I’m thinking of adding sisters to my attic floor joists to strengthen them before finishing the space. They are 2×6 with 12′ span. But they’re the old 1920’s solid steel type of 2×6’s, if you know what I mean. I’m trying to preserve as much headroom as possible. Should I:
1. Add 1x stock, glued and screwed
2. Add 2x stock, glued and screwed
3. Add 2×4 to the top, I beam style, but give up headroom.
I want to put a master suite in the attic. Plaster and lathe ceilings.
The LG Inverter Heat Pump Water Heater uses advanced inverter technology to ramp up or down in response to hot water demand, maximizing energy savings.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
#3 won't make an "I" beam. You need a chord top and bottom glued securely to the web to get the benefit of an "I" beam and the bottom chord must take the load on top plate of the wall or on a joist hanger; then the bottom chord would be in tension and the top chord in compression making a very strong joist.
Why not simply drop in 2x6 joists between the existing ones for double the load capacity? You would have to shim them to the same height as the old ones and maybe rip them down a little to clear the plaster that is squeezed up above the ceiling laths.
All of this assumes that the outside walls and foundations can carry the addition dead and live loads of your master suite, but you've probably done the calcs for that already.
i would date the better looking one with more money.
You need 2x8@ 16" oc. You don't say what layout these 2x6s are
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
What Piffin said.
Or.
Glue and screw good 1/2" ply top and bottom. Block all ply edges.
It's called Stressed Skin. Very strong.SamTA Pragmatic Classical Liberal, aka Libertarian.
I'm always right! Except when I'm not.
Thanks everyone.I don't have access to the undersides to make the I beam work. I was just wondering if it was any benefit to add just the one side of it on the top, but it sounds like you really want the one underneath to be in tension to get the most benefit.So, if I'm going to add a sister, it sounds like a 2x6 ripped down a little to clear the plaster squeeze-through might be my best bet. What about 1x? Is that even worth the effort?The house is roughly 24x40, with 12' spans across the rooms. There is a T shaped load bearing wall in the middle of the house. The front room is 12x24, with the joists all spanning the 12'. At that front wall (the top of the T), the joists all turn and run perpendicular to the front room, spanning from the middle load bearing wall to the outside of the house over the various smaller rooms.Thanks all.
Are you planning to get a permit? If so you'll be using 2x8's on 16" centers to make the span.
If it were my house I would sister select structural 2x6 on 12" centers after breaking off the plaster keys that are in the way. Lots of glue and nails are called for. Then use 3/4" subfloor.
Maybe 4x6's on 16" centers...
OB
Edited 9/11/2009 10:52 am ET by klhoush
Edited 9/11/2009 10:54 am ET by klhoush
Do the codes have absolute dimension requirements (must be 2x8's, no ifs ands ors about it), or do they allow for the same strength to be obtained in other ways? I had an engineer tell me I could achieve the added strength without losing headroom by going the sister method. Makes sense to me. It's been several years ago that I talked to him, though.
The I-codes DO have set requirements for prescriptive building. That is to say, if you want to build it without an engineered designed, you follow the span tables per the applicable code.
If you use a licensed structural engineer to do the design, and he/she provides stamped documents to the building official, a design other than the code tables may be accepted.
mj
There are other ways to acheive the required live load rating.But you still have not answered what the layout is. How much distance is there between each of your existing joists.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Sorry - they are 16" on center.
Not necessarily. I did an addition about 4 years ago that the architect spec'd double 2x6's to span 14 feet. It had to be 2x6 to match up to the existing floor that it met. No problems passing inspection. But thats only because i had a seal on it I assume.
Edited 9/11/2009 3:46 pm ET by rnsykes
I had an archy spec sistered 2x6s for a10'6" span once too that came out rock solid, but I thnk it was 14" OC IIRC
Too bad this OP can't say what his layout is.Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Edited 9/11/2009 5:29 pm ET by Piffin
Yeah, I'm sure if you run the calcs it works.
Those existing joists might be sagging and would be a liability in the system!
OB
You might run this past your engineer:
Sister a steel stud to each side of the wood joists with lots of screws. 2 screws 12" OC.
You'll get the added bending resistance of darn near 1/8" x 4" of steel plus the increased flex resistance of the flanges.
Using steel makes it a lot easier to block. So easy you can block 4' OC.SamTA Pragmatic Classical Liberal, aka Libertarian.
