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#32735 - 01/23/15 09:27 AM 6x6 joist spacing for workshop floor
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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 10:35 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Dave Shepard Offline
Member

Registered: 02/19/06
Posts: 707
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 10:41 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Roger Nair Offline
Member

Registered: 10/20/99
Posts: 449
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 10:42 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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 10:52 AM Re: 6x6 joist spacing for workshop floor [Re: Roger Nair]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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 11:15 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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 11:17 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
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 12:11 PM Re: 6x6 joist spacing for workshop floor [Re: Jay White Cloud]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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 09:26 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1875
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 07:56 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
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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#32745 - 01/24/15 10:17 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Originally Posted By: Brent
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!


Hi Brent,

I figured you could muddle through the math...but...like the rest of us, its just nice to "bounce concepts" of others. I just try to always plug in the disclaimer...just in case someone is trying to DIYer a frame over their heads.

Thanks for understanding...


Originally Posted By: Brent
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!


That sounds like a very solid foundation...:) All we use is gravel trench and stone most often when we can get away with it. The trend today is to "throw" concrete at everything and think that is better. I always get a kick out of folks that don't think stone is stable enough...Often while they are standing inside a vintage timber frame that has been sitting on stone for a few centuries.

Your foundation (assuming the concrete is of good quality) should be around for at least that long...

Originally Posted By: Brent
Absolutely. This is why I'd planned on a fully housed dovetail.


Excellent...and to be clear...this means the entire end of the joist is housed into the 8x8. I do like Timbeal's suggestion "tusk" or "soffit" tenons. "Overlap" where the heel of the joist is house and the rest extends over the sill is also excellent. This would save you a great deal of joinery cutting...actually be stronger than the dove tail and would only ad at most 2" in elevation gain in one of the possible renditions.



Originally Posted By: Brent
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.


Hmmm....Well, it all depends on the joist spacing...etc. You will need a minimum of 2" for the kind of loads you are possibly subjecting that floor to...So...it all depends on the final configuration chosen.

Originally Posted By: Brent
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.


In general Brent...it will be your call. I am not fond of "dovetail joints" in general and the only ones I do like or have ever employed in a frame work in concert with other tying members and are only executed in the "Asian moralities" (i.e. Japanese - Korean forms) not European configurations. Most of the contemporary forms of this joint I have had the opportunity to go back and look at...well...not impressed with how they age.

Technically you could just set down a simple very rot resistant 2x plate (wood does not like sitting on OPC) and have the joist simply rest on the OPC stem wall with a "header sill" let into the bottom of the posts. this is more than strong enough and is the fastest foundation type we do on simple sheds, barns, garages, etc..

Good luck, and keep us up to date...Can't wait to see photos.

Regards,

j
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#32748 - 01/24/15 06:23 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
Loc: Canada
Excellent excellent excellent, thank you. This is all great stuff, and thanks for the diagrams too. Lots to mull over, and final decisions will be determined by timber availability etc, but I think I can make anything work.

To be honest, the DT joints to me just sort of look elegant but I hear you on the shrinkage issues and there seem to be a few votes against it. Steve seems to employ them regularly, but the are quite fussy to get right, so a more simple approach is just fine with me!

Regarding concrete....it's that combination of great stuff that's also evil. It sure is handy, but we're happy to avoid it as much as we can. We actually took a course in stone construction, and were thinking about trying this, but we're worried about biting off too much on our first building. We'll try it when we build the house depending on local availability etc.

Thanks again, appreciate it!

Brent

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#32749 - 01/25/15 06:51 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine
Dovetails can be crude and simple and still work just as well as a finely crafted one, and after drying the extra effort will be negated. More over the elegance will only be seen by you while your cutting the joint, it gets hidden once installed.

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#32750 - 01/25/15 08:34 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hi Brent,

OPC (ordinary portland cement) and the industries behind it are the primary challenge in my view. Since about 1880, when the more "energy intensive" methods...(read mass production for profit)...that moved away from "natural cements" like Rosendale when issues really began. The Brooklyn Bridge...still going strong...is stone and natural cements and lime mortars...Note, bridges a fraction its age are falling apart and being replace with...you guessed it...more of the same nasty OPC...Talk about a scam and money racket! I can't wait for Limecretes, Natural Cements and Geopolymers (Roman Cement) to start taking hold in this market...IF...the OPC Lobbyist and Industry actually let that happen...

As for Dovetail joints, the only one I have ever seen that function as intended and endure are those I have seen in Asian frames...particularly Japanese modalities. The common aspect of them...they are smaller...always hidden...and usually very deep and working in concert with other tying members in close proximity.

As for most I see in contemporary work...there is always a better joint to use...usually stronger and almost always as easy or easier to cut...

As Tim pointed out..."it gets hidden"...so why bother with a less strong and more difficult joint to facilitate?

Regards,

j
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#32751 - 01/25/15 06:55 PM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
timberframe Offline
Member

Registered: 08/23/11
Posts: 26
Loc: Canada

THanks again! Do you have a link for some more info on the natural cements? Familiar with lime mortars and limecretes, but less on the others. I heard that very soon cement production will soon surpass coal fired plants as the largest source of airborne mercury in NA.

Cheers,
B

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#32752 - 01/26/15 06:58 AM Re: 6x6 joist spacing for workshop floor [Re: timberframe]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hey Brent,

Sure do...a colleague and friend of my owns the last quarry and facilities that production of these natural cements....as well as...limes, and other related materials. His name is Mike Edison, and he is probably one of the countries leading authorities/Engineers on OPC, Natural Cements, and limes, with related materials as well. You can find his web pages at:

Natural Mortars

Rosendale Cement

One more point on Dovetail Joints for clarity, The Asian forms, though often (not always) smaller...they are much deeper in form often running almost the entire depth of the joining members end. They act and perform more like a "dovetail keying joints" than just a lapping joint form.

In historical restoration-conservation, I see Dovetail joinery as applicable in honoring the "like for like" ethos of this branch of the Timberwrights art form, so here we do employ them and as was the intentions of the original designers of any given vintage frame...Here is where they are most applicable and germane in my view.

Good luck and keep us posted!

j


Edited by Jay White Cloud (01/26/15 07:00 AM)
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