New floor joists across old ones
I have an unfinished second story space I am about finish out. Currently the ceiling below the unfinished space is attached to 24″ oc 2 x 6 joists. For a variety of reasons it makes more sense for me to run new 2×8 floor joists 16″ oc perpendicular to the existing 2 x 6’s. I have 14″ of height to work with (before sub floor) to match the existing second story floor level. So, I have the room to hang them slightly above the existing joists – completely independent of the current ceiling. Alternatively, I can lay them directly on the existing 2 x 6’s and build up the subfloor a bit to match the other rooms. Do I gain any stiffness by laying them directly across the existing joists or am I asking for trouble with squeaks or the ceiling below?
Replies
I wouldn't sit them directly on top, regardless of direction.
Any chance of finishing the upstairs completely before removing the ceiling that exists altogether? (Just be sure that if existing ceiling acts to tie exterior walls together, new framing addresses this issue.)
J. D. Reynolds
Home Improvements
gain stiffness? no. Asking for trouble? yes.
What are the dimensions and what is the span you planning on running the 2x8's?
What is the height from the top of the existing 2x6's to the top of the existing 2nd floor joists that the top of the new proposed 2x8's will be flush with?
Is that 14" from the top or bottom of the existing 2x6's?
Joe Carola
Edited 3/7/2006 10:12 pm ET by Framer
Wow - amazed and appreciate all the help - answers to a few questions.
New room size is 11 x 16. The current joists supporting the ceiling below run the long dimension (supported by a couple of load bearing walls that break up the span) They sit on the top plate of the the first story wall. Current plan would be to hang the 2 x 8's perpendicular across the short dimension (11 ft.) between two existing 14" high LVLS on either side. The LVL's also sit on the top plate. So - I have 14 inches from the bottom of the existing 2 x 6 joists to the top of the LVL's. Assuming I hang them flush with the top of the LVL's I would have 5.5 inches of existing 2x 6 joists supporting the ceiling below. A clear air space of 1 1/4 inches, and a completely independent new set of 2 x 8 joists with a 11 foot span above that air space. The top of the new joists would be flush with the LVL's and the rest of the existing second floor joists.
Ignoring the span length of the new joists, what will be supporting the LVLs?...that's not a mistake, it's rustic
JN,
2x8 floor spanning 11'?
JMHO, but, . . . NO.
I'ld think about putting some support shim blocks on top of the bearing walls and running 2x12s in between the ceiling joists.
SamT
Where are these 14" lvl's?I just framed an addition exactly like this but a little bigger. It was 11' x 22'. The ceiling joists were 2x6's also that ran 22' with a mid-span girder.I bolted a 2x8 ledger flush with the top of the existing floor joists. On the other wall across the 11'which was sitting on a foundation way it worked out where I had used a double 2x8 sitting on top of the plate spanning the 22' length. I then nailed my 11' 2x8 joist across using joist hangers on the ledger on the existing house side and then sitting full bearing on top of the double 2x8's on the opposite wall solid blocking in between.These new 2x8 joists had nothing to do with the bottom ceiling. I'm trying to figure out why you can't just do the same thing with your joists and also trying to figure out where your lvl's are and what they have to do with you just running your new 2x8's the 11' way and sitting them on the outside wall like I did.It sounds like the lvl's are on the front and back wall holding up the 2x6's nailed to them with hangers and the 2x6's are flush with the bottom of the lvl's. Which makes me think that under those lvl's is a big opening on each side for windows on both walls or windows on one wall and doors on the other.If this is the case and you frame this addition above will the new rafters be sitting above the 14" lvl's?Joe Carola
Thanks for the feedback. The situation is a lot like the room Joe described and I can do pretty much what he did. The only difference is I happen to already have double 14" LVL's on both sides of the room - 11 feet apart. I can use these as ledgers so to speak to hang new 2 x 8 joists that sit above and have nothing to do with the old ceiling joists below. They will just happen to be perpendicular to the old ceiling joists. My main question was since it just so happens because the height of a 2x 6 and the height of a 2 x 8 are a bit under 14" I could hang the 2 x 8"s a little lower so that the bottom of the new joists also sit on top of the old ceiling joists and add another layer of subfloor to get my full 14" height. I wondered if that might make for a stiffer floor. I got the message pretty clearly though that is not a good idea.
Both LVL's sit directly on top of the top plate of load bearing walls that transfer the load directly to the foundation. Apparently when the house was originally framed they ran double 14" LVL's around the rim of each second floor space to be finished out - probably because the ceiling below most of the rooms is "popped up" in various ways, and in a few of the rooms below (not this one) a span required it. May have been overkill - but that's what they did! Everywhere the second floor space is unfinished they simply installed 2 x 6 ceiling joists to attach the ceiling below.
The only real alternative I saw was what SamT suggested go longwise in between the existing ceiling joists with 2 x 12's the long run of the room. Seemed like more expensive and I would have to reroute quite a few vent lines and electrical. I figured 2 x 8's were sufficient from the span tables (SYP around here) on either 16" or 12" centers for an 11' span. I'll block them and they will have 2 layers of 5/8" t&G plywood on top for subfloor. Did I miss something?
Thanks for all the suggestions.
So the 14" lvl's run the 22' way and the 2x8's would go in between with hangers. Also the lvl's are supported by walls underneath. We use doug fir around here and going 11' span with 2x8's is not a problem at all.I'm sure you can go with 2x8's 11' span 12" centers. I can't see that an 11' span is good for doug fir 16" centers and not be good for syp 12" centers. Just keep them flush with the top of the lvl's and forget about the ceiling below and hang them with blocking in between.Joe Carola
"Current plan would be to hang the 2 x 8's perpendicular across the short dimension (11 ft.) between two existing 14" high LVLS on either side."
As with all structural members that are existing in a building.....the exist LVL's are there for a purpose...apparently to support the ceil you mention, but......do they carry any other loads?
They don't put extra or oversized beams in during initial const on the offchance that a future owner "might want to add a floor here".
I would be hesitant to add new floor loads to those exist LVL's until I am sure that they can carry the extra weight.
A little bit of homework now might save you a lot of cleanup later.
My first thought when I read and tried to visualise your plan: frame it but don't stand under or on top of it and you should be fine.