There’s a house going up in the neighborhood, and one of the trusses caught my eye. Granted, I haven’t seen a lot of trusses, being as young as I am, but I was surprised at how much open space there is to this one. Looks like the very top triangle might be a separate piece.
I’m sorry, I thought you wanted it done the right way.
Edited 1/30/2005 11:50 am ET by Ed Hilton
Replies
I hope they had a crane...ouch.
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It is obviously designed to make use of the space - see the heavier floor joist at bottom chord level, but I wonder about the energy package. The top chords are too slim for much insulation at the sloped walls. They'll need to use foam to transition that area
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I'm wondering why the front wall is higher then the side walls. It looks like the front wall top plate might be even with the top of the floor joist. For some reason it looks like to me that there's no top plate on the side walls unless I'm seeing things or not seeing things. I saved the picture and zoomed in but it's not clear.As far as the front wall I wonder why it's higher and not just make it the same height as the side walls and use a gable end truss.Joe Carola
Looks to me like the fron wall is framed that way because of the RO height of the entry door unit. it probably will have a transom window or arc lite over door. Seems like too much trouble to nothch like your drawing, more likely just a shorter side wall. I hadn't thought of it 'till you pointed that out.
I like studying these little mysteries. BTW, I'm also pretty impresseed with all you've been able to accomplish with just a MS paint program
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As far as the front wall I wonder why it's higher and not just make it the same height as the side walls and use a gable end truss.
To me it looks like the top of that front wall is even with the top of the truss floor
so that when the decking is run it can run over the top of the wall.
edited
I didn't read all the posts and see that blue beat me to it
Edited 1/30/2005 6:58 pm ET by butch
Piffin,Maybe the plates are the same and the truss is notched and sits on top of the plate.Joe Carola
Seems like it would have been a good time for stick built, but maybe they felt they could get the clear span in the lower room more effectively with a truss design... Heck - maybe even floor trusses with stick built roof...
As far as the insulation, maybe they intend to "strip down" the sloped ceilings to accommodate the insulation? To clarify the terminology, when I say strip down, I mean add 2x4s to the bottom of the top chords in the sloped ceiling areas. Ed: what is the ~ span of the trusses? Matt
Would that be a a Mooney roof?
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Not really... The edge of the 2x4s would attached to the edge of the bottom of the top chords... As opposed to perpendicular. Matt
Gconst is correct. The framers have raised the front gable wall 9.25". This effectively puts the top plate at the exact height of the built in floor members. The plywood underlayment will nail directly to the top plate of the wall and they will be framing the gable wall on top of the plywood.
I often adjust front gable walls to accomplish something similar to that. Sometimes I think I'm being clever, only to find out that I've caused myself more work, other times it actually is a timesaving technique. Either way, I've learned to carefully consider the height of each wall, and have steered away from assuming that all wall should be equal. Once you get into that mindset, it's easy to create significant timesavings with little or no extra effort.
Heres some pics of a bonus room situation that we did last fall. We didn't adjust the height of the front wall, but we did some creative framing to facillitate the installation of a "normal" 4" wall on the front.
This particular room had a full 8' ceiling but most aren't that nice. The "piggys" are fairly substantial...much bigger than most garage piggies. I've got a shot of Ben installing the piggies somewhere...if this thread continues, I'll dig them out amd post them.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Satisfy my curiousity?Wouldn't the subfloor/flooring have a tendency to flaex at that junction and stress the gable wall framed over it? Trusslift is what I'm thinking. I have only done a few trussed roofs in my life...
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The question of trusslift is a good one Piffin and it's an issue that I don't know enough about, especially regarding these types of trusses. If truss uplift was in fact going to occur, it would be better that trusses weren't built into the gable wall like the pictures I posted. If it did, it would be forcing itself upward into the eventual window that we had to install in our wall. Maybe Boss can tell us more about truss uplift and bonus room trusses. I've never heard builders discussing any issues with it, but that doesn't mean some problems haven't occured.
