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Collar tie does not resist roof sagging & wall spreading © Daniel Friedman at InspectApedia.comCathedral Ceiling / Roof Framing: Structural Ridge Beams

Cathedral Ceiling & Roof Framing:

Roof structure choices for cathedral ceiling roofs. Why do so many otherwise bright construction people confuse collar ties and rafter ties? And why do the same people compound this error by framing a cathedral or a vaulted ceiling on a gable roof without using a structural ridge? Despite the training programs for construction supervisors now mandated by many state inspection bureaus, this misstep in the framing of a single family dwelling seems to happen as much today as it did twenty years ago.

This article series describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings, including definitions of collar ties, rafter ties, and structural ridge beams. Without the proper support of rafter ties or a structural ridge, a typical gable or sloped roof will sag downwards while pushing the building walls outwards towards a catastrophe. We include sketches of collar ties, rafter ties, and structural ridge beams as well as illustrations of collapsing and collapsed structures where these roof rafter ties were lost or omitted.

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Roof Collar Ties, Rafter Ties, Structural Ridge Beams for Cathedral Ceiling Framing

Ridge beam structure below a cathedral ceiling © Daniel Friedman at InspectApedia.com

Structural Ridge vs. Ceiling Joists vs. "Nothing" for Cathedral Ceilings

- Paul DeBaggis

Paul DeBaggis, a Massachusetts building code official having a particular interest in wood framing standards, describes what goes wrong in cathedral ceiling roof framing SNAFUs and what can be done about it.

When a framer installs collar ties, he or she must place them horizontally against one side of the roof rafters and in the top third of the vertical distance between the ridge board and the plane of the top plates of the exterior walls. This is done is to stabilize the connection between the ridge board and the tops of the rafters. The collar ties do nothing to hold the exterior building walls together.

Rafter ties, on the other hand, create a rigid triangle that presses straight down rather than pressing outwards on the outside walls. Without rafter ties, the ridge sags onwards, and the top of the walls supporting the lower ends of the rafters push or “kick” outward. Inspecting a building constructed without rafter ties and that also lacks a structural ridge beam, we will often notice first that the ridge has sagged downwards, mostly in the center between the gable end walls.

[Click to enlarge any image]

From outside, take a second look with great care by sighting along the top of the front and rear walls on which the lower ends of the roof are resting. You may be shocked at the amount of outwards bulge seen at the top center of these walls. Inspecting inside the building where a cathedral ceiling design has been used, you may notice separation or cracks at the top of the front and rear walls and in severe cases you'll easily see that the top of the walls lean mysteriously "out". You may find this roof sagging, wall bulging in new construction that was not properly designed, or you may encounter it in an older building whose owners decided to "open up" the top floor rooms by tearing out all of the ceiling joists to "raise the ceiling".

The International Residential Code prohibit omission of rafter ties unless a ridge beam or an equivalent design has been provided.

Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice.” - 2012 IRC, Section R 802.3.1

For the past several code cycles, the IRC code commentaries have also contained a detailed explanation, including sketches, of this crucial rafter and exterior wall relationship.

Structural Ridge Beams Required for Cathedral Ceilings

Structural ridge detail © Daniel Friedman at InspectApedia.com

Above: this detail shows the vertical post supporting a built-up structural ridge supporting a cathedral ceiling spanning 27 feet and constructed by one of the authors [DF] in 1979. The rafters rest atop this ridge beam and were strapped together using steel strap-ties nailed along the rafter upper edges before the roof sheathing was set in place. Below one of the authors [DF again] stands at the lower edge of this roof in 2010: the rafters "hung" over the structural ridge beam and the walls upon which they terminate never moved at all during the ensuing 31 years.

Lower end of cathedral ceiling roof shows no damage below a structural ridge © Daniel Friedman at InspectApedia.com

To help permit applicants at our office [PD], whoever approves the plans for a cathedral or a vaulted ceiling clearly marks them, “structural engineered ridge required.” If the contractor seems uncertain about the meaning of this, we add a verbal explanation. But once in awhile, even as we explain, we have the uneasy feeling the applicant has already planned the roof framing, detail by detail, in his or her brain. In those cases, the nod or the verbal agreement is more of a, “Just give me that permit. I KNOW how to build it,” kind of a yes, as opposed to a yes that means, “Right. The way I showed it would not have worked.

Whenever I find this flaw on a job and point it out, the contractor usually says, “But I have collar ties, there.” I suppose it should be written as a building inspector’s commandment:

One shall not use collar ties to try to hold exterior walls together.”

So when the inspector finds this, should he or she issue a notice of violation or a stop work order? To date, in the dozen or so times I have pointed out this error, each has been corrected by the framer or builder responding to my verbal order.

