I've seen a lot of variation in what's been written about and practiced with regard to dovetail layout. Before cutting the pockets in 7x7 tie beams to connect with 4x6 floor joists (2' on center), I thought I'd put it out there to the forum members for input on what I've laid up (see image below). The ties and joists are eastern hemlock, spanning 10'x10' bays, forming the floor of a loft in an equipment shed (loft size of 10'x30').

Some questions that I've been wrestling with:
1)How do you optimize the balance between wood removed from the tie beam (vertical dimension of dovetail pocket) and thickness of the joist at the tenon?
2) What is the minimum acceptable length of dovetail tenon (horizontal dimension - I've set mine at 2.5", leaving 2" between opposing joists.)

Thanks for your thoughts.

Kevin
If you house the entire end of the joist into the beam to 1" deep This will carry the load. Then use a smaller dovetail at the top... say 2" deep to prevent pull-out.
Another way is to have a tenon near the center point(neutral zone) of the beam then peg it.

Thane,

I debated about whether to go with a housed dovetail, but given the smaller size of the ties (7x7), I wasn't sure if I had enough room to include the housing while still having adequate length tenon. I ended up sticking with the un-housed dovetail for simplicity's sake but I still wonder/worry about any weakening of the tie beam. I also debated as to whether or not I should alternate the joists so as not to have them opposing one another, but, after seeing a minimum spec of 2 inches between pockets in a Benson book, I thought I'd be okay. In the end, I drew up 2 1/2 inch long tenons (with a 1 in five angle) that are 3 1/2 inches tall. (If I'd been working with 8x8 tie beams I'd probably have drawn up the pockets at 4 inches deep.)

Perhaps I'm fretting over small differences?

Kevin - am I to understand you are taking ((3.5 inches x ~2.5 inches) x 2)) @ 2' OC out of your tie?

Mike,

That's my current thinking. Any thoughts?

Kevin

What are you basing your timber sizing on? What floor load are you working with?

I know 10' isn't much of a span for the tie... but that is alot of meat being removed.

It will be the floor for a loft that will be used for storage. Don't know for sure what the total load will be - assorted boxed-up household-type items that now sit in a storage unit. The loft is 10'x30' with a 2' knee wall (dropped tie) and a 6:12 roof. The peak of the roof is centered over the loft, making the maximum height in the loft a bit over 5 feet. Loaded up, I'm not sure if that space falls within a typical residential live load floor spec.

Timber sizing was based on formula given in Benson's "Building the Timber Frame House." The tables in the appendix do not list values for eastern hemlock, so I ran the calculations for pine.

The part I'm unsure of is how much the numbers change with the removal of wood for the joist pockets. (I'm assuming that we're primarily dealing with a loss of compressive strength on the top of the beam.) Does the remaining 2" between joist pockets provide ample resistance to compression?

Additionally, the braces are 3.5' from the shoulder of the tie, therefore supporting the tie at approximately equal intervals along its 10' length.

Thanks for any input you can give me on this.

Essentially, the exercise seems to come down to finding the balance between the loss of compressive strength in the tie beams (larger joist pockets) and the loss of shear strength on the joist tenons (smaller tenons).

Here's what I've come up with on the shear strength of the tenons: Assuming I'm doing the math right, a 100 sq ft space with a load of 50 psf (5000 lbs) distributed across 5 joists will result in a load of 500 lbs on each joist tenon. Calculating for horizontal shear (H), I'd divide the cross-section of the joist tenon where it enters the tie (3.5" x 3" = 10.5 sq in) into the reactive force (Rf) of 500 lbs, then multiply times 3/2. This gives a result of 71.43. Referring to a table published by Northeastern Lumber Manufacturing Association (http://www.nelma.org/files/File/Eastern_Hemlock-Balsam_Fir_Table.pdf), the maximum allowable horizontal shear for eastern hemlock is 140. Unless my math is flawed, I'm well within that spec, right?

Kevin-
I just completed a frame with a similar loft-- an 8x8 spanning 10' between queenposts holding 5 4x8x12' joists 28" o.c.
I used very similar proportions to what you describe--
3" long tenons with 1" x4" housed portion and a 2" x3" stub.

