Overspan?

[MFortie]

2"x6"x26' span Doug Fir with 24" spacing?

The ceiling joists in the little garage on the property we bought is built as above. The previous yo-yo (owner) had drywalled the ceiling, added insulation (they had some folks living in it) and had some sheet goods stored on the joists.

They also put a partial wall down the center -- probably to help support the weight! When I removed the wall studs (that's all they were), the ceiling kind bounced if I pushed on it with my hand!

I pulled the drywall, insulation & removed the sheet goods and it's quite a bit better, but still moves 'a bit'.

The garage is built with 2"x6" on 16" rafters (stick built, no trusses) with a 2"x10" ridge board. Skinny little sheathing (3/8" maybe) and asphalt 3-tab shingles.

I'm thinking about adding ceiling joists to make it 16" spacing and maybe sistering another 2"x6" on each side of the rafters just for peace of mind...

Thoughts?

Thanks,

Mark

 

[6768rogues]

According to the span tables I have at hand, ceiling joists of Douglas Fir on 16" centers can span 13' 2" if it is #2 Douglas Fir and 13' 5" if it is #1.
The only way to get close with Douglas Fir is to use #1 2X10s on 12" centers for an allowable span of 24' 11".
The table is calculated for a dead load of 6 psf, live load of 10 psf, and a deflection of L/360.
If you want to do it right, you should consider manufactured joists such as wood I-joists or you could install a central wall to reduce the span. Cutting the span in half would work with 16" centered 2x6s.
Also consider what the ceiling joists sit on. If your wall has a double top plate, it is ok. If it has a single top plate, the ceiling joists need some additional support if not located over the studs. They are probably not going to be over the studs, because with a single top plate the rafters need to be over the studs.

 

[bigdav160]

Obviously those 2x6 were only meant to keep the walls from spreading.

You could leave it as designed or sister more wood would be fine also.

What do you want to do with the space?

 

[MFortie]

Obviously those 2x6 were only meant to keep the walls from spreading.

You could leave it as designed or sister more wood would be fine also.

What do you want to do with the space?

That's what I determined as well -- the additional load on the ceiling joists made for a very scary ceiling!

The garage is a standalone two car that right now is storing materials and tools -- we are rehabbing the two houses on the property. Down the road, I plan to build a workshop - 36'x60' or so, and also put in a barn for the horses, tack, etc. But for now, the garage will have to house all my tools and equipment.

Like most of us, I collect tools -- woodworking, metal working, auto, construction -- if it's made to do work, I will probably end up owning it! And I don't make a living with any of it, but my sons and friends are very appreciative that I own them!

While parking a car in a garage is a very foreign concept to me, I might end up using it for that purpose in the future!

Thanks,

Mark

 

[MoonRise]

2x6 ceiling joists or roof rafters for a 26 ft wide structure are undersized pretty much no matter what you do, unless you have that center load-bearing wall down the middle of the garage.

Sistering more 2x6 onto the existing 2x6's will not do enough. Splitting the OC spacing from 24" OC down to 12" OC will not do enough. 2x6's are really too small for that wide of a span.

Smallest live loading of 10 psf and 5 psf dead load (drywall ceiling, no storage!) and 'bouncy' at a deflection limit of L/240 for the ceiling joists calls out for minimum 2x10 with E=1.6 x 10^6 or better (Douglas Fir - Larch #2 or better meets this, but NOT Southern Doug-Fir!, Hem-Fir 2x10 would have to be graded "Select Structural" to meet the E value, Hem-Fir Northern 2x10 #1/#2 meets the E value, visually-graded #2 or better Southern Pine 2x10 meets the E value, etc, etc).

Smallest live loading of 20 psf and dead load of 10 psf for the 'bounciest' roof rafters at L/180 deflection limit calls for pretty much 'good' 2x8's on 24" OC (or better).

And 3/8 roof sheathing no 24" OC rafters is going to be bouncy-bouncy-bouncy. I wouldn't want to be up on that roof!

You -could- call or talk to your local building department and find out what the structural requirements are in your locale. Hint, hint.

 

[MFortie]

2x6 ceiling joists or roof rafters for a 26 ft wide structure are undersized pretty much no matter what you do, unless you have that center load-bearing wall down the middle of the garage.

