How To Fix A Sagging Roof With Ease

If you have just stepped outside your house and realized that your roof is no longer straight, this could signal a problem. Fixing a sagging roof as soon as you spot it is very important, otherwise you could find that the problem will only worsen over time.

In the end, you may need to have the entire roof replaced, which could be extremely costly, not to mention a lot of hassle.

If you having a sagging roof, you will not be able to even begin to think about repairing it before you take some time to investigate why the problem has occurred in the first place.

There can be several reasons why your roof is no longer arrow straight, although some reasons are more common than others.

In this article, we will take a look at the main reasons why you could be experiencing this issue with your roof and then we will look at some of the best ways of rectifying the problem so that you can restore your roof to its original condition before further damage is caused.

Batterbee Florida Style Roofing

How Do I Know I Have A Sagging Roof?

Your roof line should look arrow straight when you look directly at it. You can therefore easily identify whether your roof is sagging if you can see a swag, curve or dip at its peak when you stand on the street.

While some sagging roof causes can easily be handled by anyone who has a little DIY knowledge, some problems are a lot more complex and need the help of a professional to repair.

Related: Power Tools Every Homeowner Should Have

How Does Your Roof’s Anatomy Work?

If you go up into the attic you will be able to see how the structural anatomy of your roof works.

Basically put, the frame of your roof line is reduced to triangle. If you stand in your attic, all of the boards which are laid horizontally under your feet are the roof or ceiling joists.

Over your head, you will see sloped boards – these are the rafters.

Looking along the rafters, you will see that they are attached to a further beam which is the ridge line, right at the very top.

These three boards form a roof’s familiar triangular shape. This shape is very strong and can support a lot of weight – ideal when holding up shingles or tiles.

Usually, the three boards can support the full weight of not just the roof, but also its shingles and roof sheathing and even external weather forces like ice and snow.

It can support this weight as the rafters transfer all the weight onto the joints, which in turn transfer weight onto the exterior wall. If everything is functioning as it should, you would see a nice straight roof line.

Is Decay The Problem?

Some roofs sag because of decay to the inside beams and sheathing.

Decay can occur over time due to a number of reasons including leaks in the roof or leaks from guttering or downpipes, wet rot or even insect attacks, such as termites damaging the ends of the bearings.

Any of these could cause a structural defect which could seriously undermine the integrity of your roof and even cause problems that could prove to be life threatening if not rectified since your roof could give way and collapse into your property or onto passers by.

What Do I Need To Know About Lapping?

A sagging roof line may originate from the ceiling’s horizontal rafters.

When the framing of the roof is put together, quite frequently, two of the ceiling rafters will be fixed together as this will create a much longer span.

Typically, they are lapped and then toe nailed together in its center so that the correct length can be achieved.

When the combined weight of the roof together with any heavy snow puts pressure onto the roof, it then pushes out the rafters, and then in turn, they push onto both sides of the exterior wall.

However, if those joints are improperly lapped or are not lapped at all but instead are butted together, it is possible that the extra weight of snow could pull them apart.

In fact, even if joints have been lapped properly, sufficient pressure and weight placed on the roof in a very severe snowfall, for example, could cause the joints to loosen too.

When this happens, and the joints come apart, the ridge line will appear to sag or drop when the exterior wall begins to tilt outwards slightly.

Sometimes, the sagging will not be noticeable from outside the house, however signs that indicate that sagging is occurring may be visible from inside the house.

You should look out for any cracks appearing in the ceiling’s drywall as a symptom of the problem.

What About Beams?

Sometimes your roof will use a different kind of roof framing which uses a central beam rather than lapping.

While this is a very similar system to lapped joists, rather than lapping the two joists together, both individual beams will be joined to a bigger beam which runs in a perpendicular direction to the roof joists.

These are then attached on each side of the beam using a metal hanger.

The weight of the roof will create pressure, and then the hangers may pull away from their beam, causing the walls on the exterior to come outwards to cause a visibly sagging roof line on the top of your roof.

Rafter Ties – Another Cause

Depending on which kind of framing has been used for your roof, you may find that a further component has been added to your two sloping rafters’ triangular shape.

A rafter collar or tie is a piece which is horizontally laid to connect both rafters on each side of it. Typically, it is nailed to each of the rafters at about halfway down their length.

