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Re: Use of Collar Ties in Light Frame Wo

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Dennis ---

I have been lurking here, but have recalled that I had a similar
post-earthquake repair in 1994.  Rafters had moved outward on the
supporting walls, allowing the ridge to drop.  No cracked ridge board
however.  

Repairs were accomplished easily using rods and turmbuckles with bolted
plate clevis brackets.  Ceiling joists were not considered as having any
value, and each rafter required a rod for a lower chord.   No jacking
required - just turn the turnbuckles until dimensions returned to normal.
 I found that the rods had to be attached close to the walls to reduce
tail stresses to acceptable levels.  Roof repairs were not required, and
no demolition or temporary construction of any kind necessary.

Many older custom homes in Los Angeles were constructed with similar
systems and with the rod systems exposed in vaulted ceiling rooms.

--- Russ Nester
    rnester(--nospam--at)juno.com

_________________________________________________________________________
_______

On Wed, 6 Jun 2001 11:20:38 -0700 "Structuralist" <dennis.wish(--nospam--at)gte.net>
writes:
> Roger,
> I guess I am recommending that they continue the "bandaid" approach 
> in the
> this case. I have no other choice. The buyer is not negotiating the 
> price on
> the fix - in fact the owner has agreed to repair the roof prior to 
> the close
> of escrow in the next 10 days which is really not possible. The 
> buyer is
> only interested in moving into the home, the seller getting out and 
> the
> agent (a resale office in the development) the commission for the 
> sale.
> However, to suggest tearing off the roof and starting over to build
> something better than what was there - which, as you suggest is a
> non-structural problem since there really is nothing wrong with the 
> roof -
> would kill the sale and probably place me in a rather delicate 
> situation of
> having to defend myself to all parties.
> This is one of those damned if I do and damned if I don't situations 
> so, in
> my opinion, the best thing I can do is offer a reasonable 
> explanation for
> why what was perceived to be a structural failure is not structural.
> Something has caused the ridgeboard to crack - even if it is
> "non-structural".
> The truth is that by adding the collar ties, I am not harming the 
> existing
> roof further and adding a lot of psychological support for the new 
> owners. I
> am also saving the existing structure which I really don't believe 
> needs to
> be torn down and replaced.
> 
> Finally, it is not uncommon here to use the garage for a workspace. 
> There is
> a number of work benches, a Washer and Dryer as well as a Freezer in 
> the
> garage. The insulation and gypsum was added to allow the room to be 
> used in
> the warmer parts of the year (probably not the hotest times). My own 
> garage
> is finished to allow the possiblity of adding a swamp cooler and 
> using it as
> a workshop in the near future (I have an old Shopsmith waiting for 
> my kind
> restoration).
> 
> I understand you arguments and they make a lot of sense. Sometimes 
> it is
> easier and more diplomatic to fix the problem and tell the client 
> what they
> want to hear even if the fix is more psychological. Truthfully, I 
> might have
> suggested doing nothing until I saw the conditions of the ceiling 
> joists as
> I believe this needs to be addressed. I still feel the collar ties 
> can, in
> this case be useful as a redundant system to overcompensate the 
> rafter ties.
> 
> Thanks Roger, but sometimes we got to go with our gut feelings.
> 
> Dennis
> 
> > -----Original Message-----
> > From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
> > Sent: Wednesday, June 06, 2001 6:27 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: RE: Use of Collar Ties in Light Frame Wo
> >
> >
> > Dennis,
> >
> > Bear in mind that I am writing this quickly before I am fully 
> awake.
> >
> > Frankly, I think that you are grasping at straws for an
> > explanation as to why
> > the garage roof sagged "a couple of inches" and that the reason
> > for this is
> > non-failure related.
> >
> > It seems that everything that has been done prior to your 
> involvement has
> > been a "band-aid" approach.  Is what you are recommending a
> > continuation of
> > this approach?
> >
> > As several people have pointed out, the ridge plate is
> > non-structural and the
> > crack in it is not relevant.  The plate could have been a 1 X as
> > well as a
> > 2 X.  A lot of carpenters splice ridge plates where a rafter 
> connects so
> > that there is not a long unsupported tail and a lot of these 
> splices are
> > hard to see.  Slope of grain in lumber can be as much as 1:6, so
> > the crack
> > parallel to the grain is not an "undetected defect" if the grain
> > meets the
> > slope requirements.
> >
> > As for your explanation of the deflecting ceiling joists "pushing" 
> the
> > rafters up, don't forget that the thrust from the rafters is
> > putting tension
> > in the ceiling joists and trying to keep the ceiling joists from
> > deflecting,
> > like an archery bow keeps the bowstring straight and returns it
> > to straight
> > after being deflected.
> >
> > A quick calculation shows that a 2" drop in the ridge would
