My Roof Is Sagging — What’s Causing It?

You step outside, look up at your house, and something looks off. The roofline isn’t as straight as it used to be. It’s easy to shrug it off at first, but a sagging roof usually means there’s a bigger problem hiding underneath.

At Robb’s Roofing, we’ve seen this more times than we can count in Tacoma. Most sagging starts small, but if you ignore it too long, it can turn into structural damage that’s not just expensive, but unsafe.

Why Roofs Sag in Tacoma’s Weather

A roof isn’t supposed to bend or dip — it’s meant to hold firm against everything the Pacific Northwest throws at it. When it starts sagging, it’s a sign something inside is losing strength.

Here are the most common reasons we see around Tacoma:

• Water-damaged decking: Constant rain seeps into the wood beneath your shingles. Over time, that plywood softens and starts to give way.
• Broken or undersized rafters: Older homes, especially those with multiple roof layers, sometimes can’t handle the extra weight.
• Heavy snow or standing water: Even a few inches of wet snow or clogged gutters can add hundreds of pounds of weight.
• Poor ventilation: Warm, trapped air in the attic builds up moisture and slowly weakens wooden framing.

Quick Guide

Quick answer: Water-damaged decking, weak rafters, or too much weight from rain and snow.

Try this: Peek into the attic — look for rot, damp wood, or cracked beams.

Stop signs: Rapid sagging, creaking, or visible shifts — get out of that area and call for help.

Typical cost: Decking repairs $2,000–$6,000+, depending on how bad it is.

Early Warning Signs to Watch For

A sagging roof doesn’t happen overnight. It starts quietly. You might notice the ridge line bowing a little, or maybe the ceiling inside has new cracks along the corners. Doors and windows might stick suddenly — that’s your house shifting slightly as the roof sags.

If you head into the attic and see damp insulation, dark spots, or wood that looks warped, those are red flags. And if you ever hear creaking or notice the roofline dipping more than it did last month, don’t try to inspect it yourself — it could be unsafe.

How Tacoma’s Climate Makes Things Worse

Our climate doesn’t give roofs much of a break. All that rain keeps wood damp, and the humidity means it doesn’t dry quickly.

In winter, wet snow can add serious weight, pressing down on an already weakened roof. By spring, that “slight dip” might be a full-blown sag.

What You Should Do Next

If you notice sagging, don’t wait to see if it gets worse. It will. Here’s what to do:

• Stay clear of the area if it looks like it’s bowing or shifting.
• Check your attic for obvious water damage or cracks in the framing.
• Call a roofing professional before attempting any fixes — they’ll know if it’s just a small repair or something structural.

Final Thoughts

A sagging roof isn’t just a cosmetic issue — it’s your home telling you something’s wrong. Tacoma weather is hard on roofs, but quick action can save you from major repairs later. Call Robb’s Roofing at (253) 820-2163 for a full inspection and honest evaluation.