It might be possible to use knee walls and the attic floor to provide
support. Since you don't want to simply replace the collar ties, I vote that
you need to get an engineer to take a look.
So it looks like 4 votes for getting an engineer and 2 votes by folks who
don't seem to know what collar ties accomplish.
Obviously someone doesn't know what a collar tie does.
It's main purpose is to stop that slab of roof from becoming an
airplane wing with a strong wind. They are usually every 4 ft and
down about 1/3 of the rafter. They also do give some support to
the rafter to keep it from sagging. A collar tie just below the
ridge will hold the roof together just as well but gives no
support to the center of the rafter. If the rafter is sized
right, it doesn't need any support anyway.
Someone here seems to think it will help keep the building from
spreading. That is total nonsense The only one that thinks you
need a permit or an engineer must need the consulting work.
Can you say "Triangulation" It sounds like this could be fixed with
nothing more than a string-line, a hefty jack and some new collar
1) The Jack(s) will put it back where it started.
2) The string-line will determine what is straight.
3) The collar ties hold it in place
Once the collar ties are properly secured, the rafters shouldn't go
anywhere. If needed, and there is ample support below, the need for
"Ridge Poles" could be put into place for added support. But ONLY if
there is ample support from below.
I suspect that in the OP's case you may be right, but without seeing it
firsthand and determining exactly what is happening and why, I wouldn't
bet the farm on it.
Installing a post under a ridge, essentially creating a structural
ridge, can put a very large load on that post, and that load must be
carried down to the foundation. I would strongly suggest not
installing a post without a pro designing a complete solution.
That is not true. A cathedral ceiling supported by a ridge beam does
not historically have any different connections at the ridge and it
does not have collar ties, yet it doesn't become an airplane wing.
That is true.
That is not exactly true.
This statement indicates you do not understand the forces a rafter
That is not true. I could use a 2x16 rafter and that does exactly
nothing to the connections or loads at either end.
You do not know what you're talking about. Could you diagram the
forces on the rafters? Do a little moment diagram for a section
through the rafter? Do you engineer your nailed connections and
determine what shear load a connection will experience when you decide
how many and what size nails to use? You're lack of understanding is
misleading others. This is not a good thing.
I would suspect some structural damage. Take cross measurement in the
attic and height at all four corners. IMHO if the differences are less
than 1/4", I wouldn't worry about it. I would replace collar ties also.
Cheap fix would be to pull rafters closer and then nail collar ties.
If I was able to get a passing grade on stresses on a multi-span
bridge years ago in engineering school, I really believe I do
understand stresses on a simple roof but I bow to your "superior
knowledge". (laughing and bye)_
Apparently it's time for a refresher course. You're letting your
assumptions run away with your diagnosis.
Let's let the facts speak for themselves, and not your assumptions.
Collar ties are not necessary to tie the walls together _if_ there is a
suitably connected rafter/ceiling joist system to take the load. There
is separation at the ridge. Differental movement in structural members
is by definition a failure. Neither of us have seen the place and have
no idea of how the place is framed, whether there are other existing
structural issues or not, right? So we're starting at the same place.
Let's summarize the information to date.
The OP has done a substantial amount of work to the house, including
foundation work and replacing the roofing, and he's been living in the
house since February. I think it's fair to say he is familiar with the
house. His descriptions have been clear, and it is also clear that he
is not clueless when it comes to construction. The OP is observant and
is asking a question about the gaps that have appeared at the bottom of
the plumb cuts only on the rafters where the collar ties were removed.
I won't use the word if in any of this because that requires an
There are gaps at the rafters where the collar ties were removed and
not at the rafters with the remaining collar ties.
The OP did not mention whether the gaps were on only one side of the
ridge or both. No assumptions, let's deal with both situations.
Gap at only one side of the ridge:
The OP did a fair amount of foundation work, so there were obviously
some issues there, and we can't conclusively eliminate the foundation
as the proximate cause of the gaps. A gap at the bottom of the plumb
cut on only one side requires either the ridge to drop in elevation or
for the foundation to move in one of two ways.
