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#32735 - 01/23/15 10:27 AM 6x6 joist spacing for workshop floor
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada

Hi folks, been lurking here a while but have never posted. Been interested in TF for years (took the Fox Maple courses) but only getting down to it the last year. Cut and milled a bunch of eastern white pine for a 24x42' workshop which will serve as my TF workshop but also my furniture making shop. Will probably build a separate TF shop later on. I'm concerned now about having a strong enough wooden joist floor for my collection of nice old (HEAVY) machinery. My big table saw weighs 2200lbs, jointer 1400, mortiser 1600, shaper 1200 you get the gist. Joists are cut at true 6x6 now, and will be dovetail mortised into 8x8 sills which sit on a concrete stem wall over crawl space. There won't be vehicles in the building, just lots of machines and occasionally a load of timbers for cutting. I know many will say we should do concrete floor, but we just don't want to. On top of the joists will be (flexible here) 3/4" ply and full 1" T&G White Oak I am milling from my own stock. I can cut more pine for joists if necessary. The number I have now is sufficient for spacing for residential 1st floor loading (40 and 10 I think...don't have it in front of me) but I'm thinking I should beef it up a bit. Any thoughts would be appreciated!

Brent

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#32736 - 01/23/15 11:35 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Dave Shepard Online   content
Member

Registered: 02/19/06
Posts: 706
Loc: Alford, MA
I would err on the side of too much. It wouldn't take too many extra joists to cut the center to center spacing down by quite a bit. What is your span? You will probably need more than a residential loading for you machinery, especially with high point loads.
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#32737 - 01/23/15 11:41 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Roger Nair Offline
Member

Registered: 10/20/99
Posts: 446
Loc: Bakerton, WV, USA
For a heavy duty industrial type concentrated floor loads I suggest forgetting the 6 x 6 joist and look more toward 3 x 12 or 3 x 14 floor joists similar board feet but far more capable bearing capacity, assuming a central longitudinal beam. The dovetail connection to me is a weakening joint regarding the central beam.

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#32738 - 01/23/15 11:42 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada
Hey Dave, span is 12 feet between bearing surfaces. I'm wondering what loading I should aim for. I've seen numbers for garages before ( I think 50 and 10) and my guess is that it would be sufficient for my shop. All my machines together will weigh more than an SUV, but they will be fairly evenly spread out over the whole 24x42' surface, and never all be resting on the space between two 12' sills.

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#32739 - 01/23/15 11:52 AM Re: 6x6 joist spacing for workshop floor [Re: Roger Nair]
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada
Originally Posted By: Roger Nair
For a heavy duty industrial type concentrated floor loads I suggest forgetting the 6 x 6 joist and look more toward 3 x 12 or 3 x 14 floor joists similar board feet but far more capable bearing capacity, assuming a central longitudinal beam. The dovetail connection to me is a weakening joint regarding the central beam.


Hey Roger, thanks for the note. I'm feeling a little foolish now and wishing I'd thought about the loading when cutting the timbers, but to be honest, I've only recently gotten into the world of large industrial machines so wasn't thinking of weight too much at the time. So I'm sort of stuck with 8x8 sills that the joists will be attached to. Would you suggest scalloping out the bottom of the 3x12s so they could rest in pockets cut into the 8x8? Would reduce the overall capacity of the 3x12s I suppose.

Thanks again!
B

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#32740 - 01/23/15 12:15 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada


So I just did a little quick math on the weight of my machines and even if I round up a little for a safety margin, I'm only looking at 15 000lbs of machines spread out over the whole space, so I guess it's a little less than 15lbs/square foot. Of course on top of that would be regular things like work benches assembly tables hand tool storage etc. However, even the heavy machines only have 6 square foot platforms and that doesn't consider yet having a stack of green timbers in there for cutting.

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#32741 - 01/23/15 12:17 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 479
Loc: Vermont
Hi Brent,

Well sounds exciting!! smile

First, before even writing one sentence, I have made it a habit when "assisting and suggesting" possible timber framing scenarios that involve clear needs of PE expertise...to suggest just that...GET A PE with timber framing background...

Sorry, that is just a disclaimer that I have be well advised to give, in as such that if one has to ask the questions..."is this big enough"...then they either need a PE and/or can't properly do the engineering, timber, and joinery assessment themselves.

Please know I am very excited for you and wish you all the best, yet our share "opinions" are just that..."opinions" and not the replacement of good knowledge and experience and/or the help of a PE...

With that stated...here is my two cents:

As a facilitator of traditional historical and natural builds...concrete of any kind is the last thing I like seeing on a job (unless a natural concrete of some form is applicable for a historical restoration) so I am pleased you are going with a raised floor and a stem wall.

From what I have gleaned thus far, you need the floor of an old Mill or Barn...not a garage or house. Having restored, blueprinted and seen thousands of such structures over the decades, I think a 6x6 is barely the minimum...

I would also suggest that a "fully housed dovetail" is going to be the only form of this joint I would even possibly consider as any other "dovetail" shall be inadequate and present with possible shearing issues especially over time and in White Pine.

So with that said, your loads are going to be "transient point loads" of "high weight amounts"...very similar to a barn, mill, and/or industrial garage or other such structure.

The planking on top should be a minimum of 50mm (2") to 80mm (3.15") splined or T&G and/or toggled at 300mm (11.81") intervals. Plywood can be part of this floor diaphragm matrix, but is neither necessary nor traditional.

If staying with 150mm x 150mm (~6"x6") then my rough math suggest a spacing of 400mm (15.75") to 500mm (19.69") minimum for the potential loads this floor could (and probably will be) subjected to.

