Ridge Beam Support

[azgreg]

I have a general question concerning ridge beam support. I'm not concerned with details (spans, size, etc.), but rather general building practices. I know it needs to go from foundation to beam but what about when it passes through a floor? Let's say you have a structure that requires two support posts other than the end posts. You don't run one continuous post do you?

[John Raabe]

See if this search helps.

https://goo.gl/yLiKlk

[akwoodchuck]

Sometimes posts are continuous....that's usually a function of aesthetics, as in exposed timber framing, etc. For general platform framing in which structural posts are hidden in walls or whatever, the posts are typically separate members with blocking added at the floor framing to carry the loads...."squash blocking" it's sometimes called....

[Don_P]

A post is a type of column. The support conditions can vary but the assumption is that the ends of a column are laterally supported in residential construction. Don't break a column between floors but rather at floors (lateral support) and don't build on flagpoles. I would pass unbroken through a pier supported floor and run from footing to second floor or ridge. If the column runs between the plates of a wall then the floor above probably need the squash blocking ak described (if in doubt, block it), then the column begins again above the floor. You do need to do your math here. The side grain bearing capacity of any wood you are bearing on or under, the beam, the plates, etc need to be capable of taking the post load without crushing.

[azgreg]

A post is a type of column. The support conditions can vary but the assumption is that the ends of a column are laterally supported in residential construction. Don't break a column between floors but rather at floors (lateral support) and don't build on flagpoles. I would pass unbroken through a pier supported floor and run from footing to second floor or ridge. If the column runs between the plates of a wall then the floor above probably need the squash blocking ak described (if in doubt, block it), then the column begins again above the floor. You do need to do your math here. The side grain bearing capacity of any wood you are bearing on or under, the beam, the plates, etc need to be capable of taking the post load without crushing.

What do you mean by 'don't build on flagpoles'?

Here's what I'm thinking here. We plan on building a 1.5 story home somewhere from 16'-20' wide with a full (gable end to gable end) loft and my wife would like opposing shed dormers. I guess my options are either engineered trusses of a ridge beam (I'm a big fan of beams, love the looks). All over a crawl space (wife wants a basement) foundation like Cougr67's here.



So my question is how do you run a post from that to the beam through the second floor?

[NathanS]

I think 'flagpole' is a warning about building on piers. One of the many reasons (and I can't explain them all because I'm not an engineer) everyone recommends against building on piers is because you're counting on the soil to stabilize sideways movement of the piers. The other safety measure would be to use triangular bracing on all of the piers, but this is still a back of the envelope calculation. By the time you have an engineer design a pier foundation for your soil type it is probably cheaper to lay block.

Building a residential sized structure on a continuous perimeter (full foundation, poured or blocks) basically takes the complicated engineering out of it. Your soil characteristics barely matter on a continuous foundation.

I do not have the 1.5 story plans but I imagine they detail how to 'balloon frame' the loft part of the building. A main concern with framing a loft with rafters is that the rafters will actually push outward against the load bearing walls. On a platform framed house, the attic joists create a truss, which causes the rafter force to be directed straight down the walls, rather than down and out. If you look at old houses, and see that the roof is sagging, I believe it is likely that the load bearing walls have actually been pushed outward, and are out of plumb. The nice thing about trusses is that they ensure that all the force is directed downward at the top plate.

Not sure if this helps answer some of your questions..

[azgreg]

I think 'flagpole' is a warning about building on piers. One of the many reasons (and I can't explain them all because I'm not an engineer) everyone recommends against building on piers is because you're counting on the soil to stabilize sideways movement of the piers. The other safety measure would be to use triangular bracing on all of the piers, but this is still a back of the envelope calculation. By the time you have an engineer design a pier foundation for your soil type it is probably cheaper to lay block.

Building a residential sized structure on a continuous perimeter (full foundation, poured or blocks) basically takes the complicated engineering out of it. Your soil characteristics barely matter on a continuous foundation.

I have no interest in building on piers.

I do not have the 1.5 story plans but I imagine they detail how to 'balloon frame' the loft part of the building. A main concern with framing a loft with rafters is that the rafters will actually push outward against the load bearing walls. On a platform framed house, the attic joists create a truss, which causes the rafter force to be directed straight down the walls, rather than down and out. If you look at old houses, and see that the roof is sagging, I believe it is likely that the load bearing walls have actually been pushed outward, and are out of plumb. The nice thing about trusses is that they ensure that all the force is directed downward at the top plate.

it's my understanding that a shed dormer makes this condition worse which is why I would use a ridge beam or engineered trusses (ridge beam is my preference).

Not sure if this helps answer some of your questions..

No, but thanks.  My questing just has to do with the building practice to bring the supporting posts from the foundation through the floors to the ridge beam.

All the engineering questions will be dealt with much further down the line once we determine the type of structure we want to build and where it will be built.

[Don_P]

Frame the main floor. At post locations stand up a stack of blocks the size of the post and the height of the floor framing and secure well. Apply floor sheathing. Build walls and incorporate posts, top plate, frame second floor, apply squash blocks in framing, sheath, incorporate posts, set ridge.

There are 5 opportunities for posts in the pic, you should have a straight line of support from ridge to footing.

Another way that might work depending on width, pitches etc, is to build full 2 story with common or scissor trusses in the dormer section. I've typically built those 2nd story walls 2-4' short of each end. Set the trusses on the dormer area and frame steeply pitched end sections with overhangs that run from 2nd floor to truss peak at each end of the building.

Nathan, scroll down to the end conditions pic;
http://www.engineeringtoolbox.com/euler-column-formula-d_1813.html
We are typically pin-pin, fig1, look at the buckling reduction factor for the flagpole fig4.

[azgreg]

Makes sense now Don. I was really struggling with what you guys were saying earlier. I blame the post holiday hangover. 

[Don_P]

I was thinking if I'd kept my mouth shut ak would have gotten you there quicker 

[NathanS]

Nathan, scroll down to the end conditions pic;
http://www.engineeringtoolbox.com/euler-column-formula-d_1813.html
We are typically pin-pin, fig1, look at the buckling reduction factor for the flagpole fig4.

Thanks for explaining Don.

fig1 column pivoted in both ends : n = 1
fig2 both ends fixed : n = 4
fig3 one end fixed, the other end rounded : n = 2
fig4 one end fixed, one end free : n = 0.25

I looked at some simpson post bases and they specify they "do not provide adequate resistance to prevent members from rotating about the base and therefore are not recommended for non top-supported installations" .. which they are saying it needs to be pin-pin, like you said.

How would you typically fix the ends of a column, as opposed to it just being pinned?

[Don_P]

Wood is typically pinned, it is hard to weld or bolt up to a truly fixed condition from the ends the way steel can be.

Run the post up into a braced wall it is then cantilevered out of the floor (fixed) and down to the footing (some fixity) or pier (pinned) fig3 flipped upside down.


You're asking about a pier and beam as seen here frequently I think. In that series of graphics they are showing translation fixed in all conditions except the top of the flagpole. Something is holding the top in place laterally.
  The simpson base is a pin connection into a 6x6 post, translation is fixed(hopefully) rotation is free. The top nails or bolts also form a pin connection from post to beam, translation free, rotation free. This is not shown as a type of column, n=0

If the post extends up through the braced wall and deep into the ground it will approach fig4. As you explore this deeper you'll get into post frame engineering, google Dr Bonhoff's papers for more down that path.