yep. I would know where my stuff was going well before construction. I knew exactly (+/- 3 inches) where my stuff was going in the Atlanta basement before it came up the stairs of the Michigan basement - requires nothing more than paper cutouts and graph paper. NBD - sooner or later a fellow has to make those decisions - I'm in the "sooner" camp. (B) Nope. I'd do myself it after the fact - and stay waaaaay clear of the construction guys. (C) Nope - see A - I would know where its all going. And - seeing as how there is only one dust-generating machine I don't have that I might want to get, that would be in the plans as well - as it was for ATL before I left Michigan.

As I said - I doubt many people would do it this way, for a number of different reasons including cost and other factors, but I sure as heck would, and offerred this simply as an alternate point-of-view.

The table lamp casts a completely different shadow on the same object, depending on where you stand and how you look at it. Doesn't mean anyone is right or anyone is wrong about what that object looks like. You can certainly tell me you wouldn't/couldn't do it this way, and you absolutely should do it the way in which you are most comfortable. However, you can't say my approach is wrong - because it isn't wrong - Sorry - but please feel free to try anyway - "press on regardless"

EDIT: BTW - Alan - I have nothing further to add for gen pop knowledge base. Will be happy to continue the quote-discussion-end quote via PM, tho.

[Tom Rick]

Ok- the follow up!

I ordered my lumber package and used the 2x10 @ 16 oc.. beams- 2x 2x10.

Over the tables by enough that it should be fine I think.
I am decking with 3/4" t&g ply with oak over.

I got scissor trusses for most of the run & am actually going to put in some windows. I just figured I am going to insure the tools and alarm the building.
If I can figure out how to post a sketchup dwg. I will post it.

Thanks all