The question of shrinkage wouldn't be a factor, as the side walls and front wall would shrink at basically the same rate. The question would be...would the 2x10's built into the floor sytstem shrink at different rate than the wall...the answer is yes, but not by enough difference to make a differnce. In the building "real world" nothing is perfect.
blue
Just because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
I don't understand truss uplift that much either, but it seems liek there would not be as much danger with thios type, because it has something to do with temperature differentials. This one seems to be making the most of the truss be inside the conditioned space., depending how they do the insulation/ventilation package, and the three samller triabgular sections would not independently exert as much fiorce as a single larger truss anyway.
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blue, what is the benefit of this method over just using a gable truss? I've seen and have done this with TJI's but not with roof trusses.
I didn't do it....the buck does NOT stop here.
More info ...
The trusses are over a garage, spanning front to back. The bottom c hord is a 2x10 about 13 ft long with a section of 2x6 about 6 ft on each end. The rest of the house roof is being stick built. I saw a label on the trusses from "Stock (something ... company name)" and "228 Attic".
View Image
I'm sorry, I thought you wanted it done the right way.
Edited 1/30/2005 4:50 pm ET by Ed Hilton
Thanks for the photo Ed!
As I suspected this truss is a series of three trusses connected by large members used to resolve the forces of the entire truss while providing the rigidity to be able to clear span thereby creating the bonus room.
The top cord bearing of a truss of this type is unusual (at least here in Texas) and was likely done so for some specific design reason (architectural or structural) that would only be clear after asking the designer.
To the question of truss creep, the floor loading restrictions on the house that I used this truss type on were very restrictive. The owners wanted it to be 100 PSF, so we ended up putting the trusses on 12 inch centers. The joint betweet the individual trusses and the larger members effectively becomes a pin joint for the purposes of designing the truss. This can present some problems. As I remember it we were required to solid block the floor member at 1/3 points of the span between the sidewalls of the bonus room. both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
"he joint betweet the individual trusses and the larger members effectively becomes a pin joint for the purposes of designing the truss. "
Actually it's considered as a "semi-rigid" connection.
Pin joint modeling is an old version of truss design that's no longer widely used. And it's restricted to triangulated trusses.
The key management tool is still words, delivered face-to-face. Hasn't changed since the dawn of time and is not likely to in the future. [The Way of the Warrior]
It's still a truss, IMHO. But the analysis is different. I was taught to call it an "indeterminate structure", since not everything is triangulated.
The way these work is complicated. I can go into what I know of the theory if anyone is interested.
Believe me, it has been 30 years since I took a structures course, so my descriptions and methods are clearly rooted in the past. ;-)
Your description is more accurate and although I didn't say it correctly, that is what I meant. I was taught that indeterminate structures are somewhat fuzzy in that the moment connection is based upon the creation of leverage via a cantilever. The connection of the upper and lower truss via the large roof member is an example of this type of connection as it works in compression and therefore must resolve moment. The lower chord (or floor of the attic) can be a simple pin connection as evidenced by Ed's last photo, as it is a tension connection only and does not resolve any moment. Indeed, there would likely not be splices in the lower chord as shown in an earlier photo, if moment was a problem.
Although this is likely way more information than many people even care about, it is fun to recharge the old, long asleep, brain cells that were filled with knowledge so long ago by Dr. Buckley in my structures classes at UT Almost.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
Been 30 years, huh? It's amazing how much structural design has changed. The faster computers get, the more complicated design methodology gets. And the more complicated it gets, the faster we need computers to be. It's an endless spiral. It's probably just a matter of time before pin joint modelling is no longer allowed for trusses. The design methodology they use now is so complex I just barely sort of understand it.Used to be you could hand calc a pin jpint modeled truss in a few minutes. With new modelling techniques it would take all day. I don't mind talking about the specifics a bit if someone is interested. But I susect to most folks it would be as exciting as watching paint dry.
Anger is the wind that blows out the candle of the mind. [The Mafia Manager]
I don't mind talking about the specifics a bit if someone is interested. But I suspect to most folks it would be as exciting as watching paint dry.
I don't suspect you are right, I know you are right.
The funny part is, the more complex the formula, the more refined the solution, the more refined the safety factors and more critical the connections, the more likely the failure. There were all too many failures of complex roof forms during the 80's and 90's.