This rafter tie is supposed to prevent the rafters from being pulled away from each other, however if the rafter ties have been placed incorrectly, so they do not form a proper triangle with the tie at the time, their strength can be compromised, making them insufficient to prevent the rafters from being able to spread.

A further problem can occur if the rafter ties have been nailed poorly to the rafters. In this case the nails can pull loose, causing the rafters to spread further apart.

Again, the effect of this is that the roof line begins to sag.

Struts And Beams

There are some roof frame designs which use a beam or strut which runs in a perpendicular direction across the base of the rafters in your attic.

This beam will be attached to each of the exterior walls as well as to the base of every sloping rafter as this is intended to give your roof additional strength to withstand pressure from snow and ice.

Should the beam be incorrectly nailed to the rafters, it may eventually pull loose, contributing to the roof sagging problems.

It is possible for more problems to occur when the strut or beam has been cut to an incorrect size, or if the struct is defective with splits or cracks in it.

Rotting Sheathing

Sometimes the problem with your roof may be nothing to do with its frame but instead the sheathing.

If your roof’s sheathing has become saturated or rotten, roof lines may sag. If this does turn out to be the problem this is actually good news since this is a simple problem to fix.

If your roof framing is still sound, and there are no problems anywhere else however your roof is still sagging, it is likely that the problem has occurred because the shingles or plywood sheathing have been installed poorly.

When rain water comes through your roof’s shingles, the plywood will wrap, rot or weaken, and this will make the roof look like it is sagging between its rafters.

Seeking Professional Help

Some problems relating to a sagging roof line should definitely be evaluated by a professional roofer.

While some of the issues can be fixed easily by adding struts, jacking up some loose rafters or replacing shingles and sheathing, other problems will require an experienced expert to work on it.

The best rule of thumb is ‘if in doubt’ call a professional!


I know you are a DIY’er so we will still take a look at how you can fix a sagging roof yourself…

Repairing Sagging Rafters

If you have a problem with sagging rafters, there are a few things that you can do to sort the problem out.

You should never leave sagging rafters as they are without carrying out some kind of remedial work as it can prove to be a very serious issue in time if not treated correctly and quickly.

Sagging rafters can result in water leaking and roof caving which can be very difficult and expensive to rectify.

Although repairing rafters is not difficult, you will need to have some access to get the job done, so if you are struggling to get easy access you may need to get professional assistance.

However, if you have enough roof to easily access your rafters, you shouldn’t have too many difficulties in repairing your sagging rafters yourself.

Metal Shingle Roofing Material


What You Will Need:

  • Carriage bolts
  • Metal drill bit
  • Hydraulic jack
  • 1/2″ thick angle iron
  • Drill


  • First, before you do anything else, you need to take a look inside your attic to determine how many of your rafters are sagging and where the sagging is coming from. Once you have identified the extent of the damage, you can then repair it much more easily. If you spot any other damage at this point, you should fix that too before you move on to the following step. Some rafters may require straightening, and some may have to be replaced with some new sheathing.
  • Straightening your rafters is quite easy to do. You simply jack them up, one over another. Don’t be tempted to rush this job, however, as it is a task which must be accomplished carefully and slowly. Sometimes, it could take as long as several weeks until your rafters have returned to the original position that they were once in. You should your rafters up, giving them 1″ of space between each, as this will enable the roof to effectively move without causing cracking or damage.
  • Once your rafters have been fully straightened, you need to find a way of preventing them from bending out of shape again. You can do this by guarding it using an angle iron piece. You should obtain a piece that measures 1/2 “, with sides that measure 4” in length and an overall length of the entire piece being a minimum of 2 feet. This is intended to form an added protective layer, helping to avoid any cracks occurring in the wood.
  • Drill your angle iron, making 4 or 5 holes into it on one of the piece’s sides. You will require a metal bit to do this.
  • Once you have your rafters back in their original position, you need to put one of the section of your iron piece over the rafter’s topmost section. Make sure that you fix it securely on the area where the sagging is occurring. Using the carriage bolts when attaching them, however as a word of warning, avoid fixing them too tightly as this could cause more damage.
  • Once the iron is attached, you will need to rapidly relocate your jack. If you’re not quick enough, you may find that the rafter starts to sag again and you will have to start from the beginning. So, be quick, but also be very cautious when you are removing the jack. Set the iron onto the whole beam then put your jack back under the beam, however this time, put it under your iron piece. This is a tricky step, and it requires patience and plenty of concentration. It’s important that you don’t panic. All you have to do is follow these steps carefully one at a time and you’ll be fine.
  • You are now ready to tighten your carriage bolts that you already put in place. Put the carriage bolts which remain into the 2’6″ rafter and then secure them tightly. When you are fixing them in, make sure to lower down your jack as the metal will then be able to afford the roof’s weight to avoid damage.
  • Should there be further rafters to fix in the same way, simply follow these steps again until all of your rafters have been fully repaired and your roof no longer sags.