Above the neutral plane, everything is in compression, so assuming the 7x7 is capable of bearing the loads with a good margin of safety, I don't see a problem. If this were main tie, I could see getting more picky.

-Devin Smith
Rockingham, VT

Hi everyone

One thing that I would do is after the dovetails are all in place I would wedge around the dovetail ends and sides to ensure that the upper surface cannot sag due to voids that might give in the compression mode.

NH

NH - How would this work? Assuming someone puts a floor down shortly after raising... those wedges will need to be cut flush, assuming that the joint is open enough to insert one.

As the frame dries it will still shrink away from the wedges... no?

We are having a similar discussion on the Forestry forum timber framing section.

Here is a link to that discussion: Link to discussion-click here http://www.forestryforum.com/board/index.php/topic,41639.0.html

Here is what I posted about the subject:

The problem with using dovetail joints for floor joists are that the dovetail is going to shrink.

If you're looking down at the dovetail from above the shrinkage is going to happen from left to right. This makes the dovetail smaller than the dovetail pocket cut into the side of a sill, for example. If the dovetail tenon is smaller then the dovetail pocket then the joist can pull out of the pocket.



In the above drawing the red dimension is what is going to shrink. To offset the expected shrinkage hardwood wedges are driven in on the sides shown here at the blue lines.

I hope that helps.

Jim

Thanks Jim.
I don't use them (never have) - but know folks have used them from the Benson Book effect.

I'm curious to help out Kevin (the OP), and curious as to how NH's wedges work... which I don't see working for long unless the flooring stays off and you come back 6 months or a year later and tap tap them in.

Kevin's frame design doesn't rely on the wedged dovetail to resist pull out (his bent / wall design does this) - so he'll be OK, assuming he designed the dovetail tenon stout enough to take the floor load. But - there should be no assumption that notching out that material and then replacing it with the tenon will give you any compressive advantage across the top of the timber.

I'm a fan of one of the early golden rules of joinery - 'Thou shalt remove only as much wood as needed...'

(followed by 'Thou shalt not covet thy neighbor's tools...'

Mike:
Personally I don't like this type of joint and I don't usually use it.
As mentioned in the other site thread, they rely on the eastern white pine to compress when they drive in the wedges and then when it drys out to expand some and not let the joist pull out of the timber it's connected to.
So further pounding in of the wedges is not done even if it is needed.

Holding of the frame together by other timbers is best.

My approach to joinery would be different, but if 7 x 7 is the required beam to carry the load, I would suggest that you oversize the tie so a 7 x 7 remains uncut in the cross section under the joist.

Please pardon my inexperienced opinion, but first, it sounds like, given that his floor to ceiling height goes from 2 to 5 feet, there isn't much room to maneuver or to get as much weight up on this storage floor as Kevin suggests, unless he is storing cast iron engine blocks and heads up there. Is Kevin over building this floor? Granted, you may want this sized joists for looks/proportion from underneath. Now, you cannot see the dovetails once finished, and given the frame structure, it doesn't seem that he would need dovetails to hold force along the joists length, the frame does that if I understand the short spans described. You only need the joist to hold the vertical weight. A simple drop in joist, no pinning, should work fine, and save a lot of unnecessary work of the dovetail joint(which should be housed if doing it). What do you think Mike and Jim and all? Is Kevin over complicating this?

My understanding is that the loft is 10'X30', but we are NOT talking 30'free span, but broken up into 10'X10' floor sections, supported by ties and posts every 10 feet across the span. Which would imply to me that drop in joists would work fine.

To really simplify it just skip the pocket and run long 20' timber on top of the 7x7.

As for the wedges going into the gap and depressing the wood to have it shrink and still gap after, I don't know, I have never taken one apart to see what it looks like after 15 years.

A curiosity I see when handling logs just before they go onto the saw mill is the grapple bucket putting dimples in the log, after the log is sawn and set for a period of time the dimple protrudes out beyond the sawn surface of the timber or board. This is similar to the hammer track left after missing a nail, the elephant tracks, if you wet the spot with spit it will smooth out in time.

Could the same thing happen with these wedges driven hard into the dovetail joints?

