A building envelope is the physical separators between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer. The three basic elements of a building envelope are a weather barrier, air barrier, and thermal barrier. This part of construction is usually taken very seriously in commercial construction. Not so in home construction. The building envelope can be viewed as a perfunctory requirement but not something that matters that much. Yet, the building envelope is usually the cause and effect of water leaks into the living spaces, air leaks out of the living spaces and the cost of thousands of dollars in repairs.
Your home should have a building envelope that is impenetrable from water and will not let air escape. Theoretically, this envelope should keep water out even without the exterior wall cover. In other words, your house should be able to keep water out without any brick wall at all. It needs a roof decking, but not necessarily a roofing tiles or roofing shingles. So it should be obvious that when a home's envelope is not put up correctly or with attention to detail, then water is bound to get in. It is the equivalent of having a raincoat that has gaps where the shoulder meets the sleeves. If it does, then water is bound to get inside. Same with the building envelope.
The key areas where building envelopes fail are the joints between sheets or rolls of waterproofing material. Another major fault area are windows and doors which require special taping that is often done wrong. Joints also have to be taped and even in expensive homes, they are frequently overlooked.
If you are worried about your home's envelope, you should look up systems envelope experts in your area and have your house examined before even worse things happen.