Archive




TimberKing Sawmills



The Largest Inventory of Used Chainsaw Parts in the World

Toll Free 1-800-582-0470

LogRite Tools


Forest Products Industry Insurance

Norwood Industries Inc.

Sawmill & Woodlot Magazine



Wood Processing equpment. Splitters, Processors, Conveyors

Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL

Woodland Sawmills

Margeson Insurance

Peterson Swingmills

Pacforest Supply Company

 KASCO SharpTech WoodMaxx Blades

 Farmi Winch Direct

Comstock Logging

Forestry Forum Tool Box

Author Topic: joinery help on kingpost truss  (Read 10324 times)

0 Members and 1 Guest are viewing this topic.

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
joinery help on kingpost truss
« on: April 05, 2005, 10:57:15 pm »
Hoping some of you can steer me in the right direction.  I would like to cut/assemble 8 Kingpost trusses for the new house I am planning to build.  All trusses will be the same.  They will have a clearspan of 24' and be 8' OC.    Roof pitch will be 12:12, 30 PSF. 90MPH wind load. I am planning to use 6"X8" 's for top chords 8"X10"for the kingposts, 4"X6" 's will be used for braces and 8"X8", Bottom chord of Trusses will be tied to a 2"X10" plate on top of ICF walls.  The roof will be ICF over T&G plank.  Wood species will be Virginia Pine and Yellow poplar for timbers/posts with Cherry Walnut or Red Oak for accents and braces.  Pegs will be Red Oak or Black Locust. All wood will be cut from the property and milled on a portable band mill and then hand planed.  I have priced the trusses made and for the price of one truss I can buy a portable mill so I have opted to do it "The hard way" and learn something along the way as well as produce something I can look at and be proud of.
   I think I understand everything conceptually but could use some help with the types of joints I should use.  The intersection of the Top Chords and kingpost are my main concern. I am assuming all other joints will be pretty standard using Mortise and Tenon?   I will follow this post up tomorrow w/ a proposed sketch of the truss I have planned.  Am I on the right track here or am I missing some things? ???  I just found this board and so far I have been amazed at the quality and amt of information found here.  Thanks to all.

Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline MSU_Keith

  • Full Member
  • **
  • Posts: 89
  • Age: 48
  • Location: Ann Arbor, MI
  • Gender: Male
Re: joinery help on kingpost truss
« Reply #1 on: April 06, 2005, 01:03:40 pm »
I am in the process of designing a similar structure only with three post bents spanning 32' total.  Not sure if I'll ever be able to actually build it but it is fun to tinker with the design  :-\.  As a resource for design I have found the historic truss section at the Timberframe Guild site to be really helpful:

http://www.tfguild.org/publications/historictrusses.html

In addition, the TimberCAD addition to AutoCAD is helpful once you get the conventions understood.

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on king-post truss
« Reply #2 on: April 06, 2005, 07:25:35 pm »
Are you planning on having a second floor above the bottom cord or is this all roof system?
Are you planning on having any purlins or ridge beam?
What is the roof decking going to be? Sips?
Are you planning on some common rafters between the trusses?

You will probably need some struts going from the king post to the rafters.
And you may need some prince or queen posts going from the bottom cord to the rafters.

(All timbers are given names based on there locations in the frames. A strut is like a brace but it has one end with a 90 tenon on it and the other end has a tenon on an angle. It usually, but not always leaves the rafter at a 90 angle and enters the king post at the other angle.)

I help you if I can.

Jim Rogers

Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
Re: joinery help on kingpost truss
« Reply #3 on: April 06, 2005, 11:36:27 pm »
Jim,

Thanks.  The trusses will be all roof system.  They will be placed on top of the second story walls and Fully exposed to view.  I am not opposed to a ridge beam and actually would like to use one but I'm not sure how to tie it in with the king post and top chords without weakening the timbers too much at the joint.  could this be accomplished by using a tusk tennon placed below in th king post? The trusses will be decked with 1X T&G Pine and then topped off with 4X8 SIP's which will span between the Trusses and be splined together.

I am planning to have a strut on either side of the King Post (leaving at 45 and intersect which will top chords at a 90. Braces will be placed under each truss and tied to the ICF walls as if it was a full bent with a post.

Should the bottom chords use half lap dovetails at the top chord intersection or are housed mortice and tenons sufficient?  I have seen illustrations of both.  I have also seen the bottom chord extend over the bearing wall with the top chord morticed into it and pegged.  Other designs have the top chord extend past the bearing wall using a birds mouth cut and bottom chord tied in with half lapped dovetail of some sort.  I have an idea for this joint which would use a centered half-dovetailed joint with a pinned key to lock it in place. 

I am working on finding a format that I can post picture and try to show what I can't put into words.
Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on king post truss
« Reply #4 on: April 07, 2005, 09:48:25 am »
More questions and then some comments.

