Collar Tie Length - Width
Douglas J. Sorocco
We have a third story ball-room which we have removed all the plaster and
lathe due to water damage and the need to rewire and insulate. It is a
gabled roof with a south facing gabled dormer. The pitch is 12/12.
We have collar ties/ceiling joists running across the dormer every 24 inches
(rafters are 24 o.c.). The collar ties are 2x4s and are at 8 feet off the
floor and basically are worthless - i.e. not realy holding the roof or
providing any type of stiffening to the structure.
We would like to raise the collar ties up so that we have the ceiling 10
feet off the floor which would leave 3-4 feet above the ceiling for
insulation and attic ventilation at the ridge cap. The roof has been
reroofed with sheathing and laminate shingles.
Question: can we go up to 10 feet without having the roof sag on us? If so,
what type of lumber should be use for the new collar ties - 2x6, 2x8 etc.
Also, a friend recommended that we scab in 2x4 firestops above the ceiling
to strengthen the span length of the roof -- is this necessary with the
sheathing?
Thanks for any help.
Douglas
The tool man
How big are your rafters?
What is the roof span?
--
The right tool for the job is in your head.
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
Michael Edelman
>
...
> We have a third story ball-room which we have removed all the plaster and
> lathe due to water damage and the need to rewire and insulate. It is a
> gabled roof with a south facing gabled dormer. The pitch is 12/12.
>
> We have collar ties/ceiling joists running across the dormer every 24 inches
> (rafters are 24 o.c.). The collar ties are 2x4s and are at 8 feet off the
> floor and basically are worthless - i.e. not realy holding the roof or
> providing any type of stiffening to the structure.
>
> We would like to raise the collar ties up so that we have the ceiling 10
> feet off the floor which would leave 3-4 feet above the ceiling for
> insulation and attic ventilation at the ridge cap.
What makes you think the collar ties are
"worthless"?
From the description they're well-placed to do
exactly what collar ties are intended to do-
resist the roof load that forces the rafters (and
walls) outward.
If you're going to move them, make sure the ends
of the rafter are tied securely to the floor
beams.
Douglas J. Sorocco
The reason I felt that the 2x4 collar ties were worthless is because they
sag terribly, are cracked and splintered in serveral places and are barely
nailed into the rafters. Sorry to leave this info out.
The rafters are 2x4 and the span is 34 feet from the east to the west gable.
Lets try again. =)
Douglas
Douglas J. Sorocco <dsor...@ionet.net> wrote in message
news:7qjk94$bhd$1...@ionews.ionet.net...
> Hello folks -
>
> We have a third story ball-room which we have removed all the plaster and
> lathe due to water damage and the need to rewire and insulate. It is a
> gabled roof with a south facing gabled dormer. The pitch is 12/12.
>
> We have collar ties/ceiling joists running across the dormer every 24
inches
> (rafters are 24 o.c.). The collar ties are 2x4s and are at 8 feet off the
> floor and basically are worthless - i.e. not realy holding the roof or
> providing any type of stiffening to the structure.
>
> We would like to raise the collar ties up so that we have the ceiling 10
> feet off the floor which would leave 3-4 feet above the ceiling for
Larry Caldwell
> The reason I felt that the 2x4 collar ties were worthless is because they
> sag terribly, are cracked and splintered in serveral places and are barely
> nailed into the rafters. Sorry to leave this info out.
> The rafters are 2x4 and the span is 34 feet from the east to the west gable.
Holy sheeit, bud. You better pray real hard, because hot air is the only
thing holding your roof up. You have 2x4's 24" on center spanning 17'?
That 12/12 pitch is the only thing saving your roof from collapsing under
a snow load. That and those collar ties halfway up. If you framed it to
modern standards you would be looking at 2x10 rafters, minimum.
> > Question: can we go up to 10 feet without having the roof sag on us?
Probably not.
> > If so,
> > what type of lumber should be use for the new collar ties - 2x6, 2x8 etc.
1x4 would work fine, except it would be hard to nail sheetrock to.
> > Also, a friend recommended that we scab in 2x4 firestops above the ceiling
> > to strengthen the span length of the roof -- is this necessary with the
> > sheathing?
Why don't you draw up a set of plans and take them in to your local
building official for a plan check? You pay your plan check fee, he will
calc your roof for you, and you won't end up ruining your house.
-- Larry
Curtis
inward. They should be installed at approx. 1/3 of the length of the rafter.
They can be removed, but not until you build pony walls(stub) at approx. 1/3
of the length from the bottom. These will then support the roof, as well as
you will still need a horizontal member near the top for added strength.
Curtis
http://www.cwhrenovations.com
Douglas J. Sorocco <dsor...@ionet.net> wrote in message
news:7qjk94$bhd$1...@ionews.ionet.net...
> Hello folks -
>
> We have a third story ball-room which we have removed all the plaster and
> lathe due to water damage and the need to rewire and insulate. It is a
> gabled roof with a south facing gabled dormer. The pitch is 12/12.
>
> We have collar ties/ceiling joists running across the dormer every 24
inches
> (rafters are 24 o.c.). The collar ties are 2x4s and are at 8 feet off the
> floor and basically are worthless - i.e. not realy holding the roof or
> providing any type of stiffening to the structure.
>
> We would like to raise the collar ties up so that we have the ceiling 10
> feet off the floor which would leave 3-4 feet above the ceiling for
> insulation and attic ventilation at the ridge cap. The roof has been
> reroofed with sheathing and laminate shingles.