Clearly, the code says either a violation notice or a stop work order shall be in writing. Despite this morsel of legalese, in my opinion the answer depends on the contractor’s response to the verbal comments. Keep in mind the language of the ICC book, Basic Code Enforcement, which I paraphrase here: At times, it is better, faster, and easier to persuade the party to make corrections than to pursue formal (legal) action. If you use good judgment, you should get a good result.

Below: at this vaulted ceiling the rafters are hung over and rest upon a structural ridge beam. The end of the beam is carried to the foundation by a built-up post.

Ridge beam structure below a cathedral ceiling © Daniel Friedman at InspectApedia.com

Regardless of whether or not the rafters but into the ridge beam or rest upon its upper surface, the building inspector will typically require that steel strapping connectors be installed along the top edge of opposing rafters to form a mechanical tie so that while hanging on or from the structural ridge, the rafters do not separate at their upper ends.

Rafter separation at ridge © Daniel Friedman at InspectApedia.com

Above: in conventional roof framing the rafters may be nailed-through the ridge board into the rafter end (the weakest possible connection) or they may be toe-nailed through the rafter sides to the ridge board or beam, or steel rafter hanger-connectors may be used. But as you can see from our photos above and just below, without strapping and rafter ties, the spreading forces effected by roof loads can easily separate a nailed rafter from the ridge.

Toe-nailed rafter separating at ridge board © Daniel Friedman at InspectApedia.com

How to Fix a Cathedral / Vaulted Ceiling Roof that Lacks a Structural Ridge

How does a contractor fix one of these mini-disasters? He or she will probably ask this question. You should clearly indicate you are not in the design business, and it is the contractor’s job to present you with a proposed solution. Having stated this, I am happy to point out the three types of successful fixes I have seen.

First, through the gable end, the contractor can slide an engineered structural ridge beam into position under the non-structural ridge framing. As a part of the beam package, many lumber dealers will work with a licensed engineer and provide a stamped report specifying the loading capacity and a fastening schedule.

At the job site, set the beam tight under the framing using cant strips, if needed. Be sure both ends of the new beam are secure and posted directly or indirectly to the foundation, then install plenty of approved framing connectors.

Structural Ridge Beam © Daniel Friedman at InspectApedia.com

Second, across the clear span of the room, at the top plates and parallel with the rafters, install “beams.” These will act as rafter ties. Use four by sixes or four by eights based on the span of the room—very large spans will require an engineer’s design-- and put them four to six feet apart (the code does state a maximum of four foot centers for rafter ties). Be sure the contractor uses approved connectors—screws or bolts as usually nails won’t work-- to secure these beams to the wall plates. The beams will keep the two exterior walls from kicking out.

And third, have a structural engineer evaluate the situation. He or she may recommend methods one or two or a different solution. On occasion, and depending on what the customer wants for a final ceiling design, the engineer may offer more than one alternative.

With each of these options, you must check whether the two long walls are plumb at mid-span. If they have kicked out more than a quarter of an inch, you need some combination of spring braces, turnbuckles, and raising the ridge by posting where it sags, to bring the walls near to plumb, again. As to whether the contractor uses method one, two, or three, the building official has the last word. Methods one and two will remedy most situations, but in all of these cases the inspector can require the engineer’s report. If it’s your first case, and if you feel uncomfortable, call for the engineer.

Finally, when a cathedral or a vaulted ceiling (or any gable roof) is framed without either an engineered structural ridge, ceiling joists or rafter ties, or an engineered solution, some amount of ridge sag and wall kick out is guaranteed. In a worst case scenario such as the record snow loads of the winters of 2011 and 2015, the roof could collapse.


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Comments

Mike Cadenhead · Sept 23, 2023

My home in Ohio was built in 1955. There are 2x6 boards tying the top plates of front and rear walls of the house spaced at 25". No trusses or upward supports exist. I suppose there have been tremendous snow loads at times over the years. No evidence of damage. Should I add vertical bracing?

InspectApedia Publisher (mod) · Sept 23, 2023

@Mike Cadenhead,

If I understand your question correctly, your home is framed with rafters (not trusses) of un-specified size and spacing, and while there are no collar ties between rafters above the attic floor (if there is one - or the home may have cathedral ceilings - you didn't say),

there are horizontal 2x6 joists acting as ties connecting the top plates of the front and rear walls onto which the roof rests.

Those ties prevent roof loads from pushing the wall tops outwards.

But they have absolutely no role in providing snow load resistance to the plane of the roof surfaces themselves. All of that resistance comes from the rafters - size and spacing and connectors, and from the roof sheathing (probably plywood on a 1955 home), and of course also from the pitch of the roof (steeper is usually better).

When you say there is no sign of damage I take that to mean you see no roof sagging and no evidence of broken or loose or dislocated framing, and no rot, insect damage, loose connections, etc. in the roof framing system.

If that's the case then the roof is performing adequately, and if the framing dimensions and fasteners meet current framing size, spacing, and fastening standards, and if it isn't damaged I don't know of a reason that you'd be replacing or reinforcing it.