Tim

When I first did the math for timber sizes I was looking at code requirements for first floor loading given that the loft will be packed pretty much full of household belongings. I wasn't (am not) sure how much all that will weigh, so I went conservative and plugged in 50 psf (live plus dead loads). The reality, however, is that there is only a total of 1000 cubic feet up there, spread across 3 ten-foot spans. The number I came up with (from moving companies) for "typical" household stuff is 7 lbs/cubic foot. So, if I stuff the loft at that weight for every available inch, I'd have 7000 lbs spread across four 7x7 ties and fifteen 4x6 floor joists. The ties in the middle would have a maximum of 2333 lbs on them - i.e. less than half the weight of the 50 psf number I started with. Given that, the 7x7 ties seem to be okay, but I wasn't sure how much I'd be weakening them with the joist pockets.

There are no permits or inspections at all required here on my land so I'm not looking to satisfy the building inspectors. I just want to be sure that it's gonna last for the farm.

As for the dovetails, given that I'm still a rookie timber framer, I felt that this equipment shed would serve as a good practice frame in preparation for the new main barn that I'm planning on building a couple years down the road. I also thought that, given the lack of room in the 7x7 beam to created pegged lap joints, the dovetail would be an alternative for securing the tenon in a more limited space. I have the time to cut them, but it sounds as if there is some sentiment among framers they are not a particularly useful joint. Am I reading that right?

I'm about as fond of dovetails as I am of Hemlock, never use either.

Tim's on it there with the overriding joists. Never understood why folks get hung up on having everything come together at the same height, in houses even, but especially outbuildings. I use continuous joists whenever possible, though cogged into the ties an inch or three so they are both self-situating and so they do tie the bents together and help make the building a cohesive unit.

In this case there is a three-fold advantage, with the joists, up go the connecting girts, avoiding a three-way joint and the weakening of the posts removing that much section at one point represents. Up also goes the moment, (IMO a twofoot kneewall is pushing it even on a ten foot building) it would be a balance act with a relief cut to a barefaced tenon on the CG's, but if you make the girts planer with the raised joists and tie all the way across with ten foot decking, you will spread the moment over more square inches of joinery/timber and shift the bending moment up, and effectively shorten the kneewall. It would at the same time provide ready and full access to the dovetail tenons wedge

Will, I agree with the dovetails and hemlock, and I cringe when someone wants more that 2' on the knee wall.

I am not sure I follow the last two sentences of the last paragraph, almost but not fully.

I have been raising the tie beam on the first or last bent and tusk tenoning the long joists into it with either no very shallow daps to locate the joist. Trying to reduce joinery, time, wear on the body, money and so on.

The other part is I am leaving out the CG, less wood removed at the critical point where the post and tie intersect. I use longer braces as well, bracing to the top plate. To support the flooring I run the boards to the wall and fasten a support under after the boarding is done, there is not much load in there anyway.

It would be interesting the hear from folks that are using wedged dovetailed joist or purlins.

Tim

Tim and Will,

Looking outside my window as I write this, I see farmland surrounded by forest that is primarily a mix of beech, birch, maple and hemlock - not too dissimilar to much of Vermont. From the healthy maples, I produce sugar. The unhealthy maples give me warmth. (It was 18 below zero this morning.) Given the choice between the scattering of beech and large stands of hemlock, for better or worse, I choose hemlock.

Dovetails? Well, I'm an admitted rookie at timber framing (though an experienced woodworker) who's still trying to sort out the best practices. I ended up choosing to dovetail the floor joists because this building will only be sided on three sides (board and batten). Knowing that it will not be stiffened by a continuous skin, my thinking was that I'd take advantage of any opportunity to tie frame members together with the hope that every tied connection would improve the overall integrity of the structure.



I've done the same for this building. I haven't put wall girts at the post/tie intersection. The joists are only in the ties. My braces have a rise/run of 3.5 feet between the post and the top plate.

Thanks so much for all the feedback. I've learned a lot from the input and the rethinking it leads to.

tim -

a 2' kneewall is perfectly workable if you have a structural ridge, principle purlins, or other such arrangement to keep the roof from spreading.

the op's design has 10' of roof being spread to the plates, with 10' bays, and something akin to a principle purlin / saltbox type design - so it shouldn't be a big deal. not how i would have done things - but then again - my first frame (a porch in white oak) had plenty of 'book learned' things in it that i wouldn't do again...

