Adding Rafter Ties to Old Roof: A Guide

When it comes to adding rafter ties to an old roof, there are several factors to consider. The first thing to check is whether or not the rafters are sagging. If they are not sagging and line up opposite each other, then a simple solution may work. However, if the slope of the roof is less than 3:12, a structural ridge beam may be required.

The International Residential Code (IRC) requires a structural ridge for roofs with pitches below 3:12. This is because these types of roofs are more susceptible to wind uplift and need additional support to resist this force. A structural ridge provides this necessary support by connecting the rafters together at the top and preventing them from spreading apart.

In addition to a structural ridge, collar ties can also be used to add extra support to the roof. Collar ties are designed to resist wind uplift and can be spaced up to 4 feet apart. They should be installed in the upper third of the attic space and can be made of less-substantial material than ceiling joists.

Rafter ties, on the other hand, are designed to resist the outward thrust of the rafters and can be raised a maximum distance (HC) that is no more than one-third the distance between the top of the supporting wall plates and the top of the ridge (HR). This means that if the ridge height is 9 feet above the top of the support walls, the maximum height that a rafter tie can be raised is 3 feet.

In some cases, a properly engineered structural ridge may be enough to eliminate the need for rafter ties altogether. However, in other situations, rafter ties may still be necessary to add extra support to the roof.

When installing rafter ties, it's important to follow the specific fastening requirements outlined in the 2018 IRC Table R802.5.2. This includes using the correct number and type of nails at each connection, based on the rafter slope, rafter spacing, and snow load.

In conclusion, adding rafter ties to an old roof can be a complex process that requires careful consideration of several factors. By following the guidelines outlined in this article, homeowners can ensure that their roof is safe and secure for years to come.

Adding rafter ties to old roof