I'm also not sure what you were imagining would be "vertical bracing" - perhaps you could post some photos and a sketch of what you had in mind, and also tell me what raised the question for you in the first place.

Thanks

DF

Pete taylor · Apr 30, 2023

What blocking is required in between rafters at the ridge on a ridge beam supported rafter with Bird's mouth cut I was thinking of using 2x10 blocking with 2x10 rafters on 10/10 pitch roof leaving 1inch for venting before plywood sheathing . Is one block ok for 2 rafters from opposite side of ridge with 3/4 in coverage on each rafter or put in two blocks with small chanel for insulation on top of ridge

InspectApedia Editor (mod) · Apr 30, 2023

@Pete taylor,

Can you post a photo or sketch of the situation?

I don't understand the question because a bird's mouth cut, as I use the term, is made where the lower end of a rafter sits on the wall top plate. Not at the ridge.

At the ridge a plumb cut puts the face end of the rafter against the ridge board where the rafter is either toe-nailed or back-nailed from the other side of the ridge board. I don't see blocking in that location.

InspectApedia-911 (mod) · Oct 10, 2022

I'm reposting a question that I accidentally deleted

AUTHOR: Neal Diener (no email)

COMMENT: I have a cathedral ceiling with 2 exposed beams (about 6"x16"x28') running parallel at about mid-span of the rafters on each side supported by build up posts. The space is 27' x27. Are those considered to be ridge beams ?

InspectApedia-911 (mod) · Oct 10, 2022

@Neal


If I understand your question correctly the answer is no. The rich beam is only found at the ridge or Peak or highest point of the roof. If you have beans that run parallel to the house walls extending from Gable and to Gable and at lower locations under the roof those would be called purlins.

danjoefriedman (mod) · Feb 1, 2021

In concept you can certinly do that, though nobody can do or even guess at loads, connections, framing lumber sizes, from just the nice illustrations you posted.

An alternative I've used is to install a structural ridge beam that is supported by posts in the two gable end walls;

If your ridge beam isn't sized for the full building width then you'd indeed need to support it as you describe.

Ian Johnson · Feb 1, 2021

I have a garage that is 20x30 with 11ft walls. It is an open space, essentially a cathedral ceiling built with a ridge board. There is a loft at one end, and a loft at the other which is the top of the laundry room. There are two rafter ties in the center 6ft apart, and big cross brace between the ridge and the top of the laundry room. I would like to connect the lofts and open the space, which would require removing the rafter ties. Would it be enough to support the ridge board with posts at 10' and 20' along the length? Or maybe 20ft of beam under the ridge board in the center, supported by two posts?

Anonymous · Jan 11, 2021

David

Please see the procedure at ROOF SLOPE CALCULATIONS inspectapedia.com/roof/Roof_Slope_Calculation.php


David Hutchins · Jan 11, 2021

How much separation of the rafter from the ridge board would it take to have a ten foot high wall tilt out and inch from top to bottom?

danjoefriedman (mod) · Jan 11, 2021

Jennifer,

take a look at TRUSSES, FLOOR & ROOF inspectapedia.com/structure/Floor_or_Roof_Trusses.php

and you'll see that we warn that roof truss members should not be cut; if your roof trusses were cut then some additional repair or reinforcement may be needed.

Jennifer Palmer · Jan 11, 2021

I swear my entire house is moving as I live and breathe. I also recently discovered that there was a modification made to existing existing airspace up in the attic and they put in a pull down attic stairs/ladder, put up drywall, cut a bunch of (I don’t know if they called trusses or rafters or joists or what they’re called) but I hate the attic and I was too scared to go up and get a picture right now. But there’s like nine of them that are cut Like the webbing that would’ve gone across the attic at an angle and you wouldn’t of been able to use the space... so they made modifications cutting out all that out, so that they had a room up there like straight up sawzalled them right off there’s only two that are still whole. Have cathedral ceiling, gabled roof ends, annnnd I see evidence of it moving daily and it’s freaking me out I need to sell it but I don’t know what to do my partner 15 years walked out for a girl I work with and never came home; so, I’m left with a big mess and we were in various stages of renovation when he left so it’s been a year now; I have been quite depressed, my mental health is keeping me in bed most days. I don’t know what to do if anybody knows what is up with this place I’d love to hear it. Thanks in advance!

By the way my ex was a genius and decided to do a home inspection without knowing anything I don’t know why i used to believe that he was so brilliant! Ugh what a fu@king moron; pardon my language.

Anonymous · May 17, 2021

@Jennifer Palmer, I would really need to see what you have going on in the attic. Do the 2 trusses that are not cut apart look like this? See attached picture

danjoefriedman (mod) · May 18, 2021

@Anonymous,

Thanks for helping out,

Let's see if Jennifer replies.

 

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