I got a set of plans over the weekend for a 30×40 barn. The homeowner hired an architect to design the building so that it would fit in with his house and a possible future addition. In general the plan is fine. The layout is sensible, it adopts some features of the existing house without absurdly copying it and holds no structural pitfalls.
I did notice that the plans called for 2×12 lvls for the rafters. We do have to build for a snow load here but this seems a little ridiculous. I am sure that I will be able to talk the owner into using 2×10’s (either solid lumber or tjis) or even 2×8’s with the addition of collar ties but I am wondering why the architect specified these. If I did not have a good relationship with the building inspector in this town, I might not even have the option of changing the framing.
There obviously was no calculation done to determine what was actually needed though there are three steel headers which are properly sized for the load.
Has this type of thing happened to any of you and how did you deal with it? Going back to the architect is not really an option in this case since the owner is not going to pay him any more.
Replies
You could try your lumberyard. Sometimes they have someone who can size beams and rafters. You could try your building department. We've found them to be willing to help when we have questions. Here is a link to an online span calculator. You could size the rafters and then ask the building department. http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
Why the LVLs? and on what centers?
Are there interior posts? What style is the building?
Kinda hard to know if they make sense or not without knowing more details.
If the architect specifies it and the owner is willing to pay for it I have to wonder if it is really worth your time to question it. I know it seems over-kill (2x12 LVLs!), but screw the architect and owner and give them what they want.
Now, if it is a problem of costs, material integration, etc. I can see why you would want to question it.
"but screw the architect and owner and give them what they want."
I don't care about the architect but if I am going to be working for someone, I want to give them my best effort. That includes using my head. In this case I have the full confidence of the owner having built his house which was a lot more complicated than this barn. If the owner would not listen to me, I would do what I was told as long as it wouldn't result in a code violation. The only problem aside from cost here is that I wouldn't be looking forward to jackassing those 24' lvls into place.
I don't understand how you can deviate from the plans using something smaller than what the plans =say and get away with it without the Architect signing off on it. Some things sound crazy but I always call the Architect and when he changes it and signs off on it I frame it that way but around here you can never put in a 2x8 rafter if the plans call for microlams and get a way with it.What happens if you do change it and when the inspector says he wants to see the Architect sign off on your changes not the Architects and then the Architect doesn't, your liable not the homeowner.If this homeowner is not willing to call the Architect and question the lvl's because they don't want to pay, who's going to pay for it if it dosen't pass inspections because of a change that you made?Again around here we can't change the size of a beam to a smaller one wiithout Architect signing off on it, can you?Why can't the homeowner call the Architect, he might have made a mistake and agree that you don't need the lvl's and if he does agree that you can use a 2x8 or something it will probably save hundreds of dollars in material and alot less than what he would charge to make the change. If he did make a mistake he shouldn't charge at all but if he does and agrees to your change I'm sure it will be alot less than the cost of what they would pay for lvl's.Joe Carola
Edited 5/6/2005 7:16 pm ET by Framer
Joe- I wouldn't think about making any change without running it by the building inspector first. I have worked from stamped plans that neither of us was comfortable with because the framing and the connections were inadequate in our opinion. We came up with solutions that satisfied him. In that case we would have had no liability if we had simply followed the engineer's plan but we chose to add a little greater safety factor.
I'll meet with the owner on Sunday and I will let you all know the outcome. I will encourage him to question the architect about this.
ya, if money is his concern, a simple question and minor plan change incorporated via addendun notes could save quite a lot of materials cost on something this large.
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You might consider double plating that loft floor deck edge, then bearing your rafters atop the plates, and using something like the Simpson TBE6, as shown here, as the means of tying the rafters to the floor diaphragm. You'll want a lot of nailing of the bottom plate to the floor, and the top plate well-nailed to the bottom.
View Image
A doubled truss is shown, not a birdsmouthed rafter, but you can get the idea.
24" centers
No interior posts.
Floor trusses for the 30 ft floor span to be designed by the truss company.
The rafters are plain common rafters. There are two hipped dormers (8ft. wide) with doubled rafters on each side.
A while ago I designed a house and sent it to an engineer to size beams, and told him to design to L/480. I had already rough-engineered everything, so I was surprised when the roof system came back significantly beefed up.
Turns out I should have specified that the L/480 deflection was for floor loads only. I assumed he would still design the roof to L/240, as is standard, but you know what they say about assuming things....
On the other hand, at 2' o.c., with a big span and snow load, 12" LVL's doesn't sound like that much overkill. My rafter tables say that 2x12 fir rafters with a 40 psf live load are maxed out at about a 16' span, and I bet your snow load out there is at least 40#.
