Is this quote correct? I asked an engineer, a framer, and a code enforcer and they all said it is not correct. Cathedral ceilings, A-frame, etc. The engineer said you can raise the rafter ties and/or lower the collar ties and put a bird’s mouth at the bottom and a whole host of other options.
“Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses. A lack of rafter ties is a serious structural issue in a conventionally framed roof.”
But the engineer, code enforcer, and framer all said that it wasn’t. They used the example of an A-frame where you wouldn’t typically have rafter ties. Also, a traditionally framed cathedral ceiling would have the rafter ties raised, or the collar ties lowered to compensate. The engineer even said that there are provisions in the code that allow for no rafter ties and no self supported ridge beam if you put a bird’s mouth at the bottom and collar ties in.
There is a neighborhood here that has dozens of houses framed that way with no rafter ties and they are straight as an arrow and have been there for 50, 60 + years. Should I be calling all of them out as defects?
Here are a couple attic shots from a 1948 house.
Heavy framing to accommodate slate roofing, hence the knee walls.
Rafter ties, if you mean metal plates connecting the bottom of the rafters to
the structure were not in use back then.
So the lack of them in an older house is not a defect per se.
I bet they do. Correct me if I am wrong but you may be confused in terminology, rafter ties are the ceiling joists. As in older homes they may serve 3 purposes rafter tie, ceiling joist and floor joist.
The ceiling joists look like they are the rafter ties in those pictures above. As for my comments, the rafter ties are not always there. It is usually the collar tie dropped to the lowest level it can and then a bird’s mouth at the exterior walls. I see it all the time. I even had a code enforcer make us do that one time on a framing job
rcloyd
(Russell Cloyd, KY LIC #166164, IN LIC#HI02300068)
7
With rafters, if there are ceiling joists in place, collar ties are not necessary. If there are collar ties in place, ceiling joists can be eliminated. The quote is only partly correct in that a lack of rafter ties (ceiling joists) can be a serious structural defect if there is no self-supported ridge beam or collar ties.
FYI - The attached article from Fine Home Building will shed some light on the subject. The metal strap over the top is a good alternative for an A-Frame.
Traditionally-framed cathedral ceilings use structural ridges or rafter ties on extended centers with more heavily reinforced framing to accommodate the increased lateral loads.
Things sort of turn into a mess every time you start dealing with terms. The “Rafter Ties” are whatever struts connect the bottoms of opposing rafter pairs together to keep the bottoms of the rafter pairs from spreading due to the weight of the roof.
Collar ties go in the upper 1/3 of the roof and are designed to prevent damage form wind uplift.
Rafter ties go in the lower 1/3 of he roof and are designed to prevent the walls from spreading.
In a typical home, rafters are resting on tops of walls and the ceiling joists keep the walls from spreading. In an A-frame, the rafters connect with the floor assembly instead of the tops of the walls, so instead of the ceiling joists, the floor joists serve as the rafter ties.
Whatever you call the struts that connects the bottoms of opposing rafter pairs, they need to terminate in the lower 1/3 of the height of the roof, measured from the point of bearing of the rafter heel (whatever the rafter rests on at the lower end) to the bottom of the plumb cut at the ridge. Some people might argue that it’s the top of the ridge, but I’ve never seen any specific dimension, only the lower third of the roof called out as correct.
A bird’s mouth has almost nothing to do with the need for struts connecting opposing rafter pairs, and the forces that try to rafter bottoms apart. Bird’s mouths are just notches in rafter bottoms that provide better bearing and nailing characteristics.
The laws of physics don’t change, and if you’ve got a bunch of homes that appear to defy the laws of physics, they obviously don’t, so you might try to get your hands on a set of plans. I’d like to know how they’re built. No! Don’t call them out as defective. Please investigate and post.
Traditionally-framed cathedral ceilings sometimes use rafter ties on extended centers with more heavily reinforced framing to accommodate the increased lateral loads.
Things sort of turn into a mess every time you start dealing with terms. The “Rafter Ties” are whatever struts connect the bottoms of opposing rafter pairs together to keep the bottoms of the rafter pairs from spreading due to the weight of the roof.
Collar ties go in the upper 1/3 of the roof and are designed to prevent damage form wind uplift.
Rafter ties go in the lower 1/3 of he roof and are designed to prevent the walls from spreading.