Sistering more 2x6 onto the existing 2x6's will not do enough. Splitting the OC spacing from 24" OC down to 12" OC will not do enough. 2x6's are really too small for that wide of a span.

Smallest live loading of 10 psf and 5 psf dead load (drywall ceiling, no storage!) and 'bouncy' at a deflection limit of L/240 for the ceiling joists calls out for minimum 2x10 with E=1.6 x 10^6 or better (Douglas Fir - Larch #2 or better meets this, but NOT Southern Doug-Fir!, Hem-Fir 2x10 would have to be graded "Select Structural" to meet the E value, Hem-Fir Northern 2x10 #1/#2 meets the E value, visually-graded #2 or better Southern Pine 2x10 meets the E value, etc, etc).

Smallest live loading of 20 psf and dead load of 10 psf for the 'bounciest' roof rafters at L/180 deflection limit calls for pretty much 'good' 2x8's on 24" OC (or better).

And 3/8 roof sheathing no 24" OC rafters is going to be bouncy-bouncy-bouncy. I wouldn't want to be up on that roof!

You -could- call or talk to your local building department and find out what the structural requirements are in your locale. Hint, hint.

Thanks. We are doing a FHA rehab on the houses and the garage requires minimal work (or so we thought). We will be required to re-roof as the shingles are shot and I was planning on replacing the sheathing 'cause it looks so-so.

As part of the FHA requirements, we have a GC on board (who happens to be a family member); I'll talk with him about it -- maybe I should just rebuild the structure to make lots more room!

We've already pulled all the permits for roofing, siding, plumbing, electrical & HVAC for the houses (the garage only had roofing, electrical and siding). Guess it's time to go back to the building department!

 

[Justanoldguy]

You could run a 2x10 or 12 on top of the joists at 90 degrees to them.
It will act as a strongback and tie them all together and spread the load.
Also put ties (maybe 2x4s) from the strongback to the ridgebeam.
In effect you are adding a type of truss system.

 

[theoldwizard1]

If the rafters are properly sized you could probably do the following.

Carefully measure the span at the bottom plate and at the top plate. If they are not equal, use cables to bring the walls into plumb. Once you are certain that the walls are truly vertical, then you you can add a collar tie (horizontal member connected to the rafter between 1/4 and 2/3 of the way up the rafter).

Again, if the rafters are properly sized (my guess is they are not) you could even double 2x6s, one on each side of the rafter, bolted through the rafter.

 

[MFortie]

I spoke with a local truss company today and can get new trusses and gable ends for under a grand delivered. Since I planned on replacing the sheathing anyway, I think this is probably the way to go.

I can recycle the 2x lumber when I rebuild what the RE agent euphemistically called 'a barn'. It's a 1940's shed roof structure that will probably fall over is I lean on it too hard! Fortunately it's not part of the FHA rehab work, so I have some leeway...

 

[Justanoldguy]

If the rafters are properly sized you could probably do the following.

Carefully measure the span at the bottom plate and at the top plate. If they are not equal, use cables to bring the walls into plumb. Once you are certain that the walls are truly vertical, then you you can add a collar tie (horizontal member connected to the rafter between 1/4 and 2/3 of the way up the rafter).

Again, if the rafters are properly sized (my guess is they are not) you could even double 2x6s, one on each side of the rafter, bolted through the rafter.

I don't think collar ties will help the ceiling joist problem. JM2CW

 

[davedriveschevys]

You could easily turn the collar ties into the bottom chord of a truss , a vertical 2x4 nailed just off center to clear the ridge, two more going from the center of the bottom chord to the center span of your rafter, and two going from center span of your rafter back down to your bottom chord at a point halfway between your wall and the vertical member at center.
This cuts your ceiling joist span to 25% of what it is now and your rafter span in half.

And you have to straiten the bottom out as you go, a 2x4 cut to the height of the top plate of the wall works well, assuming the floor is flat.

 

[Justanoldguy]

Be easier to replace it all with new trusses as the OP said above.
You know you have the engineering right then.

 

[trainer]

Just a thought, but if you are doing new roof, including trusses, new siding, and new electrical, why not just demo the entire structure and build everything new on the existing pad? It will probably be cheaper than trying to rehab a poorly built structure.