Scissor truss beam sizing?

[bluegrassben]

Hi, I'm new to the forum. I am currently in the process of building a timber frame home. dimensions are 24x32 with 16 foot sidewall height. The problem I am running into is determining the size of beams to use for scissor trusses to either fully span the 24ft or to build the bents with a center post to support the peak of the trusses. as of now I am thinking of using 10x10 post for my uprights. all timbers will be white oak. I do have a small amount of experience in timber framing and joinery but do not know much about the engineering part. any advise would be greatly appreciated. can post pics of bent design and/or floorplan if needed. thankyou!

[Jim_Rogers]

Welcome to the forum, and post what you have drawn up.
Thanks

Jim Rogers

[bluegrassben]

House will be comprised of five bents on 8' center and i'm thinking 8/12 pitch roof but im flexible on that at this point.





  

  

  

 

[Thehardway]

Bluegrass,
Your footprint and layout is nearly identical to mine.  I used a Kingpost truss to span 24' and our LR/kitchen is open all the way to the roof from first floor.  We love the open feeling it gives.  If I had it to do over again I would have added about 5-6' to both length and width of the house. Things are very tight and I only have a 2bd. 1 bath.  I don't think you will like adding that post in the center of your room. The center post idea goes against the leveraged design of the scissor truss. With upward thrust(support post) in the middle, there is the potential to unseat the upper chords at the rafter feet as the truss settles,  and it places the cross-members of the bottom chord in compression, right at their weakest point. Additional joinery here would weaken the truss significantly.  The bottom chords are meant to be in tension and the weight of the top chords on them locks everything in.   IMHO it would be better to leave the post out and design for full span.

We would need to know more information regarding your, roof construction.  Will the truss support purlins or will there be a ridge board and rafters? Snow loads?  Roofing material weights?  Wind loads? Wall construction/joinery detail, etc. to help with the sizing of the truss members. They will be pretty massive. 

I have seen a lot of old historic barn structures that use a scissor truss that is relatively small in size (8x8, 6X8) and has held for over 100 yrs. but they would never pass today's codes or inspections.  You will need to get a qualified engineer to sign off on the design after you do all your load calculations and get your beam sizes down.  You say you are using white oak, I would estimate you are looking at something like a 12"H X  8 or 10"W for both top and bottom chords if using a half lap joint in the middle, fork and tongue at the peak and through tenons where bottom chords intersect the top chords.  Just a guess.

Do you have access to timbers of this size and length and the ability to handle them?  You will also need to pay great attention to how you make the truss to post joint.  I would rather see a truss sit on a plate than a post as it helps to control thrust better than a post.

That said,  the scissor truss is one of the oldest and most elegant trusses and I love the look of it.

[bluegrassben]

Thehardway
Thanks for that info, very helpful. I did not WANT the center post there I just didn't know if I needed the support for that span. I would rather it span the 24ft. about the footprint size. what do you consider cramped? is the inside so small that having guest is uncomfortable? I have considered 30x40. I was going to use a kingpost truss but since the lower level has 10ft ceiling that leaves 6ft wall height upstairs thus I chose scissor truss. I like the idea of setting them on a top plate better, I drew that design thinking it would be easier to raise with the equipment available to me, but I may bite the bullet a rent some equipment to lift the trusses. I am in Arkansas and the most snow ive seen here in the last 20 yrs is 18". we do get gusty wind from time to time. plan on using metal roofing. walls will be infill between timbers flush with the outside of timbers and sheathed. back to house size. we live very simply but are about to have a second child. we have lived in a two bed 1 bath 1000 sqft cabin for the last 6 years and other than needing another bedroom we find the room adequate for us the layout just isn't very efficient. I can see how the timbers may take up some interior room so I may consider going slightly bigger

I do have access to lots of timber as im on 175 acres with lots of white oak. going to be pouring foundation this spring so need to decide on footprint and design fairly soon.

thanks again!

[bluegrassben]

ok, talked to the wife size is settled. we will keep the 24ft span but go 36ft long. looking for some more input on bent and truss design to get a 9 to 10 ft ceiling on first floor and still have headroom upstairs with a total sidewall height of 16ft. is there a different truss design that is more suited to be attached and raised as part of the bent or is it just always better to build with a top plate and then set trusses separately?

[witterbound]

I'm in nw arkansas.  I've got plates and a ridge beam.  6 x 12 pitch.   My bent span is only 16 ft. 