Hey Mike,

You put it so kindly

Yup, I'm pretty much self-taught in everything I do. I read books, ask questions of those with experience (such as the broad range of skilled practitioners represented in this forum), refine my own techniques, repeat.

I don't have any aspirations to make my living from timber framing, but I do have a need for a few structures on this hillside farm and one will, I'm sure, see the progression of my learning as those projects evolve.

Thanks again for your feedback.

Hi Mike, I think we chased this tail around a few months ago. I am in 100% agreement when additional paths are taken, as Ken often says. It is when no other additional structure is involved, which concerns my previous statement.

I should also clarify my hemlock aversion. The hemlock which grows around here is full of shakes. When I do use it, and that is not often, I am careful where it goes. A new framer should be on the look out for shaky hemlock.

That said, when working on my own frames I will use a lot of wild stuff, pushing the limits for sure. I am now scraping along my blueberry field edges for rafter stock, I am finding balsam fir to be another discouraging species due to the rot content, but I am using it all the same, and making some poor fire wood to boot.

Tim

Will T and Timbeal, have you guys ever heard someone describe what you all propose as "galloping" joists? Think that sounds cool.

Tim,

The hemlock in my forest is relatively young and shake free, for the most part. I agree that it can be a problem if one does not keep an eye open for that downside. Otherwise, hemlock has been commonly used in these parts and seems to be wearing well in the old frames I've seen built with it.

Tim – Where did I lose you? I was trying to be both descriptive and vague at the same time, to plant some seeds and provoke thought.

Kevin - I had nothing to add to this conversation until you asked out loud if there had been an awakening like change of opinion regarding drop-in dovetails since the books you've been reading had gone to print. Yes there has, most framers avoid them and have for some while now.

You did make it clear that you were a newbie, which is why I threw in a bit about the kneewall and my unabashed opinion of Hemlock. There's plenty of it right outside my window also, and I consider myself part my local forest economy, I buy local almost with out exception. It is not just Hemlocks propensity for ring shake that has me dismiss it as a framing timber (or that that often doesn't rear its ugly head until a timber is laid out and joinery is being cut) but that it's gnarly grain makes it hard, unpleasant and time consuming to work. It's a wonderful first layer for a two layer barn floor, makes good skip sheathing on a roof, there's a mill up the way that dresses it up into handsome, durable and nicely priced strip flooring. I do buy it, I just don't frame with it.

Old growth, dense ring count wood, is night and day in many species, this one especially

Mo – I know of no other name and I like the one you just coined, good stuff !

Will, right here along these lines...

" you will spread the moment over more square inches of joinery/timber and shift the bending moment up, and effectively shorten the kneewall. It would at the same time provide ready and full access to the dovetail tenons wedge"

Moment spread around? At first I thought you may have been alluding to the wedge on the tie to post connection, but that is covered by the boarding. So how are the theoretical dovetail wedges still accessible?

Spruce, what do you think of that for a workable wood? And I am loaded with it. I don't have a choice at times, gnarly, snarly spruce it is.

Galloping joist? Can that now be found in the wiki pages?

Tim

Okay, so there's been some weigh-in about whether the dovetail is even a joint that should be used in floor joists. Just so I'm clear, what do you see as the primary reason why the dovetail has fallen out of favor with contemporary framers? Is it a structural concern or an economic concern?

for me, both.
lots of labor to cut, and you remove lots of wood...

if you need to pin the joists together - i'm a fan of the tusk tenon and stepped or tapered housing (assuming you can get a tenon on the NA of the carry beam)

or drop ins with lag, panel screw, spikes or nothing, again - depending on the application.


for production shops - i'm sure there are ways to jig up the dovetails for hand work (routers, etc.) - and i've seen a fancy tool head for a hundegger that will do a dovetail like housing that you can automate and cut that allows a tapered dovetail end to be tapped in from the top... but i've only actually seen it in use once, for a tool shed roof.



as noted - in green material they will shrink across the grain and the carry beam will not shrink noticeably along its length - so you are putting plenty of work into something that will be ineffective for its intended design pretty quickly as the material starts to dry. not to mention all the material you are taking out of the compressive face of the timber, replacing it with something that may go in tight, but never be as sound as leaving the material in the first place.

my $.02, which isn't worth much in this economy...