Do they still teach people how to solve a truss graphically?
Grace and structures don't often work well together, unless you are talking tension. Frank Lloyd Wright's columns at Johnson Wax and his cantilevers at Falling Waters are two examples of compression turning out gracefully. Even then FLWs main spark of genius was likely his very successful collaboration with his structural engineer (whose name escapes me). Even with that many of FLWs buildings leaked like a sieve as he often pushed the envelope way to far for the day. The waffle slab roof structure used in Italy (if I remember correctly) that is laid out to match the load patterns is also beautiful. It is too early, it has been too long and I haven't had any coffee, so I can't remember the name of the building or the architect.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
"The more complex the formula, the more refined the solution, the more refined the safety factors and more critical the connections, the more likely the failure."
I don't agree with that at all. The safety factors are the same for virtually ALL trusses. There are only a couple of exceptions to this. First would be for handling. Once trusses get up to around 40', we over-plate the joints near the center of the truss. That helps with handling problems. (Like picking them up with a crane)
The second scenario would be on really large trusses, like 70' and over. We over-design them to some degree again because of their handling charachteristics.
Connections are ALWAYS critical, no matter what the design.
Regarding complex formulas - I'd say they're more accurate now than they ever were. They used to be based on testing of small samples of wood to failure, then using math formulas to predict how larger samples would act. Eventully they stated testing full sizes samples of wood, and found that their assumptions weren't correct at all. So the lumber values and the NDS were revised in the early 90s. (Can't recall which version)
"There were all too many failures of complex roof forms during the 80's and 90's."
I don't know what you're referring to there. The only "failures" I've heard about were due to improper design, failure to account for drift loading, or inadequate design loads. And none of the ones I heard about were complex roofs.
"Do they still teach people how to solve a truss graphically?"
They do in many advanced math courses. Can't tell you exactly which ones, though. I never went to college or had advanced math.
Even if trusses design is no longer done that way, I think there's value in learning to do pin joint analysis. At least it gives you a feel for how trusses work.
A miser is hard to live with, but makes a fine ancestor.
I don't know what you're referring to there. The only "failures" I've heard about were due to improper design, failure to account for drift loading, or inadequate design loads. And none of the ones I heard about were complex roofs.
Kemper is but one example. As computers get better, design has moved back into the realm of the lab coats. They "thought" they had accounted for all the potential loads. Pesky things that they are a few got missed. They have had catostrophic failures sine the dawn of recorded time in the field of construction and there will be many more as we move farther down the path of human evolution.
Say what you want, but when it takes 5 cranes to hold up a roof structure (Reunion Arena in Dallas) while it is being built, there is inherent instability and extreme emphasis placed upon construction accuracy.
I am not trying to say that we can't model structures on the computer and that we know better than ever how to size members, but it all boils down to human perceptions eventually. One small (at the time anyway) field change cost a bunch of lives at a dance in Kansas City.
With my Errors & Omissions on the line every time I send a project out the door, I look closely at the overall "idea" behind the structural system proposed.
As I have said many times before ... Computers allow us to draw bad faster. There is no substitute for experience.
Some things are obvious, some are not. We cannot trust computers to tell us the answers while allowing people in construction with high school educations to build complex structures while being supervised by cubs two years out of college with a pair of binoculars in their hand.
Ford thought they had produced a winner in the early 80's with the Bronco II 4x4. One ride in one scared me half to death and it proved to have the highest roll over rate of any vehicle on the road back in the late 90's. Didn't the designers ever ride in the vehicle?
Boss: I am not trying to debate structure as much as relate perceptions and realities within the architectural field as to the problems that have to be addressed as one moves farther and farther away from the dashed white line along the path of human knowledge. I really like space frame structures and have even been involved in a few. I have designed way more than my share of high rises with everything from skip joist, to waffle slab, to PT floor and beam systems. I now spent my days working on Historic Restoration of buildings from the 20's and 30's with my oldest being one from the late 1890's. Newer buildings may have the safety factors, but according to the structural engineers that work with me on the restorations, they do not have the redundancy. It is hard to explain to someone that they cannot punch a hole through a PT floor as the result might kill them and people around when they do so. We started specifying red stained concrete for all areas of a building with PT systems.