>
> Question: can we go up to 10 feet without having the roof sag on us? If
so,
> what type of lumber should be use for the new collar ties - 2x6, 2x8 etc.
>
> Also, a friend recommended that we scab in 2x4 firestops above the ceiling
> to strengthen the span length of the roof -- is this necessary with the
> sheathing?
>
The tool man
I'd have to agree with Larry on this. If I understand you correctly, a
cross-section of your roof would be a triangle with a 34 foot bottom
side and 24 foot (approximately) sides sloping at 12/12 pitch. Your
roof consists of two layers of sheathing and shingles supported by 2x4's
on 24 inch centers? Yikes! No wonder your collar ties are cracked. It
sounds like they're being pulled apart.
Without seeing it, I find it hard to believe it didn't collapse when the
roofers were walking around up there.
You will almost certainly need to "sister" on new rafters that are 2x8's
or larger. Even if it weren't necessary for structural reasons, you'll
need the space for insulation and ventilation. You will also probably
need knee walls at the sides and larger collar ties. Can you move them
up? Yes IF your rafters, knee walls and collar ties are designed as a
structural system by someone who knows what they are doing.
You are probably better off drawing up plans and consulting with a
building inspector, or better yet, a registered professional engineer.
Regards,
John.
Tim Werbstein
Hey! What about an architect?
The tool man
I forgot about you guys. I'm an Engineer, so I recommended what I would
do.
Douglas, use any professional you would consider qualified to perform a
thorough and proper structual analysis for your situation.
BTW, you know what they say...
Engineers build weapons. Architects build targets. ;)
Tim Werbstein
You FORGOT about us guys!... even after all the nice targets we built
for you engineers to destroy! That's gratitude for ya!
Larry Caldwell
> Collar ties are there for a reason. To support the roof from collapsing
> inward.
Well, yes and no. Collar ties do form a truss chord from rafter to
rafter if they are installed on every rafter. When the ceiling is
finished in an attic, collar ties do a lot to stiffen the roof.
However, collar ties also protect a roof against uplift. An example like
this one, with a 12/12 pitch, can be subject to pretty fierce uplift
forces during high winds. The collar ties keep the roof from pulling
apart at the peak and blowing away.
Oddly enough, the current CABO does not require collar ties on stick
framed roofs.
lo...@crestedbutte.net
>In article <qqnz3.13667$c8.1...@news1.rdc1.ab.home.com>,
>cur...@cwhrenovations.com writes:
>
>> Collar ties are there for a reason. To support the roof from
collapsing
>> inward.
>
>Well, yes and no. Collar ties do form a truss chord from rafter>to
>rafter if they are installed on every rafter. When the ceiling>is
>finished in an attic, collar ties do a lot to stiffen the roof.
>
>However, collar ties also protect a roof against uplift.
prevent the walls from spreading out under roof load. You can skip
them by simply over building the ridge to carry more load without
sagging. If uplift is a concern use hurricane clips. To sum up, a
collar tie is meant to function under tension, not compression.
thats my .02 worth
rob
--{ BuilderNews, http://www.buildernews.com/newsgroups/news }--
Providing Quality Web Based News Group Access to Leading
Building Industry Sites like Remodel Online, BuildNET,
BIX, Building.Com and more
Larry Caldwell
> I think your both missing the real reason for them. they are there to
> prevent the walls from spreading out under roof load.
Certainly, if you forgot to nail your ceiling joists for some reason.
Open vaulted designs are an exception.
-- Larry
Daniel Hicks
>
> lar...@teleport.com (Larry Caldwell) wrote:
> >In article <qqnz3.13667$c8.1...@news1.rdc1.ab.home.com>,
> >cur...@cwhrenovations.com writes:
> >
> >> Collar ties are there for a reason. To support the roof from
> collapsing
> >> inward.
> >
> >Well, yes and no. Collar ties do form a truss chord from rafter>to
> >rafter if they are installed on every rafter. When the ceiling>is
> >finished in an attic, collar ties do a lot to stiffen the roof.
> >
> >However, collar ties also protect a roof against uplift.
>
> them by simply over building the ridge to carry more load without
> sagging. If uplift is a concern use hurricane clips. To sum up, a
> collar tie is meant to function under tension, not compression.
> thats my .02 worth
> rob
True when there are no ceiling joists to tie the roof rafters together
at the bottom, but collar ties are also sometimes used in addition to
joists to prevent sag in the roof. I doubt that they would contribute
much in the way of protection against uplift, though.
The tool man
I hate to disagree, but I really don't see how collar ties reduce the
liklihood of losing the roof in high winds.
Studies of homes damaged by hurricane Andrew showed that roofs failed
by one of several means. In some cases, the high velocity air moving
over the roof perpendicular to the ridge caused a vacuum (just like an
airplane's wings). If the sheathing wasn't properly fastened with
nails, the sheathing was literally sucked off of the framing. In other
cases, inadequate end bracing caused gable ends to collapse inward from
wind pressure. In others, wind lift caused failure of gable overhangs
which peeled back the roof sheathing. Also, there were some houses
that literally exploded when a door or window on the windward side gave
in and the entire house was suddenly pressurized.
The lessons? Better rafter-to-wall connections (they're even called
hurricane ties!), nails instead of staples for roof sheathing, and
better gable end bracing (or use a hip roof). In none of these cases
could collar ties make much difference. Once the sheathing is
breached, you lose, regardless.
Sorry for the long-winded post. BTW - check out Fine Homebuilding #78,
p 82 for some pictures of the above. Not pretty.
Regards,
John.