What Causes a Sagging Roof Line?


Straight as an arrow should be the roof lines. Your roof has an issue if, when you stand on the street in front of it, you can see that the peak has a dip, curve, or swag in it. It is possible that it is something simple that you are able to manage on your own, but it is more probable that it is something more sophisticated and requires the assistance of a professional.

It’s Above Your Head

Get up into the attic and get acquainted with the structural anatomy of your roof. A simple triangle may be used to represent the framing terms for a roof line. If you are in the attic in a crouching position or upright, the horizontal planks that are under your feet are the ceiling or roof joists. The sloping planks that are located above your head and referred to as rafters. At the very top, the rafters should be attached to another beam known as the ridge line. The recognisable shape of the roof’s triangle is created by the three planks placed in this order. This configuration is strong enough to sustain a significant amount of weight. It is normally sufficient to sustain the weight of the roof as it has collected through time, including the roof sheathing and shingles, as well as additional stresses from the environment, such as snow and ice. The weight is transferred from the rafters to the joists, which in turn transfers the weight to the outside walls of the structure. If everything is functioning as it should, the roof line should be straight.

Lapping It Up

In certain cases, sagging roof lines may be traced back to the horizontal ceiling rafters: In order to generate a greater span and facilitate the assembly of the roof structure, two ceiling rafters are often linked together. In order to obtain the desired length, they are normally lapped and toenailed together in the middle. When the pressure from the accumulated weight of the roof and/or heavy snow is applied to the roof, it pulls the rafters outward, which then causes the rafters to put pressure on the outer walls on both sides of the structure. It is possible for the joints to come apart if they are not lapped but are instead butted together. Even joints that have been adequately lapped might become loose if there is sufficient weight and strain. When the joints begin to separate, it causes the ridge line to sink or sag, and it also causes the outer walls to lean ever-so-slightly outward. Even if the sagging cannot be seen from the outside of your house, there is still a possibility that there are indicators of sagging inside of it. Examine the drywall on the ceiling for any signs of cracks.

Beam Me Up

A central beam is used in the construction of yet another kind of roof framework. The system works in a manner that is similar to that of lapped ceiling joists; however, rather than simply overlapping two joists together, this one consists of two independent beams that are joined to a bigger beam that runs perpendicular to the joists. Hangers made of metal are used on both sides of the beam in order to connect the joists. The hangers detach themselves from the beam and the outside walls shift outward as a consequence of the pressure that is created by the accumulated weight of the roof. This results in the drooping roof line at the top.

It’s a Tie

The form of a triangle formed by two sloping rafters may sometimes have another component attached to it, however this is contingent on the design of the frame. A rafter tie, also known as a rafter collar, is a piece of horizontal lumber that links two rafters on each side of the roof. It is normally attached to both rafters at roughly the midway point of the structure. The purpose of the rafter tie is to ensure that the rafters remain in close proximity to one another. It is possible for the rafter ties to be compromised and become inadequate to prevent the rafters from spreading if the placement of the ties is not proper; the objective is to make a perfect triangle at the top of the structure with the tie. When rafter ties are not attached to the rafters securely enough, this might cause other difficulties as well. As the nails come free, the rafters begin to separate from one another.

Struts Are Us

A strut or beam may be used in the construction of the roof framework in certain designs. This strut or beam is installed such that it is perpendicular to the bottom of the rafters within the attic. For the purpose of providing the roof with strength, the beam is fastened to both of the external walls as well as the base of each sloping rafter. It is also possible for the beam to come loose if it is not correctly fastened, which is another factor that leads to the roof drooping. The beam or strut may also cause issues if it is the incorrect size or if it is damaged in any way, such as having cracks or splits.

Sheathed and Rotten

Problems with the framework of the roof may not always be the culprit when it comes to drooping roofs. The sagging of roof lines may also be caused by sheathing that has rotted or become moist. This is the issue that can be fixed with the least amount of effort. If the framework is solid and there are no issues detected elsewhere, but the roof still sags, the issue may have been caused by improper installation of the plywood sheathing or the shingles. This is especially likely if the roof was installed more than ten years ago. When water seeps in between the shingles, it causes the plywood below to bend, become brittle, or decay, which gives the impression that the roof is drooping between the rafters.

Professionals Needed

A professional assessment is required prior to making any changes or repairs to a roof that is drooping. It is possible that the problem may be solved quickly and easily by jacking up loose rafters, installing struts, or, for a more cost-effective solution, simply replacing the sheathing and the shingles. If you see damaged rafters, joists, or beams on your roof, you should get in touch with a roofing contractor as soon as possible to guarantee that your roof is fixed correctly. Determining the full scope of the necessary repairs might be challenging.