Collar + Rafter Ties Roof Framing - No Load Bearing walls needed, right? 3

[Grimloktt]

Hello. I searched for a forum where I could post this question. So, I hope I'm in the right spot...

From everything I know and read, this house's roof framing does not require any type of interior load bearing walls. Can anyone confirm that understanding?

The house's roof framing consists of collar and rafter ties with the rafter ties sitting directly on exterior walls and are also acting as the ceiling joists. I cannot find any information pointing to the need for an interior load bearing wall with this design. Picture attached. Thnx in advance!

 

[XR250]

Unless your ceiling joists are un-spliced and can span from exterior wall to exterior wall, then you will need an interior wall or beam. From the looks of your situation I would say that is the case. The framing could be modified with some 2x4's to create "trusses" to eliminate the need for interior support. Also can add a beam in the attic on top of the ceiling joists to support them from above. Would still need to bear the beam somewhere.

 

[Grimloktt]

Yes. The rafter ties/ceiling joists do span the entire length from exterior walls with no splicing.

 

[BAretired]

Should be okay without interior wall if nailing is in accordance with the code.

BA

 

[JAE]

BAretired - I'm not sure that is true - if the ceiling joists are small 2x4's or 2x6's, there's no way they can span the full width of a house without some secondary vertical support.
Typically they are carrying the weight of plaster or gypsum board ceilings so something that small will sag excessively.

 

[BAretired]

Good point, JAE. Figuring out the ceiling joist capacity from a photograph is a little above my pay grade. I suspect they are 2x6 joists, same size as the rafters, but I don't really know.

If there are walls or partitions available, might as well use them. Alternatively, perhaps the ceiling joists could be suspended from the roof framing.

I am wondering if this thread was prompted by Grimloktt noticing excessive sag in the ceiling.



BA

 

[r13]

Your subject title is miss leading. From the photo, it looks like the horizontal members (joists) are quite strong without splices (more than 2x..), thus you may not require interior support, but you do need end bearing walls.

 

[kipfoot]

The ceiling joists must have the capacity to carry 20 psf attic load. If there's a bearing wall under these joists, they probably are not designed to span the full width.

 

[oldestguy]

Unless you see obvious sag of the ceilings, and seeing the age (roughly) of the house, I'd not do anything. Don't fix what ain't broke.

 

[Grimloktt]

I really appreciate all the feedback!

They are 2*6 joists. There is an interior wall but believe it is non-load bearing and in-place to provide space for more kitchen cabinets, refrigerator, and oven. We want to remove the interior wall. I'm fairly confident it's not needed except possibly to support the ceiling drywall and plaster. The spanned length is somewhere around 25'. I do not know the type of wood the rafter ties/ceiling joists are made from--perhaps I can look for a marking...

 

[hokie66]

Keep the wall. 2x6 ceiling joists can't span that far.

 

[r13]

Don't trust my response below, it is designed by web calculator.

Required Span = 25'
Joist spacing 16"
Live Load 10 psf
Dead load 10 psf
Deflection limit L/360

Douglas Fir-Larch (North) - 2x10 (selected structural), 2x12 (grade no. 1 & grade &2)
Hem-Fir (North) - 2x10 (all grades as above)

 

[JAE]

Agree with hokie66. A 2x6 cannot span 26 feet without intermediate support.

 

[Grimloktt]

What's the best way to ensure proper support to remove the interior wall? We've done LVLs before but feel that may be overkill. Is there an easy way to support the rafter ties/ceiling joists from the collar ties--or similar?

 

[XR250]

25 ft. 2x6's? Never seen one that long. Are you sure they are one piece? Not that it matters anyway because, as others have stated, it can't span that far.

 

[JAE]

Grimloktt,
Three options that I see:
1. Leave the interior walls as is (probably not one of your preferences)
2. Shore up the ceilings on each side and remove the wall - insert a line of LVL beam, or beams, supported by columns and columns supported by the wall below (solid blocking)
3. Hire an engineer to analyze the collar-tie framing and see if a truss system could be developed to span the 25 feet - adding to and altering the existing framing. (note - connections will be very important here)

 

[BAretired]

The rafter ties/ceiling joists do span the entire length from exterior walls with no splicing.

I think you are mistaken about this. As others have stated, lumber does not come in such lengths. It is possible that the ceiling joists were adequately spliced to act as a tension member, but we don't know that and we cannot advise you to assume it is true without further checking.

They are 2*6 joists. [highlight yellow]There is an interior wall but believe it is non-load bearing[/highlight] and in-place to provide space for more kitchen cabinets, refrigerator, and oven. We want to remove the interior wall. [highlight yellow]I'm fairly confident it's not needed except possibly to support the ceiling drywall and plaster.[/highlight] The spanned length is somewhere around 25'. I do not know the type of wood the rafter ties/ceiling joists are made from--perhaps I can look for a marking...

I believe you are correct in the two comments highlighted in yellow. It is quite possible that the existing roof could support the existing ceiling by means of wire or wood hangers, but this would rely on competent nailing and splicing of the bottom ties (ceiling joists), which may or may not be the case. The type of wood would not change the fact that a 2x6 cannot span 26'.

I agree with JAE's three options as stated in his post above.



BA

 

[msquared48]

A couple additional thoughts...

1. Depending on the age of the structure, 26 foot sticks were available in years past, even if special order.
2. To supplement those spans, transverse strong-back beams in the attic area were used with periodic 2X vertical members from the roof structure to the strongbacks.

OP: can you provide any comments on the above possible scenarios?

Mike McCann, PE, SE (WA, HI)

 

[oldestguy]

Here is an explanation that I don't agree with.

https://www.nachi.org/collar-rafter-ties.htm

The writer gives these collar ties a function of tension in case of uplift. However, under loads the rafter tends to sag and this puts the tie into compression. That effectively reduces the length of the rafter as a beam carrying load. Put in more of these at lower heights and you can get away with a lighter rafter, effectively..

When it comes to analyzing the stresses in the rafters, it is not just calling bending the critical factor before failure. The inclination puts added compression in the rafter, in addition to that caused by bending. In addition the stress diagram in the rafter under a failure test that may not be pure triangular compression or tension as typically diagrammed for bending. Put the rafter in steep slope and failure may be wholly compression, not tension. A detailed discussion by theoretical structural guys will help on this, particularly for the characteristics of wood.

 

[BAretired]

1. Depending on the age of the structure, 26 foot sticks were available in years past, even if special order.

If that were true, it would negate my comment about probable splices in the ceiling joists. However, even then, it would be prudent to retain a local engineer to check the roof structure before adding ceiling weight to the existing structure.

BA