Kevin, fellow framers,

I don't work in the same tradition as most of the people here, therefore some of my comments may be of limited usefulness; all the same I thought I would offer them. Please excuse my presumption in that regard.

There is some use of housed dovetail joints in Japanese timber work- let's say it is one option at least - however, like most of the people posting ahead of me, I agree it is an inferior joint option in most if not all circumstances.

The dovetail promises something it really can't deliver, most especially when green timber is used. You might say that the dovetail joint has excellent branding, but like the New Coke, perhaps, doesn't quite deliver on what it appears to be selling.

The 'promise' is that the dovetail will act to keep together the girts or beams in between which it ties, that is, resist tension. It also offers convenience in assembly.

It doesn't deliver on these promises for a variety of reasons:

- in green timber, one can expect shrinkage in service, especially in that first 1~2 years as the building dries out. The performance of the dovetail is absolutely dependent upon a tight fit of the tenon cheeks to the mortise side walls (which are end grain, largely). As the timbers shrink, the tenon will shrink disproportionately more across the width of the joist than the mortise will (in that same direction as the joist) due to their grain orientation. The slightest shrinkage however, and the fit is loose, and with it the mechanical 'benefits' of the joint are largely gone. A joint with slop allows easy movement and is more likely to fail than a joint which maintains a tight on-going fit between surfaces.

- even if one is using dry timber, the dovetail joint is problematic in terms of what it is supposed to do. If in the life of the building there is ever some sort of spreading load moving the floor girts/beams in the frame apart from one another and the joists with their dovetail tenons are thereby loaded, what happens is that the end grain walls in the dovetail mortise, which are harder and less compressible than the side/face grain surfaces of the dovetail cheeks, will simply crush the sides of the tenon as it tries to withdraw. Even if the load on the frame is not tending to fully separate the involved pieces, or is seasonal/occasional, the crushing of the side grain when load is applied causes the tenon cheeks to take a compression set, and thus the fit is worsened anyway.

Further, after a small amount of shrinkage in the tenon, most of which will be manifest at the fat end of the dovetail and less at the neck of the dovetail, the only portion of the mortise which will be doing anything is the sharp corner at its narrow end, and this small amount of material can fail in tension perpendicular to grain. Some woods are particularly vulnerable to such loads, Douglas Fir being one example.

Unfortunately, despite all appearances, the single dovetail tenon really offers limited resistance to withdrawal - worse than most other joinery options for that type of connection at least.

- a further negative about this form of joint is that it does not exploit the neutral axis of the receiving timber, but rather chops excessive material out of a critical compression surface (the top of the girt/receiving beam), and I say this especially when the dovetail tenon connection is compared to another relatively poor joint, the drop-in joist. A much better connection, in terms of the neutral axis issue, for cases where the joist and beams are flush with one another is the tusk tenon, though it is not so overtly convenient for frame assembly. That 'convenience' however really boils down to design, in terms of how the frame will be assembled, and I would say as well that in-service long term performance of the frame trumps a few extra hours here and there during the brief assembly process.

I imagine many people might choose a dovetail tenon for its apparent convenience when it comes to assembly, in that the joist can be installed after the surrounding frame members are installed. However, given that fact that it offers no real structural performance advantage, is not really going to do much to resist tension loads, that it weakens the receiving timber excessively (or requires that the receiving timber be up-sized to compensate, which is wasteful), comparing the two connections the drop in simple housed connection is to be preferred.

Additionally, the drop-in joist may be strengthened to give it reasonable tension-resisting performance by the addition of an angled timber screw or two.

If I might offer some design points...

The dovetail can be improved somewhat, in my view, by a few modifications, though I would, personally, still avoid it.

