We live in a poorly insulated home in a cold climate. Every fall when the furnace kicks in I cringe a little bit thinking about the fossil fuels that are burning in the basement because know that we use more fuel than a well insulated home would use. If more insulation would lighten our carbon footprint, why don't we just insulate more? Minnesota is a harsh climate for building enclosures (walls, roofs, foundations). It gets really cold here for many months then it is quite hot and very humid for several months. Our poorly insulated home takes on a lot of moisture in the summer. It also sheds that moisture as hot air passes through the walls, roof and foundation during the winter. This annual cycle is what has allowed the 90 year old building to remain very healthy.
The fact that dry, warm air passes through our walls and dries them out for six months a year is the main reason we don't have a mold problem. Although I cringe thinking about how much extra fuel we burn in the winter I am appeased knowing that we are preventing mold.
When we do renovate, it will be critical that we do so in the right order to allow moisture to exit the building and stay out of the enclosure. Renovating your home's enclosure is not as easy as stuffing insulation into the cracks. It is important to remember, "Ventilate right, then make it tight." If you install proper ventilation into a home you can prevent moisture problems.
This is only one aspect of renovating. If you are interested in reading more, I highly recommend articles by Joseph Lstiburek, Ph.D., P.Eng., ASHRAE Fellow. Lstiburek has written a series of articles that are must reads for anyone considering a home renovation.
Related Link: Controlling Humidity Levels at Home