I bought an early 1900's farmhouse in August and am looking to finish off the old room over the living room and kitchen.  Right now it's just letting all the heat out because the insulation between the wood flooring and the first floor ceiling isn't worth 2 cents.  My dilemma is the room is 24x17 and the floor joists run the short direction (17') and it is a clear span.  The joists are 16" on center, a 2x8 dimensional lumber and my guess would be that they are just pine.

From all the information I can find online you shouldn't use nominal 2x8 over 14 ft and 2x10 over 19.  Being that I have the extra 1/2" in both directions am I ok or do I need to reinforce it?  If reinforcement is necessary what are my options.

Don't sweat the 1/2"

You could always put a LVL or two in there. Its stupid heavy but incredibly strong.

I'm not sweating the 1/2".  I'm concerned about the span being 3' longer than recommended for a 2x8.  I was just hoping that being dimensional lumber would give me enough strength that I wouldn't have to mess with it.

I've thought about this but I'm not sure if it would be feasible to install without the project turning into a full first floor remodel too.

Someone had recommended using 3/4" sheeting grade plywood and construction adhesive to sandwich the existing joists.  Basically it would be making your own lvl.

I assumed the joists were open. Is it all finished? Picture?

It's a tough call, Maxtrax.  Personally, I would remove about half of the flooring to include an area at the ledger end to see how the joist land.  At that point, a engineer can look at the quality of the joists, the bearing points and identify the wood species.  Assuming the house is ballooned framed....  the notch of the joist at the ledger is something that the engineer will have to see so don't skip exposing that if you do hire the engineer to avoid a second trip charge.  

You're absolutely right, that extra ½ inch gives you about one third more joist which isn't reflected in current span charts.  If the floor doesn't bounce when you walk across it that's a decent clue..  It could be ok as is or need only minor tweaking.  An engineer can stamp a letter for you too which will satisfy the building department if necessary.

Be glad that you don't have a tile floor in that room.  

What is under the existing room?

If you have easy access, some 2x4 lumber on the flat nailed to the bottom of every joist would significantly stiffen things up.

The longer the better for the 2x4s, but even is you only cover the middle 2/3 to 3/4 of the span it will stiffen up nicely.

If there is any sag in the floor you should try and jack it out while attaching the 2x4.

You fasten the 2x4 in the middle with a few nails, then use a large beam to remove the sag (lift about 1/8 inch per month till flat as desired).

Then fasten the rest of the 2x4 to the bottom edge, then remove the supports for the beam.

This actually works even with 1./8 inch thick steel straps if you use enough screws in minimum clearance holes to fasten it to the bottom edge.

You are making a composite beam, and trying to get the two pieces (old joist and new material) to act as a single load bearing assembly.


The 1/360 defection limits are based on not cracking a ceiling below the joists.

When I-joists first came out, some of the available spans created 'bouncy' floors.

They met the code of 1/360 deflection, but the span was so large the floors had excessive bounce.

Customers complained.

Taller I-joists (stiffer for length) came out, especially in the longer lengths with much smaller deflections (1/450, 1/540, 1/630, 1/720, etc.) than the code minimum.

The living room and kitchen are below this room. Both of those are finished off.  The floor doesn't bounce by I can get feel it bounce slightly when I land from a hard jump.  

If it isn't notched at the ends am I good to go?  What type of okace do I call to have someone cone look at it.

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Edit... Don't mind the load bearing hole I found in the sidewall.

I just checked through one of the holes along the wall (it's 12 degrees up there so I wasn't going to pull anything up) but they don't appear to be notched.  It looks like they are side-hung from the wall studs which continue up to where the headwall begins.

I had a similar situation on my old house. My plan was to remove the flooring and run the proper sized joist along each existing joist. I also needed to insulate between the joists. I sold the place prior to doing the work.  Good luck, looks like a great space up there

I don't know where you are getting that a 2x8 is good for a 14' span and a 2x10 is good for a 19' span. Those numbers seem pretty optimistic. http://www.awc.org/calculators/span/calc/timbercalcstyle.asp this is a good online calculator I have used.

if its stood for 100 years I think its fine unless you are greatly increasing the loading.

