Rafter/collar ties as cathedral ceiling & rafter thrust
Robert Valenti| Posted inGeneral Questionson
Does anybody know what the new MA Residential code says about this? The rafter span charts all have a multiplier table below them for when this condition is being built. My local inspector says that you now have a truss, which a builder can not engineer.
I have seen cathedral/raised ceilings done with rafter teis many, many times.
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Replies
Robert,
I don't know about the Massachusetts code, so I hope a Massachusetts builder or engineer will be able to answer your question.
In the meantime, I thought I'd point out that there's been a change to the 2006 IRC requirements concerning the location of rafter ties.
See
http://74.125.155.132/search?q=cache:7dOREoDMgjwJ:www.iccsafe.org/cgi-bin/ultimatebb.cgi%3Fubb%3Dget_topic%3Bf%3D10%3Bt%3D001542+rafter+ties+cathedral+ceiling&cd=2&hl=en&ct=clnk&gl=us&client=firefox-a
Also here
http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic%3Bf=10%3Bt=001542
Martin,
The comments under your first link are helpful in explaining the picture. I believe there is a typo, because I can't imagine not allowing collar ties in the upper two thirds of the span.
Robert,
The picture describes the long-standing prescriptive code that says it's alright to place a rafter tie at the bottom third of the rafter span. I don't know what the current MA code says; I used to have a builder's license there but it's long expired now. I do know that it's easy to overstress a rafter when you have large loads or spans and a raised rafter tie. It usually shows up as kneewalls out of plumb, when the problem is a rafter with a big kink in it at the rafter tie.