Collar ties or rafter ties?
I recently moved into a new construction house and I am starting to plan my attic renovation. I have been trying to research how to add extra support to the collar ties to support the weight of blown in insulation above them as well as the sheetrock that I will hang under them to act as the ceiling.
The total height from floor to peak in the attic is 183" and the bottom of the existing ties are 97" from the floor. Since these ties are neither in the upper 1/3rd nor the lower 1/3rd I am scratching my head as to if these are collar ties or raftor ties. Most of the ties are 16' 2x8's but there are some shorter spans of 12' using 2x6's. The ties are installed on every 2nd joist but I will be adding additional ties so each joist has one. Because of the long runs I expect these are going to suffer from sagging and so I want to brace them somehow. Can I use 2x4's to vertically connect the ties to the joist near the peak of the roof? Any advice would be great.
I have attached a photo to help illustrate.
As a follow-up:
The ceiling joists for the main floor (floor joists for the attic) of the house are 2x10's spaced 16"OC. The raftors are also 2x10's spaced 16"OC.
If not, you have to ask your architect who drew the plans. He's the only one that will know. No one here can tell you this.
Are you getting permits and inspections?
The floor joists are the rafter ties in your case. The 2x8's at 97 inches up are collar ties, albeit not in the upper third, as they generally are. I am unable to answer why they were built that way, the designer or contractor who built the house can presumably answer that question.
As to you converting the attic into living space, which I assume is why you want to sheet rock the ceiling, you need to discuss this with the local building inspector. Especially if the house was not permitted with living space in the attic. Assuming it is OK, you simply figure the loading on the collar ties (it will probably be approximately 15 pounds per square foot), and look up in span tables if the deflection is OK, and if the strength is OK. Also check to make sure the connections on the ends are going to be OK (adequate nailing). Also check the floor joists for strength and connection, since if you convert to living space the required loading on the floor is going to be higher than if it was permitted and built as dead storage attic space.
There must be a story here somewhere, this is new construction and yet you are engaging in a major renovation before the house is complete? Foreclosure perhaps?
I have not pulled a permit but I have spoken to the inspector in our small town. This is a new house and was not a foreclosure.
I'll start with him and go back and talk to the builder then too.
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