Sistering Joists issue...

[jconnor3]

Hi All,

Not so much for my garage, but still figured a lot of members here would have solid ideas. So i'm putting an addition on my house. I'm turning the attic into a master retreat and to do so I need to sister the current existing 2x6's with 2x8's. Not that big of a deal other than the wiring running through the joists will be a PITA to deal with. Well so I thought.

I was removing the current subfloor planks that are up there and removing the blown-in insulation and I noticed that the bottom plate for the walls and roof line are resting ontop of the current 2x6's. Which makes sense but didn't think of that before. Anyway so I figured the best option would be to just notch the new 2x8's to fit into the existing space and onto the load bearing outside wall.

Well, I ran this past my architect and he wasn't sure that would work so he asked an inspector and the inspector said this would be a no-go. What?!? What has everyone else been doing? I took some pictures and drew a terrible illustration and the architect sent that over to the inspector in case he wasn't sure what we were really asking. I should be hearing back any day now on that, but if it really isn't an option....what else can I do? Can anyone thing of any other options?

Some of the walls and roof will be demoed for new 7ft walls and roof, but 1/3 of the structure is suppose to stay in place.

Here are a few pictures and a terrible drawing showing the notch i'd use.

 

[Kaizen]

If I was paying money to an architect and he said he didn't know I'd be concerned. one of you should consult a structural engineer. Not like you can just gut the bottom plate out. I expect they will spec a laminated wood and steel flitch beam or something of that sort. no idea how many you'd need.

 

[matt_i]

You can notch, I personally don't see an issue. The max bending stress is at the center of the span, there is already sufficient bearing for the wall, but what about the other side? If identical to this, its going to be nearly impossible to swing a double-notched timber into place in the short joist space.

Also, you should get a nail pattern to adhere to when sistering. Have to have enough pins (nails) so that they don't get wiped out by the shear in between the beams.

 

[theoldwizard1]

Well, I ran this past my architect and he wasn't sure that would work so he asked an inspector and the inspector said this would be a no-go. What?!?

Your floor joists are a "beam". (to any architectural engineer pretty much every "long" horizontal item is a beam !) If you drilled a whole bunch of holes in it, it would like sort of like

.

This is sometimes called a "truss beam" or a "parallel chord truss". The reason any truss works id because when loaded the top plate is in compression and the bottom plate is in tension (think of a large load in the center causing the beam to bow). Anything in the middle is called the "webbing" and its only purpose is to hold the top to the bottom in the same continuous position.

In you case the "bottom plate" is just the bottom edge of the 2x8 and the "top plate" is the top edge. Your notch will "compromise" the top edge/plate right at one of the 2 load points !

Check back with the inspector and see if sistering a 2x6 LVL is acceptable (check the span tables for a 2x8 and the compare them to a 2x6 LVL).

 

[theoldwizard1]

If I was paying money to an architect and he said he didn't know I'd be concerned. one of you should consult a structural engineer. Not like you can just gut the bottom plate out. I expect they will spec a laminated wood and steel flitch beam or something of that sort. no idea how many you'd need.

Concerned ? I would be down right PISSED !

2x6 flitch beam is another good solution, but you will need an engineer to spec it out.

 

[theoldwizard1]

You can notch, I personally don't see an issue.

But you are not the building inspector !

 

[ishiboo]

Your inspector is the final word on this, so it's really up to him/her... the IBC allows it. From an engineering standpoint, what you propose is really fine. You can notch up to a quarter of the depth of the joist. A 2x6 is 5.5" tall, a 2x8 is 7.25". So taking out a quarter of the total depth gets you just below the height of the 2x4.

The bigger concern I would have is if you will be able to flex the wood sufficiently to get it between the two ends, since I am assuming this problem happens on both sides. You definitely don't want to cut them short and loose bearing area. Also, what is the total span and are there load-bearing mid-walls?

 

[ishiboo]

Oh, and if you go with an engineered product, you will be limited by the manufacturer's installation guidelines... the code goes out the window. I'm sure that all of them will still allow at least a 1/4 depth notch as well, but be prepared to show it

 

[jconnor3]

So the total span from side to side is 25ft, but I have a load bearing wall running down the middle so my real span is 12.5ft. I was planning on just buying 2x8x14's so I wouldn't have to worry about wiggling in a huge 2x8x25 sister joist.

The costs for LVL's would be pretty much a deal breaker for the project. I don't have the budget to stomach that so hopefully that isn't the only option!

Thanks guys!

 

[ishiboo]

So the total span from side to side is 25ft, but I have a load bearing wall running down the middle so my real span is 12.5ft. I was planning on just buying 2x8x14's so I wouldn't have to worry about wiggling in a huge 2x8x25 sister joist.

