cutting ceiling joists for attic stairs
I’m preparing to install pull-down stairs in my garage to utilize the attic space above for storage. I’ve read through the achives and find much advice about not cutting trusses, but I get the impression that cutting ceiling joists is ok if you do it right. I want to make sure I do it right.
The ceiling in my garage has 2X8 joists 16″ on centers. The garage space is 22’X22′, but there is a 14″-deep steel beam spanning the middle of the garage perpendicular to the joists, so the effective unsupported span of any of the joists is about 12′. I should be able to cut just one joist if I install the stairs parallel with the joists, but I may need to configure them perpendicular for clearance reasons, which would necessitate cutting 2 or 3 joists.
What guidelines do I need to keep in mind if I just cut 1 joist? I assume I should frame the openning with doubled-up 2X8 headers. Do I need to double up any of the joists? Do I need to worry about the placement (close to a wall or perpendicular support member vs. in the middle of the span)? What about cutting multiple joists? At what point am I doing structural damage?
I suspect this is a rookie question, but I get a bit leary when it comes to modifying structural members.
Thanks in advance!
Rob
Replies
I would use double headers but only a single stringer. It may also be wise to install strongbacks on both sides of the proposed rough opening before you start chopping out material. They can be removed once the opening is framed.
As far as doing structural damage, I am not an engineer, so I can't help you there. But I do know that some installation instructions will tell you to consult an engineer if there is bracing running from the rafters to the ceiling joists.
in vino veritas
Excuse my ignorance, but when you say "stringer" your referring to the framing member that runs parallel to the adjoining joist, right?
Second question - flooring material. I'm going to use the space for storing garage and other seasonal stuff. Is 1/2 or 5/8 plywood enough, or do I need to use 3/4?
Rob
When I say stringer that is exactly what I mean. Basically the new member spanning the headers.
I used 5/8 plywood in my own house. I thought it a nice balance between stiffness and added weight to the ceiling joists. in vino veritas
Thanks!
When I say stringer that is exactly what I mean.
Bad answer. Obviously he does not understand the word. Pretend you're trying to explain to your mother.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Ryan, Wrong answer.
Hear is why - When you cut the jooist that you refer to as a striner, to header the hole, you have transfered the weight that it used to carry onto the adjoining joists via that header. Those joists on either side of the hole are now carying more load than they were intended in the origianal design. So they need to be stiffened up. That is generally done by doubling them. Some designs would require that they be tripled but that is clearly not so here. Sometimes the header can be left as a single, as when the hole is only a couple feet from the supporting wall at end, but to be safe, it is usually doubled too. A stringer is a fairly generic term and can be applied to other structural members so you would do better to define in answer than to jump on the guy for asking. It might be clear as a bell to you, but clearly not so to him. A little patience is good when trying to communicate things, something I need to remember occasionally.
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Attached is a quick sketch of the correct way to frame it. It will work if you want to cut 1 or 2 joists.
>> Is 1/2 or 5/8 plywood enough, or do I need to use 3/4? << Assuming you mean OSB, 1/2" (actually 7/16) would work but would feel kind of 'mushy' under foot, and you would have to make sure you didn't 'piece it in'. 5/8 would be much better, and T&G would be better still although you may have trouble finding 5/8 T&G.
Edited 12/2/2005 6:12 am ET by Matt
Thanks for the picture, Matt - that helps a bunch.
Why OSB and not plywood? Just a cost issue, or is OSB better for other reasons?
Generally, OSB (Oriented Strand Board) will save you money. The lumber market has been so crazy lately though you need to check. Even on $500K - $1mil houses we don't use plywood for floor sheathing - we use something called Advantec OSB which I feel is a superior product to plywood because the Advantec is flatter and more water resistant. Regular OSB is fine for your application though as the Advantec is more $.
General rule of thumb..... double up the framing all the way around. That means the two headers and the two joists forming the frame. Add hangers all the way around it.
FWIW, I do not recommend 1/2" OSB even just for storage. It's not hard at all to put your foot through that stuff and you don't want that to happen while you're hunched over carrying a heavy box of Christmas decorations across your attic. I'd go with 5/8" at a minimum.
So uhhh? You got lead and concrete decorations huh? (G) Spheramid Enterprises Architectural Woodworks
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I consider kegs of nails "decorations".
Thanks, guys!
Rob
can you post that picture again.
Can you please post that picture again. I am doing the same thing to my home and I need something to reference it, and making sure it will be done correctly.
You're responding to a thread that is 6 years old. Those people don't even post here anymore.