1). the foundation must rise on the side of the gap (possible due to
frost heaving or the foundation work, but an extremely remote chance);
2). the foundation must drop on the opposite side of the gap
(possible for the same reasons as above).
You would have to make some assumptions to calculate how much
differential settlement would have to occur in the foundation for a
1/4" gap to open up at the plumb cuts, but, no assumptions > no
calculation. Suffice it to say the foundation would need to settle a
lot to open up a gap at the that size. Foundation failures show up on
lower floors before they show up on upper floors due to distribution of
the stresses through wall and floor diaphragms. The OP would have
noticed a whole host of problem areas, such as doors and windows
binding, wall and ceiling cracks, etc.
Gap at both sides of the ridge:
The ridge has to settle. Again, only two possible scenarios:
1). the rafters have to bow _up_ as the ridge settles.
Hmmmm....okay, that's not a possible scenario.
Which leaves us with only two possibilities:
1). the walls the rafters are bearing upon have spread apart.
2). the OP isn't observant, or not able to make a coherent statement.
I've seen nothing to support that conclusion.
I checked out that link and it doesn't really differ from this one.
There is a lot of misinformation being bandied about. Let me put it
another way that should make it easier to digest.
In a correctly framed house there is a lot of redundancy and a lot of
dual/triple purpose structural members. Floor joists tie the walls
together, act as a diaphragm (even if not designed that way) to
distribute racking and shear forces, and also provide support for the
floor. Compromising any one of those functions can be problematic. In
the OP's situation, there has been a localized failure due to the
removal of the collar ties. Regardless of the designer's primary
reason for their installation (stabilizing rafters, preventing uplift,
tying walls together, etc.) their removal has caused the walls to
spread apart. The evidence certainly seems to point to the collar ties
tying the rafters together as an important function, whether designed
that way or not.
As far as the size of the collar ties, a 1x4 with a sufficient number
of nails in the correct pattern (no splitting) can take a very
substantial load - wood is good in tension. Which also begs the
question, why would someone use a 1x4 in axial compression to tie
rafters together? Uplift is certainly one explanation, but as I posted
earlier, the nailed rafter/ridge connection, and sheathing/rafter/ridge
connections would perform that function in almost all areas except
hurricane-prone areas. In my area I am currently required to strap
over the top of the ridge and tied the rafter pairs together. That
obviates the need for collar ties to prevent uplift right there, but it
does nothing to prevent the rafters from splaying.
In that other thread in that other forum, someone pointed to code as
not requiring a sufficient number of nails in the collar ties to handle
the load required to hold the walls together. Since we have no idea of
the construction of the OP's collar ties, house framing, whether or not
it was over or under built, and it's unlikely we can ask the original
designer their intentions for the collar ties. We can't say why they
were installed. All we have is that they were removed and gaps opened
It's also not a suitable defense to say you followed code for your
nailed connections if you're an engineer, architect or simply
interested in quality construction. Code is the minimum acceptable
codified construction and does not address the requirements of a
particular structure. Loads and connections must be designed. I hope
everyone understands that something built to code and no more is not
Amen, Glenn. Every statement you made jives with what I know
about collar ties. I am not an engineer, but I think some people
should do a bit more research before spouting off as experts.
Most collar ties are 1x material nailed on with 8d nails. I
really can't envision any circumstance where they could prevent
the spread of the side walls. It is my understanding that a
collar tie is to stiffen and prevent uplift on the leeward rafter.
Does installing a stiff back (purlin?) braced off to top plates
take the place of collar ties? I would appreciate Bob Morrison's
clarification of the issues.
There seems to be a general misunderstanding about the difference
between "rafter ties" and "collar ties". I wanted to verify my
information so I googled. For an interesting discussion of the
same thing go here:
Keep the whole world singing. . . .
I would attempt to put all back the way it was. The biggest problem would
be closing the gap at the ridge board and rafter plumb cuts.
If the rafters have not lifted at the exterior wall, there may be a way with
lateral leverage and weight on the roof to close the gap and reapply collar
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