Mike
Fill in some blanks and us structural engineers will help you out with this, Schelly. If you like.
Is the plan a simple rectangle, 30' width x 40' length?
Ridge running down the 40' length?
Roof pitch?
Overhang?
50 psf ground snow load? We're at 85 here in the high peaks region, but I believe you might be as low as 50 over on the lake. Maybe 70. I'll check the code map.
Structural ridge? If so, posts at what centering? If not, we're gonna get real big with collar ties!
Width of dormers? Setback of dormer face from outside wall, if any?
I just went here, for a quick check http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Plugged in SPF #2, 24 centers, snow 50 psf, light roofing, no ceiling, spancalc showed me a max span for 2x12 at about 14'3". Maybe you do need LVLs.
Is framing the roof on 16" centers an option?
Edited 5/6/2005 4:25 pm ET by Gene Davis
Fill in some blanks and us structural engineers will help you out with this, Schelly. If you like.
Is the plan a simple rectangle, 30' width x 40' length?
Simple rectangle
Ridge running down the 40' length?
Non-structural ridge down the 40'
Roof pitch?
10 in 12
Overhang?
2'
50 psf ground snow load? We're at 85 here in the high peaks region, but I believe you might be as low as 50 over on the lake. Maybe 70. I'll check the code map.
50
Structural ridge? If so, posts at what centering? If not, we're gonna get real big with collar ties!
Rafters go to the floor and are connected with metal connectors to the floor trusses
Width of dormers? Setback of dormer face from outside wall, if any?
8' with no setback.
I just went here, for a quick check http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Plugged in SPF #2, 24 centers, snow 50 psf, light roofing, no ceiling, spancalc showed me a max span for 2x12 at about 14'3". Maybe you do need LVLs.
Is framing the roof on 16" centers an option?
I would prefer to use 16" centers. We only frame roofs on 24" centers if we are using trusses.
Take a look at the attached sketch. I made the presumption that you will birdsmouth these rafters with a 5.5" seat cut and that the rafters will bear on the "floor" of the upper barn.
You said the "floor" was trussed, and if so, it is providing a structural diaphragm and tying the roof structure, so no collar ties are required. You will want to use some good judgement in selecting Simpson or USP connectors where the rafters tie to the floor.
The good news, and it is straight from those span tables I referenced earlier, is that 2x12 sawn lumber will be more than fine as roof rafters, if spaced at 16" centers, which you prefer. I presumed no ceiling finish up in this barn loft.
If it were me, I would use LSL rim board at 16" of depth as a ridge board, as the sketch shows. Non-structural ridge boards are really only providing lateral tying, but I hate to see rafters hanging at their top ends with nothing to bear against for their bottom thirds.
The bad news is that you will have to special-order the rafters, due to their lengths.
Good luck, and let us know how it turns out.
"The bad news is that you will have to special-order the rafters, due to their lengths."Gene,24' 2x12's are special order where your from?We use doug fir and 24' isn't a special order, in fact Wednesday I picked up 10 2x12's 26' on my truck and they were stock in the yard. Maybe from where Shellingm is from they're not special order.Joe Carola
Thanks for the advice. The plans show fasteners as you have detailed and a single plate bolted through the subfloor. They also have a 2x10 and 2x8 stacked over each other at the ridge.
According to their website, Ward's has 167 2x12x24's in stock.
According to their website, Ward's has 167 2x12x24's in stock.
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Consider all the handling you'll do detailing those big sticks. Is it time to invest in the saws you need to gang cut the bunch?
Or do you have all the gear already?
I don't know why there should be a cost in askuing an archy to substantiate his design or clarify something. His live load should be indicated on the plans. Another option for the rafters might be TJIs which are a whole lot lighter to work with at those altitudes.
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We need to resolve the snow load, but at an 85 psf ground load, no unbalanced conditions, it is looking to me as if Trus Joist series 230, at 11-7/8 depth, will work just fine for rafters. I presumed a high slope roof.
I am concerned now with how to tie the walls, because Schelly seems to have said we've no structural ridge, and those big dormers are transferring a lot to the top with their king valleys (if that is what is going on.) Maybe there is some support happening under the dormers.
More info needed.
"Trus Joist series 230, at 11-7/8 depth, will work just fine for rafters. I presumed a high slope roof.....no structural ridge"
The use of I-joists requires a ridge beam.
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You are correct, Boss. I forgot.
Right. I'm not about to try to redesign it wotyhout full knowledge, and something is missing in this picture, just throwing out options to be considered.
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