Roof Problems · Sagging Roof
A dip in the roofline means something underneath has failed or is overloaded. Here's how to read the sag and what the fix involves.
Stand back from the house and sight along the ridgeline and eaves — both should be straight lines. A sag shows as a dip or swayback in the ridge, a wave across a slope, or a droop between rafters (a 'wavy' look often means thin or deteriorated decking rather than failed framing).
Inside the attic, look for cracked or separated rafter connections, rafters that bow visibly between supports, and decking that is dark, soft, or delaminating. Water-damaged OSB loses most of its stiffness long before it looks 'rotted' from below.
Long-term leaks are the most common cause: slow water intrusion rots decking and, eventually, the framing members it rests on. A sag localized around a chimney or valley almost always traces to a chronic leak.
Load is the other cause. Illinois snow events can put substantial weight on a roof — especially wet, compacted snow followed by rain that the snow absorbs. Homes with multiple layers of shingles (a past cost-saving practice) carry extra dead weight year-round. And some older homes were framed with undersized rafters that have crept downward over decades.
Common causes
Any visible sag warrants a prompt structural assessment. A sag that is growing, cracking sounds from the attic, or doors on the upper floor suddenly sticking are urgent signs — stay off that section of roof and call immediately.
During heavy snow events, watch for new sag, ceiling cracks, or popping noises. Those are overload warnings.
The fix depends on what has failed. Rotted decking alone is repaired during a re-roof: the affected sheets are replaced before new shingles go down. Compromised rafters or trusses require carpentry repair — sistering new members alongside weakened ones — before any roofing work. Either way, a sagging roof is a replace-the-roof moment, not a patch job, because the roofing must come off to fix what's under it.
A uniform slight wave between rafters on an older home can reflect thin original decking and may be stable for decades — but only an attic inspection can distinguish that from active rot. New or growing waviness is never 'normal settling.'
A roof rake used from the ground to pull snow off the first few feet above the eaves is reasonable and also helps prevent ice dams. Never climb on a snow-covered roof, and don't try to remove all snow — partial, even removal near the eaves is the goal.
Collapse from the weight of snow or ice is a covered peril in most Illinois policies. Gradual sag from long-term rot or deferred maintenance generally is not. Early documentation and inspection matter.
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