Who knows, in 50 years my grandson may be restoring some of the structures being built today.
In that this conversation had deviated WAY off the dashed white line of the original post, I think I will retire back to sidelines on this one.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
"Kemper is but one example."
Don't really know what you're talking about. Was this related to trusses, or soemthing else?
"Computers allow us to draw bad faster. There is no substitute for experience."
No arguement there. Everything that comes off the computer needs to have a "reality check".
"...according to the structural engineers that work with me on the restorations, they do not have the redundancy. "
I don't agree there. Although I mostly deal with residential buildings, I'd say there much better now than ever.
Doesn't seem to be anyone else interested in the original post topic now anyway, so I wouldn't let that bother you.
What sort of work do you do exactly?
There is a great man who makes every man feel small. But the really great man is the man who makes every man feel great. [Chinese proverb]
Boss Hog:
Here is a link to a page that lists a number of different failures. All are commercial projects. Funny in a way, but building codes build a tremendous amount of redundancy into residential construction by design and then you place a building near a fault line, where snow loads are severe or winds strong and they get even more redundant. Hopefully you will find the information interesting.
http://carbon.cudenver.edu/~mclark/Buildings.html
Doesn't seem to be anyone else interested in the original post topic now anyway, so I wouldn't let that bother you.
I see your point, as only you, Bill and I are still rambling on. I guess others may be reading, but they are probably saying huh?
I have learned from you that there is a lot out there that I don't know that has changes since I got out of school in the fall of 1975. Thank you for the insight. I need to start paying much more attention. It is hard enough to keep up with all the building, handicap and energy code issues, never mind structural where I hire someone to tell me what to do.
What sort of work do you do exactly?
I started my own firm in 1998 and founded it on the principal that I learned first in the field, was modified by my schooling and finally subjugated by the marketplace.
That principal is that everything SHOULD be buildable. It is a shame, but much of the work that architects do daily is for naught. It is unneeded and unheeded.
I try and focus on historic renovations and downtown revitalization, but as the bills dictate, I delve off into new construction. I am wrapping up a Chevrolet Dealership in Bandera Texas as we speak. I do residential design for fun and only for friends.
I used to be a superintendent and have driven more than my fair share of nails, putting forms and building frames together. As a general contractor, I have handled everything from layout to collecting the bills and suing the clients for payment.
I may well be the only architect alive that has been a general contractor and a subcontractor (millwork and casework) prior to moving into architecture. My grandfather was a general contractor in central Texas and my father a civil engineer.
By God's grace my hands have had the pleasure of doing things that I am only barely knowledgeable of, so I know I am being guided by those that preceded me. I honor their memory by always trying to do my best with everything I do.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
Oh man - You're an ARCHITECT ??? NOt one of those !!!.O.K., just kidding. Have you talked to Wrecked Angle? He's an Architect in Texas that's building his own house. You guys might have a lot in common. Has been interesting chatting with you. We can all learn from each other here, I think.
If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization.
Oh man - You're an ARCHITECT ??? NOt one of those !!!
Hee Hee, yep! I can still drive nails with the best of them and if it wasn't for the broken bones in my feet that hurt when I walk plates I would be walking 2x4s everyday that I could.
O.K., just kidding. Have you talked to Wrecked Angle? He's an Architect in Texas that's building his own house. You guys might have a lot in common.
As a matter of fact, yes! Kevin is in the Abilene area and came to tour my latest project, which is the National Historic Restoration of the Hotel Wooten. We restored the public areas to their original configuration and finish and constructed 55 apartments in the upper stories of the 17 story tower. I am proud of the project as I spent 10+ years of my life getting it to the point it is now. Kevin and I have had many long talks about design while wandering through the construction debris at the Wooten.
Has been interesting chatting with you. We can all learn from each other here, I think.
I know we all learn from each other. Thank you for sharing your insight and experience. Knowledge begets humility. The more I know the more I know I have to learn.