The Joist could also just rest on top of the sills with added height to the posts to compensate for elevation gain.

Spacing could go to 600mm (23.62") and maybe a bit further if a thicker plank floor matrix is employed.

Many (most?) traditional structures of this nature (i.e. barns, and older mills) only used log bolt sections as joists, hewed on two side laid on the flat...no joint often...resting on sills...Their average spacing is 400mm (15.75") to 600mm (23.69") with most being 175mm (6.89") to 250mm (9.84") thick with a 50mm (2") plank floor on top...This is just a mean average range I have observed...

Good Luck and post pictures as you progress...

Thanks for sharing the project,

j

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#32742 - 01/23/15 01:11 PM Re: 6x6 joist spacing for workshop floor [Re: Jay White Cloud]
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada
Originally Posted By: Jay White Cloud
Hi Brent,

Well sounds exciting!! smile

First, before even writing one sentence, I have made it a habit when "assisting and suggesting" possible timber framing scenarios that involve clear needs of PE expertise...to suggest just that...GET A PE with timber framing background...

Sorry, that is just a disclaimer that I have be well advised to give, in as such that if one has to ask the questions..."is this big enough"...then they either need a PE and/or can't properly do the engineering, timber, and joinery assessment themselves.

Please know I am very excited for you and wish you all the best, yet our share "opinions" are just that..."opinions" and not the replacement of good knowledge and experience and/or the help of a PE...


Completely understood! To be fair, no aspects of the math intimidate me, I'm just partly being lazy and partly uncertain about the different loading scenarios because I haven't had time to read up on them yet and time is getting short! Good to see confirmation my understanding of the concepts and principles are sound though!

Originally Posted By: Jay White Cloud

With that stated...here is my two cents:

As a facilitator of traditional historical and natural builds...concrete of any kind is the last thing I like seeing on a job (unless a natural concrete of some form is applicable for a historical restoration) so I am pleased you are going with a raised floor and a stem wall.


So a few more details. We are doing a rubble trench scenario with short stem wall, but also stem walls running across the building under the bents upon which another 8x8 "sill" will sit. Since the bents are 12' spacing and the building is 24' wide, the interior space that is to be filled with the raised wooden floor is 24x12'. So joists going across the gap the shortest way are 12' long and will join with 8x8s that sit on concrete. Maybe you figured that out, but I just wanted to make sure!

Originally Posted By: Jay White Cloud

From what I have gleaned thus far, you need the floor of an old Mill or Barn...not a garage or house. Having restored, blueprinted and seen thousands of such structures over the decades, I think a 6x6 is barely the minimum...

I would also suggest that a "fully housed dovetail" is going to be the only form of this joint I would even possibly consider as any other "dovetail" shall be inadequate and present with possible shearing issues especially over time and in White Pine.
Absolutely. This is why I'd planned on a fully housed dovetail.

Originally Posted By: Jay White Cloud

So with that said, your loads are going to be "transient point loads" of "high weight amounts"...very similar to a barn, mill, and/or industrial garage or other such structure.


Excellent to see the terminology, thank you.

Originally Posted By: Jay White Cloud

The planking on top should be a minimum of 50mm to 80mm splined or T&G and/or toggled at 300mm intervals. Plywood can be part of this floor diaphragm matrix, but is neither necessary nor traditional.

If staying with 150mm x 150mm (~6"x6") then my rough math suggest a spacing of 400mm to 500mm minimum for the potential loads this floor could (and probably will be) subjected to.


Wondering about the legendary strength of my full 1" T&G white oak though and how much ply material would be required in concert with this? Would love to have plank underlay, but didn't have time to saw the material.

Originally Posted By: Jay White Cloud

The Joist could also just rest on top of the sills with added height to the posts to compensate for elevation gain.

Spacing could go to 600mm and maybe a bit further if a thicker plank floor matrix is employed.

Many (most?) traditional structures of this nature (i.e. barns, and older mills) only used log bolt sections as joists, hewed on two side laid on the flat...no joint often...resting on sills...Their average spacing is 400mm to 600mm with most being 175mm to 250mm thick with a 50mm plank floor on top...This is just a mean average range I have observed...

Good Luck and post pictures as you progress...

Thanks for sharing the project,

j


Alternatively, what if I made a slightly wider stem wall such that wider and deeper joists could rest on the concrete itself with no housing in the sills. Could even consider 8x8 joists with dovetails cut in the ends to tie everything together but a housing would be exchanged for a good bearing surface on the wider concrete. I could cut some more joists, and save the 6x6 for other projects. I'm cutting it tight already for height on on the first floor, and already have the posts cut so I can't really put joists on top of the sills.

Thanks very much for your helpful post Jay, appreciate it!

B

p.s. This building is based heavily on the 24x24 high posted cape in Steve Chappell's book.

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#32743 - 01/23/15 10:26 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1873
Loc: Maine
Look into tusk tenons or soffit tenons for connectors.

I often let just the lower portion of a joist into the carrying beam and leave joist as much above. If the joist were 12" deep you could let it into the beam 5" and have 7 hanging above. Kind of lodged but not. Still just simple drop in pockets with one or two with the tusk tenon. A little more to do when assembling but it give it a clear chance to hold things. Dove tails shrink and distort and stress the wood if you wedge them tight.

You could also put some metal strapping over the tops to tie the works together.

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#32744 - 01/24/15 08:56 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 25
Loc: Canada
Interesting, looks like the tusk tenon could bear both on the housing in the sill and the concrete stem wall.

So I guess I could have the 6x6s closer together and/or add more decking material under my oak flooring or go with deeper joists which might raise the deck a bit too. A couple of options then, thank you all.

B

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