[Thehardway]

what do you consider cramped? is the inside so small that having guest is uncomfortable?

Bluegrass,
I drew my footprint all out to scale similar to what you have done and everything looked like it fit with room to spare, but when we actually started building and putting things in, it came out much different.  I designed for topload washer/dryer but wife wanted front load which are slightly larger and I didn;t allow enough room for doors to swing open fully on on the front.  I also neglected to realize that doors on frontload washers cannot be reversed like dryers and the dryer needs to be to the right of the washer for convenient transfer. I had them reversed.  Not a huge deal, just a minor inconvenience and something I will be remodeling soon to make it all work right.  We used an oversized shower  (2 person) and  oversized soaking tub with a custom double bowl vanity. The vanity is longer than standard but only 13" deep which saved room. We had no space to store linens so we built a linen cabinet into the bathroom so now the bathroom is pretty full and there is little place for towel drying racks.
I used 36" pocket doors to save door swing space, (wouldn't do that again, very time consuming and cost $$ for the hardware)

I have no hallways to save space, and I moved the hot water heater and well tank outside to save space. We used the eave on second floor for storage out to the 4' kneewall.  This is is really our only interior storage.  Once I get the garage built things should be a lot more comfortable. We had a queen size bed but decided to get a king size which made furniture placement in the bedroom a bit tight.  I made a storage compartment under the bed platform for storing seldom used items and winter clothes. We have no place for guests to sleep unless we buy a sleep sofa.  I am planning to have guest accommodations over the garage.  This sometimes works better anyway giving everyone more privacy.

Since you have a full second floor, yours should have considerably more interior space than mine but I did notice a few things look a little tight. Not trying to tear your plans apart, just being a second set of eyeballs there are a few things you may want to look at closer.  The landing at the foot of your stairway is only about 2.5' that would be a little cramped for me walking between the newell post and the wall or trying to move furniture upstairs. Same goes for stair width.  You have 3' but no railing.  Rail will take a minimum of 3" on one side.  You are calling out a 9-10' ceiling height this means you need at least 16 or 17 steps at 7.25" which is standard rise.  I think you are a bit short on steps. Standard run of 11"  will require 14.5-15.5' of run for that number of steps.  The stairs are the most difficult thing to get right.  I fought with them in the design phase for a long time and finally I used a spiral staircase to save space. It allows a higher rise and less run.  It is not easier to build! rotation, support, landing and head room clearance become a big deal.

We have a rather large, eat in kitchen.  We eat at the island/bar with stools.  Great for up to 4 people, after that we break out TV trays.  We do not have a table.

I think adding that additional bay will serve you well and give you additional space you won't regret.  One nice thing about 10' ceiling on the first floor is that it allows you to easily punch through and add a shed roof for a first floor addition down the road.

As for plate connection vs. post connection, this is a great topic of debate between traditional framers and contemporary framers.  Traditional TF called for continuous sills and plates with posts and braces morticed into them forming a rigid box.  Rafters or trusses were then set on the plates.  Plates helped control thrust at eave and also limited vertical movement at the eave during settling.

Contemporary bent style framing eliminated  continuous sills and plates and opted for girts or interrupted sills and plates.  They were usually easier to factory build, transport, and assemble and did not require many long timbers.  They were also easier to add on to or modify at a later period. 

The higher your walls and shallower your pitch, the greater the thrust at the eave.  I would consider using a 9' ceiling height downstairs, allow 12" for ceiling and floor finishing between floors and 6' wall at at the eave on the second floor. Using 16' posts this gets your floor girders closer to the eave and it helps control thrust acting as a tie beam on the post.  Toppping your posts with a continuous plate and adding some knee brace would give you another 6-8" of height at the eave.  6'8" is comfortable walking height for all but giants and this would make your frame a lot more rigid and help control the thrust of your scissor trusses.  You would assemble your posts and second floor as you would in bent style construction. Once the posts are all vertical and the floor members in place you install your top plate on the post tops tying all the post together.  Then transfer your timbers for your rafters and scissor trusses unassembled to your second floor deck.  Put the trusses together on the second floor. Now you would raise your trusses and rafters off your second floor deck rather than as a whole assembled bent.  I don't see it being any more difficult than raising a 2 story bent with a large scissor truss on top which would definitely require a lifting apparatus of some sort. Using the steeper pitch lowers thrust and raises your ceiling height quicker moving toward the center of the room.  It will also look better.  Does this all make sense? 

Of course this is just one idea and there are more ways to do it. 