In a typical home, rafters are resting on tops of walls and the ceiling joists keep the walls from spreading. In an A-frame, the rafters connect with the floor assembly instead of the tops of the walls, so instead of the ceiling joists, the floor joists serve as the rafter ties.
Whatever you call the struts that connects the bottoms of opposing rafter pairs, they need to terminate in the lower 1/3 of the height of the roof, measured from the point of bearing of the rafter heel (whatever the rafter rests on at the lower end) to the bottom of the plumb cut at the ridge. Some people might argue that it’s the top of the ridge, but I’ve never seen any specific dimension, only the lower third of the roof called out as correct.
A bird’s mouth has almost nothing to do with the need for struts connecting opposing rafter pairs, and the forces that try to rafter bottoms apart. Bird’s mouths are just notches in rafter bottoms that provide better bearing and nailing characteristics.
The laws of physics don’t change, and if you’ve got a bunch of homes that appear to defy the laws of physics, they obviously don’t, so you might try to get your hands on a set of plans. I’d like to know how they’re built. No! Don’t call them out as defective. Please investigate and post.
Traditionally-framed cathedral ceilings sometimes use rafter ties on extended centers with more heavily reinforced framing to accommodate the increased lateral loads.
Things sort of turn into a mess every time you start dealing with terms. The “Rafter Ties” are whatever struts connect the bottoms of opposing rafter pairs together to keep the bottoms of the rafter pairs from spreading due to the weight of the roof.
Collar ties go in the upper 1/3 of the roof and are designed to prevent damage form wind uplift.
Rafter ties go in the lower 1/3 of he roof and are designed to prevent the walls from spreading.
In a typical home, rafters are resting on tops of walls and the ceiling joists keep the walls from spreading. In an A-frame, the rafters connect with the floor assembly instead of the tops of the walls, so instead of the ceiling joists, the floor joists serve as the rafter ties.
Whatever you call the struts that connect the bottoms of opposing rafter pairs, they need to terminate in the lower 1/3 of the height of the roof, measured from the point of bearing of the rafter heel (whatever the rafter rests on at the lower end) to the bottom of the plumb cut at the ridge. Some people might argue that it’s the top of the ridge, but I’ve never seen any specific dimension, only the lower third of the roof called out as correct.
A bird’s mouth has almost nothing to do with the need for struts connecting opposing rafter pairs, and the forces that try to rafter bottoms apart. Bird’s mouths are just notches in rafter bottoms that provide better bearing and nailing characteristics.
The laws of physics don’t change, and if you’ve got a bunch of homes that appear to defy the laws of physics, they obviously don’t, so you might try to get your hands on a set of plans. I’d like to know how they’re built. No! Don’t call them out as defective. Please investigate and post.
Traditionally-framed cathedral ceilings sometimes use rafter ties on extended centers with more heavily reinforced framing to accommodate the increased lateral loads.
Things sort of turn into a mess every time you start dealing with terms. The “Rafter Ties” are whatever struts connect the bottoms of opposing rafter pairs together to keep the bottoms of the rafter pairs from spreading due to the weight of the roof.
Collar ties go in the upper 1/3 of the roof and are designed to prevent damage form wind uplift.
Rafter ties go in the lower 1/3 of he roof and are designed to prevent the walls from spreading.
In a typical home, rafters are resting on tops of walls and the ceiling joists keep the walls from spreading. In an A-frame, the rafters connect with the floor assembly instead of the tops of the walls, so instead of the ceiling joists, the floor joists serve as the rafter ties.
Whatever you call the struts that connect the bottoms of opposing rafter pairs, they need to terminate in the lower 1/3 of the height of the roof, measured from the point of bearing of the rafter heel (whatever the rafter rests on at the lower end) to the bottom of the plumb cut at the ridge. Some people might argue that it’s the top of the ridge, but I’ve never seen any specific dimension, only the lower third of the roof called out as correct.
A bird’s mouth has almost nothing to do with the need for struts connecting opposing rafter pairs, and the forces that try to spread rafter bottoms apart. Bird’s mouths are just notches in rafter bottoms that provide better bearing and nailing characteristics.
The laws of physics don’t change, and if you’ve got a bunch of homes that appear to defy the laws of physics, they obviously don’t, so you might try to get your hands on a set of plans. I’d like to know how they’re built. No! Don’t call them out as defective. Please investigate and post.