Being that it was a more of an attic I don't think there was much load.  I'm planning on turning it into a bedroom and full bath with a tub.

I found that but the issue I run into is what type of wood it is.  They provide so many options it's like Greek to me.

Hem-Fir is what we usually use around here for framing. Either way if you play around with the calculator it calls for 2x10 or 2x12 usually for the 17' span.

But that 2x10 is actually 1-1/2"x9-1/2".  I'm dealing with dimensionsl lumber so the calculators aren't going g to give me accurate numbers except if I want to over engineer it.

My 14' span came from a 30lb/square foot live load.  I had read somewhere that 30lb was sufficient for bedrooms.
Edit-  found at the top of this chart

If you don't know a "structural" engineer in your area you could try google.  Type your home town and state for structural engineers then the map link and you should get a decent list.  A local builder could probably recommend one too.

Get a bunch of 2x8s 18ft long and bolt a new joist to each existing joist with 1/2" lag bolts. Essentially gives you a 4x8 joist. I did this to some 2x6 joists in my attic and it significanlty strengthened the area.

Awesome.  I guess the part that I was at a loss for was what to search.  When trying to come up with different things to search I could only think of architectural engineers, carpenters or contractors.

This is a great idea and really wouldn't cost too terribly much.  The hardest part would be trying to work them into the spaces..

i had the same problem, only worse.  2x6's @ 24" o/c for floor joists.  
this was a 1930's carriage house converted by the previous owners to a garage, with a bonus room upstairs.

everything had to be sistered, and LVL's cut in as beams.
the end result was great but it was a hella lot of work and money.

and of course once you have LVL's in, running plumbing and electrical becomes a nightmare.
there was existing HVAC ducting and pipe that had to be rerouted up and over etc.
in a space with limited headroom to begin with, it was tough going.
make sure you have a complete plan for the HVAC runs before you start.

ar-jedi















ps...

i kid you not, someone did this 80 or so years ago.

that's a 2x6 the second floor is sitting on...  
what could possibly go wrong?  





...

glue and bolt

Field aplied glue has ZERO structural rating.

You need a shear calculation for the joists to determine the bolt patter,

ANything over 3/8 diamter usually does not work since the crsh load of the wood is exceeded.

Higher grades of lumber have lnger span limits.

If you switch to something other than #2 all sorts of nice lengths appear.

The wood costs more.

Simple sistering means you often have a lazy engineer.
The moment of inertia calculations for a 2x4 flat on the bottom of the joist are not all that hard, and for 1.5 inches of headroom loss you get
A large increase in strength and stiffness.
Adding steel strapping is even better.

For a joist to bend under load the bottom has to get longer (curves are longer than straight lines).
By converting the steel to an equivalent wood member (ratio of Young's modulus)  you have added the equivalent of a HUGE wood section.

The shear loading determines the fastener spacing, and the holes must be almost zero clearance.

This is by far the easiest option you have. If you are really concerned with the extra 1/2"  find a local saw mill they will cut what ever you ask for.

Yellow Pine designated by a "YP" stamp on the board is much stronger than "S-P-F" (spruce, pine, or fir) lumber. Always use YP for floor joists.

You need full up grade stamps.
Not just a wood type mark.

Yeah that too.

#1 YP 2x10 is a hell of a strong board.

Was going to suggest this, but instead of lag bolting them, take the sag out of the floor as noted above, then just nail with a standard header pattern.

The joists in my parent's house are all sistered together this way, and the joists in a portion of a 1940s rental house we used to live in were sistered together this way also.

 

In many cases easier said than done.

Wiring, plumbing (supplies, vents), and cross bracing all have to be moved out of the way, the replaced.

Do not forget to go back and install cross bracing.
It plays a significant role in longer spans and taller joists by limiting twisting under load.