My walls were ICF so it helped control the thrust of my kingpost.

One thing I mention to couples who are building homes is to think past your young years and enjoying your present good health.  How will the house function for you when you are old or if you happen to become sick or disabled.

For this reason we decided to go with a first floor master suite and laundry and place my sons bedroom on the second floor.  That way if one of us becomes disabled or unable to ascend stairs, we are still able to have a somewhat normal routine.  Will your shower/tub be accessible if you are disabled?

My son will eventually move out and then thatroom will become a library or guest room and we don't need to go up unless we want to.  We can age gracefully in our home. If all was reversed we would have empty downstairs rooms in our old age and be climbing stairs every night.  Seems pointless.  We usually will spend more years in a house without children than with.

People selling homes are finding one level living very attractive to the retired folks wishing to downsize from larger homes and can add value to your home if you plan to resell.  On this flip side, if a loft master bed is always what you wanted, don't settle for less because of someone elses opinion, your the one who is living in it, not them.   All things to consider before you take the plunge past paper and pencil stage.

Take a holistic approach to designing.  Don't forget about room needed for mechanical and heating/cooling.  Make sure you have light switch locations conveniently planned out and room for them (hard to put them in a post and you don't want them 2 feet from the door). Make sure there is space/pathway planned for ductwork, returns and plumbing with allowance for fall, especially for a second floor bath.  Will the noise of a second floor toilet flushing be heard like a flood because of exposed overhead pipes?  Is there a wall big enough for a stack pipe to go upstairs and vent to get out the roof and does it line up correctly? Is freeze protection for plumbing in exterior walls considered? You might get lucky and have everything work out just right but if it doesn't it can cost you a lot of time, money and headaches to do a work around.  Geographical and solar orientation are huge.  Spend a lot of time evaluating the homesite and the orientation of the house at different seasons and times of day.  Know how the light passes and where the predominant winds or breezes blow.  This effects lighting, heating, cooling, exterior maintenance and general liveability.  If you plan to use an OWB or woodstove, fireplce for heating, think about where they will be located and where the smoke will blow.  If you later decide to install solar panels, will your roof face the right direction and have the right slope? What about radiant heat?  When you consider all this, the framing and floorplan take on more significant meaning.  I like that you stacked your baths.  that will save you some headache.  Plan in advance for tub and shower drains/traps/vents.  They cant fall on a beam and must exit between them if you don't want unsightly box outs or a false ceiling.  Where will your electrical service entrance be and your breaker panel located.  Distance between them is limited.  Hot water heater location?  Is there a basement or crawlspace?   The smaller the house, the less room for error correction.  Most important, have fun.  House building can take a toll on a marriage and your relationship with the kids.  It takes a lot of time which is time away from them unless they are really good helpers and enjoy being there with you every minute.

[Jim_Rogers]

Lots and lots of good advice there.... thanks for posting.

Jim Rogers

[bluegrassben]

Thehardway,
Thanks for all the advice so far it all is making sense. so if im reading correctly a more proper way to build this would be to raise H-shaped bents and put a top plate and then scissor trusses. I plan on putting knee braces on every post. as far as stairs go the design has not been truly decided, we consider spiral and an exterior staircase for furniture and such. as far as heating and cooling main source will be mini-split ductless systems, we will also have propane and woodstove backup. hot water will be propane on demand and hopefully add solar water in the future. some things not shown in drawings are full wrap around porch and a 12x12 cellar/basement for water heater and solar equipment. we plan on having spray foam insulation. I am working on some revisions to my plan and will post them when done.
thanks again for all your advise it has been very helpful!

[Thehardway]

I wouldn't go as far as saying it is a more "proper" way, it's just the way I would go about it. I believe it would be easier with limited people and equipment with less stress on critical joints and less chance of mishaps and would in my opinion give you a stronger and more rigid frame.

Mini-splits are a good way to go to avoid the pitfalls of ductwork but don't forget that each indoor unit requires a line set to the outdoor unit.  With 2 insulated lines and a condensate line for each, it will be too large to run through your beams/girders so make sure you have the path planned out.  2" Spray foam entire envelope with the remainder blown cellulose is the way to go in my book.  It makes a really tight box.  You will likely need some kind of mechanical air exchange such as an ERV/HRV especially while the timbers are drying out.  They can produce a lot of moisture.  as can activities such as cooking, showering etc.  Mini-splits don't do much to circulate fresh air through house. Also make sure you can access condensate lines to blow them out a couple times each year.  If not they will plug up and back up with algae.  I know this from experience. I have one 12,000BTu mini-split.  It is able to heat and cool my entire house with little effort.