Are these timbers going to be planned on all four sides to true dimensions or are they going to be rough sawn stock? (Answer was all ready posted, "they will be hand planed".)
Are you going to house all joints? Using square rule joinery?

During a design phase I generally create some "General Frame Rules". These rules will help you in laying out and cutting all joints.
Such rules are:
1. All joints are laid out form the west side of the building (a gable end) except the east most bent.
2. All timbers are sized down to the next half inch in size.
3. All joints are laid out 2" off the layout face and 2" thick tenons or mortises, (with exceptions).

In designing a king post truss there are several very important things to understand.

First is the way the loads are traveling.
The king post does not sit on the bottom cord. It is wedged between two opposing rafters and is being held up by these rafters, which in turn holds up the middle of the bottom cord.
The struts hold up the rafters so that they don't sag with the weight of the roof and snow loads. Queens posts from bottom cord to rafter also hold up the rafter to prevent sag.

Knowing all this then the important joint becomes the end of the rafter (known as the rafter foot) to bottom cord connection. This is where all the load from the truss will enter and be transfered down the wall to the foundation. This joint has to be very strong and cut correctly to insure no movement.

You have asked several questions about the length of the bottom cord. As to whether or not it should "hang" over the outside wall.
These are your design decisions. If you want to have an over hang for shedding the water away from your building this is one way to do it.
If you can purchase or mill and create a longer bottom cord then this may be an option.

I'm not familiar with a top cord passing over the end of the bottom cord to create an over hang connection. This would be a tension joint and should be looked at very carefully.

Most of the ones I've seen have ended with a long tenon being pegged into a housed deep mortise on the top of the bottom cord. With the end of the bottom cord cut back to match the roof slope. But to do this you need to have your load paths reviewed and make sure you have enough "relish" to hold the rafter foot to the bottom cord.

The way it's done in Europe is to move the top cord in a little and place a secondary rafter over the top cord.

Such as this:


Using this type of system you have to be careful because the load being placed onto the bottom cord is moved back away from the end of the beam and you need to make sure this load is properly supported so that the bottom cord doesn't fail.

If you wanted to have an over hanging bottom cord to create a cornice then you could use this system and place the location of the principal rafter (top cord) foot over the wall. This would give your truss support and create an over hang. Just some ideas to help muddy the water.

Jim Rogers

If you have a drawing program in your computer and you are creating drawings there, then do a screen capture and create a jpg of the drawing. Reduce this in size and volume to fit the rules of the gallery section. Create your own galley and albums and upload the file there, then you can post the picture here.

If you are drawing by hand, scan in the drawing with a flat bed scanner and follow the procedure above.
If you don't have a scanner, take a digital picture of the drawing and follow the procedure above.
These are some ways to get drawings into your posts.
Also, email them to me using my regular email address and I can reduce them and send them back to you for posting into your gallery album, or post them for you.
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Jim Haslip

  • member
  • *
  • Posts: 49
  • Location: Golden, B.C.,Canada
  • Gender: Male
Re: joinery help on kingpost truss
« Reply #5 on: April 08, 2005, 01:45:08 pm »
Jim and others,

I've found this link Click here for link to joinery download page on guild site to be quite helpful for answering joinery questions and providing guidance  The series of articles are down loadable (free). No sense re-inventing the wheel .  :D Use these examples to base your design on joinery which has already stood the test of time.

Here is a thread on their Ask the Experts bulletin board discussing a similar topic. Click here for link to TFG Forum Thread
But the difference is major . This thread concerns issues about a 'structural'  ridge. Jim Rogers' answer here is discussing a 'structural truss' system. The two are different . And not to be confused. 

Hope these links are helpful...

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on kingpost truss
« Reply #6 on: April 08, 2005, 05:42:46 pm »
After that set of articles was published in the magazine they combined them into one booklet. The booklet is available from the online store for only $10.
My copy :P is signed by the author ;D.
I use it all the time.

He is writing another series about something else, but I can't remember what right now.
I had lots of conversations with him when I was in Ohio last month.

If you're not a member of the guild you could join and get the magazine or even back issues. The just got done a series of articles about trusses.
Very interesting reading.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
Re: joinery help on kingpost truss
« Reply #7 on: April 09, 2005, 11:11:41 pm »
I downloaded and read the article on kingpost trusses and though very informative it is not comprehensive enough to include a couple specific items.  All of the historic trusses in the article utilize an uninterrupted bottom chord.  In order to keep my timber lengths more managable I would like to use two separate timbers in the bottom chord joined at the kingpost like the picture of the trusses built for Joey.

If I am undersanding the engineering principlels  correctly the bottom chord halves will be in tension as well as the kingpost itself.  The top chord rafters will be in compression holding the king post in place. 