The costs for LVL's would be pretty much a deal breaker for the project. I don't have the budget to stomach that so hopefully that isn't the only option!

Thanks guys!

Gotcha. That helps a lot.

You don't need LVLs. But 12'5" is right at the top of what a 2x8 of regular framing lumber can carry, you'll need to go with #2 or better douglas fir or a high grade of another lumber to meet the deflection requirements at 16" OC.

It would be ideal to go with 2x10 of cheap lumber, but you couldn't notch that far down and still be to code.

Looks like a fun project!

 

[CTyankee]

Even with the higher cost, I'd bite the bullet and go with LVL's. We sister them in older homes all the time when remodeling. The fact that they are reasonable consistent in size and straightness helps a lot when putting them in place...which isn't that big a deal once you get a program down.

 

[lakeroadster]

Ishiboo... The specifications you are referencing... based on what Live Loads and Dead Loads?

12'5" is right at the top of what a 2x8 of regular framing lumber can carry

you'll need to go with #2 or better douglas fir or a high grade of another lumber to meet the deflection requirements at 16" OC.

 

[ishiboo]

Ishiboo... The specifications you are referencing... based on what Live Loads and Dead Loads?

I looked at the minimum I believe for the application - 40/10 L/360. With the existing joists carrying some of the weight, I believe the floor performance will be acceptable. OP/architect/contractor will need to consult the span tables for what lumber is available to them and the exact requirements of the application, of course.

The point is, it's doable, according to IBC, using solid lumber.

 

[theoldwizard1]

I looked at the minimum I believe for the application - 40/10 L/360. With the existing joists carrying some of the weight, I believe the floor performance will be acceptable. OP/architect/contractor will need to consult the span tables for what lumber is available to them and the exact requirements of the application, of course.

The point is, it's doable, according to IBC, using solid lumber.

Looking at the 40/10 span table for #2 SPF, 2x8, 16" O.C. will span 11-10. Dropping down to 30/10 table #2 SPF, 2x6, 16" O.C. will span 10-3, 12" O.C. 11-3.

Even if you you notch your 2x8, at worst, they are as good as a 2x6. My span table does not show rating for doubled joists. (40/20 ?)

See if you can find a span table that shows 8" O.C.

 

[lakeroadster]

The point is, it's doable, according to IBC, using solid lumber.

Assuming those minimums are in fact acceptable to the jurisdiction.

I'm always concerned someone will read these posts and then run with the advice given... without doing their due diligence.

Then install a huge bath tub, pool table, water bed and baby grand piano..

 

[theoldwizard1]

2x8x14 is about $11. 2x6x14 is about $7. Using TRIPLE 2x6 would be about a $3 per joist cost penalty.

Check with you inspector about this.

 

[bczygan]

Assuming those minimums are in fact acceptable to the jurisdiction.

I'm always concerned someone will read these posts and then run with the advice given... without doing their due diligence.

Then install a huge bath tub, pool table, water bed and baby grand piano..

You mean I can't put a 10,000 gallon cistern up there?

Bill

 

[bczygan]

LVL's are a ridiculous suggestion for this.

2x8's in hem-fir #2 and better 40LL 10DL L/360 16"o.c. span 12'0" in my AWC calculator. Very close to the unsupported span. A different species or grade would make it. Existing ceiling joists support the existing ceiling. So with adequate bridging 2x8's will do fine for the floor.

As to the height, is there a way to raise the plate and slip the joists under it?

Bill

 

[CTyankee]

LVL's are a ridiculous suggestion for this.

Bill

We all have our own opinions. The use of LVL's when adding/mating to seasoned lumber saves a lot of guess work and potential future problems. One big reason LVLs are used when mating to old dimensional material is the fact that it won't shrink like new dimensional lumber. Having sistered joists in situations such as this one using both dimensional and LVL's more times than I've cared too, I'll stick with my suggestion.

 

[bczygan]

We all have our own opinions. The use of LVL's when adding/mating to seasoned lumber saves a lot of guess work and potential future problems. One big reason LVLs are used when mating to old dimensional material is the fact that it won't shrink like new dimensional lumber. Having sistered joists in situations such as this one using both dimensional and LVL's more times than I've cared too, I'll stick with my suggestion.

From a structural point of view, in this case, they are a waste of money.

Dimensional lumber will do the job, and it need not contact the existing joists.

It can be totally separate. If actually sistered, I can see your point, and it is a good one about moisture.

Bill

 

[matt_i]

Dimensional lumber will do the job, and it need not contact the existing joists.

The only issue with not connecting them is you don't get any benefit from the "sistering". The new taller timber is the only thing doing any bearing. The old timber is basically along for the ride then. I would want to pin them together (nails) and get a lamination that's good for significantly more.

 

[Ironcrow]

Your inspector is the final word on this, so it's really up to him/her...

