Structure of the Roof
Some roofing systems have what is called collar ties installed on the roof rafters. Collar ties are important in the construction of the roofing system because they prevent the roof rafters from sagging inward. Rafters can sagg inward from the weight of the roof covering, especially with more the one layer of roof covering. The rafters can also sag from the weight of snow and ice. Needless to say sagging rafters is a major structural issue in a roofing system.
Collar ties are typically wood members, usually two by fours or two by sixes. They are installed horizontally half way up in attic spaces. The collar ties are connected to either end of opposing rafters and act as stiffeners to prevent the rafters from sagging in the middle. The picture above shows a collar tie installed in the attic at a recent home inspection.
The problem with the roof system above is there are not enough collar ties installed. There should be one collar tie for each pair of opposing rafters. That will give each rafter the support it needs to prevent inward sagging. Home inspectors also look for the location of the collar ties. Often we find they are installed too high up or to low down on the rafters. They should be nailed near the mid-point of the rafter span.
Collar ties are only effective on some roof slopes. Your home inspector will measure the slope of your roof to determine if collar ties are needed. Collar ties are simple to install, and very important for many roofing systems.
Closer Look Property Inspections Inc.
For more on the value of a home inspection visit: www.closerlookpi.com
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