The drier the wood the better, the longer the tenon the better, and the narrower the tenon the better (to a point!). A wider dovetail, as is often illustrated in books, will shrink more across the width of the timber than a narrower dovetail will shrink. To give an example from outside the Western (er, North American) tradition, a Japanese dovetail on a floor joist, say on a 6" wide timber, might be 1/5 ~ 1/4 the width, or 1.2" ~1.5". A longer dovetail (I mean in the vertical orientation) offers more surface area and potential strength than a shorter one, however this approach would normally be paired with a joist that was deeper in section than width (as is structurally logical considering the vertical load that floor timbers are meant to resist).

A longer dovetail lends itself also to tapering, so that the fit tightens as the joist is lowered. This fact can be exploited, in some instances, by having the assembled joist sit slightly proud of the receiving beam, so that drying in service will cause it to shrink and drop down into a flush position with the surrounding beam, and still be reasonably snug in fit (one of course would need to consider the floorboard fastening situation carefully if this was the plan).

The wedged dovetail. This somewhat offsets the shrinkage problem described earlier, by pre-compressing the wood in the tenon, however, as an earlier poster pointed out, the wedge cannot be easily accessed after the floor goes on above it, so it is only useful for the period up to the floor going on, and in most cases that is a short time interval and the frame will have hardly done any drying. As far as mechanical performance goes, the wedging only adds very slightly, again by compressing the side grain of the tenon, to any hope that the joist's dovetail will resist withdrawal. Further, in order for the wedge to achieve an evenly-tight fit against the dovetail tenon cheeks, it would be better practice to slightly taper the opening (i.e., the tenon cheek and/or the mortise wall) into which the wedge is to be driven, along with tapering the wedge itself, and this adds time and cost to the work, and if the cut out is not really clean, it only increases the odds of the joint having less-than-ideal mechanical performance.

A better reason to use the wedged dovetail tenon, in my view at least, is that it allows for a horizontal assembly - the joist can be slid in along its length and then wedged, rather than dropped in. In some circumstances, this might offer a handy solution to a frame-raising difficulty (say some place where there was inadequate vertical clearance to drop any timber into place on a beam). However, that said, the dovetail joint is still better avoided and the design of the frame thought out so as to not require such joints.

As far as using a connection for floor framing which needs, for some reason, to resist tension, then a better option, in my opinion (and with the given that the situation will allow it, considering building/floor/ceiling height issues, etc), is to put the joists on top of the beams/girts (again, as another framer pointed out previously in this thread), and employ some form of partial cogged lap joint, with the halves secured to one another with a timber screw (or with a wooden connection if desired). That's likely to be the strongest connection, and is simple and quick to cut out, as an added benefit. If the floor joists must be flush with their receiving timbers, then the tusk tenon is the suggested choice in most instances. My $0.02

the Carpentry Way (my blog)

Very well put, Chris!

Here, Here, Chris.

Will, not coined by me, just trying to resurrect the term.

Galloping: Although the exact meaning of the term is not entirely clear, it probably referred to a framing member that rests or rides over the top of another framing element, such as a bridging joist over a binding one or a common rafter carried on the back of a purlin.

1711 The joists of a courthouse were "to be all galloping joyce." Talbot Co, Md., Land Records Book No. 12

1790 Framing at Hampton in Baltimore, County, Maryland, included "6 sqr 88 feet of galoping joice framing." MHM, 33.

Source: see below

For my fellow bookworms: An Illustrated Glossary of Early Southern Architecture and Landscape. The amount of research that went into this glossary is remarkable.

p.s. is something amiss with the wiki glossary?

Okay, gang, you've given some great arguments here. I can't say enough about how much I appreciate it. I've revised the plans to use dovetails and now plan to use a tenon such as in the drawing below. (The cogged joint that had been suggested would take up too much of the already limited room in the loft.) Below are the dimensions I've sketched up. I'm taking much less wood out of the tie, and none out of the top of the beam.

Do you see anything amiss with my dimensions from a strength standpoint?

Kevin, you are on the right track, to further refine the joint to maintain beam strength, center the mortise on the centerline of the beam face and to augment bearing capacity of the tenon abut the shoulder cut with a diminishing haunch. Another consideration is to limit the reduction in the joist by no more than one quarter of the joist height.

