Hoisting an I-beam …

[radair]

The notch at the tail end doesn't weaken the rafter because the rafter is sitting on your wall top plate. The full thickness of rafter is bearing on the plate, the notch just locates the end so your rafter tails line up.

The top notch takes a piece out of the x-section, so that the dead & live loads will tend to split the rafter. Look at the plumb cut ends in a few years and you will likely see cracks or splits extending from the corner of the notch toward the middle of the rafter span. The solution is to add plywood gussets (kind of L-shaped) that reinforce the notched area.

I wasn't trying to imply that you were recommending this detail. I am a structural engineer and was stating I would never recommend it.

It looks like a great building and you may never have any issue with the roof framing.

 

[johnday]

Fungus; Collarties, we must have collarties. They should be installed 1/3 of the way down from your ridge board [Ibeam]. They will keep the roof from trying to spread your bearing walls. /forums/images/graemlins/grin.gif

 

[Henro]

<font color="blue">They will keep the roof from trying to spread your bearing walls. </font>

John,

When a beam is used in place of a ridge board, the tendency for the roof to spread the walls is reduced to about zero in my experience and from what I learned in the past...

I don't think cross ties between the rafters in Fungus' design would do much to keep the roof from spreading (since it does not want to do that anyway) but if short ones were put just under the beam, they certainly would help hold the roof to the beam if the wind picked up!

 

[johnday]

Bill; I think this is the first time I've ever disagreed with you. /forums/images/graemlins/blush.gif It doesn't matter what you use for a ridge board, be it Ibeam, LVL, glulam, or dimentional lumber. Weight in the form of snow, roofing and sheathing, and even wind load, can and does cause the bearing walls to spread outward from the top plate. In the case of everything but wind load, picture 2 triangles joined at their highpoints. Weight because of mean old mr.gravity, will move in a downward direction loading the top plate on bearing walls. The collarties prevent this by tieing rafters together on either side of the ridge. Take a look around some of the old neighborhoods in your area, and look for some of the old garages [and some not so old] and checkout the used to be horizontal ridge. I'll bet if you walk around to the gable end and sight down the wall, the wall will be off plumb towards the outside of the building. Come on you carpenters, defend my honor, Henro's smarter than me, ya know /forums/images/graemlins/grin.gif

 

[Inspector507]

I'm not a carpenter, but if I get your post correctly, you're referring to lumber as a ridge board versus this beam which won't sag like wood in the middle. When a ridge board sags a bit, the rafters lower and in turn push out on the walls.

 

[johnday]

Jerry; Right, Hopefully that beam wouldn't sag, but, and maybe it;s the way I see the photo, there is nothing tieing the oppossing rafters to each other. IMHO, the rafters could seperate themselves at the ridge. Someone said something about plywood gussets, that would tie the rafters together. But an easier, quicker, and most likely stronger approach would be collarties. Hey, ask the guys in your office what they think, I'd bet they'll back me, and you can even tell me publicly /forums/images/graemlins/grin.gif I might be a framer, but that doesn't mean I can't learn, and my mastery of explaining without paper and pencil does leave something to be desired. /forums/images/graemlins/grin.gif

At any rate, I wish Jan would fork over some of her bucks so I could build a barn that nice for myself. /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif

 

[johnday]

Guys; Oh boy, I just went back and looked the photos Fungus posted. /forums/images/graemlins/blush.gif Some how I missed the ones about the straptie and steel plate. With that setup, I probably wouldn't use collar ties either. /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif But, if not for that, collarties would be called for. Man, I hate getting old, the older I get, the more I miss. /forums/images/graemlins/confused.gif /forums/images/graemlins/grin.gif

 

[Inspector507]

I think I saw where he had some sort of strapping across the tops tying them together.

 

[Henro]

John,

Think of one of those shed type buildings used by towhships to store salt or whatever.

Across the front opening there is a beam. Across the back is a wall. The roof is supported by the beam in the front and the wall in the rear. The roof does not have any cross ties because there is nothing on the other side of the beam to tie into.

Granted these roofs usually have something other than wooden rafters, but the principle is the same. The roof does not try to push the back wall out, because the load on both the back wall and the front beam is vertical. It is transmitted to the ground along the length of the back wall and by the posts or whatever is supporting the ends of the front beam.

By the way, my house is rock sold even in the strongest winds so far (after 20 plus years, we don't get that much snow load...) but not because of any kind of cross ties at the roof...it is post and beam design and all my roof sections are essentially like Fungus' has, but without cuts in the rafters at the high end... /forums/images/graemlins/grin.gif

A regular roof with a standard ridge board is like a hinge laying on the kitchen table. It wants to lay flat. Cross ties are important with the ridge board and hold the roof in shape.

A roof like Fungus, has with the load bearing beam at the ridge, is like a hinge laying on the kitchen table with a pencil under the middle. The hinge with the pencil under it looks like a roof, and if you push down on the middle, the ends do not spread because the pencil acts like Fungus' load bearing beam...

Edit: John, I forgot to ask in both of my posts above, what is a "collartie?" I assumed you were referring to a cross tie of some type...but I don't know the term... /forums/images/graemlins/blush.gif

 

[johnday]

Jerry; Yeah, I sure did miss that. /forums/images/graemlins/blush.gif/forums/images/graemlins/grin.gif

Thanks for being nice guys. /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif