I’m new here but I’ve been getting the magazine for 15 years. I’m adding a rather large cupola/clock tower to my building. The copola is 8 x 8 square and about 1o’ tall to the top of the hip roof. Probably weighs about 1000 pounds. I want to install the cupola on the front of the building set back two feet or so. I’m concerned about the additional weight on the roof and want to beef it up first. The existing roof is a truss system with 2×6 rafters and 2×4 supports. It’s a manufactured truss with steel plates. The trusses are 24″ OC. The roof is a 5/12 pitch. The building is 30’wide with no interior walls. The rafter run is 24′. I live in uptate New York so snow load is also a concern. Now to the question, how can I beef up the rafters to support the additional weight?? I’ve had a couple of local builders make various suggestions but I would like to do it right. I have access to the attic thru front hay loft type doors. Any suggestions would be appreciated.
Thanks in advance.
Replies
whip.... i'd take all the measurements to a Structural Engr and have him come up with a solution..
not only do you have to support the cupola, you also have to transfer the new loads to the foundation
if this were new construction , it would be relatively easy.... but it's not and it isn't
Another vote for an engineer. There are strength/weight issues that need to be dealt with and an engineer can do that. Randomly adding pieces can be self defeating unless they're added at the right places.
The other guys are right on - An engineer needs to design any modifications.
Holding the cupola *UP* is only half the battle. You also have to hold it in place for wind loads. I've designed roof trusses for several churches with steeples. Often the forces from the wind loads are 2 or 3 times what the gravity forces are.
If the building is relatively new, the truss company who built them would be your best bet. They will likely charge you for getting the engineering. But they'll know exactly what you've got there, and will be able to get the modifications designed quickly.
I wouldn't bother measuring the trusses before going to an engineer. They'll like want to check the structure out for themselves. (I know I would)
> If the building is relatively new, the truss company who built them would be your best bet.
Do they commonly put their name and phone number on the trusses?
-- J.S.
Not that I have seen, when I am done framing a house I climb back up into the attic and staple the truss info up in the bag they came in. I usually staple it around head height so when someone is up there they will easily be able to see it.
The information in the package would help someone down the road possibly with repairs or contacting the truss manufacturer.
Wishful thinking probably, but worth a shot.Can't you hear the violin playing your song.
Interesting idea - I've never heard of anyone doing that. Most framers throw the packet away as soon as they get it. Some will refuse the info packet, thinking that it somehow absolves them of any liabilty if they don't ever see it.
No sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be. [Isaac Asimov]
I don't see how refusing the package limits your liability.
I started doing this when I was crawling up into attics with truss salesmen and measuring heels and bottom chords in 16 inches of blown cellulose insulation.
Thought one day it would be nice to find the information from the people who made the trusses, on an addition project one day.
Like I said wishful thinking. Can't you hear the violin playing your song.
"I don't see how refusing the package limits your liability."
I don't think it does. But there's no reasoning with them...
There are times not to flirt. When you're sick. When you're with children. When you're on the witness stand. [Joyce Jillson]
I agree with you on that one.
My grandpa used to say "stupidity or ignorance is no reason to break the rules."Can't you hear the violin playing your song.
Good idea Stilletto. I'm going to start doing that.
blue
It's a better idea than throwing the stuff away or keeping it.
I hope you start to use it, it will make me feel better about borrowing your hip framing on the ground. :)Can't you hear the violin playing your song.
"Do they commonly put their name and phone number on the trusses?"
Heck, no. We don't want people calling us who want to modify them.
(-:
I just meant that whomever framed the thing might know where they came from. Truss companies generally keep records for a long time, so they might be able to come up with the specific designs. That would save a lot of time in the engineering process.
Q: What's the major difference between wives and husbands who are trying to have children?
A: Wives want to videotape the birth of their child. Husbands want to videotape the conception.
Very interesting, I think worthy of a new thread. I'll go start one in General Discussion.
-- J.S.
Having engineering support will also alleviate you of the design responisbilty if anything were to go wrong after the installation. Looks better in court if you have a pro engineer supporting the deesign with his math than you referring back to us on the BT page. It's sad that we need to think of litgation issues all the time but it's a fact of life.
I agree with everything the others said. In Michigan, modifications to trusses must be done by an engineer--it's required by code, IIRC.
Another vote from the department of redundency. NEVER cut or alter a truss without an engineer. That way if something bad happens its not on you.
if something bad happens its not on you.
In more ways than one!
Personally, instead of paying an engineer $500 I'd invest that in materials.
Supporting a 1000 lb load above a roof is no big deal, just treat it like the roof isn't there and it's any other load. It's a square structure so two LVLs directly below and spanning to the outside walls would each have to hold up only 500 lbs plus any wind loads. It's easy enough to frame (and sheath) shear walls from the LVLs directly to the roof sheathing, which should essentially remove the existing roof trusses from the new load path. Some decent shear wall anchors on either side of the roof intersection would allow the whole works above and below to be solidly bolted together.
The LVLs need to have a stud under each end to transmit the load to the foundation. This isn't rocket science so far.
Now for the wind loads. When sizing the LVLs you'll want to factor in something for the winds common to your area.
For those who say there's no way to figure in the wind forces pushing on the new appendage, I'd simply suggest that what you're building isn't any different from a 14' tall tower that's 8' square. Remember, the existing roof is simply sandwiched in the middle and provides side to side support rather than verticle support. A few 2x6s run diagnally from on top of the LVLs up to the point where the shear walls reaches the roof will take most of those side to side forces. (I'm not considering the additional load capacity given by the 2x6s, but it's not too much of a stretch to argue that it's significant).
Who knows, maybe the engineer, if used to working with trusses, would simply have you sheath the sides of the trusses directly under your addition with 3/4" CDX, or something equally simple along those lines, and it would be done. If you're lucky.
My guess is that some engineers would not want to treat it as a roof load, but rather give it a separate load path as I've sketched out. In the absense of an engineer that's the route I'd take since it's pretty straight forward to figure out and just as easy to explain to a building offical using typical load charts. I'd rather use the $500 for materials.
Cheers
"Who knows, maybe the engineer, if used to working with trusses, would simply have you sheath the sides of the trusses directly under your addition with 3/4" CDX, or something equally simple along those lines, and it would be done. If you're lucky."sounds excellent..make your own luck!
Ooops. I now see that you probably have a pickle in getting those lvls in place. At first I thought there weren't any interior walls or ceiling. Now I get it. A 24" LVL would probably have to come through a hole in the roof to one side or the other. Maybe beefing up the trusses is starting to make more sense if your roof is hard to patch.