In my jurisdiction the sealed architect/engineer drawing is the final word. With a sealed drawing if the inspector doesn't like/understand it he/she can get stuffed.

 

[Kaizen]

LVL's are a ridiculous suggestion for this.

2x8's in hem-fir #2 and better 40LL 10DL L/360 16"o.c. span 12'0" in my AWC calculator. Very close to the unsupported span. A different species or grade would make it. Existing ceiling joists support the existing ceiling. So with adequate bridging 2x8's will do fine for the floor.

As to the height, is there a way to raise the plate and slip the joists under it?

Bill

I suggested LVL's because notching is the issue. an lvl 5.5 tall would fit and take care of the notch problem. agreed not needed if he can spec out dimensional lumber.

 

[drjcustis]

This looks like another incident when a quick consult with a structural engineer would be worth the expense (though, I think that the architect should be able to answer the question).

I like the suggestion of the LVL's. You would have a stronger and stiffer floor with a smaller size. But, with additional cost.

I also think that this project could be done with conventional lumber... at a reduced cost compared to LVL.

An Engineer can look at the project including the weight loads, do a few calculations and give you the best recommendation. He also draw up the plans and override any inspector. The inspector is looking for you to meet minimum code. Where I live, they won't allow you to notch the ends of a 2X like you want. However, an Engineer can draw up plans that he then certifies meets or exceeds the code requirements.

Hope that helps.

 

[jconnor3]

Hey guys, I appreciate all of the follow up. I had a structural engineer come by this morning. He said not only would a notch be fine, but that it wouldn't even be needed if I wanted. I could dead the 2x8 up against that 2x4 bottle plate. Even though that would land before the end load wall, he said with a heavy nailing pattern it wouldn't matter as the 2x8 is for deflection and the 2x6 is more than capable holding up a 7ft wall and roof on it's own.

So, I guess that answers that. I'm still going to notch the ends for piece of mind, it wont take that much extra effort and it can't hurt to have the extra support.

 

[Ironcrow]

Thanks for the feedback from the engineer. I was tempted to say just do it (notch the 2x8), being pretty confident there would be no problem. If it was mine I'd do it, but I'd hesitate to suggest to someone else to do it. Beams that are sized for maximum bending moment in the center with distributed load are typically oversized for shear load at the ends. For example here's a feature on the end of a glu-lam that can typically be executed without a load derate. As always, get professional input if you are not comfortable (or if you need to satisfy an inspector):

 

[theoldwizard1]

I had a structural engineer come by this morning. He said not only would a notch be fine, but that it wouldn't even be needed if I wanted.

Got that in writing ?

How do you plan on dealing with the inspector ?

 

[jconnor3]

Well the "inspector" in this case is just a contact that my architect reached out to when I posed the question to him. He was unsure, so he emailed an inspector. When I submitted for my permits, it shows and states that I will be sistering with 2x8's. They didn't have a problem with it.

I was just trying to be proactive and get an answer before it could have possibly became an issue and went through all of the trouble.

Also, this was just the "inspectors" initial response. My architect wasn't sure the guy fully understood what we were asking so we made up a quick drawing showing exactly what I was planning on doing and we haven't heard back after that which was Friday. So after seeing what we were talking about, he may change his mind as well.

 

[ishiboo]

Well the "inspector" in this case is just a contact that my architect reached out to when I posed the question to him. He was unsure, so he emailed an inspector. When I submitted for my permits, it shows and states that I will be sistering with 2x8's. They didn't have a problem with it.

I was just trying to be proactive and get an answer before it could have possibly became an issue and went through all of the trouble.

Also, this was just the "inspectors" initial response. My architect wasn't sure the guy fully understood what we were asking so we made up a quick drawing showing exactly what I was planning on doing and we haven't heard back after that which was Friday. So after seeing what we were talking about, he may change his mind as well.

If there any concerns, they can consult with the IBC's section on notching and see that it is allowed.

http://co.routt.co.us/building/handouts/notching.pdf

 

[theoldwizard1]

If there any concerns, they can consult with the IBC's section on notching and see that it is allowed.

http://co.routt.co.us/building/handouts/notching.pdf

PERFECT !

R502.8.1 Sawn lumber. Notches in solid lumber joists, rafters and beams shall not exceed one-sixth of the depth of the member, shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span. Notches at the ends of the member shall not exceed one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness shall not be notched except at the ends of the members.

Good to know for future reference !

 

[Ironcrow]

By the way, in situation such as this, even an engineered joist can be bevel cut on the end.

 

[lakeroadster]

If there any concerns, they can consult with the IBC's section on notching and see that it is allowed.

http://co.routt.co.us/building/handouts/notching.pdf

Great information... thanks for posting this.