Why Is My Roof Bowing and What Should I Do About It

Why is my roof bowing? A sagging roof is a sure sign of structural damage. There are several issues that a sagging roof can indicate, none of which you should ignore. Here are some explanations for your sagging roof, as well as what might happen if you ignore the issues. In some severe instances, you may inevitably need a roof replacement.

Here’s a quick rundown of what you may be facing when your roof is sagging:

• Snow and ice weight
• Pressure spread
• Foundation and settling damage
• Roof rot
• Poor quality materials
• Rafter and truss damage
• Storm damage

Snow and Ice Weight can cause Roof Bowing

Sitting snow has a saturated weight of about 20 pounds per cubic foot. So if you have 1.5 feet of snow on your roof, for every square foot that comprises your roof, you have about 30 pounds sitting on it. Your rafters hold that up. Underlayment might pick up part of it, but the rafters also hold that up.

Nobody stops to think that it doesn’t take much snow buildup to put a lot of weight on your roof and rafters. Even six inches of snow means every square foot of your roof has about 10 pounds sitting on it. Add the shingles and underlayment, and you get to the point where your rafters start to sag.

You should examine your roof after any snow or ice accumulation. Estimate the weight of your roof using the formula above. If your roof has more than six inches of snow, you should grab a rake and pull as much snow off your roof as possible. Ignoring the weight on your roof risks collapse, particularly in older buildings. This is particularly dangerous if the depth is more than a foot. Getting rid of these snow and ice loads can help with avoiding roof bowing. Lots of people like to hire residential roof cleaning services to ensure safety and a thorough job, but you can do the same thing on your own. Make sure to use a long-handled rake so you don’t damage your roof in the process.

Pressure Spread

When your roof has a lot of snow or ice on it, it could cause damage from sheer weight. Weight on the roof puts pressure downwards on the rafters, which displaces the pressure outwards. That outward pressure pulls the seams apart and stresses the underlayment and shingles.

Eventually, that stress will lead to leaking, shingle damage, and displaced flashing in addition to bowing. In extreme cases, it can permanently damage the sides of your home and require significant repair work to correct. As soon as you see bowing, you should inspect it and try and figure out what is causing it. If you cannot figure it out, pay for a professional inspection.

Foundation and Settling Damage

Every home settles. That explains why one floor in the room seems to have become uneven for some reason. When your home settles, it also puts stress on your roof. That stress can lead to sustained pressure on your rafters and, eventually, bowing. In most cases, settling does not affect the roof at all, but in some instances, the settling is severe. The severity of the setting shows in the condition of the rafters.

If your home has foundation damage, that bowing can show itself much sooner and can have more serious implications. Depending on the damage, severe downward and outward pressure can pull and twist your rafters in different directions. Pulled apart and twisted rafters can lead to leaks, separating underlayment, rafter cracks, and bowing. In this case, bowing is a foreshadowing of a larger issue.

Unfortunately, bowing due to a foundational issue is the least of your home repair problems. Fixing the foundation is a major job that most DIYers are not experienced enough to pull off safely or effectively. Once the foundation issue is corrected you should find the bowing issue resolved.

Roof Rot

Saturated underlayment adds overall weight to the roof, increasing stress on rafters and could lead to the bowing and weakening of the infrastructure underneath. When that happens, rafters can sag and bow. This issue is particularly prevalent in sections that have softened due to roof rot.

Roof rot does not happen overnight. Some parts of the roof must become exposed to the elements, and water must saturate that point repeatedly. The wood eventually starts to rot if the materials absorb enough water. In extreme cases, that rot can permeate the under-roof and get into the rafters. When this happens, you should consider a roof replacement.

When inspecting potential underlayment rot, you should assume that a collapse is very likely to happen. Do not walk on the area directly because the sudden pressure at a concentrated point might cause the softened roofing to give in.

Poor Quality Materials

If your original roofers used subpar materials, rotting can happen much faster. One of the consequences of using poor materials is that the roof starts separating and sagging since substandard materials weaken faster over time. While obvious damage rarely happens soon after installation, the poorness of the material quality should show itself over time and right under your nose. This is why it’s important to ask questions to your contractors and monitor the construction of your home. If you’re buying a home instead, have a professional inspect the condition of the roof as well as the foundations.

Rafter and Truss Damage

Your roof may be bowing due to rafter or truss damage. Weakened supports can cause sections of your roof to sag or tilt.

If you see rafter or truss damage, call a professional immediately. Explain your concerns clearly so the contractor knows what to expect. Putting it off will jeopardize your property and the safety of anyone living under your roof.

Storm Damage

Whenever a huge rain or hail storm passes through your area, you will want to do a thorough inspection of your roof. High velocity winds could throw debris against your roof and puncture holes into it. Deeper issues are sure to crop up if you drag your feet about starting the inspection.

Your safest bet is to climb into the attic with a flashlight in hand after it has rained. Check the floor for any dark spots in the wood which indicate excessive moisture. It’s likely that the section in the ceiling directly above the wet spot has suffered damage from the recent storm.

Final Thoughts

Several issues can cause sagging or bowing roofs. Whenever you see damage, leaking, or sagging, these are indicators that you need roof repair. If the damage is to a large section of your roof, then a complete roof replacement is your best bet at restoring the integrity of your home.

Photo by James Rathmell on Unsplash