Because this kind of work may involve removing old building materials, it is HIGHLY RECOMMENDED that construction professionals undertake all of the necessary safety precautions to protect their workers and themselves.
Altering a building and it's conditions for air tightness, insulation and comfort may see you dealing with the following:
Toxic materials like asbestos, vermiculite and others.
Dust and spores from animals that could lead to respiratory and nervous system damage
Unstable structure, rotted or deteriorated because of moisture damage
Moldy surfaces
Always treat these situations with care and use your personal protective equipment (PPE). Don't take chances with your health!!