Attic stairs in house with roof trusses

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  #1  
Old 07-06-09, 04:37 PM
J
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Attic stairs in house with roof trusses

Hello all,

I have a 1965 house with roof trusses (must have been re-done at some point in the recent past). I currently have a set of fold down attic stairs in the garage but I'd like to add another set to the other side of the house in a hallway. I'm assuming that one of the ceiling joists (which is part of the roof truss) will be smack dab in the center of the opening I need to make for the stairs. I'm usually just that lucky.

I've heard that cutting into roof trusses is a big no-no and requires a professional. I have an engineering degree so I have a pretty good understanding of what I'm doing, though I suspect most of what I know won't apply here (much the same way that what an electrical engineer knows won't apply to AC wiring in a home). I'm guessing there is a special, industry-accepted way to do this, but I just don't know what it is. Can anyone offer some sage advice?

Thanks a million!

- Joe

EDIT: The roof trusses in question are king-post roof trusses
 
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Old 07-06-09, 04:55 PM
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Joe, most likely the trusses are running across your hallway, and, therefore, would be supported on both sides by the walls themselves. That in itself would allow you to remove the lower chord on one of the trusses, replace it with bridging the size of the opening required by your stair choice. It is very important that complete bridging takes place on all sides of the opening, and is tied to the joisting and any of the kings that come into that area. You'd just have to look to see if that is the case in your situation. Let us know after you crawl up in the hot attic and see what 's there.
 
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Old 07-06-09, 05:05 PM
J
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Hi Chandler,

Thanks for the quick reply! I do remember from the last time I was up there that the roof trusses run the length of the hallway (parallel to the hallway). I don't believe any walls in my home are load bearing as there aren't any walls that run the full length of the house (or interrupted with headers) that are perpendicular to the trusses. It is a single-story concrete block house if that matters.

The hallway isn't too long though, maybe 13 or 14 ft. Lowes.com mentioned a "Hog Frame". Would that be appropriate in this case?

Thanks,

- Joe
 
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Old 07-06-09, 10:13 PM
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I wouldn't cut any trusses, especially the bottom chord (under tension) holding the outside walls from spreading and the truss together. Without the continuous bottom chord you will have two 1/2 trusses, though they wouldn't be trusses, just triangles. Trusses span out to out, not out to an inside wall, unless engineered that way.

Please read this before you cut: Safe building: a treatise giving ... - Google Books

You need a Structural Engineer to accept liability for this, not you for any time after you sell the house. Your Home-owner's Insurance would not cover this, especially in FL.

Look on the bottom chords for the manufacturer's name, it's probably local. Though their records may not go back that far for the spec's, they were original to the building.

The new attic stairways fit between the chords as do some of the old ones.

Be safe, G
 
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Old 07-07-09, 04:43 AM
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Running the length of the hallway, I agree with G on not cutting them. Too much tension will be released. BUT, you may have the best of two worlds. If they are on 24" centers, you can install a comparable set of stairs between the truss chords and not have to cut any of them, depending on whether or not their centering over the hallway will accommodate it.
 
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Old 07-07-09, 06:42 AM
J
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Hi Guys,

Thanks for the advice. I didn't know they used roof trusses back in the '60s. The trusses look very new (and they have hurricane tie-down straps) and the roof was re-done in '97 so I just assumed they had to update the entire thing then.

I guess it is time to get up in the attic and see where the trusses fall in the hallway. What's the best way to do this? I have about 1 foot of blown in insulation in the attic making accessing the area very difficult (even before the insulation was blown in it was difficult to access). I could drill a very small hole on either end of the hallway ceiling and stick two long pieces of copper wire up there. Any better ideas?

Thanks,

- Joe
 
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Old 07-09-09, 03:36 PM
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Sounds like a good plan. Insulate the stairs when you're done: Energy Savers: Attic Access Insulation and Air Sealing Be safe, G
 
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