[Greenlight1]

Our floor joists span 17’ 6” from foundation to middle wall (load bearing). The joists are 2” x 8” original wood (built 1900-1905) and are in good shape (no notches, big holes or cracks)
The middle of the span is sagging a little bit (1/4”-3/8”) and I would like to install a beam in the middle to take out sag. The beam would span approx 23’. Would a “homemade” beam consisting of (2) 2x10’s with 3/4” ply between suffice for this installation? I am planning to have the beam rest of the exterior foundation sill plate and have 3 additional steel beams under the post spaced approx. 7’ 6” apart that will sit on footings.

 

[sixeightten]

I have never seen a 2 ply beam in a basement. Not knowing your exact situation, I can only guess, but I think I would go for a 3 ply 2x10 and keep the post spacing as you suggested. If your deflection is only 1/4 or 3/8 as you say, I would be inclined to not do anything, unless I was adding a piano, aquarium, or something else heavy to the existing load.

 

[Greenlight1]

I have never seen a 2 ply beam in a basement. Not knowing your exact situation, I can only guess, but I think I would go for a 3 ply 2x10 and keep the post spacing as you suggested. If your deflection is only 1/4 or 3/8 as you say, I would be inclined to not do anything, unless I was adding a piano, aquarium, or something else heavy to the existing load.

“3 ply” meaning (3) 2x10’s with plywood?
As for the sag, the home is gutted and we are working on getting the floors “even” and ready for new flooring. While it’s prob not a huge deal for the flooring install, it’s something that I would rather do now then have to deal with down the road. Flooring will most likely be some sort of engineered wood or bamboo.

 

[sixeightten]

“3 ply” meaning (3) 2x10’s with plywood?
As for the sag, the home is gutted and we are working on getting the floors “even” and ready for new flooring. While it’s prob not a huge deal for the flooring install, it’s something that I would rather do now then have to deal with down the road. Flooring will most likely be some sort of engineered wood or bamboo.

Yes, just the 3 ply 2x10. The plywood does not really add any meaningful support, since it is limited to 8' sections. Depending on where you are, the footings will be the most difficult part. Cut the concrete and remove, excavate for the footing, add rebar/concrete.

Another possiblility would be to sister a few 7 1/4 lvl's to the existing 2x8, if you don't have wires/pipes in the way. Adding these every 3rd or 4th joist would add some support without having posts in the way, and also less work.

 

[carpdad]

I think double 2x10 will be fine with middle spans also supported about 8'. An engineer could save you materials, middle post footings and room.

 

[Greenlight1]

Yes, just the 3 ply 2x10. The plywood does not really add any meaningful support, since it is limited to 8' sections. Depending on where you are, the footings will be the most difficult part. Cut the concrete and remove, excavate for the footing, add rebar/concrete.

Another possiblility would be to sister a few 7 1/4 lvl's to the existing 2x8, if you don't have wires/pipes in the way. Adding these every 3rd or 4th joist would add some support without having posts in the way, and also less work.[/QUOTE]

The one footing is already present as it was there for the chimney that was removed. We would only need 2 more footings dug which is rather simple since the basement floor has been removed. I just want to make sure we have everything in order before we start prepping the basement for it’s new concrete floor

 

[3onthetree]

1/4" and probably 24"o.c. joists with 120 years of people, stuff, and hacking up? Not bad at all.

You may very well be the first thread ever asking to split a span and add columns that make a basement more unusable, usually everyone asks how to remove columns. Listen to 6-8-10's alternative.

 

[Greenlight1]

Wires and pipes are not present at this time so the LVL’s sistered to the joists would be doable.
That does seem a little easier.
Thanks for the info guys!!

 

[Nealtw]

I like to compare one job with other jobs carrying similar weights. We build floors with 2x10s and often build staircase openings that are more than 10 ft long and the floor and often the wall above is supported with 2 2x10.

So 2 2x10s nailed together with a post every 10 feet on footing would do the job, no problem. You don't need plywood between them just 5 nails 16" OC.

 

[Old Thomas]

I didn’t want to break up my concrete floor to put in footers so I put a 12”square piece of 1/4” steel plate on the floor to rest my column on. I figured that if it cracked the floor or appeared to move at all I would dig footers. That was 1980 and no movement yet.

 

[sixeightten]

I like to compare one job with other jobs carrying similar weights. We build floors with 2x10s and often build staircase openings that are more than 10 ft long and the floor and often the wall above is supported with 2 2x10.

So 2 2x10s nailed together with a post every 10 feet on footing would do the job, no problem. You don't need plywood between them just 5 nails 16" OC.

Neal, I agree with you. I was just overshooting it because of not being there and putting eyes on it. Although, in your case, the joists are fastened INTO the beam rather than sit on top. A 2 ply beam 23' long will be somewhat succeptible to a roll/lean in the center. Now as long as the posts are imbedded, and the beam post connection is good, that wouldn't be an issue.

 

[Nealtw]

Neal, I agree with you. I was just overshooting it because of not being there and putting eyes on it. Although, in your case, the joists are fastened INTO the beam rather than sit on top. A 2 ply beam 23' long will be somewhat succeptible to a roll/lean in the center. Now as long as the posts are imbedded, and the beam post connection is good, that wouldn't be an issue.

We would use a 6x6 post here and it would sit in a saddle and be notched for the beams, but yes I can see a problem for a steel post. :wink2:
It doesn't have to be more than you would do for a deck beam.