> > result in a 1/2"
> > outward push on each of the exterior walls.
> >
> > Why is there insulation in the attic of the garage?  Around here, 
> getting
> > insulation in the garage attic is like pulling hen's teeth.
> >
> > Even without insulation in the attic, it would be very difficult
> > to inspect
> > the condition of the rafter/ceiling joist/wall connection.
> >
> > I think that the truth of the matter is that at this time, none
> > of us has any
> > idea of what might have happened.
> >
> > The house is in escrow --- it is not yet sold and I am sure that
> > the buyers
> > (your clients?) are awaiting your report to negotiate an
> > appropriate purchase
> > price.  And, they would be relying on your report and solution to 
> take
> > complete care of the problem.  With what is not known, I don't
> > know if you
> > could provide that kind of assurance.
> >
> > I would be tempted to report that it cannot be determined what
> > caused the sag
> > in the roof and I would probably recommend that in order to 
> provide a
> > structurally adequate roof, that the existing roof be removed and 
> replace
> > with a new structure.  Engineering wise, it is a lot easier than 
> futzing
> > around trying to jack up and patch a sagging roof system.
> > Construction cost
> > wise, it is probably less expensive than the uncertain repairs and
> > engineering fee would be.
> >
> > A. Roger Turk, P.E.(Structural)
> > Tucson, Arizona
> >
> > Dennis Wish wrote:
> >
> > . > Nels,
> >
> > . > I thought I pretty well got to the root of that one. One
> > assumption that
> > . > was made was that the roof ridge dropped where the ridge
> > board cracked.
> > . > Since you and most of the others would agree that it is
> > unlikely that a
> > . > cracked ridgeboard would have caused this type of damage if
> > the existing
> > . > rafter ties were properly connected then the problem would 
> have to be
> > . > elsewhere.
> >
> > . > So let's look at the basic construction of the "carpenter 
> truss":
> >
> > . > 2x8 RR @ 24" o.c. slope 3:12
> > . > 2x12 Ridge Board
> > . > 2x6 Rafter Ties @ 24" o.c. - 25-feet long (continuous)
> >
> > . > The first obvious fact is that a 25'-0" long 2x6 based upon
> > current stress
> > . > values (assuming DF #1 grade) will deflect approximately
> > 2-inches from
> > . > just the addition of a 1/2" gypsum ceiling and R-11 batt
> > insulation using
> > . > a less than conservative 6.0-psf. This assumes no live load
> > application
> > . > (who knows what the last owner stored in that attic space).
> >
> > . > The two inch deflection is enough to substantiate the crack
> > in the ceiling
> > . > at mid-span. Although the builder tried to brace the ceiling 
> with a
> > . > built-up 2-2x8 beam 22'-6" long, the chances are that it was
> > very little
> > . > help since it was so deficient in depth to help control 
> bending much
> > . > better than the 2x6's acting alone.
> >
> > . > So now we have the rafter ties deflecting causing the rafter
> > tails to pull
> > . > inward. Am I wrong to conclude that it is possible, by the
> > squeezing the
> > . > ends of the rafters together, one might cause the ridge to
> > rise? While the
> > . > initial problem assumed that the ridge dropped because of a 
> broken
> > . > ridgeboard, the ridge actually rose, except where the broken 
> board
> > . > occurred, because of the weight of a ceiling and insulation
> > installed on
> > . > Rafter Ties which deterred from their actual purpose?
> >
> > . > The double 2x8 beam was not stiff enough to compensate for
> > the defection
> > . > of the ties. Had it been, the ridge may never have changed.
> >
> > . > I have decided to write this up as my professional opinion
> > and to suggest
> > . > that in the process of installation of the new beam to check 
> the
> > . > connection of the rafter ties to the roof rafters to insure
> > that the 3-16d
> > . > nails are in place and there is sufficient connection to the
> > double top
> > . > plate to eliminate the possibility that the rafter tails cut 
> lose and
> > . > trust out under the weight of the roof.
> >
> > . > I did inspect the exterior of the building and could see no
> > cracking at
> > . > the corner where the stucco covering the eave meets the wall.
> > In fact the
> > . > exterior finish had not been upgraded (painted or repaired)
> > for at least a
> > . > few years and there are not cracks. The photos that I took
> > show the ridge
> > . > and the eave. It takes a lot to see the deflection in the
> > roof ridge and
> > . > it is highly likely that the deflection is more likely caused 
> by
> > . > workmanship and not any rise or fall that is noticeable. I 
> think what
> > . > draws more attention is the crack in the ceiling at mid-span
> > of the rafter
> > . > ties and the noticeable ceiling deflection than at the roof.
> > I've replaced
> > . > many a compo roof with flat tiles and have never seen a
> > perfectly flat
> > . > roof - there is always some imperfection caused by crowning of 
> the
> > . > rafters and I would think that even though this is the
> > original roof, the
> > . > same high's and low's might be related to rafter crowning.
> >
> > . > Does anyone think I'm on the right track here???>)
> >
> > . > Thanks for all the help from everyone.
> >
> > . > Dennis
> >
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