Don Vandervort, Head Homeboy, has written more than 30 DIY home improvement books, been a segment host on HGTV, served as MSN.com's home improvement expert and written countless magazine articles.
In profile, the framing of a conventional pitched roof forms a triangle: mirrored pairs of rafters meet at a ridge and are connected across the base by a ceiling joist.
The inherent strength and integrity of the triangular form makes the roof a sound structure. The bottom “chord” of the triangle—the system of ceiling joists—keeps the house walls from spreading apart under the significant roof loads pushing down and outward. A collar tie—sometimes called a collar beam—runs parallel to the ceiling joists, but higher. Each collar tie connects a matching pair of rafters at mid-span, stiffening rafters and strengthening the overall structure.
Above rooms with vaulted or raised ceilings, collar ties sometimes double as the ceiling joists, providing the essential lower chord of the triangle, and may provide a backing for attaching a flat portion of the ceiling.
