Guess I didn't follow where we added a floor! And didn't you post a pic of a king post truss?

Difference in language I guess. I never refer to a king or queen unless it is in a truss or bent that supports the roof.

You have to support 24' either way - in the ridge or in the tie... I'm a fan of supported ridges - even with a simple truss like you linked too.

I have not read where BJC added a floor either. There is the possibility of a floor in the future perhaps? Or at least some timber laid on top of the tie and endless stuff placed upon that. Shouldn't we look at the future?

Isn't a truss different than a bent?

Yes, I posted a picture of a king post truss with no ridge beam in the building.

Tim

Hey Guys,

I think I see what you all are talking about with two different arrangements.

One you can build a truss with a kingpost by either dropping the rafters (upper chords) which, allow for a continuous ridge (this would require building upon the chords to get back to the plane of the roof with purlins and commons)

Or you can have the principal rafters land on the kingpost at the roof plane requiring a interupted ridge.

But either way, in order to span without a center post under the tie, the compression member (chord or rafter depending) has to be joined to the two tension members (kingpost and tie). Therefore zeroing out the forces and defining a truss. On the other hand if you can find a piece for the tie that can handle a 24' span, you won't need a truss. But that would have to be one big honkin tie.


BJC, this reading might help http://www.tfguild.org/publications/kingposttrussTF72.pdf

p.s. these Guild publications are simply awesome. Give thanks.
notice the hand drawn joinery as well.

Thanks guys for all the feed back. I'm sorry that I did not give more info to start with let me see if this adds any flesh to the question:

We are in Alabama, so minimal to NO snow... occasional tornado but snow is not a problem.

Initially the structure will be left open as sort of a pavillion to park vehicles under. I may enclose the sides later to make a true garage out of it.

Again, initially I will put an aluminum "tin" roof on... my plan was to put 2x6 (or 8) rafters between the bents and then 2x4 purlins on them on which to attach the aluminum sheets. I say initially because I may want to later either upgrade to a true tin roof or possibly (if the structure ends up looking nice) do something more traditional (shakes, etc).

As a foundation I will either simply put the posts in the ground (3-4 ft) or will pour piers - again very little cold and thus a freeze line of about 6 inches and little to no heaving to deal with.

This will be my first TF project. I have the bandsaw to mill the SYP so I can custom the beams as necessary...

Not having a center post in the bent is appealing: nothing to hit with the van when backing in (except the truck), three less piers to pour, etc.

It sounds like the initial idea posted would actually create a situation where the 24' cross beam is "hung" from the ridge... is that accurate??

Thanks
Ben

Post in ground will rot, place on piers for sure.

If I were building this in my backyard using stick rafters and purlins it might look something like this:

I like it.

I do have a question. Do the opposing rafters contact each other at the peak?

If so what is the ridge beam doing?

What I am suggesting is to leave a gap between each rafter at the peak. If they do touch, in a few years of shrinkage and settling, the rafters could be free of the ridge beam and it would not be doing the job intended.

This type of structure will eliminate rafter thrust, allowing a simpler joint at the tie to post connection. If the rafters do touch each other they will add thrust to the side walls and more attention will be needed at the tie to post joint.

The tie is not suspended form the ridge. It is the truss that is suspending the tie. If this was not true, what would be supporting the ridge? The ridge is adding more load to the truss.

Last question, did I over analyze this?

Tim

Tim -

You could clip the rafters short or push the ridge up so the rafters hit the sides of the ridge.

The ridge is taking a distributed load from the rafters. This is 1/2 the span of the rafter x 2 x the area between bents - so you have in the center case 12' x 12' = 144 sq ft of area (not much). The ridge then transfers this to the KP. If the KP gets pushed down, the struts hold it up by diverting the load out to the ends of the tie. With proper joinery at the feet of the strut the KP is nearly useless as you could just push the struts up to hold the ridge - but the KP would be useful if you added a loft - and it makes for easier joinery. If the tie is strong enough to take a centered point load (in my neighborhood maybe 55 lbs sq ft roof load x 144) you don't really need the struts. And if the tie were designed with a tension joint at the post you wouldn't really need the ridge or the truss - assuming your top plate was stiff enough to take the distributed outward thrust and your tie to post connection was same.

But - the ridge gives us an easy place to set our rafters - and we can brace the building along its length - esp seeing as this will be open with no sheathing on the roof.

Not really anything too difficult in this example - its a small building. But it will make a nice learning frame and a fine structure.

Mike

Wow! Those are some neat graphics. Do you have a design program that generates those?

You know, even though I am now beginning to read some books on TF and learn the lingo, it would be really helpful I one of those diagrams had each piece labeled with their proper name - i.e. tie, KP, ridge, strut, etc. Some of these I know from modern stick framing but others (like KP?) I'm still learning.

Thanks

He has a FREE program that generates them. Evangelize him, Mike!