Hang the roof beams to side of trusses
Gene_Davis
| Posted in General Discussion on
A little thing I am cooking up has roof spans too long for anything reasonable, and I must break up the spans with some intermediate flush beams.
A shed dormer offers, in its cheek walls, a way to place monotruss girders and side-hang the beams to the trusses. At least that is the way I see to solve this.
I’ll be asking the truss engineer about this, but I thought I would ask here. Ever seen anything like this in trusses?
The pics show the arrangement. I did not bother to flesh out the trusses with chord sizing and webbing. The sketch just shows the general idea.
Replies
Given the right engineer I bet you could do away with the trusses and sheath both sides of the studs in the cheek walls to create box beams.
Truss or box beam, wouldn't it be easier to run the rafters from side to side so you don't have to split up the span and create another point load?
I see ventilation problems
Just how long is this?
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Spray foam, hot roof. Our insulation of choice.
Now I'm thinking of giving that little shed eave a swoop. Just a little subtle eyebrow warp. My inspiration is shown in the photo, attached.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Not sure I see the reason for a truss there along the side of the dormer, why not a built-up LVL common rafter with the beam side-hung using a nail-on hanger and the rest of the cheek wall framing stacked on the beam? My shop has essentially the same deal... tripled common rafters at either end of the shed dormers, dormer headers hung between those triples using HUC hangers.... dormer headers needed because dormer originates well below main ridge.
Anyway, I rarely work with trusses but have not seen a point load hung on the bottom chord like your pic shows.
If ventilation were needed you could use a beam slightly lower than the top of the rafters and let the vent path run right up over the beam.
They can hang loads off any point on the truss. To do so, they engineer in enough "stuff" to keep it all together. They can cobble almost anything up to do a job.
That little swoop looks like a lot of work compared to its straight counterpart, but might be worth it. It is beautiful.
Edited 9/11/2009 2:59 pm ET by fingersandtoes
Why not frame roof(s) w/ I joists?
Hardware can be a pain, but it would simplify the whole shootin match from where I sit.
Bing
Why not frame roof(s) w/ I joists?
Because I-Level is telling me that because of my roof load, their deepest and heaviest joists must be used, on 12-inch centers.
Sawn lumber with midway headers is way way cheaper, and I can do it on 24-inch centers. Much better insulation scheme. Plain old 2x10s will do, but I will use 2x12s over the dormer, just because their depth will match the header and the whole ceiling can be flush.
The headers may be able to be supported with LVLs buried in the bases of the dormer cheeks, as shown in the attached. I am waiting for I-Level to comment.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
"Sawn lumber with midway headers is way way cheaper"Are you counting labor and hardware too, or just the lumber vs I-joists cost?
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Compare the cost of a foot of 2x10 to two feet of an I-Level 16" depth 560 series. Look for the one with the full 2x4-sized flanges.
Now figure that all seat cuts and soffit overhangs will need to be detailed more elaborately than the simple cuts we can make on those sawn lumber joists.
We will need web packers at all joist-to-ridge connections, and squishers of some type where we bear on walls.
What dismays me most is packing 3-1/2" of flange up against the bottom side of the roof deck, every 12 inches, versus doing only 1-1/2" every 24.
Finally, at 16 deep, the roof diaphragm is quite a bit thicker and beefier looking, height-wise, than one done with 2x10s.
While a centering for rafters at 12 might allow thinner roof sheathing, our AHJ will insist on the same old 5/8.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
The labor would be significantly less with the sawn lumber...if I was bidding it.
I'm convinced
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lol
I know you aren't sold but the reality is: the Ibeams are significantly slower, especially at 12". They requires so much labor to beef up the ends and there really isn't enough room to get tools in there at decent angles to get the job done.
The hangers that would be required at the midpoint beams would be timeconsuming too but there are several factors. One is that the work would be lower and there would be significantly more room to maneuver.
I joist have their advantages (longer spans) and in some limited situations, they might be faster. That is the the exception though, not the rule.
Your comment on the labor component of this roof as proposed, made me wonder about the use, or no use, of hangers in roof framing.
See my separate thread, just started. Your comments are welcome.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Well, after working with this house design, I decided that the roof is best framed using engineered trusses almost everywhere.
Hand-framed rafters, 2x10 #2 SPF on 24" centers, are used on the rearmost plane of the main roof, where we need max overhead room for a pair of bed alcoves in the loft, and the rest of the main roof is a truss arrangement, using a parallel-chord two-ply girder that functions as a ridge, offset from the actual roof ridge so as to allow easy chimney chase routing.
I positioned the girder truss "ridge" to sit directly atop the two-stud pair that is the "frontside" king and jack for the gable window openings that are mirrored in each tall gable, thus we'll need no structural headers over those window openings, which are centered on each gable.
I realized this could be done when looking at the full house section, and seeing how much excessive overhead I had in the single under-roof vault. Dropping the ceiling down for a better spatial feel and scale, gave me plenty of overhead between ceiling and roof for truss depths. The cheek wall frames for the dormer simply sit atop doubled trusses.
The pics are worth another thousand words.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
There ya go! My labor price (on the roof framing portion) would be half that of a TJI roof system.
Yes, better from my POV too.I was nor being facetious earlier when I said I'm convinced. I have use TJIs mostly on floors and only a couple simple roofs and never had problems with it costing me more. I always saw it as a labor savor.But I know wthe you have more framing experience than I do on both so I am convinced that they could cost more on this, esp after g=Gene confirming that he had run comp numbers to include everything.It still could be a matter of local methods and what a crew is used to somewhat.
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Each situation is different. I used them on in one sub and it was a wash. There weren't many "odd" situations. On the next custom house we did, we used them and it took me longer to sort through the pile than it would have for me to spread all the sawn lumber. TJIs are all about getting longer spans and flatter floors....but there aren't always a labor saver. Here in Texas, I wouldn't want to use anything but floor trusses. They are a necessary evil to facilitate the HVAC systems.
On new that I design, I like the open web floor trusses, but I do more addditions so the I-joists are more often the way I go for dimension matching with existing.
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The open web floor truss thing bit my butt a little recently.
We had everything final, ready for printing the docs, when I'm told that the sawn lumber 2x10s for the main floor deck frame are out, the client doesn't want to do the HVAC ducting in soffits below.
Wants them within a floor frame done with 14-deep OWFTs.
Fine, sez me. I re-doodle, taking out some bearings and beams we had, because now we can span rooms big time. The house grows 4-3/4" in height. Different detail for the rim. Done.
But Mr. Stupid left the stair header over the flight from midway landing to lower floor in the same place. Stairway clearance overhead went from 82-1/2" to a forehead-busting 78-and-something.
We had an out, in that we could frame for a two-step landing, but I learned a lesson.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Mt Micro tangled with Mr stupid and lost!Ha Ha;)
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Do you ever use bar joists instead? I'm curious about the cost as compared to wood floor trusses.
The only barjoist I ever set was in my early days when I was fabbing and setting structural steel on small commmercial jobs. I've never seen it on a residential home but I remember a thread about it in here.
That is why I asked how long the span is. Didn't appear to be that great that it ould not easily be done with the right material instead of dinking around with all these parts
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This is a different take on a similar roof of a very nice house with loft. Maybe not much help with your problem but worth looking at for pure pleasure.
http://balanceassociates.com/projects/beachint.html