[pullenpoynt]

hello all

need help with a problem i have on a proposed remodleing job - seems that a former owner of the house in question cut the collar ties so that he could finish off the attic - now -- the exterior walls of the second floor are bowing out in the middle of the structure and the roof has dropped 3"-4 " off the chimmeny -

i thought of trying to secure a plate to the header and the other end to a joist and try to pull it back in with either a turnbuckle or comealong -

just thought i would throw this out there for some other thoughts

thanks

 

[Tom R]

Can't say I've done this type of job before, - - and I rarely 'ever' turn a job down because I 'fear' it, - - but this one I would walk away from.

Seems to me, - - that it's not only too much liability (on you) to begin with, - - but what other 'hair-brained' stunts did the previous homeowner pull??

You may not find out 'til right after the collapse!!

Other than that, - - if you're insistent on doing it, - - all I can say is you would need to be able to jack up the ridge at the same time and at the same (proportional) rate as you were pulling in the walls.

All this movement that took years has a 'high resistance' to being moved back all at once.

If I were even going to attempt it, - - I would do it over the course of several days.

Maybe someone else on board has experienced this 'maneuver'.

 

[Glasshousebltr]

Sound advice Tom.

Come alongs between the walls, Lift the ridge at the same time, a little each day, plenty of temporary sub support, then brace it and bolt it off.

If your not familiar with doing this type of structural repair, better get some on site advice, or we'll be digging you out like a Pakistani peasant.

Bob

 

[Tom R]

or we'll be digging you out like a Pakistani peasant.

:cheesygri :cheesygri :cheesygri

No :innocent: for you!! :no:

You're banned forever from any P.C. clubs around here.

That one rates right up there with the black (bear) comment.

Keep 'em comin'!!

 

[The Yaz Man]

Personally I think that you should enlist the help of an engineer or architect that you know on this one. Then it's his liability not yours. He is the guy that should really be putting together the correction plans anyway as there appears to be significant structural degredation.

Not to mention if the engineer/architect is tight with you you can make some on his end, or bill his work through you and collect the markup if your not tight with him. Either way his liablity takes center stage.

It's the best of all worlds because you take care of the homeowner who thinks your superman. You kick a contact some billable work and because you have to follow "plans" and "specs." you can justify your grossly inflated bill.

Heres a noteworthy thing, when you recommend a contact especially an engineer that is competent he's selling you. Good work from him will be what is called value added partnering. If the homeowner is happy and content you can even have your guy do some information mining to see what the house has in the bank for a reserve for the work. That way you can size the mark up and get it closest to the pin.

Far from walking away from this one, I would utilize it as a way to make my support and resource network work and earn for me.

 

[mighty anvil]

Your description of the structural problem doesn't sound right to me. The structrual purpose of collar ties is to brace the rafters against each other, effectively reducing their span and allowing smaller sized rafters. If their purpose was to resist the horizontal component of the rafter force at the top plates, the rafters would have to be large enough to resist that bending moment and that approach is not part of a conventional framing system. Therefore, removing the ties should, at worst, result in sagging rafters, not bowing walls and a drastically dropped ridge. There must be something else seriously wrong with the house frame.

If the house is conventionally framed, it is the attic joists spanning from top plate to top plate that resist the outward component of the rafter force on the exterior walls. Perhaps the attic joists span in the other direction between interior bearing walls and it is therefore the bearing walls that tie the top plates together. Perhaps these bearing walls are too far apart or they are not connected to the top plates well enough.

You will definitely need a structural engineer in order to first determine the true nature of the problem and then to solve it safely.

 

[old27]

Your description of the structural problem doesn't sound right to me. The structrual purpose of collar ties is to brace the rafters against each other, effectively reducing their span and allowing smaller sized rafters. If their purpose was to resist the horizontal component of the rafter force at the top plates, the rafters would have to be large enough to resist that bending moment and that approach is not part of a conventional framing system. Therefore, removing the ties should, at worst, result in sagging rafters, not bowing walls and a drastically dropped ridge. There must be something else seriously wrong with the house frame.

