strenthening floor joists to finish off attic

[millworker301]

I have a cape cod style house. The attic is unfinished. To save money, I guess the builder used 2x6's for ceiling joists. I know this is not going to be strong enough to use at the floor joists when I add 2 bedrooms and a bath upstairs where the attic now is. How should I strengthen up the joists? Could I just put another 2x6 between the existing ones, which would make them 8 inches on center instead of 16. Or do I have to do something like nail a new 2x8 to the existing 2x6's? Any help is greatly appreciated. Ken

[Rich]

If you currently have a floor with 2x6 (I'll assume #2 or btr fir) @ 16" o.c. you can span approximately 8'11". If you drop that to 12" o.c. you can span 9'9. (These values are straight out of design tables which typically don't go less than 12"). So to be on the safe side at 8" o.c. I would say 10' allowable span would be maximum.
A 2x8 @ 16" o.c. will span approximately 11'. These values are with drywall below and not plaster. So if your span is within the allowable spans you should be ok. If not you're probably going to have to "sister" along side the 2x6 with a 2x8 or even a 2x10.
I'm not an engineer so take these values for what they are - allowable spans out of a published table.

[blhu]

much the samre question , I have a new construction home , with large attic that at this point is just wasted space , a full size door leads to the attic from the bonus room so access is not a concern, room is shaped like an "L" floor joist are #2 2x6 16"oc 11'8" span. Current plan is to sister 2x12 #2 , Il ripthe boards down to 2x10 3/4 so i can raise the floor level with the floor of the great room . the "nook" will be where the bathroom is , floor there is currently 2 x6 16oc with a span of 5' 8".. ill do the same to them as far as sistering etc. , bathroom will be a full bath with a tub/shower unit , ill be nailing and screwing the joist together and blocking once done, ---- any thing I might be missing ?

[Don_P]

Just at first glance... you cannot rip down structural lumber and maintain grade. A 2x12 is allowed larger knots than say a 2x10 and each has a set of rules about how close to an edge each size range knot can be. By ripping down a larger board you are probably putting too large a knot too close to an edge... darn the bad luck.

[Richard A Hetzel]

Another comment worth making: the allowable spans depend greatly on the species and grade of lumber used. No one can, nor should, state that a 2x6 can span anything, without knowing the species and grade of the lumber.

[rwanders]

If you buy your lumber from one of the big boxes (HD , Lowes, etc) you should be very careful---they often do not use standard terminology or markings and the store personnel often do not know what they are selling. (see remarks from R.Hetzel above!)

[Don_P]

Drifting off topic but actually the markings are standardized by the American Lumber Standards Comittee and are codified as the NGR, the National Grade Rule, I have trained as a lumber grader. The big boxes have indeed "enhanced" some of the grades for the buying public. "Prime" is one example, a #2 and a #2 prime joist of the same species have the same allowable design values, one is prettier for the consumer market.

The Lowes here does interchangeably stock european species in the SPF bins. The eurotrash is about 20% weaker. The stamps on the lumber do indicate correctly what the wood is though. Neither the employees nor the inspectors know how to read a gradestamp unfortunately. I've actually recieved bootleg stamped lumber from one of our local small suppliers and unstamped lumber from another... their way of trying to keep up with the competition from the big boxes. The bootleg stuff was some of the better lumber I've seen in awhile.

Back to the topic, a #2 SPF 2x8 joist at 16" on center with a 40 psf live load is allowed to span 12-3". do better than that and you're ducky.

[talkradiobuilder]

Why not crunch the numbers on TJI. Use web stiffening on the sister side, check the ceiling for sag, and re-nail the joists. Also glue it with PL-400. One question is; what is the cut for the roof pitch at the top plate, and can you get the material to set?
And another question is; How much fall for waste are you gonna need from the closet ring. Ie. joist height.

[Richard A Hetzel]

Huh???????

[blhu]

thanks.. sounds like Im on the right rack .. should be more them enough to span the needed distance , my only real concern is ripping the 1/2 " off the 2x12, to level off the
floor with the exsisting door way ..

[pjcampo]

How can I figure out what kind of wood I have? our house is 1950 maybe 1952 vintage. It is a cape in NJ. The attic has 2x6's on 16". We have a walk up attic that we'd like to convert to a BR.

I really cannot tell the span right now, due to a full wood floor.