As a matter of fact, what is your background? From our conversation over the last few days I have learned that you know one whale of a lot about structural design and that you are in the residential end of the business.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
I'm in the truss business. Have been almost exclusively since 1984. I mainly do roof trusses, but also do wood and steel beam design, and wall panels. I've been fortunate to work with some pretty sharp engineers over the years who have taught me a great deal. So even without college, I feel like I know more about the practical application of wood trusses than most engineers. (Unless they work in the truss industry, and not many do)By "practical application", I mean figuring out what will work best in the field, figuring out what the customers want, making sure they get the right trusses and get them when they need them, etc. I understand the techinical theory of trusses quite a bit, but not 100%. I know enough to know when I'm in over my head, and stick to doing what I do best.
I'm a paranoid exhibitionist. I always feel like I'm being watched, but I don't particularly care.
"Frank Lloyd Wright's columns at Johnson Wax and his cantilevers at Falling Waters are two examples of compression turning out gracefully. Even then FLWs main spark of genius was likely his very successful collaboration with his structural engineer (whose name escapes me)."So sucessful that they just spent millions reinforcing Falling Waters before it fell.And that was after the contractor put in lots more steel that FLW speced.Otherwise it would have fallen long ago.
So successful that they just spent millions reinforcing Falling Waters before it fell.
And that was after the contractor put in lots more steel that FLW speced.
Otherwise it would have fallen long ago.
True, True and True.
At best FLW was an genius and at worst an egomaniac. Don't most "Architectural Geniuses" fit into that mold? I know I have wanted to slap the you know what out of many of the ones I have come face to face with. They live in a world all their own and defy many (if not all) of the laws of physics that the rest of us have to work with. I was saddened to learn of Phillip Johnson's death recently. I had the pleasure of working on a group of buildings he provided design concepts for back in the early 1980's and remember how genuine everyone thought he was.
Real progress is only found in exploration and that sometimes results in failure. When asked what his most famous building was, I.M. Pei stated that the John Hancock Tower in Boston put him on the map. When asked why (as it isn't that great), he said that it was because of the failure of all the glass and the media attention.
Maybe it is true that people rise to their own level of incompetence or fail their way to the top.both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
Ed:
I would ( and I am sure others would as well) love to see a closeup photo of the truss bearing point.
I have used "trusses" like that before, but according to the fabricator, they can only loosely be described as trusses, because of the way that they resolve the forces. The fabrication is indeed two trusses with the little one on the top being there primarily because of haul restrictions on heights of the trusses. The main truss is actually three separate systems with large members bridging the gap to transfer/resolve the forces. The endwall truss has a plate member scabbed onto the face of the truss flush with the top face of the top chord, I assume to allow for the infill of the endwall. I suspect the endwall plate line is where it is located simply to get the header in the wall to the correct height.
Funny, but the roof to the left appears to be going up conventionally.
both God and the devil are in the details
If you cannot visualize it in 3D, you will not be able to draw it in 2D and it cannot be constructed in 3D
Hard to tell from the pic, maybe they are sticking the gable hence the higher wall to get same HAP. My guess ,to save a $$. And yes, they will have to 'strip' the top chords for insulation.
I didn't do it....the buck does NOT stop here.
Trusses like this are not uncommon. They are used to frame bonus rooms over garages etc. Much faster and larger spans than stick framing. The heals are raised to allow the top of the floor to be level with the top of the main house floor trusses. These look to be pretty straight forward some get very complicated. Like some one mentioned the tops appear to be a separate piece. The over all truss height was probably to high to ship so they are built in 2 pieces. You do need to be a little more careful how you brace them, follow the instructions carefully. Oh yea, why would you not use a boom to set most trussed roof's? I all most always hire a boom to set roof's. It is easer, faster, safer, and many times less expensive. If I can use my fork I do, but if it is more than one story or a lot of trusses ( say over 50 pieces) it is faster to use a crane. I can hire a boom for around 70.00 / hr. it has a 40' reach which is enough for many jobs.
