How it Works: Collar and Rafter Ties.

There is a reason collar ties are in the attic of your home.The role of collar and rafter ties in the framing of a roof is explained in this article.There is a need for collar ties to prevent the ridge from being separated by wind.The roof would pancake if gravity loads caused it to push out the sidewalls.Unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof, Rafter ties are not required.

For years, space-starved homeowners have been asking for collar ties to be removed if they plan on remodeling their attic.Knowing why they are there is the proper thing to do.

Contrary to popular belief, collar ties are not used to support rafters or to keep walls from spreading under the weight of the roof.That is the job of the rafter ties.If you don't know if you need collar ties, you should talk to an engineer.

The rafter ties are located in the bottom third of the roof structure, which makes them resistant to horizontal forces caused by gravity loads.Unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof, rafter ties are required.

There are ways to deal with the need for rafter ties when framing a cathedral ceiling.If you want to support a structural ridge, you can include posts in the gable walls.If this isn't an option, the next best thing would be to space several large rafter ties out, using either attractive timbers–as you would see in a traditional timber frame– or wrapping them in order to make them architectural elements in the space.To compensate for the wide spacing of this type of rafter tie, you may need to add reinforcement to the top plates of the walls; again, consult an engineer to make sure this is feasible and that you get the details right.

The collar ties in the top third of the roof prevent the ridge from being separated by wind.

A basic building block of roof framing is Laying Out a Common Rafter.

The rest of the roof falls into place easily if you focus on the pattern rafter.

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