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What Causes a Roof to Sag? – Professional Insight

September 18, 2023

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what causes roof to sag

A sagging roof is no laughing matter for homeowners. But while a drooping roof is bad news for your house, it does provide some comedic material to lift your spirits while you deal with repairs.

What causes a roof to sag? A roof can sag due to age, excessive weight from snow or water damage, inadequate structural support, insufficient ventilation leading to heat and moisture buildup, pests deteriorating rafters and sheathing, improper patch jobs, and foundation settling over time. Identifying the specific cause is key to making the necessary reinforcements and repairs to lift and stabilize a sagging roof.

Let’s take a deeper look at what causes roofs to sag and the related factors causing this to occur.

The Age of a Roof

They say old age causes all sorts of things to go south. Roofs are no exception. As your roof system ages, elements like the sheathing, rafters, and ridge beam simply wear out and start heading downhill fast.

You might find the lifespan of your roof dropping faster than your decades-old gym socks. But just like those stinky socks, it doesn’t hurt to replace the roof before things start sagging too far.

leaking roof

Prolonged, Heavy Snow

For homeowners in colder climates, the weight of heavy snow is often the culprit behind sagging roofs. While picturesque to look at, feet of dense snow pack on quite a bit of extra load.

Before you know it, the roof starts looking more droopy than your old basset hound. Proper roof bracing and framing that meets snow load requirements is key to avoiding snow-related sags.

heavy snow on roof

What Causes Roof to Sag? Water Damage is a Culprit

Speaking of loads, water absorption can also weigh a roof down. Sources like rainwater leaks, poor attic ventilation leading to condensation, or flash flooding can cause moisture damage and rotting of the roof deck and framework.

Pretty soon, your roof looks about as stable as a sponge filled with water. Identifying and repairing any moisture damage is crucial to getting things looking up again.

professional roof leak repair

Improper Roof Support

Just like your achy back needs proper posture and care, roofs need adequate bracing and structural support, too. Weak points due to inadequate framing, overloaded rafters, or sanctioned areas can lead to bending under strain.

Before you know it, things are starting to look as concerning as your grandpa’s hunched-over spine. Call in a structural engineer to evaluate and make recommendations to lift that roof back up.

roofing newport

Inadequate Attic Ventilation

Trapped hot air and moisture in the attic are bad news for roofs. Proper soffit and rooftop ventilation allows air to circulate freely under the roof decking, preventing excess heat concentration in the summer and moisture condensation in winter.

Ignore those pesky ventilation problems, and you’ll find your roof drooping quicker than your freshly microwaved slice of pizza. Make the necessary ventilation upgrades to keep air flowing and your roof perky.

roof inspection rhode island

Pests and Rot

Cute as some may look, squirrels, raccoons, mice, and insects that take up residence in your attic can cause damage. Their gnawing, nest building, and waste products lead to wood rot and deterioration over time.

Before you know it, your roof starts sinking lower than your teen’s pants or a millennial’s social media feed. Call an exterminator and make repairs to give those critters the boot.

can a roof leak stop on its own

Improper Patch Jobs

After roof repairs or installations, sometimes contractors take shortcuts and leave inadequate patches that don’t properly attach to rafters or sheathing. Seems fine at first, but over time, these weak sections start to buckle.

Get a qualified roofer to do a thorough evaluation and make all necessary patches to strengthen the roof. Otherwise, things will be hanging lower than a bulldog’s jowls.

roof patching

Foundation Settling

Last but not least, issues below the roofline can also create sagging up top. Settling foundation issues like sinking footers, soil erosion, or unstable soil causes the entire structure to compress. The roof framing naturally drops lower along with the rest of the house.

what causes roof to sag

Final Thoughts on Roof Sag

Before panicking and calling a roofer, consider that a structural or foundation expert may be needed to lift things up from below first. Then, roof reinforcements can shore things up for good.

In summary, a host of issues like age, snow loads, moisture, lack of support, pests, and more can make your roof sink like your battered souffle. But with some humor and TLC, you can get your roof looking lifted in no time.

About The Rhode Island Roofers

With nearly 20 years of experience assessing, repairing, and replacing roofs throughout Rhode Island, our skilled technicians know exactly how to diagnose and fix sagging roofs. 

From replacing worn rafters to installing proper ventilation, we use quality materials and proven methods to lift and reinforce drooping roofs. For reliable roof repairs done right the first time, call The Rhode Island Roofers at (401) 496-9491 today.


How serious is a sagging roof?

A sagging roof is a very serious issue that requires prompt attention and repairs to prevent further damage. Over time, the downward bending puts immense strain on roofing materials, rafters, and walls, leading to cracks, leaks, potential collapse, and even impacting the structural integrity of the entire building.

What does a dip in the roof mean?

A dip, sag, or downward bend in a roof typically indicates potential structural problems with the roof framing or sheathing that requires further evaluation. Common causes of a bowed roof include deteriorated rafters or ridge beams, moisture damage weakening roof decking, inadequate bracing, excessive weight from snow or water buildup, and overall aging of roofing materials.

How long does it take to fix sagging roof?

Fixing a sagging roof can take anywhere from 1-2 days for minor repairs to up to 1 week for extensive reinforcements, depending on the size of the roof and the underlying causes that need to be addressed.

Is a sagging roof normal?

No, a sagging, dipping, or drooping roof is not normal and typically indicates some type of underlying problem or deterioration that requires inspection and repairs.

How do you know if your roof is collapsing?

Signs your roof may be in danger of collapsing include major dips, sagging, or drooping in the roofline, separating or cracked rafters and roof sheathing allowing light inside, and new cracks in walls or ceilings from shifting framing. If you notice these warning signs, evacuate the home immediately and contact a structural engineer and roofer to assess the roof’s integrity before attempting repairs.

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