I thought about that, but I worried about not leaving enough wood between the tenon and the bottom of the beam. Is there a recommended minimum dimension in that direction? (My sketch shows 3.5" and I've seen both 3" and 2.5" referred to.)

I would reduce the thickness of the tenon to 1-1/2", using a 3/4" haunch, the bottom of the mortice placed at 4". My reason for 1-1/2" mortice/tenon is they are easier to cut as you are removing even less wood. The haunch gives meat above the tenon.

I heard a well know engineer say you can go to within 2" of the bottom of the timber. I still like to leave a reasonable amount of stock below the mortice.

Do you have a plan on how it will assemble?

Tim

Tim,

Lots of hands

Kevin,

I too have never used dovetail joists. And I would 2nd or 3rd Roger and Tim's comments. I used all tusk tenons once on a frame (with 5 or 6 black birch log floor joists), and it required a lot of strong people.

And Chris,
Your dovetail commentary reminded me of a question I had on the traditional Japanese joinery for the tie beam to plate connection (which I believe is often dovetailed). I started a new thread in the Japanese forum.

Brad

Tim – I think this might pay off my 2¢ debt. I was alluding to capturing some of the moment through the decking and the raised connecting girt it is fastened to, literally augmenting the Tyeing Joint by creating a viable quantifiable load path in this adjacent system by designing the joinery (hence the barefaced) and placing well fastened (to the girts) continuous decking to do so.

We were forced to throw just this into the quotient, in the historic replication of a 16 X 30 herb drying shed at the area Shaker Village a few years back.( the smaller building pictured here in the 2nd image down http://www.galenfrysinger.com/new_hampshire_shaker_farm.htm ) It had been sold off and removed in the declining years of Shaker population. Archaeological excavations confirmed it's footprint, photographs its architectural details and high kneewall, a village wide survey of all framing its likely joinery and configuration..

We had to keep tweaking things to make the calcs and the FEA model work.. Upsized the posts to 9 X 12, nice low collars on the rafters (requiring ducking for some but convenient for hanging herbs - The CSV is an island of common rafters in an ocean of common purlins, the original crew of Shaker carpenters came in from a NY village) and finally adding the continuous decking.

In the last sentence I am suggesting that there will be unobstructed access to the wedge because the flooring will be above it. I always wedge a dovetail tenon from the interior (making it deeper than the floor is thick if need be) to be able to properly snub them up as the frame seasons.

Mo - Even better, establishing etymology by citing historical usage, is great stuff !

Will, you are talking about the wedge on top of the tie beam not the wedges in the joist dovetails, now that is a different topic. One in which I see the wedge coming in from the exterior due to the make up of the wedging action. I am often tempted to install them from the inside though. The last ones I did were from the outside and I screwed them down once set in place, for what it was worth. I add substantial pegs as well.

I did follow the flooring and the additional job it was doing. I see it being susceptible to creep over time as well. Many paths make a strong journey or something like that.

Tim

The concept of runnning the joists over the tie is a no-brainer--
a good solution especially in an outbuilding. Kind of like the old dutch barn style temporary loft joists-- they just threw up some poles over the anchor beam to add seasonal hay storage.

I suppose you could make this work in a house frame as well.

I personally like dovetail lap tenons, but think making every joist or purlin tenon a dovetail is unnecessary. I usually make 2 of them dovetails-- spaced 1/4 in from either side. Overkill for sure-- nails and subfloor will tie everything together way more than the dovetail tenons will, but I like that there is some joinery performing that function for the long run. Basically I look at it as a nice touch that doesn't really take that much more time.

Wedging seems to work best with pine joists-- they squish and I imagine the squished part doesn't continue to shrink. I also cut frames seasonally in the outdoors-- it takes a couple of months to cut and raise, normally in the summer, so things have a chance to dry quite a bit.

I'm no hemlock hater myself. Shake and splinters aside, its cheap and versatile. Looks beautiful planed in my opinion. Pine works much more nicely, but hemlock has that sort of satisfying crunch when you chisel it. Every wood has its virtues and vices. Hemlock is the wood of choice around here for boarding, strapping, and studding. Its pretty much the only choice for local studs. Put 'em up green though, or not at all.