Common Causes of a Sagging Roof and How to Address Them

If the ridge of your roof is starting to dip in the middle, you probably have a sagging roof. This is a common issue in homes with roofs that have not been replaced in a long time. Any form of sagging generally indicates that the roofing structure does not have sufficient support for the load. Solutions to this problem can range from simple to complicated, and unless you possess advanced carpentry or engineering skills, fixing a sagging roof almost always requires the help of a roof replacement company.

In this post, Shine Construction Inc. discusses the common causes of roof sagging and what you can do to fix it.

Basic Roofing Structures

Rafter Roofs

A rafter is a structural component of a sloped roof. On a basic gable roof, the framing is based on a right-angle triangle. Looking at the triangle upright, you’ll recognize the rafters as the angled boards that meet at the top. Meanwhile, the horizontal boards at the bottom are called rafter ties, which sometimes double as the ceiling joists for the living area right under the roof. The top edges of the rafters are nailed into the ridge board that runs the full length of the roof, and the rafters are covered with sheathing. Sagging in this type of roof construction is typically caused by insufficient internal bracing or undersized rafters.

Truss Roofs

Instead of traditional rafters, most modern homes are framed with trusses. This structural component utilizes the same principles of triangulation but features more internal supports, therefore allowing for smaller pieces of lumber. Trusses are engineered for each specific application and manufactured off-site to reduce the amount of waste produced. Trusses should never be modified as doing so can compromise the integrity of the entire structure. If you really want to cut the framing of your roof or attic, it is best to consult a licensed structural engineer. Similar to the sagging that occurs on rafter roofs, sagging or low spots in truss roofs are often caused by undersized trusses or weak internal bracing combined with excessive loads of weight.

Flat Roofs

Unlike sloped roofs, flat roofs are created a lot like standard floor frames, with horizontal beams spanning the top of the building walls. Roof joists can be solid lumber, trusses, laminated beams or other engineered structural members. While flat roofs are called flat, these systems are still built with a slight slope for effective drainage, which can be fabricated by the frame itself, a sloped sheet of insulation or another material underneath the exposed roof. On a flat roof, sagging can result from undersized or weakened joists or issues with the layers beneath the bare roofing.

Why Do Roofs Sag?

Water Damage

A variety of things can cause a roof to sag. Water damage is one of them. If the roof is not properly draining rainwater or snowmelt away, the excess moisture can seep into the sheathing, causing it to rot or decay, which then leads to sagging. In order to prevent a water-damaged roof from sinking, or even worse collapsing, the sheathing must be replaced with new material by a qualified roofing contractor.

Undersized Materials

Undersized structural components are another common culprit behind roof sagging. Even something as simple as utilizing a 2 × 4 piece of rafter instead of a 2 × 6 board can kickstart the collapse of a roof. If there is no internal bracing or if it is not enough, the walls will become vulnerable to spreading, which can result in sagging as well. A roof ridge that droops in the middle and a roof that sags along its plane are likely caused by either one of these issues.

Excessive Loads

Another culprit behind roof sagging is excessive weight on the roof. Too much load can weaken and damage the structure due to the pressure. It is important to remove snow and ice on a regular basis during the winter season to prevent a large buildup from collecting on the roof. Though most roofing systems are designed to carry the additional weight of snowfall, an excessive amount can have an adverse effect on the internal structure, especially if the roof is already approaching the end of its life. Having too many layers of shingles and other roofing materials can also cause a roof to sag due to excessive weight.

Old Age

Some roofs sag because of their old age. While routine upkeep of a roof helps preserve its life, old age is only natural and can cause the structure to break down. There is not much you can do in this situation, and it is probably best to call a roofing company and have your roof replaced completely.

How Do You Fix a Sagging Roof?

Make no bones about it — fixing a sagging roof is not an easy, straightforward task by any means. For roofs with traditional rafter-style frames, there can be a number of remedies, and the appropriate one depends on the root cause of the problem and how serious it is. In most cases, roofing contractors reinforce the internal framing of the roof to strengthen and support it. But if the roofing material is in need of replacement anyway, a better choice would be to simply tear off the old sheathing and install larger rafters while the framing of the roof is exposed.

On truss-style roofs, problems with the sheathing can be fixed by replacing it altogether. However, widespread sagging associated with the framing is a severe matter that should be taken up with the builder of the home. On any type of roofing, modifications to the original construction should be examined thoroughly by a structural engineer or an experienced builder. These professionals can assess a sagging roof and recommend fitting solutions that can help you restore the form and function of your home.

Contact Professionals for All Your Roofing Needs!

Whether you need to perform a minor roof repair or completely replace your existing roof, our roofing professionals at Shine Construction Inc. can deliver the great results you expect. Our goal is to boost the curb appeal, durability and energy efficiency of your home with top-notch exterior improvements. To schedule an appointment, give us a call at (508) 278-3300 or fill out our convenient online form.