If the house is conventionally framed, it is the attic joists spanning from top plate to top plate that resist the outward component of the rafter force on the exterior walls. Perhaps the attic joists span in the other direction between interior bearing walls and it is therefore the bearing walls that tie the top plates together. Perhaps these bearing walls are too far apart or they are not connected to the top plates well enough.

You will definitely need a structural engineer in order to first determine the true nature of the problem and then to solve it safely.

I disagree. collar ties keep walls from blowing out.

 

[Glasshousebltr]

Mighty, in some areas of the country they call the bottom cord of the truss a collar tie.

Bob

 

[mighty anvil]

I'm talking about rafters in a conventionally framed roof, not a truss. A "rafter tie" can occur at any point on a rafter. An attic floor joist nailed to a rafter can be considered a rafter tie. The term "collar tie" is used for all typical rafter ties because they are usually installed above the mid point of the rafter.

For conventional framing, most if not all codes require rafters to be nailed to attic joists if they span in the same direction as the rafters in order "to form a continuous tie between exterior walls". When attic joists span the other way the code allows "rafter ties" to be used "as near the plate as practical" in order to indirectly provide a tie between the walls. In this condition it is up to the judgement of the designer or the contractor or ultimately the inspector to determine how high a "rafter tie" can be placed for a given rafter size. slope and span so that it will tie the plates together but not cause the lower portion of the rafters to bend over time allowing the walls to spread and the rafters to bow.

I'm just pointing out that the primary purpose of a rafter tie is to strengthen the rafters by reducing the effective rafter span and that in the specific case of attic joists running parallel to the bearing walls, the top plates should be tied together through the attic sub-floor or other means, rather than with rafter/collar ties since in the long run (at least in snow country) it is possible for rafter ties to cause the rafters to bow and because, if the ridge is high enough, someone bonehead will inevitably remove the ties.

I would say that collar ties might keep walls from blowing out in certain conditions but that it is wiser to use them only for the purpose of strengthening rafters and hold up ceilings.

I would not use a cable to pull the walls together since it can cause serious damage when it breaks. I would find a house mover or other contractor who might have rods and turnbuckles that can do it more safely. You might even have to notch the attic joists (assuming they run that way) and leave the rods in place.

 

[K2]

More info from pullen would be nice.

 

[Glasshousebltr]

And the last rafter attached to the lookouts is called? fly rafter, rake rafter, barge rafter, soffit rafter, etc. For the past 25 years I've watched these guys in at least 8 different parts of the country make their own terms and descriptions......I'm aware of the technical term.

Also I think your incorrect on the principal reasoning of structural support for the attic joist, collar tie, bottom cord, ceiling joist or whatever we want to label it. Holding the ceiling, supporting the roof and preventing wall expansion are equally important. I also believe it was intended that way, from design, all the way back to the old timers throwing up balloon frames.

I couldn't count how many times my repair consisted of this failure, or a similar one, gusset, notches, etc, resulted in a problem such as this.

Come along's will work, but you'll have to use several, you have to support the ridge as well as lift it as you go, and you have to brace like hell.

Bob

 

[pullenpoynt]

thanks for all the input
the current owners wanted to add a full dormer on one side of the roof - but when i noticed this problem i had to reconsider as i didn't want the exterior walls to fall out once the rafters were cut -
i do like anvil's idea the best - as i was leaning towards that in the first place ( rods and turnbuckle)- and simultanesously jacking up the ridge to put things back in perspective - prior to ripping out and putting in the dormer -
come to find out - the house was originally a single family structure and sometime ago (about50yrs ago) a second level was added and was used as a income property for the original owners -
the current owners still have the same plans to retain the rental income but have decieded to utilize the second floor as their residence and thus wanted to make better use of the upper (attic) space -

again thanks for the input
bob

 

[Joe Carola]

thanks for all the input
the current owners wanted to add a full dormer on one side of the roof - but when i noticed this problem i had to reconsider as i didn't want the exterior walls to fall out once the rafters were cut -
i do like anvil's idea the best - as i was leaning towards that in the first place ( rods and turnbuckle)- and simultanesously jacking up the ridge to put things back in perspective - prior to ripping out and putting in the dormer -
come to find out - the house was originally a single family structure and sometime ago (about50yrs ago) a second level was added and was used as a income property for the original owners -
the current owners still have the same plans to retain the rental income but have decieded to utilize the second floor as their residence and thus wanted to make better use of the upper (attic) space -

again thanks for the input
bob

Leaving out adding a full dormer changes a lot of things here. But to start, you shouldn't be the one asking how to fix this. The Architect or Engineer should be figuring this out.