Don't have but a minute this evening online, but -
Trusses like this are relatively common. I'll post more about them tomorrow, as well as comment on some of the details...
tease
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A floor hanging from above doesn't seem right to me. The advantage of truss in this situation is?
Seems like the bottom cord/floor joist should be attacached to the sidewalls w/ a ledger board & hangers .?
You really can't tell from the photos if the peak is piggy backed, but I suspect it is. Ed could climb up there and check it out.<G>
Ed's second photo shows a dropped bottom chord truss (might be called something else in other areas) sort of like what you would expect to see in a standard parallel chord top hung floor truss. Trusses do not have to sit on the top plate although the majority do. There will be a bearing block buried under that large gang plate.
Looking at the top chord where it spans the distance between the knee wall and the horizontal member that will be the ceiling of the room you can see the chord is at least a 2x6. Extra strapping for insulation depth will probably not be needed.
The clear span of the bonus rom floor is a deeper 2x10 to minimize the flex or bounce of the span. Truss engineering determined that the bottom chord of the web arrangement on either end did not need to have the full depth continued.
Saves a little money on materials but also provides an additional solid bearing point for the diagonal web peice rather than relying strictly on the plate connection.
I am imagining that a reason for the droped bottom would or could be to let the facia and overhang line up with the rest of the house, yet get the head height desired in the upper floor, all things being relative.
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If that was the case, why not just cut garage studs down like amount and put trusses on wall. Entry door header on top of wall,too.
I didn't do it....the buck does NOT stop here.
Lotsa questions/comments to address. I'll try to do it all in one post instead of replying to everyone.
Ed Hilton:"I was surprised at how much open space there is to this one. Looks like the very top triangle might be a separate piece."
They're typically calle "attic" trusses. And they're relatively common. The top piece is a "cap truss". As Tony pointed out, there are limits on how tall trusses can be fabricated and shipped. Generally this is around 13' 6", but varies from place to place.
Piffin:"I wonder about the energy package. The top chords are too slim for much insulation at the sloped walls."
That's definitely a concern. Most people around here put 3 1/2" batts in that area and leave room for airflow above it. Although I've seen some folks who will build that area up to be thicker so they can get more insulation in.
The sloping area in attic trusses is often 2' or less. But it's obviously much more in this case.
Framer:"I'm wondering why the front wall is higher then the side walls."
I wondered that too. Seems like it would be easier and less expensive to build the walls shorter and set the trusses on top of them. (As FramerT pointed out) Could be personal preference on the part of the GC or framer. Or there might be another reason we don't know about.
Framer:"As far as the front wall I wonder why it's higher and not just make it the same height as the side walls and use a gable end truss."
Probably personal preference. If you use a gable end truss, you have to build the flat studs out to 3.5" wide to accomodate typical insulation. But some guys like to do it that way. Others just was an attic truss set out there, and they frame a typical wall in the "room" area. (That's my preference) There are several ways to do it.
Tony:"... they can only loosely be described as trusses, because of the way that they resolve the forces"
It's still a truss, IMHO. But the analysis is different. I was taught to call it an "indeterminate structure", since not everything is triangulated.
The way these work is complicated. I can go into what I know of the theory if anyone is interested.
Piffin and blue_eyed_devil:"The question of trusslift..."
I doubt truss uplift would be much of a concern. Attic trusses are almost always high pitches. And truss uplift tends to be amplified in LOWER pitched trusses.
Also - Attic trusses are used over garages roughly 90% of the time that I see them. So it obviously wouldn't be a concern in most cases.
BHACKFORD:"A floor hanging from above doesn't seem right to me. The advantage of truss in this situation is?"
Attic trusses can clear span large distances. I've done attic trusses up to 50' clear span.
Another advantage is speed. Once the trusses are set, your 2nd floor walls, ceiling, and roof are all framed.
There are 2 major downsides to attic trusses. First is cost. They're expensive, and that scares many people off. Second is quality control. It's hard to get the plant guys to understand that these have to be straighter and more consistent than regular trusses. The attic trusses I have installed needed a bit of tweaking.
JerryHill:"Seems like the bottom cord/floor joist should be attacached to the sidewalls w/ a ledger board & hangers?"