Fixing A Sagging Roof By Bolstering The Beams

Bolstering the beams of your roof is another solution to repairing a sagging roof, however it is often something that requires assistance from another able-bodied person, since beams can be extremely heavy.

It also makes sense to arrange the repair for a sunny day so you minimize the chances of any water ingress into your attic while you are carrying out the repair.

It may be easier to complete this job on smaller roofs such as garage roofs, however it is the same principle regardless of the size or type of roof that you are repairing.

1. The first step is to always check the beams so that you can determine their condition. If you find an infestation of termites, for example, you are going to need a more extensive repair than if they are fine with no infestations. If you have open beams, it will be very easy to gain access to the roof area in order to carry out the repair, however if you do not, you may require some professional assistance to get the job done.

2. Next, assuming that there are no further problems with your timber beams, you need to measure the length of the beam you need to bolster and then purchase the correct lengths. You need to buy the lumber in 2 x 6″ size. Always double check your measurements before you order the wood as you don’t want to make a costly mistake by accidentally ordering pieces of wood which are too short to complete the job properly.

3. Once you have your wood in place, you need to lay the wood out under every beam, and lifting up the side of the eaves, put a 6″ nail under the beam as this will work to hold it temporarily in the right position. This is where you can benefit from having someone with you who can help. Repeat on the beam’s other end and once it is firmly in place, you can then screw it to your old beam using 4″ brass screws. It is important to choose brass screws, since brass will not rust until iron screws. Make sure that while you work you push the roof upwards. If required, you will need to use something that forces up the roof while you are working the new beams into the right place and fastening them securely.

4. Work along the beams gradually, taking care to push up the roof while you work. All of the sagging will be lifted up gradually. By the time all of the repair is finished, you will find that the roof looks upright once more.

5. While you are working on the beams, you then need to ensure that they will not be able to sag again as this is a danger unless you strength the beams properly. You can achieve this by using some lengths of timber that are the same length as your roof. Maneuver them into the correct position under all of the beams and then secure them firmly to every beam. This works to stop them from sagging once more. You should use a minimum of four cross timbers as this will have a long lasting result.

Replacing Sheathing

Perhaps the sheathing is the problem with your sagging roof. If that is the case, you need to replace it in order to resolve your issue.

A roof can only be as good as its roof deck, and your roof sheathing is the sheet material which forms the surface that the shingles are nailed to.

Usually, sheathing is made from OSB or plywood, and it is manufactured by laminating thin veneer strips or wood fibers under pressure.

Unfortunately, if they are subject to moisture over a long term period, the sheathing can then delaminate, and this will mean that it cannot be salvaged and will need to be replaced.

If you discover that your roof’s sheathing is spongy in places or if it appears to be warped, you will need to replace it before you install any new shingles or you will just be wasting money and time.

There are different methods you can use to replace your sheathing such as…

Tear Off Method

Before you try this method, you need to determine whether or not the sheathing that remains is strong enough to be walked on, since using the tear off method requires you to begin at the ridge before progressing downwards.

This enables you to stand on lower panels while tearing off all of the upper ones.

If you find that your sheathing is no longer structurally sound, you can still use this method if you construct some scaffolding at the edge of your roof which you can stand on as you tear away the lower panels, replacing them with new ones before you tear off and replace the row of panels higher up.

You will need a cat’s paw or flat bar to pry up the panels.

Preparing The Rafters

Rafters which are made from wood will withstand any damage caused by moisture better than your sheathing will, however should your rafters be damaged, you need to replace them before you put the new sheathing in place.

Again, you would just be wasting money if you left them in place with damage already existing.