I'm always right! Except when I'm not.
I think that the idea of steel is good, but do you really mean "stud" or do you mean "joist". A steel stud is not designed to carry that type of loading. At least that is my understanding.
I think he was talking about a modified "fletch" beam. That is another option the op could take. Still neads an engineer's stamp, though.
In all due respect, that's not what he said and a metal stud is a long way from a flinch plate. Yes, it would probably be a good idea to talk to an engineer if the planning to go that route.
Yes, That's what I had in mind.
No. That use of metal is as an inside out Flitch plate.
I suggested stud material 'cuz you probably won't find a steel joist that would work as Flitches. Also, studs are very resistant to sideways force, which is where the "softness" of the existing floor is coming from. He only has to increase the existing material to equal 1.2" x 7.5" wood joists.
5&5/8" steel studs would be better than 4by types since he has 2" x 6" 2x6's.SamTA Pragmatic Classical Liberal, aka Libertarian.
I'm always right! Except when I'm not.
"Flitch plate"Thank the good Lord in Attic above!
Somebody used the right term!;)Though I did kinda like Fletch plate. The extended flanges suggestive of fletching arrows for flying this floor over the ceiling below! LOLThe steel as you suggest does sound good - I'm not much of a steel guy so I can't really say, but it's an option to run some figures on foir sure.How you doing lately?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I am aware of what he said and I think there was miscommunication.
You had as one of your options adding a 2 X 4 to the top of the existing 2 X 6 as an I-beam type installation and noted that you would lose ceiling height by doing that. That is obviously not an option.Why not just sister a 2 x 8 beside the existing (assuming 16" centers). You will only lose another 1/2" when compared to your solution and no engineering necessary.
That's true, and a good point. I've been trying to cling to every inch of space, which is why I've been resistant to increasing the height of the joists. The space is 24' wide, with a 10/12 (I think) pitch. I have 8'2" at the peak. So, an inch here, and inch there, flooring, drywall, etc., and pretty soon I'm gettin' pretty crowded. :)
I understand your concern with headroom...
You said your attic about 24' wide and 8'-2" at the peak, thats about 8/12, not 10/12
Thats not much room, only about a 6' wide path in the center of the room that the cieling is at least 6' (I think ?? the minimum allowable headroom is actually 7')
Also how will you insulate the attic ceiling? I doubt the current rafters are deep enough for ample insulation, you might need to fur them down, reducing headroom further
In other words - he is trying to fit three pounds of flour into a two pound sack
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
it sounds as if you wont be inviting a building official to this party. at the very least I would rip 11 7/8" lvl's down the middle and sister with those. nail with a very liberal nailing schedule and glue
you dont say what the layout is but you could either sister both sides of every joist or layout the lvl's on 8"centers
If the existing 2x6 is a REAL 6 inches high then sistering current 2x8 won't add much more height.
But if the extra height loss from a current 2x8 is important, you could rip a 2x8 to the same exact height as what you have. This way the new joist sits on the wall plates (remove the plaster chinks to accomodate.
Whatever you do, as previously stated, pay for a stamped engineer or archy drawing for proper specs.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
You still haven't answered the question. Are you getting permits?
Do you plan on putting an egress window in?
http://betterheader.com/default.asp
betterheader is a good product ... using it now ...
Don't knock off any more plaster keys than you absolutely have to.
I'd sister with 2x6s, and shim them up at the bearing plates with scraps of 1/2" OSB.
That should clear most of the keys, and also allow you to start from scratch as far as flattening the floor.