The half dovetailed/wedged kingpost to tie joint in the Kingpost article is very much similar to the joint I was thinking of using for the joint at the intersection of the bottom chord/rafter.  The angled side of the halfdovetail would face upward and serve as a tension joint for the bottom chord member but would also be in vertical compression from the weight/outward thrust of the rafter. 

I think the best thing to do here is get a picture posted you so you can see my ideas and critique them as useful or foolishness.  I think my mistake in posting was not reducing the size sufficiently.

I am planning to use square rule method and will house all possible joints.
Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline Jim Haslip

  • member
  • *
  • Posts: 49
  • Location: Golden, B.C.,Canada
  • Gender: Male
Re: joinery help on kingpost truss
« Reply #8 on: April 10, 2005, 02:05:00 am »
yes, you are correct about the tie-beam and kingpost being in tension.
Go back to the same link above and read the sixth article 'Scarf Joints'.
There should be several options there to satisfy your needs.

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on kingpost truss
« Reply #9 on: April 11, 2005, 03:41:38 pm »
Here are some drawings that "TheHARDway" sent me:





















Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on kingpost truss
« Reply #10 on: April 11, 2005, 03:57:58 pm »
My very first thoughts about this 24' span was that an 8x8 may not be big enough for the bottom cord, especially if it's a continuous beam. (That thought came to me the other day as I first read this post).

Since then "TheHARDway" has sent me some drawing about his ideas.

Several things pop up right away, looking at the design ideas.

First this is a complex roof design. And some things may need to be though through.

One of these is the wall that is below the circled truss in this drawing:



Viewing the first floor drawing and the second floor drawing you'll see that there is a wall under this locations (shown by the red circle).
That means this doesn't need to be a truss. As these two walls can be load bearing walls and support the loads above.

Next if this was a truss it would have to support the ends of the other trusses connecting to it as well as the load of the roof above it.
I'm not sure if you could even buy a timber large enough to support all that load.
If you don't want to use the first and second floor for load bearing walls then this area will probably have to have a steel beam in order to support the load of the other trusses as well as it's own roof load.


The next problem I see is the rafter to king post connection.

Shown here:




There needs to be a lot of improvements to this joint as there is no wood of the king post above the rafter. Cut this way all the weight of the king post and loads below will be held up by the two pegs. This isn't the best design.........

The next problem is the rafter foot to tie beam connection.

As shown here:




At the circle there is a question mark. How is it going to be possible to get a tenon shaped like that into a mortise?

Then again you're depending on the peg to hold most of the thrust. The shear key block will hold some but this will have to be calculated very carefully to work.

Just my opinions based on what I've seen and read about king post trusses.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
Re: joinery help on kingpost truss
« Reply #11 on: April 11, 2005, 09:37:54 pm »
Thanks for posting the Pics ;D

Your observation on the wall intersection is very helpful.  I will omit this truss and use the bearing wall for support.  One less truss to cut.

I will work on the King post top.

As for the question on the rafter foot tie, the idea is to make the block the same thickness as the depth of the red circled notch portion of the dovetail (2 1/2") and pegged with a 1 3/8" peg.  The dovetail tenon is inserted first in the oversized mortise and then raised, the block is then inserted locking the assembly together.

 A similar joint is used as a tension joint in the king post to bottom chord in figure 8 of the historic trusses series on king post trusses.  The difference is they used an oak wedge rather than block.  The block thickness would be cut so as to provide a tight fit of the joint assembly.  I chose to use a keyed block rather than a wedge as I think it will perform better.

Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on king post truss
« Reply #12 on: April 12, 2005, 08:55:46 am »
TheHARDway:
I've reviewed the article in magazine number 72 June 04 you stated in your last post. I believe you meant drawing #7.

And the text of that article states that these were of oak. Also, that the newer pine ones were not standing up as well.

Also, I had some discussions at the last conference in Ohio about the use of shear blocks vs. shear wedges.  The well experienced users of shear wedges told me that trying to create a shear block to the right size of two different grooves is very difficult and they don't even try do to that. They use wedges. This way they can tighten up the joint by pounding in the wedges to align the grooves, and provide the shear block capacity you'll need.

Your finial design, I would assume, will need to be reviewed by a structural engineer to comply with your building inspector. His decisions about your ideas will influence your design more than we can here at this forum.
My advice to you is to get a professional structural engineer, experienced in timber framing design and construction to review and help you with your plans, for the safety of you and your family.