We have similar tastes.  I might mention, the tiny house blog has a lot of neat ideas for those who are willing to live in smallish spaces.  They know how to make efficient use of space.  Look forward to seeing your updated drawings.

[routestep]

The hard way gave some excellent advise on planning a  house. I might just book mark his post.

My small note. You are planning on using 10 by 10 white oak posts that are 16 ft long. That size post will be plenty heavy moving about. If you need that size, fine, but if you can get by with a 9 by 9 or 8 by 8, they would be easier on the back and arms.

If you go with standard TF tenon spacing.  A posts tenons on the ends are laid out 2 inches from edge then 2 inch thick  tenon, then six inches to the far edge on a post, you need a big saw ( sixteen inch diameter,36 lbs )to cut that six inches. That or some handsaw work.

My brother and I made a barn with 9 by 9 posts and because we only had a ten inch circular saw we moved the tenon over - 3 inches from the edge then a two inch tenon, then four inches to the post edge. Not standard layout, but it saved me a lot of sawing. A ten inch saw will cut 3 3/4 inches full depth. Weight about 17 lbs.

I have some pictures in my gallery showing how we lifted the bents up. The towers that we used were a challenge all by themselves. There also a couple pics of lifting the principle rafters with a couple of shear legs and chain falls.

[Thehardway]

Routestep, Just checked out your gallery.  Nice example of the framing base structure (although your truss is slightly different, the base frame still applies).

I have not seen self-supporting towers used quite like you did.  There is certainly nothing wrong with it and my compliments to you for creativity. Good job.

There are three primary types of lifting tower structures:

1. Self support lattice tower.   3 or more legs usually tapered, widest at bottome and narrower at the top and braces with triangulation.  You had a good example of this.

2. Guyed Lattice tower.  These are usually made of 3 closely spaced legs, with triangulating members concting them to form a single rigid lightweight mast.  Mast is raised vertical and guyed with wires at 3 or more locations.  I used this method with a chainfall rigged to the top for raising my trusses.  You can see it in the pictures below.  Three nylon webb ratchet straps were used to secure it in vertical position.  It is lighter, simpler to erect, quicker to move and allows for rotation of the truss when lifted at the center.  I was able to lift and raise this mast by myself using the pipe rigging cranes you can see in the picture.  the base was bolted to a 6"x6" X to distribute weight on floor and prevent movement of the base while guying.

  

 

3. Monopole.  These are singular members without triangulation. (Think of a sailing ships mast or one of the tubular style cell towers)  For Timber raising apparatus, they are commonly referred to as a gin pole and are seldom raised completely vertical, rather usually left in a diagonal position and held there by halyards that are secured at two points.  A block and tackle is secured at the uppermost end and used to perform the lifting.  In sailing ships of larger towers not used in timberframing, the ginpole is affixed the the base of the mast and is used as a lever to raise the mast with a rope or cable.  It may also refer to a short arm affixed to the top of a mast and used for lifting.   They can be a quick and easy solution for lifting heavy loads if the base can be adequately secured.

Routestep makes a good point on post sizing vs. saw sizing.  I have a 16" Makita beam saw which I used, and a 7 1/4" circular,  but I would not let lack of a large circular saw become and issue.  You don't have that many posts to cut.  You can cut max depth with whatever saw you have and then finish by hand using the initial as a guide cut.  I suggest getting an 8pt. Stanley Sharptooth hand saw.  They only about $10 and are hard to beat.  Some folks actually prefer them to power saws as you don't need power they give you more control and they cut nearly as fast.  If you have a high quality and properly sharpened crosscut saw, there is nothing wrong with using it.  You will need a good heavy duty set of saw ponies and an assistant to help you turn your posts and beams during joinery work.  I used peices of 2"  pipe as rollers to move my beams.  Take advantage of counter weight and balance point when lifting and moving.  A 2 wheeled beam cart is handy and easy to make.  A cant hook or short handled peavey with some protection is also a useful tool for turning them.  A 2X in your first mortice can also work. I have seen all of these done.  Work smart and think primitive.  There is usually a simple solution.  They didn't have electricity or hydraulic cranes in the 1500's and they built much larger TF structures than we are working on.