AitchKay
I'm still wondering if these existing are 12", 16", 19", 24", or 30" on center for layout!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Well, ya gotta be careful about giving too much info to a complete stranger!AitchKay
"I'm still wondering if these existing are 12", 16", 19", 24", or 30" on center for layout!"You may not have a high enough security clearance for that information.:)BruceT
OK, guys, I'll quit obsessing on it now and go get some sleep.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Okay, easy guys, nothing sinister going on here. :) I just wasn't doing computer stuff this weekend. Thanks for all replies.The joists are 16" on center.I'm just trying to figure out enough about this project to see if it's doable, or worth doing. I'm not really far enough downstream to have already thought out what I am planning to do about permits.Here is the back story, if you're interested. The house is small, and we've always wished we had a larger bedroom and a second bathroom. Our attic feels huge when we walk in, and we've always considered it a great possibility for a remodel. I know that finishing the space will make it feel smaller, but we did go up there and staple up tarps where knee walls might be to get a sense of it. The roof has front and side gables, forming a T shape, with a small upstairs finished room. Because of the T shaped roof, there is a large box in the middle of the attic. With the tarps in, we have an open space there roughly 11x24, which to us sounds like a fantastic bedroom size. Add a small dormer for a bathroom and you've got yourself a master suite. Now, that's all assuming that we can find ways to preserve the space. If we have to beef up the joists for strength and rafters for insulation, then add flooring and drywall, it won't take long to lose the headroom and feel cramped. A couple of years ago we worked with an architect and builder to do some drawings and pre-planning. We paid them along the way for their time - everyone involved knew we were just feeling it out, and they were getting paid to help us. The project estimate quickly turned into $100,000, with a total removal of most of the top of the house. It escalated too fast for us and we got cold feet and stopped. Of course then the economy tanked and we were never so glad to not be the proud owners of a $100,000 line of credit. I've decided since then to start doing some of the smaller pieces of the project a little at a time. These are things that we needed to do anyway but added to the overall cost. (i.e. removing k&t wiring, updating our hvac, finishing new window installation, etc).So, now I'm thinking about insulation and the joists. I want more insulation in the attic, but don't want to just blow in cellulose and make the space unusable. I considering spray foam in the 2x4 rafter bays, directly on the underside of the roof deck. However, due to the high cost of that, I may have to wait a while. I may do something like roll out cotton bats over the current rock wool as a stop gap.So long story short - if I can reasonably beef up the joists so I don't have to worry about cracked ceilings, and if I can spray insulation on the roof for and R17 or so, then I'd preserve most of our headroom. We'd have an 11x24 bedroom, with a 6 foot or so wide hallway. If we added dormers to both sides we could have a nice closet and bathroom. In our little house, that sounds like a ton of room.chris
Edited 9/14/2009 9:55 am ET by ccampbell
Hi Chris,
I like creative thinking......gets dangerous sometimes but I still like it.
Personally I'd go 2x8 12" OC and stagger well enough to avoid contact with the existing 2x6's.....stand the ends on 1/2" or so blocks to clear the plaster squeeze. Block the sides of the ends top and bottom and block the middle with cutouts over the original joists making certain that there it "no" contact surface. This avoids any pressure that can push on the original joist causing plaster or squeek problems (glue and screw the blocking as well while you're at it). This should be a straight forward equal to or better than code.
Glue and screw 3/4 t&g plywood to the new joists out past the future knee walls....you'll want that for storage. Be sure to leave access chases for future wiring and plumbing etc.
Permit all of this and welcome your inspector telling him how solid you want your floor to be. That's the end of that stage.....save some more $ for the next phase.
Next would continue making certain you have proper chases and such for wiring and would start where the floor meets the roof and install 2" foam panels.....first section to begin with. With only one section in, you can now use DIY closed cell foam to reach inside the cavity and begin carefully layering the foam up the joist cavities. I say carefully because you want a full complete seal of the expanding foam but don't want it to aggressively push on your foam panels. This technique will garner you around R30+.
Continue to add panels and fill all the way to your rafter ties, work your way up and around them and continue to the peak with spray foam....no need for panels beyond that point just layer thicker spray at that point. Now the foam and panels is a lot more $ than fiberglass or other materials but you will preserve headroom and the quality of materials will pay for themselves over the long haul.
You will also lose a couple of inches of head room around the perimeter but not off the center height....I don't think you'll suffer too much there.
Next build the knee walls.....remember you don't even actually need them for anything more than storage space....so the actual height of them/how far back you place them is more to your tastes than anything.
Once that's done permit all of your electrical and plumbing......take lots of pictures and save all of your insulation info in case it raises an eyebrow when they come to look at the wiring and plumbing......be ready to resolve that.
Around here all that would go through just fine as you are permitting the parts that are critical and it's not like you're building a whole house. But you're area could still harass you about it.....you've got some choices to make......insurance most likely won't cover anything not permitted and you can't ever sell the house without the work being permitted unless you're actually simply dressing up an attic that was already finished when you bought the house.........
With you doing all the labor and a quality but careful budget, I predict you can completely finish the suite for $12000....with hard work and careful shopping it is quite possible.
Engineers and Inspectors are there to make sure you don't wake up in the basement....it's your call now get to it!
View Image