From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
Subject: RE: Use of Collar Ties in Light Frame Wo
Date: Wed, 6 Jun 2001 11:20:38 -0700
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
the fix - in fact the owner has agreed to repair the roof prior to the
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
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.
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
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
a workshop in the near future (I have an old Shopsmith waiting for my kind
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
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
Thanks Roger, but sometimes we got to go with our gut feelings.
> -----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
> 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
> 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
> 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,
> 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
> 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
> . > 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
> . > (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
> . > 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
> . > 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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