If your roof has trusses, you will need to seek professional help since you are not able to replace truss chords without consulting a professional engineer.

Trusses have small engineered members which have been specially designed to support your roof deck as a unit, and in some instances, the top truss chords or rafters could be in decent shape, although slightly warped.

You can fix this by adding shims onto the top rafters or chords to make a more level nailing base.

Sheathing Installation

Sheathing is supplied in 4×8′ sheets and are designed to be installed onto rafters with 16-24″ spacing. The end of a plywood or OSB sheet should align with the rafters’ center and this is called “breaking on center”.

Some special OSB roof sheets have nailing guides to align over your rafters and this makes nailing them a lot easier.

If  you are using plywood which is unlined, you will need to make chalk lines so that you can mark the locations of your rafters.

You will also need to check your local codes to find out about specific nailing patterns in your area, as in some places where there are notoriously high winds, there may be a nailing code that you will need to comply with.

If there is no nailing code, you should insert a single 8d nail at every 6″ along the edges and one for every 12″ along the plane. Always leave a gap of 1/8″ between the panels as this will enable any expansion.

You can increase the stability of the sheathing which is installed on rafters that are spaced at 24″ apart by using H-clips which fit between your panels at the point that they connect to your roof rafters.

These clips will also guarantee that you have the right expansion gap.

Should you choose not to use the H clips, you should use one 10d box nail as a 1/8″ spacing guide.

Cut off any excess sheathing using a circular saw at the roof edges and once your new sheathing has been put in the right place, always cover it immediately with some roofing felt as this will protect against damage from moisture.

Always install the shingles as quickly as possible to minimize the chance of damage from inclement weather conditions.

Old regular roof shingles

What Do I Need To Be Aware Of When I Repair My Roof?

There are a few things that you need to bear in mind when you are preparing to repair your sagging roof.

1. Safety – your safety and the safety of those around you is absolutely paramount when you are carrying out any form of repair on your home, but especially when you are working on your roof as it is very high up and one false move could lead to you falling. Also, if you make a mistake when repairing your roof, you do run the risk of making your roof structurally unstable and unsound, which could eventually result in your roof giving way and collapsing – not an ideal scenario for anyone.

2. Measurements – if you are using new beams it is always important to measure them properly to make sure that they are the right size to offer appropriate support. If you use beams that are too short, the level of support will not be adequate to take the weight of your roof, especially if snow or ice lies on it during the winter season, and you could end up causing further damage.

3. Access – before you try to carry out any work on your roof, you need to be sure that you will be able to gain access to all of the areas that you need to reach in order to carry out the repairs safely and easily. Remember that you will also need room to move and to use tools in the space, so you will need adequate room to achieve this. If you feel that there is not sufficient room for you to do the job properly, you should seek professional help.

4. Identify the problem – you should never assume that a particular issue is the problem that your roof is experiencing. Assuming that you have rotten sheathing when in fact you have truss damage will not only waste your time and money, but will also delay the essential repair which needs to be carried out. It could be much longer before you finally determine what the real problem is, and by then, the problem could have got out of hand and may need a much more extensive and expensive repair. By simply carrying out a few simple checks in your attic you can pinpoint the source of the problem so that you can get the right solution first time. If you are unsure what the problem is even after checking, it is always important to see professional guidance so that you can make sure that the problem is properly identified so that it can be fixed.

What If I Can’t Repair My Own Roof?

Sometimes the damage to a roof is so extensive that it would be impossible to carry out the repair yourself.

If you believe that there is damage to the roof truss or if the problem looks extremely extensive and would require large scale repairs and replacements that you would be unable to manage yourself, it is important to seek our professional advice from a skilled roof specialist.

Roofers are highly trained and are capable of assessing the problem, suggesting remedies for the problem and carrying out any rectification required safely and efficiently to professional standards.

You can still seek professional assistance if you think that the problem may be minor if you feel that you are unable to manage to carry out the repair yourself or if you lack the confidence in your own repair skills to be able to do the replacement or repair properly.

Your roof is a key element of your home and if you fail to carry out repairs on it appropriately you could be putting yourself and those around you in danger. If in doubt, always contact a professional.

Scroll to Top

Get tailored advice & exclusive content

Join our exclusive 2,500+ email list to get tailored advice, product roundups, and be the first to see our new content. No spam, we promise.