Have you ever heard of a "leaky condo"? Well it doesn't just happen to condos.
The exterior of a house is a system that is called the building envelope. The building envelope is comprised of everything that is keeping the weather outside of the house, including siding, stucco, windows, doors, chimneys, etc. The details of the building envelope are more complicated when there is a hole in the structure... but admittedly windows and doors are pretty nice to have.
In the first picture there is a wall and roof meeting with a window...double trouble!
Moisture, nutrients and time are required for rot or mould to start to damage a house. It is a common misconception that there will be a mould problem after a overflowing sink or hot water tank flood, but in these examples the moisture is not consistent. Mould and rot take consistent moisture, nutrients and time to develop into this. The damage from rot and mould can be structural or also it can affect the health of your home environment.
In this picture the damage was caused by water running off the window and getting between the stucco and the wall sheathing. This damage was substantial, but it had not yet affected the interior of the house. You can see the sheathing was compromised, but underneath the water travelled even further. We were able to replace the damaged structure. In this case there were no noticeable clues, inside or outside, that the building envelope was failing.
It is important when having an exterior renovation, window replacement or a new build that your contractor is overseeing and taking responsibility for all of the necessary steps in closing in the building envelope properly. Most problems occur from missing or improper flashing. There are a lot of finicky steps that are often overlooked or missed because there are many different crews involved in working on the building envelope.
The building envelope is one of the biggest reasons you need a qualified professional with the big picture, working on your project.