Can sagging floors collapse? When should you be worried?

A sagging floor can be a major concern. In some cases, it can be a sign of a serious issue, that could cause the floor to collapse

Due to the issue being in the floor and not the ceiling below, makes it even more worrying. This suggests, there could be a problem with the joists. If your joists are causing the floor to sag, this usually indicates, they are either damaged, or they are not adequate to support the load above.

can sagging floors collapse

All floors have a “dead load”. This is the weight of materials the floor is constructed from. Next, they will have an estimated “imposed load”. This is the weight of items such as beds, cupboards, baths, etc.

Based on these weights, combined with how far the joists span, will determine how big the floor joists need to be.

Therefore, if the ceiling is sagging, and none of the timbers are damaged. It is likely that the joists are not sufficient to support the floor above them.

This is an issue that needs fixing ASAP. If it isn’t rectified, there is a chance the joists could become damaged, and the floor could collapse.

For this reason, if you have sagging joists, it is highly advised that you talk with a structural engineer. They will be able to advise on the best course of action.

You can find and compare structural engineers in your area by clicking here

If the sagging is not in your floor, but instead, it is in the ceiling below, this may be less of an issue. Usually it will be a problem with the plasterboard. This is often cause by water damage and is relatively easy to fix.

With that said, even a sagging ceiling could be dangerous. Plasterboard’s are heavy and if they come lose, you don’t want them landing on you. To learn more about the dangers of a sagging ceiling click here.

Sagging undamaged joists

As we previously mentioned, the size and span of joists could be a reason for sagging floors. If for example, a loft space was used for heavy storage and the joists were only small ceiling joists, this could cause issues.

Also if you have something particularly heavy in an upstairs room. For example, let’s say you create a small gym. That would dramatically increase the load on existing joists. If the joist are already at a maximum span for their size, this could result in a load, that is far too heavy and would eventually cause sagging.

There is also a chance that a wall was removed below, this could have been supporting the floor above.

If anything like this has caused your joists to sag. Then it will need fixing before the problem gets any worse.

There are a few options to fix this type of sagging. Firstly, if a wall was removed and it was load bearing, you will need to add some kind of support back. This will usually be in the form of a steel beam such as an RSJ. This is a big job and will require a professional to do the work. Also, as we mentioned before you should really consult a structural engineer.

If the issue, is that the load above is too big for the joists, you have three main options:

  1. You can replace the joists – This is obviously a big job and should be carried out by professionals.

  2. You can double up the existing joists – To do this you will need to jack up the old sagging joists and then fix the new joists to them. Depending on what is recommended by a structural engineer, this may require you to raise the floor level upstairs with deeper joists. This is quite common in attic spaces.

  3. Add support below – Again this could be a structural beam that spreads the load and reduces the joist span.

Every case is different, and how your sagging joists are fixed, will depend on the circumstances. This is why you should speak with a professional.

Floor sagging due to damaged joists

If your floor is sagging due to damaged joists, this is usually easier to fix. It is also less likely an issue caused by the span and strength of the floor. Instead it is more likely a defect in the wood, or some type of deterioration such as rot.

If the joists are sagging towards the walls, it is very likely an issue with the ends of the joists. In most cases, this will be due to rot.

Rot is caused by excess moisture and fungus that attacks wood, deteriorating it over time.

If you do find rot, it will need removing. You will also need to treat surrounding timbers and rectify any damp issues that caused the rot.

If it is only the ends of joists that are affected, they can be cut back to a point with no rot. Next, a new section of joist can be added, to replace the removed rotten timber.

The new section of joist will then be overlapped on either side with additional timber joists, in order to hold the new piece in place. This is a technique known as sister-joisting.

If the damage is more extensive, you may need to replace the entire joist.

In most cases, damaged joists will not need the help of a structural engineer. This is often a case of several damaged joists that can be easily replaced. With that said, you will probably need the help of a joiner if you are not experienced in this type of work.

If you have damage to several joists, that is away from the walls (maybe closer to the centre), this could be a bigger issue.

Again, if you can’t determine why this is happening you should consult a professional.


A sagging floor can be a serious issue. If left long enough under certain circumstances, it could even collapse. Unless you know the exact reason the floor is sagging, and how to fix it, you should probably speak with a trained structural engineer.

A professional will be able to provide the best solution to fix your sagging floor. They will also help you avoid any mistakes, that could potentially make the problem worse.

To find structural engineers in your area click here