Cracks in the walls

If you’re seeing cracks in the walls then your house could likely be showing the first and most obvious signs of being structurally unsound. If your walls are cracking, something just isn’t right, whether the structure is uneven or, most likely, the building has issues in its foundation. Regardless, get those cracks checked before things go downhill.
Stains under the windows

Another way of telling your house has some major structural issues is if there is discolouration under your windows, either on the inside or outside. This shows that the building has serious water damage. Water has probably gotten in around the windows and is weakening the entire structure around the frame. If this is the case, your house could be close to falling apart.
Slanted floors

Maybe your walls are straight and sound as can be, but perhaps you can’t say the same about the floors. If you feel like your floors could be used as a slide, no matter how steep, you should be concerned. The construction of the house had some flaws, because it probably means that the ground beneath the foundation was not sufficiently compacted before building began.
Peeling paint in the bathroom

Old homes will have peeling paint, that’s just the way of things. You should be concerned if the bathroom paint is peeling though. It’s your house letting you know that the bathroom has some water damage going on. In fact, it’s probably not new. This means the roof might actually have leaks which can also lead to mould and rotting planks in the roof.
The baseboards are falling off

When a baseboard falls off, the instinct can be to ignore it and just prop it back up as if nothing happened, but that’s definitely not what you should be doing. There is a reason the baseboards have come unattached from the walls, and those reasons are generally to do with foundational issues that occurred when the house was first built.
The ground around the house is shifting

Sometimes the earth around your house is the best indicator that there is something wrong with the structure of the house itself. You might have water leakage going on in your house which is causing the earth around it to sink and become mushy. If the land around your house is eroding, then you likely need to get on those repairs as soon as possible.
Doors and windows are hard to close

The doors and windows in the building were almost definitely perfectly aligned when the house was first built. If they are now difficult to shut and open properly, then it could be a sign of subsidence which means the ground under the property is moving. This subsidence could have but the door and window frames askew, making their use more difficult.
Your walls are warped

If the walls are warped and just not quite flat, then they could be absorbing water. The water in the walls bulges out, creating a distorted shape. This kind of water damage can make your walls begin to crumble. If this is happening in your home, you’ll probably notice it around the baseboards first, so pay attention to them.
The floor is bouncy

A good bounce is great fun on a trampoline or diving board, but it’s not a feature you want in your home flooring. If your floors are feeling spongy and standing on them pushes them down noticeably, you are dealing with structural issues. This could be a case of a termite infestation which would explain the weakened, spongy wood perfectly.
Your home smells damp

You might think that a damp smell just means your house isn’t clean enough, but it usually goes much deeper than that. A damp smell signifies mould somewhere in your house. If there is mould, the building has some sort of structural issue that is allowing water damage. Check for leaks around your sinks, and see if your toilet is rocking – if it is, that could be causing the smell.