Roof framing from exterior view
Many roof problems are caused by issues with the framing and sheathing. In this section, we will focus on the defects that may be viewed from the exterior of the property. This is one of those cases where standing back and taking a good, hard look is better than getting "up close and personal" with the roof.
Remember, according to the Standards of Practice, a home inspector is not required to walk upon any roof surface.
One of the more common things to see, especially on older homes, is what is generally called "saddle" or "swayback." This happens when the ridge beam has settled down toward the center of the roof.
There are several potential causes for this, among them:
a rotten or broken ridge beam;
an overloaded roof surface;
undersized framing members; and/or
a lack of collar ties.
A noticeable step in the ridge can also indicate more serious problems affecting the whole home structure, such as a footing or foundation problem.
Similar to ridge sag, rafters may also be pushed down in the center. Wherever possible, try to get a view along the plane of the roof. There can be many reasons for the rafters bowing. Here is a list of possibilities:
roof loads too high;
a lack of purlins or knee walls;
poorly modified ceiling joists; and/or
improperly modified roof trusses.
Originally, roof sheathing was made from 3/4-inch to 1-inch planking, but in the 1950s and '60s, it became common to use plywood or particle board in 8x4-foot sheets laid perpendicular to the roof rafters. It is not uncommon for the roof to have a wavy appearance. This is most often caused by:
rafters or trusses set too far apart;
roof sheathing that's too thin;
sheathing that's fitted too closely together; and/or
sheathing that's missing H-clips.
provided by InterNachi