[bluegrassben]

Hi guys, I haven't forgotten about the post, I just have been to busy to finish the updated plans. I do have some other technical questions though. Why is the standard tenon layout 2 inches from edge then 2 inch tenon then remainder of post? is centering the tenon on a post bottom a no-no? Also I chose 10x10 because I am purposefully trying to overbuild a little( been living in a very unstable and flimsy house the past few years and probably a bit paranoid). Is 10x10 just a little more than I need or is it just major overkill? I lack in the knowledge of beam sizing so I tend to go bigger than I think I need. I have a book called "The Craft of Modular Post and Beam" and it has load tables for sizing but none for the post size. I also just picked up a new read called "Timber Frame Construction" by jack Sobon and Roger Schroeder and and so far I have learned way more from this newest book. My timber framing experience is from when I worked on a sawmill that also did timber framing but I was not behind the design I was simply told to cut the joints and fit them a certain way and I never asked question like "why is this beam this size and that one another size?" sorry for all the questions but I really do appreciate everyones answers. by the way, I planned on using a hand saw for cutting joints and a lot of my timbers, especially ones longer than 16 ft, will be hand hewn as my mill is really only designed to handle 16ft. thanks again, new plans coming soon!

[Jim_Rogers]

Why is the standard tenon layout 2 inches from edge then 2 inch tenon then remainder of post?

First answer is that it is easy to layout using a framing square and the 2" thick body of the square.
Second answer is that it is easy to also layout the mating mortise with the framing square.
Third answer is that the frame designer usually picks out some "General frame rules" that all joints in the frame have to follow. One if these "rules" is that the tenon is laid out 2" off and then 2" thick.
Four answer is that the tenon is usually 1/4 the timber thickness. For example, an 8x8 has a 2" tenon. A 6x6 has a 1 1/2" tenon. Both are laid out the same distance as the tenon thickness off the layout/reference face. Next the peg and it's hole is 1/2" the tenon thickness. So for a two inch tenon you use a 1" peg. For a 1 1/2" thick tenon you use a 3/4" peg.

If you don't want to do 1/4 of a 10 x 10 as it is an odd distance just use the 2x2 layout and you can use your steel framing square for easy layout. However in large factory buildings, which were made with very large timbers we have seen 3" thick tenons and mortises.

is centering the tenon on a post bottom a no-no?

You can layout and cut any joint you want. Some are easier and faster when you use your steel tools for layout and knifing of the joints. Laying out to an odd distance is a challenge and it takes more time. If you have the time then it doesn't really matter.

Square rule layout of joints was invented to save time, as time is money.

Is 10x10 just a little more than I need or is it just major overkill?

It's hard to say without seeing the entire design and understanding all the loads and connections necessary.

Jim Rogers

[timberwrestler]

I just want to point out the obvious and state that it's a bold move to design a timber scissor truss without an engineer.  There are crazy weird loads in scissor trusses.  I think it will help minimize some of the loads by having your trusses on 8' centers.  Check the Timber Frame Engineering Council to find someone that is (presumably) qualified to check your design. 

[bluegrassben]

 Ok. sorry for the delay, my schedule has been very hectic lately. here are some crude drawings of the new floor plan and bent design. as you can see I will be topping the bents with a plate and then setting trusses on plate. I have decided to downsize to 8x8's for bent construction. I am still curious on beam sizes required to use scissor trusses to span 24' with 8/12 pitch on 9 foot centers with purlins connecting them topped with metal rofing. snow load charts indicate a max 15psf snowload for my area.
visited an old friend at his home that he built himself using 6x6 pine with the same bent design I have drawn with a 20x40 footprint and he has had no problems so I figure 8x8 white oak should be plenty stout for my bents. he also hooked me up with some timber framing tools too! gonna build the Jack Sobon garden shed for practice!
I am also exploring other simpler truss options but the wife really likes the look of the scissor truss. I also downloaded sketchup and am trying to learn my way around it so maybe I can post some detailed plans.

just realize I forgot to draw the center post for the second and fourth bents in the lower floorplan (that's what lack of sleep does to you) :D
if I can get the time this week I will draw a 3d plan unless I figure out sketchup first.






  

  

 

[Thehardway]

bluegrass,

That top plate looks better and I think you will be glad for that when you raise it.  It will definitely lock things in.

As for the beam sizing, please have whatever design you come up with checked by an engineer.  We cannot stress this enough.  Even if you don't want to pay full cost of a stamp, at least have it reviewed and get an opinion as a baseline.  The only safe alternative is a real world test, by this I mean build the truss and park a truck or tractor on top of it. It needs at least a safety margin of 2X.

