How to Fix a Sagging Roof

How to Fix a Sagging Roof

There are few more concerning home issues than those associated with your roof. After all, it helps to make sure that your property is dry, safe, and secure. When the suggestion of something being wrong arises, it’s only understandable that you want to take care of it as soon as possible.

Yet, the issue of how to fix a sagging roof is not something many people know a lot about. Most of us are familiar with the prospect of leaks, perhaps even damaged or missing tiles. But this is one of the more common problems that can arise if you live in an older home or the roof has not been inspected in some time. Coming across this issue isn’t a reason to panic; in all likelihood your home isn’t about to collapse. But it’s certainly not something you can afford to ignore for long. 

Let’s take a closer look at this issue. 

Before We Go Any Further

While there are some roof repairs that an amateur may be able to handle, understanding how to fix a sagging roof is not something to be taken lightly. It’s a delicate procedure that benefits from a certain amount of roof repair expertise. We’ll go a little further into the various causes of sagging in a moment, but needless to say that it can be an indicator of structural issues. As such, the scope for mistakes is significant. This is not just from the perspective of fixing the part of the roof you’re repairing, but the long term integrity of the entire roof. 

We don’t write this to alarm you. Rather, it’s an essential note that empowers you to make an informed choice about your property. When you’re inspecting the issue, be honest with yourself. Seriously consider whether the repairs are in the remit of your abilities and expertise. Use this post as a guide to understand what might be achievable, and where you need to seek outside guidance. It’s understandable that you want to avoid unnecessary extra costs. But additional damage may be costly, and might not fall under the terms of your household insurance if you attempt to make repairs yourself. 

So, take a little time to really assess the problem; don’t rush into anything. 

The Causes

Just knowing how to fix a sagging roof isn’t enough. While repairs to the roof itself may be important, it’s just as vital to understand the root cause. If you don’t take care of this, you’re just going to have more issues in the future. 

Some of the prevalent causes of sagging include: 

Water Leakage

Your roof is designed to keep the rain out of your home, but water can also be a primary cause of roof sagging. When there has been damage to some aspects of your roof, or the roof wasn’t installed properly by experts, water can gather, settle, and leak into the underlayment. Over time, this can cause damage to the roof structure, causing it to sag. 

There can be various causes here. The most common problem is flashing issues. The flashing exists to help direct rain water safely away from places it might gather and toward the guttering, where it can drain away. When this is no longer functional, it makes your roof vulnerable to leaks and sagging. As such, as well as repairing your roof, you’ll also need to engage a professional to repair or replace your flashing. 

Weight Pressure

Metal roofs can last for a long time, but they are vulnerable to pressure damage. Tiled roofs can also be susceptible here, but this is largely if there are underlying issues with the roof structure. The problem here often revolves around significant amounts of weight being applied to a single point of the roof. This might be from trees falling following a storm, or a build up of heavy snow and ice in winter. 

In this instance there are relatively few root cause repairs to make. However, it can be worth reviewing the trees around your property for risk of falling. In addition, if you experience a lot of snow each year it’s important to install snow guards, which helps the build up to disperse and distribute evenly on your roof. 

Structural Integrity

Another issue to consider with regard to sagging is the structural integrity of your home. This can present itself in various ways. It may be that there is foundation subsidence that is making your home shift and the roof frame move out of alignment. This is a serious issue that you’d need to work with a specialist on before repairing your roof, but is thankfully rare. 


Another option is damage to the structure of your roof in the loft area. This might be due to pests, such as termites. There can also be issues with rotting wood — wet rot in particular can occur if you live in a humid climate and have poor ventilation in the attic space. As such, you’ll need to work with a team of relevant professionals — exterminators in respect of pests, roofing contractors if beams need to be repaired or replaced — alongside fixing the sag.    

Making Repairs

To take care of the sagging itself, there are generally 2 types of repair you may have to make. Some people may find they need to make decking repairs, but this really shouldn’t be undertaken by anyone but professionals.  

Attaching an L Channel

If the sag is due to a damaged rafter, you’ll need to attach an L Channel. This is a long piece of steel, angled like an “L” that helps get a sagging rafter back into its proper shape.

You’ll start by preparing the surface of the rafter or truss you’re repairing, removing any debris or shards. You’ll then mount the L channel to the underside of the rafter, fastening it in place using bolts and washers. From there it’s a matter of slowly putting the broken parts of the rafter back into their correct position, using bolts to bring the wood in alignment with the straight edge of the steel L channel. This might seem like a simple process, but without care you can cause more damage. 

Replacing a Gusset Plate

If the structure of your roof is sagging because an old gusset plate has pulled away from the surface, you’ll need to replace it. For the uninitiated, a gusset plate is a thin sheet of steel — though you can use copper or aluminum — that connects the beams and girders of your woof structure. 

You’ll first need to remove the old gusset plate. You generally can’t just swap this out for another, so you should replace it with a sturdy piece of plywood — ½ inch thickness should be enough. Simply place a piece of the plywood against the beam or girder and use a nail gun to fix it securely in place. Repeat the process on the other side of the beam. 

Again, if you’re unsure of how to approach this correctly, it’s important to seek professional advice. 

Wrapping Up

Fixing a sagging roof is no easy feat. There are a couple of solutions that you can approach personally — attaching an L channel or replacing a gusset plate — but in most cases it’s an issue beyond DIY. Make sure that you not just take care of the sag repair itself, but also pay attention to the underlying causes to prevent further issues in the future.

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