I think that would be a really bad idea. For starters it would take a lot of labor. And there's a lot of weight up there, so it would take a heck of a lot of fasteners to hold the ledger up. Then you'd have to pay someone to install all those hangers.
The way it's framed, all you have to do is set them in place.
Ralph Wicklund:"Looking at the top chord where it spans the distance between the knee wall and the horizontal member that will be the ceiling of the room you can see the chord is at least a 2x6"
Attic trusses are virtually ALWAYS a 2X6 top chord minimum. In the case of the truss shown in the picture, I would have more than likely gone with a 2X8. When the sloped top chord is longer, it has more stress on it.
Ralph Wicklund:"Truss engineering determined that the bottom chord of the web arrangement on either end did not need to have the full depth continued."
That's a point that's argued a lot. I like to continue the bottom chord through to make it as stiff as possible. But not all truss companies/engineers feel that way.
I actually don't like the design of these trusses much. I would have done them differently.
A penny saved is a Congressional oversight.
Boss, You're right about the importance of attic trusses being consistent. I had the pleasure of straightening out a set of them for another local contractor. It was his own project. The main attic trusses were way out of wack. The jig must have been setup wrong. Anyway, as he set the trusses, he didn't pick them consistently off the pile. Rotating some but not all. This caused the misalignment to be amplified. I usually try to keep the manufacturing tags facing the same direction. The same way the trusses come off the jig.(yeah, I spent some time assembling truses, way back when). The result required alot of shimming just to be able to sheath the roof. The piggy backs had a 2" sway at the peak over 50'. We cut them off, and reset straight, then shimmed the roof plane flat. The interior ceiling and walls were left at the time. These would require significant amounts of shimming as well. The truss company actually refunded a fair amount to the owner, because of this. At least they made good after the fact. No wonder some of us like to stick frame :)
I looked into attic trusses for the new shop I'm building, but the cost, and useable space scared me away. Went with an I joist floor, fully decked, and stick frame roof. Brudoggie
"The main attic trusses were way out of wack. The jig must have been setup wrong. "
Not sure what you mean by "out of wack". What's a wack, anyway ???
(-:
The chords should all be strung when the truss is set up. But sometimes that doesn't get done. It's hard to convince the shop guys to make sure they're all consistent.
"...as he set the trusses, he didn't pick them consistently off the pile. Rotating some but not all. ...I usually try to keep the manufacturing tags facing the same direction."
This is something that I think is important, but not every truss company does. The last couple of places I've worked for spray paint one end of the trusses.
The reason for this is fairly simple, but not obvious. If the shop guys jig the truss with the peak 1/2" off center, it probably isn't a big deal as long as all the trusses get set the same direction. But if one gets flipped around, then the peak is a full inch off from truss to truss.
Also, if the trusses get jigged with a slight crown or dip in one side, the trusses all match better if they're set the same direction.
"The truss company actually refunded a fair amount to the owner..."
What I prefer in situations like this is that the guys who built the trusses be sent out and fix them. I think that would teach them a great deal about customer service, and the need for getting the trusses built right. But unfortunately, the owners rarely see any value in this.
I've seen drawings of I-joist floors and stick built roofs for 2nd floors. But they always looked like too much work to me. And I think the I-joists are often undersized. But I'd still be curious to hear how it worked out. I've never seen one that was actually done.
If at first you don't succeed, destroy all the evidence.
Boss, It's a 28'x40' building. I put a 40' triple 18" microlam beam through at 12' off one side. You can offset the beams usually up to 4' from center. There is one post in the center of the beam. We looked at clear spanning with taller joist, and it was possible, The problem was the deflection was more than I could live with. Then there are 12' and 16' 11 7/8" I joists side loaded on the two spans. Fairly simple floor. Design spec was 65 psf. This upper floor space is for light storage, a room for the kids to hang out in, and an office for me. I decked out the whole floor with 3/4 T&G plywood. Then set a plate, and stick framed a 10/12 pitch gable roof on top. I've got 22' 2x10's for rafters. Will post some pics, when I have more time. Brudoggie