I think 8X8 is way under spec and here is why.  Your beam is no stronger than its weakest point(s).

I am providing a simple line diagram with intersections labelled for discussion purpose.


  

At the center crossing point of the bottom chords, (intersection "A") you will have a half-lap joint.  This means the point of the truss which bears the most stress will be relying on beams that are merely 4"X8".  They will have at least one hole bored in them  at the point of reduction, further reducing strength. General rule of thumb for conventional framing is 1" of width for every foot of span  (example, 10' floor joist use 2X10 as minimum)  In a header application, which your trusses will essentially be functioning as headers, you must double or triple and up size members to accommodate tributary loads. 

Additionally the angles of the scissors At points E and F and the height of intersection with top chords at points C and D as well as joint selection and execution will have a great deal to do with strength.  In your initial scissor truss drawing, it appears you are showing half lap joints at points C and D.  I would caution against this.  This should be a joint that does not reduce the size of the top rafter any appreciable amount and at the same time, holds the bottom cord securely in place without chance of withdrawal.  A half lap could easily peel of the side if any bow or warp occurs during drying.  The trunnel will not prevents this.  Catastrophic failure would result.  At minimum you need to reverse the laps at points C and D.  I would use a through tenon vs. a half-lap at points C and D and eliminate the chance of any failure due to dis-assembly .  This also makes for better assembly if paired with tongue and fork joint at point A.   

Comparing this to pine as a benchmark is not a best practice.  A truss must support its own weight as well as any loads.  White oak is much heavier than pine, especially when green and it dries very slowly due to its closed cell design.  In green state, white oak's strength to weight ratio is not much better than pine in the same dimension.  It may not be for 5 or 6 years, until it is getting dry that you get any significant strength advantage from using the white oak due to its additional weight it must also bear.   Once it is lighter, dry and hard, you will then see the full advantage.

When your time allows, focus on joint dimensions, drawing, and assembly as this will have bearing on timber sizing.  As mentioned, mine are White oak, same span, steeper pitch, stronger walls to control thrust and I had to use 7"X12" for rafters. which is much stronger than 8X8.  I would shoot for 8"X12" 9X12 in your scenario.  Also make sure you lay out your purlins and what points they will be notched into your rafters and allow for this material removal.  You need to make sure the notches do not overlap any of your key intersections.  This may affect angles as well if you have a fixed distance between purlins to deal with.

[bluegrassben]

Thehardway,
sorry, I wasn't clear on my 8x8 statement I was only referring to my post for my bents and not anything to do with the trusses. I was leaning towards 8x12 for the trusses. also, I got to thinking since I have a top plate couldn't I put 7 trusses on 6' center and use maybe 8x10 beams or would that just be a waste of time better spent on building with ridgebeam and rafters. would using metal plates at connections help any. I do plan on getting engineer approval.
thankyou for being patient and answering my questions!

[Thehardway]

Bluegrass,

It is best practice to keep trusses in alignment with posts, even when using a top plate.  The traditional method of joining your trusses to post/top plate would be the English Tying Joint.

6' OC would not in my opinion benefit you at all.  8'OC makes optimal use of sheet goods and dimensional lumber.  6' is a little odd and would be cluttered looking inside, detracting from the design.

Here is my recommendation.  When you fell your White Oaks, they will most likely have a butt swell at the base.  Cut them as low as possible and utiliize this butt swell into traditional gunstock posts for cutting English tying joints.  This is a slightly more complicated and time consuming but the result is outstanding both structurally and visually. You said you aren't opposed to doing some hewing or ax work if I remember right and this short little section on one side of the post  being hewn would really be a showpiece and lend authenticity. They could also be hand sawn for the angled portion if you do not want to hew.

As for metal plates, unless your inspector insists upon them, I would not go there.

I might consider a wrought iron strap at intersection "A" or perhaps a square head nut/bolt in lieu of a trunnel as it would better prevent withdrawal.  Both would be within the realm of traditional methods.

This is going to be a beautiful little house when your done.

When I lie on my couch at night and look up at my trusses, I know it really was worth it.  Most people never have that privilege and feeling of accomplishment in their home that those of us who have hand built TF or log homes have.   

[Heartwood]

You can download (free) an excellent scissor truss engineering article, or the whole Historic American Timber Trusses book at the Guild website here: http://www.tfguild.org/publications/guild-books.