[Don_P]

Easy way? See if you can find a grade stamp and let us know what it says. That may well be impossible. Although grading started to be standardized in the 20's it was finally really nationalized by congress in the early 50's. In vintage work it often takes judgement. getting the right type and size joist is only a small part of the battle. They need to rest on adequate load bearing walls that are supported all the way to the ground and then to adequate footings in the ground. When in doubt, its time for an engineer, they can often save you wasted money or more importantly save lives.

[Richard A Hetzel]

If you have unfinished ceilings in your basement, look for a grade stamp there. It's a safe assumption that the same grade of lumber was used thoughout your house. In New Jersey in the 1950's, the most common lumber used by far was #2 Douglas Fir. The grade stamp will likely be a black marking with a bunch of letters, numbers and symbols. It is usually found near the ends of the lumber on one side. If you can't decipher it, try to describe it here, and many of the people here will be able to interpret it for you.

You can determine the spans from the plan of the main floor of the house. Undoubtedly, it has a center bearing wall running from side to side. The ceiling joist span is the same as the room dimensions between the outside walls and the center bearing wall.

[blhu]

My last home started out in the 1880,s as a smaller barn, then in the 1920's-30's was
"converted" to a house , the re-modeled in '56 , and again in the 70's before I guted the place in 2002 -2005 , the wood was hand cut beams, with axe cuts visible ( still had bark in some places) and hard as steel , the only markings on the wood were from the newer stuff , all the older was either hand cut or true 2x4 . 2x6 . may have had some markings at one time .. but they had since gone away , lumber was not whit but brown.. may have something to do with it as well ..

[Don_P]

And don't misunderstand, old does not mean inferior. Sometimes I think the ink from the stamp is the only thing holding some of this modern stuff up.

[blhu]

lol .. I work in the automotive field .. amazing how similar we think

[Richard A Hetzel]

Sometimes much older houses were framed at least in part with hardwoods, which have dramatically better strength than typical modern framing lumber. I worked on a house once that had a girder spanning a room 20-plus fet wide, and it was something like a 4x6...in modern framing lumber, that would have been on the floor in two pieces. We wondered how it could have held the loads for so many years without failing, until we looked up strength figures for woods such as red oak, and we found our answer. We couldn't see the beam, so we couldn't tell by its grain. Oh, it had deflected a little, but ONLY a little. It's still there, thirty years later, still carrying the load.

Sometimes "they don't build them like they used to" holds true...other times we say "thank goodness." It all depends on the house and who framed it.

[blhu]

Finally started sisitering the attic floor/kitchen ceiling joist to provide additional support , a recap exsisting joist are 2 x6 spanning 11 feet 2 1/2 in
one side of joist sits atop sill as normal, however other side sit against a engineered beam that has a "ledge" fastened to it( see attchment) , the ledge and corrosponding "notch" in the joist measure 1 1/2 x 1 1/2 inches. My plan is to sister a 2x10 to the exsisting joist , putting the sistered joist atop the sill is not the question , attaching the other end to the engineered beam atop the "ledge " is the question , when I sister the 2x 10 tp teh existing joist there is not enough space between to two to slide and fasten a joist hanger , in I use a tie in conjunction with the "ledge" and toe nailing would that be soffcient -- if not any other suggestions?

[Richard A Hetzel]

If you also sit the 2x10 on the ledger, and nail it securely to the 2x6, there should be no problem. Ledgers were the standard way of connecting joists to flush girders before joist hangers were invented.

[blhu]

thanks, that was what I was hoping/figuring / puzzling thing thouGH . my house is a new construction , finished in june 2007,
using the "hurricane" ties wont hurt I suppose

[Don_P]

a ledger is still acceptable in modern construction but it is not as strong as a hanger, by a long shot. Instead of hurricane ties (H5's?) see if you can get some framing angles it puts more metal in the right place.

[blhu]

thanks again .. Id love to be able to "retrofit " the sistered joist with double width hangers , but dont want to remove the ceiling in the downstairs to jack up the exsisting joist , also there is the cost/benefit aspect of it , would the additonal time and $ be worth it in the long run , I might be able to notch the
ledger enough to slide a hanger in between the exsisting joist and ledger , but there again dont want to step over a dollar to pick up a dime

[Don_P]

No don't notch the ledger I think you'd cut the doller and crush the dime. The L series here is what I had in mind http://www.strongtie.com/products/connectors/L-LS-GA.asp
This is all above an beyond so its not a real big deal, they're just more "correct" than a hurricane tie.

[blhu]

thanks again -- great idea! ... and because they are larger would most lekley be easier to work with ..