Good luck with your project.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
Re: joinery help on kingpost truss
« Reply #13 on: April 18, 2005, 10:05:03 pm »
Update,

 I have taken the advice of those here and have resisted the ever tempting urge to re-invent the wheel.  I will scratch the previous idea of the wedged dovetails etc. in favor of a more conventional design.  I have adopted a design using an uninterrupted 26' bottom chord. The king post will use a through mortise/tenon to tie into the bottom chord.  I have found some structural panels that are T111 on the interior side which will look like T&G Pine for the interior finish and is OSB on the exterior They are rated for structural roof panels at a span of 8' oc.  I  will not need purlins or ridgebeam.  With the savings I am going to invest in a small bandmill that will cut the 24' beams necessary on sight.

  I have also thought the complex roof issue through and have come up with the following.  I will use conventional stick framing on top of the second story interior wall (circled red portion)  I will sheath the section with t111 to match the rest of the interior ceiling of the great room.  Conventional lightweight trusses will be placed on top of the T111 panels and secured to the trusses with Simpson straps.

 I have been puzzling where to house my air exchange unit.  This newly created space between great room and Bedroom wing will be ideal for the purpose of housing the air exchanger as it is centrally located, can be ducted into all areas with minimal expense and effort, and an access door can easily be built into the upstairs bedroom in the stick framed wall for maintenance.

 I will let everyone know of any new developments/challenges and hopefully post pictures of the trusses as I cut and assemble them.  Thank you for revealing the errors of my ways ;D and getting me back on the straight and narrow.  Jim, your a great help and your observations have inspired new and better solutions. 8)

Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on king post truss
« Reply #14 on: April 19, 2005, 08:56:33 am »
If you still want to have an overhanging rafter, I found this drawing:




If you can make a truss like this:




You could not use the common rafters and just the purlins to support your sip panels.

This truss could be made so that the point of the tie beam where the foot of the truss rafter sits is directly over the supporting wall. This would give you the over hang you wanted.

Just some ideas.

Good luck with your project.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Thehardway

  • Senior Member
  • ****
  • Posts: 913
  • Location: Virginia
  • Gender: Male
  • Doin' it the hard way!
Re: joinery help on kingpost truss
« Reply #15 on: April 19, 2005, 02:46:22 pm »
Jim,

I finally figured out what I was doing wrong with the pics.  Here is a drawing of my new truss design with the SIPs installed  The 2X splines in the SIPS will actually be functioning as purlins 4' OC and span the 8' section between trusses.   It is similar in principle to the illustration you have above but omits the common rafters and the purlins are concealed in the SIP's.  I beleive I can also use the panels for a 1' eave overhang.  Tie beam will sit in a pocket on top ICF wall or a sill plate will be installed to receive trusses.  At the ridge and overhang the panels will be routed and angled 2X material installed to box in.  At the overhang edge 1X material will then be installed over the edge to overlap panel seams.   This should be fairly straightforward and simple.  I will provide a detail later.



 
Norwood LM2000 24HP w/28' bed, Woodmaster 718 planer,  Kubota L185D, Stihl 029, Makita 16" circular saw, 10 Acres of aches to work.

Offline Don P

  • Senior Member x2
  • *****
  • Posts: 3116
  • Gender: Male
    • Calculator Index
Re: joinery help on kingpost truss
« Reply #16 on: April 19, 2005, 08:22:09 pm »
Jim,
That tie down is an interesting piece of hardware, do you have more info on it, haven't seen one before.


Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 5252
  • Age: 62
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • jrsawmill.com
Re: joinery help on king post truss
« Reply #17 on: April 20, 2005, 08:55:41 am »
Don P:
I'll have to see if I can come up with a part number for you on that.
I recently went to a trade show where I got a Simpson strong tie catalog and I'm not sure if this one is in it or not.
This drawing was made in Europe and I'm not sure if that is available over here, yet.
I'll do some research on it and get back to you, with info, as soon as I know.

Jim Rogers

(I hope I haven't lead us down a road where there isn't a part at the end).
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline JoeyLowe

  • Senior Member
  • ****
  • Posts: 388
  • Location: Gilmer
  • Gender: Male
  • "In the German Tradition"
Re: joinery help on kingpost truss
« Reply #18 on: April 20, 2005, 09:28:21 am »
Hard to tell in the drawing, but if it is a strongtie connector, that particular one is not in my catalog although there are several very similar connectors.
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Offline Don P

  • Senior Member x2
  • *****
  • Posts: 3116
  • Gender: Male
    • Calculator Index
Re: joinery help on kingpost truss
« Reply #19 on: April 20, 2005, 09:42:20 pm »
Don't go to any trouble Jim it was just one I hadn't seen, neat idea.

I was looking at the truss pic you put in the same post. I've seen rafters done something similar in older work, lightweight timberframe, heading toward stick frame/ balloon frame era. They cantilevered ceiling joists over the wall about a foot and ran a 1x on top of that flatways. The rafters had a level cut and were nailed to the 1x ribbon. This made soffit and fascia framing at the same time.



Not that this has anything to do with the thread, it just finally clicked for me where the idea for that hybrid came from...carry on  :)