Looking here for reasons and explanations of why one would be better than the other.
Assumption: a building on piers. Built up beams of 2 to 3 layers of 2x.
Choices are:
(A) Beams with joists on top of the beams. Beams at the joist ends or within something like 12 inches plus or minus a couple.
(B) Beams placed at the building perimeter (long sides) and the joists hung on Simpson (-like) joist hangers between the beams.
Discuss away!
I've always preferred B.
I have no idea if it's actually stronger or not, but purely from a psychological standpoint, I feel better when my joists are on top of the beam than hanging by a connector.
Erin: Didn't you mean to say A?
This is opinion only. I am not an engineer:
I would think that B which uses the hangers, might be better
because it makes the flooring plane compact and more rigid
with less forces acting in the z axis that might weaken it in a storm.
Not sure if I explained that well.
Bruce
Doh!
Yes, I meant A
Great question. ???
With A, I have the building code prescription. This gives me confidence that it is a no brainer and it can be used for all situations. Even by a dummy like me.
With B, Simpson brackets undergo massive amounts engineering and scientific testing. You also have the advantage of using less lumber. Such as if you have an 8 ft span between posts, you can use 8 ft lumber and not have 16 ft pieces to span two posts so that all the joints aren't over one post.
So my answer off the top of my head would be, "it depends". If the posts are close together (6 ft and under) and evenly spaced I would go with A, and if over 6ft spacing or unevenly spaced, B.
I think we need more daily questions like this. ;D
I think that as far as load support it would be hard to beat joists on top of beams, but with hangers you might create a more ridged box and eliminate the possibility of the beams rolling. Something not addressed by most folks using option A.
I prefer option "A".
I think it's the simplest and easiest to build. No disrespect to Mr. Simpson but I'd rather have gravity working in my favor with option A than relying on a bracket to hold the floor joists up. Plus with option "B", getting the top of the floor joists all perfectly flush with the top of the beam and then having to put all those nails in the hangers is a PITA, esp. when working alone.
As far as where to place the beam, I like the idea of placing it inboard enough of the ends of the joists to allow for the skirting to be applied and still leave it flush with the exterior wall.
The option A allows for plumbing waste lines to come down the wall and make the corner. This can be a problem for beams at the floor line. Might not be a problem in a one-story layout.
Quote from: John Raabe on September 01, 2011, 11:33:13 AM
The option A allows for plumbing waste lines to come down the wall and make the corner. This can be a problem for beams at the floor line. Might not be a problem in a one-story layout.
That is a good point,I did not think of the pluming thing. Thanks.
I like option A also. In most cases. I would address potential rolling of the joists by placing some blocking between them. Isn't that what most of us do? Plus the rim board also provides rolling protection as well as screwed and glued subflooring. Temp bracing while framing and sheathing can also help prevent accidents.
RW
I have a slight preference for "A", if the greater section depth is no problem. Better air crossflow. As well as service access (already pointed out). The assembly can be stiffened by using extra beam-to-joist connectors fashioned out of standard angle iron or square wood stock ... think 4's, or 6's, ... and lag screws.
In a prescriptive assembly a girder would be inboard and the perimeter would be on a foundation wall, the most satisfactory plan. I prefer a dropped girder (A) to a flush girder (B) whenever possible. The joists are bearing and supported on wood vs nails in shear. If the girder is 3 plies and the joist is bearing across all plies, as it should be let's check the bearing capacity; 1.5" wide x 4.5" long x ~350 psi allowable=2362 lbs, now look at a hanger's capacity.
A hanger mounted to the side of a girder delivers the lions share of the load to the first member, much less to the second member, VERY little to the third, and the fourth isn't doing any work (look up, it may be supporting a wall,etc). With a dropped girder each ply is doing work.
Whenever a joist crosses a girder or bearing and then cantilevers out it is blocked over that bearing to prevent rolling.