Cathedral ceiling - no collar ties-ok?

yitzieNovember 10, 2005

We recently moved into an 80 yr old home in Cleveland Oh. I'm going to begin finishing the attic (open rafters right now) and I plan to leave the cathedral ceiling, insulate and rock'- it.

The rafter height is 12' at the peak, and the floor is about 28'x28'. The rafter beams are 2x6's on 16" centers, toe nailed into a 1x6 at the ridge.

But there are no rafter ties, is that normal, is it ok to leave like that? or do I have to lose the cathedral and put them in? what about the 'lateral force/pressure pushing out on the exterior walls' thing?

(And they've never been removed, or at least there is absolutely zero signs that there were ever ties in place.)

thanks,

yitzie

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early1

You need something to resist the lateral forces. You can do a kingpost, which basically supports the ridge at the ends, but your ridge then becomes a real beam rather then just an inert pinching member. Your 1 x 6 won't handle a kingpost design. Even with kingposts the rafters need a lateral force resisting connector at the ridge. So either the walls need to be designed for lateral loads (usually not the easiest thing to do), or you need collar ties. Note that the collar ties don't have to be at the level of the top of the wall. You can put them higher up. The limit to how high depends on the capacity of the rafters, but sometimes you can get them very near to the ridge and you still have the cathedral effect. I should mention that your rafters are undersized. Consider sistering a deeper member to the 2 x 6's to make sure the weight from one of your snowstorms doesn't crack the drywall. 2 x 10 will let you insulate nicely.

    Bookmark   November 10, 2005 at 2:37PM
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early1

OK, I'm re-reading you post now. If you're in the attic, does that mean that there are ceiling joists for the attic floor? If so, if properly connect to the walls at the end, they would serve as the collar ties.

    Bookmark   November 10, 2005 at 2:41PM
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JRRR

The tops of the bearing walls need something to prevent the load of the roof from pushing them outward. Collars do this by locking the rafters, but this loses effectiveness when they are placed higher than about a third of the way up the rise. An alternative, as suggested by early1, is the structural ridge. It's supported at both ends down to the foundation, and is sized according to the dead load and live load (snow). The connections of the rafters to the ridge and to the plate is critical, calling for framing hardware at every connection.

    Bookmark   November 10, 2005 at 2:49PM
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mongoct

If the attic floor joists...which are the ceiling joists for the living space below...are PARALLEL to your attic rafters...

Then your attic floor joists are tying your exterior walls together and resisting the lateral pressure exerted by the weight of the roof, through the rafters, and outwards onto the exterior walls. "Lateral thrust."

I'd guess that you have the above. Your 1x6 at the ridge sounds more like a ridge BOARD, which a non-structural ridge. It's simply there as a nailer for the tops of the opposing rafters.

A structural ridge would be a ridge BEAM. You would need that if your attic floor joists (ceiling joists for the living space below) were running perpendicular to the attic rafters. A beam would be much more massive that a 1x6.

There are always exceptions to the rule, especially in older construction. Your house might be balloon framed for all we know. Not likely, but possible. That said...this is a simple gable roof, right?

    Bookmark   November 10, 2005 at 3:41PM
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yitzie

Ok, first this roof is original (built in 1928), why they used 2x6's I don't know.

And yes the floor joists (ceiling/liv.space/below) are parallel to the roof rafters, (and tying in the exterior walls). Which is such a relief, since I was feeling a little nervous everytime the wind would gust and I'd hear the rafters creak.

But then again, regarding lateral thrust, wind pressure, and live load, the house has lasted 77 years, so I guess how bad could it be...right?

Now Mongo, I am a builders son, and a remodeler myself, so I should know and I shouldn't get confused, and I know what a gable is when one protrudes from a perpendicular roof slope, but I'm a little confused.

The roof has, looking from the street, its front main slope pitching up and away from you, and coming down (and continuing away from you) to the rear of the house. Back to the street view, coming toward you on the right side is a high pitched gable roof with its slopes to the left and right.
I'd post pics if I could figure how.

Also, any additional thoughts on the previious or further subjects regarding the project welcome.
Eg. regarding insulating, I'm of the school that if we can shut down air movement with dense packing, then ridge/soffit vents aren't needed (and therefore I'll not need to scab 2x10's onto the 2x6's).
thanks,
yitzie

    Bookmark   November 10, 2005 at 4:52PM
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mongoct

Sounds like you have a cross-gable. Two gable roofs that intersect at a 90-degree engle. The gables can be in any proportion to one another, or be located anywhere in relation to one another. Midpoint, or at the end, or anywhere in between.

See the link below.

With a 2x6 the best you're going to do with non-foam insulation is hover around R-20.

You could fill the rafter bays with spray foam, or insulate the bays (FG or densepacked celluluose) and add 4' by 8' sheets of polyisocyanate insulation (R-7 per inch) to the rafter faces. Then drywall over that.

Polyiso or densepacked cellulose will stop air infiltration. They will also act as a radiant barrier to minimize hot attic syndrome in the summer due to radiant gain.

FG is lousy for stopping air movement in a leaky house, and radiant passes right through it. Not the best choice by itself in this case.

More details if your interested.

Here is a link that might be useful: roof types

    Bookmark   November 10, 2005 at 11:26PM
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yitzie

yup, a cross gable with the gabel to one side. It also has, lower than the roof line (not conneted with the main roof at all), a small high peak roof over the entry vestibule with the same roof lines, matching the gable.

I was think of dense pack celulose, but adding the poly sheets is a great idea, thanks.

You bet I'm interested in more. I know what I do know and I'm smart enough to admit what I don't know. I'm somewhat new to frame const. Where I came from (Miami), frame is interior only, or sometimes for second level (which is uncommon to have). Structural is all cbs, columns/tie-beam and steel.
You want to e-mail me, vienna18@hotmail.com
thanks,
yitzie

    Bookmark   November 11, 2005 at 8:51AM
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homeav

Can someone help me out I am trying to convert my home theater to cathedral ceilings. I have trusses like this:

http://www.spicyhome.com/forum/viewtopic.php?t=33

I need some advice on how to go about removing the bottom cord and webs. Is it correct that I need columns and beams?

Here is a link that might be useful: http://www.spicyhome.com/forum/viewtopic.php?t=33

    Bookmark   November 22, 2006 at 12:09AM
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mightyanvil

homeav, you should start a new topic rather than hijacking one.

The answer to your question is simple. Trusses are designed by engineers with diagonal members to allow the rafter chords to be much smaller than a normal rafter. Removal of the diagonals and/or the bottom chords will cause the roof to be structurally inadaquate and also a violation of the building code.

For a cathedral ceiling you need to add new rafters properly sized for the span and find some way to laterally brace the tops of the walls. For that you should hire an engineer.

    Bookmark   November 22, 2006 at 8:18AM
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