I’m in the planning stages to build a new house. I’m seriously considering using attic trusses to gain two bedrooms (12′ by 15′) and a bathroom on the second floor, however I have a few concerns.
1. Will i experience sheetrock cracks/ screw pops on the main level ceiling from people walking around upstairs (sometimes, little kids jumping around). Deflection was beefed up to L/535 but I’m still concerned. Anything I can do to perform preventative measures?
2. The trusses have a 15′ wide room with 8’1″ ceiling height – 3 ft wide, then 4’6″ knee walls. Will I feel cramped for what I’m trying to accomplish?
3. Would it be wise to create a conditioned space for a HRV unit somewhere in the attic?
4. Finally, i’m planning on not finishing that area until a few years down the road, any pros or cons to that idea. I’d haul the sheetrock and tub up there now, just finish later.
Thanks for any insight.
upnorthframer
Replies
I have the same type truss on my house in Pennsylvania with similar room dimensions. The knee wall seems OK - basically if you're standing an arms length away from the way you have adequate head room in mine. Top chord is about a 9/12 on mine.
We're using the attic just for storage at the present time and have experienced no cracking. I can't say I have kids jumping around though.
A conditioned space for Mechanical equipment would be wise as would hauling the tub up there now. You could probably have the sheetrock boomed in at a later date through a window.
"Will i experience sheetrock cracks/ screw pops on the main level ceiling from people walking around upstairs"
If the attic trusses are designed properly, that shouldn't be a problem.
"Deflection was beefed up to L/535 but I'm still concerned. Anything I can do to perform preventative measures?"
Where did that deflection number come from?
"The trusses have a 15' wide room with 8'1" ceiling height - 3 ft wide, then 4'6" knee walls. Will I feel cramped for what I'm trying to accomplish?"
Sounds like a pretty lousy room to me. I don't like really short kneewalls. To me, that room would only be good for storage.
If the flat ceiling is only 3' long it sounds like you just don't have much height to work with.
There are several ways to get more height. Increasing the pitch is an obvious one. Raising heel heights will also work.
In some cases, I've seen attic truss rooms made taller by dropping garage wall heights while keeping the roof plane the same height. Since I haven't seen your plans, I obviously have no idea if that will work in your case or not.
Addind dormers is another way to gain space with attic trusses. The trusses can be doubled or tripled up around a dormer to give you more light and useable space.
If you already have an attic truss design, any chance we could get a picture of it?
If not, how about the span and pitch you're working with?
Span is 34' with an 8/12 pitch. I took the L/535 deflection from the spec sheet from the manufacturer. I thought about going 10/12, however, I trying to make this design as builder friendly as possible. a 20' shed dormer out the back is certainly an option, however, It needs to be a minimum of 4/12 pitch, since i live in snow country.
A 20' dormer with attic trusses isn't an option. You're limited to more like 10' or so, depending on your loading and such.Got any way to scan and post the sheet you got from the manufacturer?
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That deflection must be a misprint or some conversion of metric...
At what live load design is it calculated? That may tell you more about the first Q.
Using strapping under them is the way we in New England avaoid a lot of the problems you anticipate. It reduces some of the vibration and nail pops, adds a bit to the overall strength, and isolates solids for noise reduction.
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After the L/535 it says
L = .71"
D= .32"
T = 1.03"
I'm guessing thats the chords?
Haven't found a way to post the spec sheet. I contacted the man. to see if he could email me. If he does, I'll post it asap. Thanks
upnorthframer
"That deflection must be a misprint or some conversion of metric..."
That's one of the reason I want to look at the drawing.
Attic truss deflections can be confusing, and what's printed on the drawing may not tell the whole story.
For instance - The max deflection may be figured at a web joint - NOT in the middle of the room. (That's what truss design programs typically display) The deflection at the center of the room may be much higher than what's shown on the drawing.
That's why I asked for a copy of the drawing, to see what I could figure out.
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LOL -
"Rember - I wasn't hired for my looks."I know, we keep you around becuse you are such a good danceer. That comes in handy for testing deflection and vibrations!BTW, that shape of room is fairly common around here. Not saying I like it best, but it isn't too bad once you get used to it
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Here is a picture of an attic truss job I recently finished, the rough dimensions are close to the ones you posted. It has two small dormers, one to left and one to the right.
View Image
Sorry about the crappy picture, I had one at the framing stage and can't find it.
View Image
I built the attic truss section on the ground, girder and floor joists w/hangers. THe space in between those are where the dormers got framed.
Were the end trusses of that unit meant to be 2 ply or 3ply ?
I have done several and all had multiple trusses next to the dormer area.
THey were 3-ply girders, I nailed the other 2 together and craned them up at once.
My truss designer stopped by and seen that I had that built and both hips for the main roof. He laughed and said "now thats the way your supposed to do it. THats got to be easier."
EDIT: Blue eyed devil was the inspiration for preassembly, it couldn't have been easier.
Edited 2/13/2007 6:45 am ET by Stilletto