 

[House Designer]

Greenlight,
I ran a quick calculation on your existing joists, assuming they are TRUE 2" x 8" rough-sawn floor joists @ 16" o.c., and they are INADEQUATE by 115%, based on 40 psf Live Load + 10 psf Dead Load. I am amazed that they are not sagging worse.
Assuming Spruce/Pine/Fir, a rough-sawn (true) 2x8 @ 16" o.c. is only rated for 13-1/2 ft span.
I would ignore the suggestion to beef up every third FJ with an 8" LVL.
Rather, I would Double EVERY FJ with a 2x10 ripped down to a true 8" tall.
That will bring you much closer to being adequate, and the floor will be more evenly strong.

 

[Nealtw]

Greenlight,
I ran a quick calculation on your existing joists, assuming they are TRUE 2" x 8" rough-sawn floor joists @ 16" o.c., and they are INADEQUATE by 115%, based on 40 psf Live Load + 10 psf Dead Load. I am amazed that they are not sagging worse.
Assuming Spruce/Pine/Fir, a rough-sawn (true) 2x8 @ 16" o.c. is only rated for 13-1/2 ft span.
I would ignore the suggestion to beef up every third FJ with an 8" LVL.
Rather, I would Double EVERY FJ with a 2x10 ripped down to a true 8" tall.
That will bring you much closer to being adequate, and the floor will be more evenly strong.

17 ft is over spanned for 2x10 doubles. A new single will have to fight the normal sag as well as the sag now built into the old ones.

 

[House Designer]

17 ft is over spanned for 2x10 doubles. A new single will have to fight the normal sag as well as the sag now built into the old ones.

Sorry, I don't think that is correct. My charts say doubled 2x10 is rated for 19'-8".
That is assuming doubled SPF #1/2 @ 16" o.c. 40 psf Live Load + 10 psf Dead Load, L/360 Live Load deflection criteria and L/240 Total Load deflection criteria.

 

[Nealtw]

Sorry, I don't think that is correct. My charts say doubled 2x10 is rated for 19'-8".
That is assuming doubled SPF #1/2 @ 16" o.c. 40 psf Live Load + 10 psf Dead Load, L/360 Live Load deflection criteria and L/240 Total Load deflection criteria.

Seen that, done that, with a young engineer that read your chart.

Double #1 fir 19 ft between walls. Sagged 1 1/2" under there own weight and the weight of the sub floor and a couple interior walls before we got the trusses up. We had to jack it up and put 6 x 14 micro lam under the center.

And as it was a garage we had to put another the same size under the front to hold that up. So no I am not wrong.

I have seen a lot of things drawn on plans from the charts that engineers with experience just cross out and that is one of them.

When the plan calls for 2x10 joist at 16 ft on a 2x4 wall, they will change the wall to 2x6 just to cheat a couple inches off the span.

 

[House Designer]

Seen that, done that, with a young engineer that read your chart.

Double #1 fir 19 ft between walls. Sagged 1 1/2" under there own weight and the weight of the sub floor and a couple interior walls before we got the trusses up. We had to jack it up and put 6 x 14 micro lam under the center.

And as it was a garage we had to put another the same size under the front to hold that up. So no I am not wrong.

I have seen a lot of things drawn on plans from the charts that engineers with experience just cross out and that is one of them.

When the plan calls for 2x10 joist at 16 ft on a 2x4 wall, they will change the wall to 2x6 just to cheat a couple inches off the span.

True, Code minimums are just that- Minimums. I agree that L/360 deflection can give poor performance when the spans get long. I like to use L/480 deflection criteria whenever possible, and so do the I-joist folks.

A single 2x10 @ 16" o.c. is rated for 15'-4" span by Code Minimums, but I don't like to span more than 14'-8 to 15'-0 because it gets bouncy.

My suggestion to the original poster to double each FJ would double the strength and reduce the deflection by doubling up the lumber, but would still come up 15% shy of Code minimum. A better tact would be to install as many 2X8 LVLs as he can afford, maybe every other joist, and double up the remaining FJ with ripped-down 2x10s.

 

[Nealtw]

True, Code minimums are just that- Minimums. I agree that L/360 deflection can give poor performance when the spans get long. I like to use L/480 deflection criteria whenever possible, and so do the I-joist folks.

A single 2x10 @ 16" o.c. is rated for 15'-4" span by Code Minimums, but I don't like to span more than 14'-8 to 15'-0 because it gets bouncy.

My suggestion to the original poster to double each FJ would double the strength and reduce the deflection by doubling up the lumber, but would still come up 15% shy of Code minimum. A better tact would be to install as many 2X8 LVLs as he can afford, maybe every other joist, and double up the remaining FJ with ripped-down 2x10s.

I think if you nailed an eight inch to the side of old growth the new would loose to the sag of the old in a very short time.

I would would stay the beam but from one end what would be the longest 2 ply 10" LVL he could put in with one post in the room off to one end with a lesser beam at the other end.

 

[Greenlight1]

Thanks for all the input on this guys. Like I said, I’m not the best when it comes to standards and what is going to actually work as opposed to what a chart tells me. I am going to proceed with the 3 ply beam underneath so that way no one will come back at me and say it is inadequate.
Again, thanks for all the help!!!

 

[Nealtw]

Thanks for all the input on this guys. Like I said, I’m not the best when it comes to standards and what is going to actually work as opposed to what a chart tells me. I am going to proceed with the 3 ply beam underneath so that way no one will come back at me and say it is inadequate.
Again, thanks for all the help!!!

Don't attempt to make one long beam. beams meet on top of the posts.