Since the one side of the house is getting a full dormer it makes no sense at all to try and fix the problem before you rip the roof off. You put a temporary wall under the ridge with bracing and remove the back roof off and it will be a lot less weight and you can jack up the ridge to pull the walls in. If the walls on the other side where the dormer roof is going are staying you can brace those up before you rip the roof off and then pull them in plumb afterwards.

This is a big job because once you have the roof ripped off you want to fixe this as fast as you can with plenty of man power to get it closed in and water tight.

There's many many ways to tackle this but your not the one who should be figuring this out unless from where your from you don't need Architectual or Engineered plans and building permits.

Joe Carola

 

[Cole]

If your not familiar with doing this type of structural repair, better get some on site advice, or we'll be digging you out like a Pakistani peasant.

Bob

Wow!!

Bob, you are a special kind of person.:shutup:

 

[mighty anvil]

It's interesting to see such strong faith in the structural capability of collar ties. I have been participating in another forum where collar ties alone were installed to prevent support walls from spreading and the inspector wouldn't accept it.

I know rafter/collar ties have been used for a long time and I believe they contribute to the strength of the structure but when installed in the conventional manner they cannot resist the forces generated by the minimum roof loading stipulated in the building code.

As an example, consider a 24 ft span with a 12 in 12 roof with the rafters 24" o.c. and the collar ties 7 ft above the top plate. Under a code load of 50 psf the tension in each end of the collar ties is 1,440 lbs. Assuming a tension design stress of about 300 lbs, a 2x8 collar tie will work. The problem then is how to connect the tie to the rafter. You could do it with a 2 1/2" split-ring connector, fifteen 12d nails or three 1" bolts with washers. Since the building code here in Boston only requires three 8d nails at this location (which might resist 240 lbs which is 1/6th of the design load), it is obvious that the building code does not intend for a collar tie to resist the minimum design load that it imposes on a roof.

As a practical matter the minimum code roof loading rarely occurs and it assumes generous safety factors as well so a collar tie might work fine but its use puts the designer or builder in that grey area between what you can get by with and what a jury of your peers will expect you to have done.

As an architect I can't even use the building code as a defense for a design failure so I use this rule: always tie rafters at the atttic floor line unless you have an alternative design stamped by an engineer.

 

[TimNJ]

A little more detail pullen. Is this a cathedral ceiling with the rafters sitting on a kneewall? or a 8' high wall? or conventional 8' high wall with ceiling joists tieing each side together?

 

[FLStructengr]

Yes, you can use turnbuckles or comealongs to pull the walls in. The problem is the only way to really fix it is to put the collar ties back. Use ingineered wood and bolt. Hire a structural engineer to provide details. That is safest way. If you can not do that you will need to stiffen the walls. Not an easy thing to do.

 

[mighty anvil]

the only way to really fix it is to put the collar ties back.

If the top plates are tied together at the floor line, what would be the structural purpose of adding collar ties?

 

[old27]

If the top plates are tied together at the floor line, what would be the structural purpose of adding collar ties?

to keep the ridge from sagging, and hence...I think you know the rest but don't want to admit it. no offense intended.

 

[mighty anvil]

The point is a simple and obvious one: if the rafters and attic floor form a structural triangle, the top joint (ridge) can't sag and collar ties would be unnecessary. If the rafters are undersized, they could sag and to prevent that would be the reason to add collar ties.

Claiming that I know something but won't admit it is a classic ankle-biter response and uncalled for considering the degree to which I have gone to present this information. You can disagree without being disrespectful.