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Re: Use of Collar Ties in Light Frame Wood Construction

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I seem to recall an intersting discussion in a recent JLC to the effect that
collar ties were a bad idea.
Chuck Utzman

Structuralist wrote:

> I have a client with a home in escrow. There is a cracked ridge board in the
> garage and it appears that the ridge has dropped a few inches. The framing
> is rafter tied by the 2x6 ceiling joists to the 2x8 roof rafters, the ridge
> board is a 2x12 DF. The crack in the ridge board is parallel to grain which
> runs diagonally through this section of the board - an obvious defect in
> material not found during original construction.
>
> I intended to jack up the roof and install 1x6 collar ties at 1/3 the
> distance down from the peak of the roof. The attic is accessible to install
> the collar ties and all other existing framing looks pretty good.
>
> The 2000 IBC lists the use of 3-10d nails to secure the 1x to the rafters.
> However, this 2000 IBC is not used in California and collar tie nailing is
> not indicated on the 97 UBC Nailing Table. The only reference to collar ties
> I could find was in Appendix Chapter 23 - Prescriptive Masonry Construction
> in High-Wind Areas where Section 2112.10.2 states: "Gabled and sloped roof
> members not supported by the ridge shall be tied by ceiling joists or
> equivalent lateral ties located as close to where the roof member bears on
> the wall as is practically possible, at not more than 48 inches on center.
> Collar ties shall not be used for these lateral ties."
>
> Now I am at a loss. In my opinion (as this was a common form of construction
> for many years) collar ties are ideal to resolve this situation but this
> condition requires them to act as lateral support. The existing ceiling ties
> obviously help, but are not restraining all of the outward thrust of the
> rafter tails since the ridge board cracked. Installing a Ridge beam seems an
> inappropriate solution here as it would redistribute the roof load and
> require the possible addition of two foundations at each end - requiring
> that we cut through one slab and underpin the exposed slab edge.
>
> Any suggestions or information that would help me justify the use of collar
> ties?
>
> If I still use collar ties (assuming the building department accepts the fix
> as I suspect they will) I intended to install a 1x6 on each side and face
> nail each end to the rafters with (3) 10d nails - spacing the collar ties
> every other bay or 48" on center.
>
> Regards,
> Dennis S. Wish, PE
> Structural Engineering Consultant
> mailto:structures(--nospam--at)engineer.com
> (208) 361-5447 E-Fax
>
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