While previous generations may have been content to live in drafty houses, most people now want comfortable warm houses. A healthy house today is well sealed, well insulated and properly ventilated.
A well-insulated house is a bit like dressing for the weather. A wool sweater will keep you
warm if the wind is not blowing and it is not raining.On a windy, rainy day, wearing a nylon shell over your wool sweater helps keep you reasonably dry and warm.
A house is similar. On the outside, underneath the brick or siding, there is an air barrier that does the same thing as the nylon — it keeps the wind from blowing through. Then there is the insulation (like your sweater) and a vapour barrier, which helps keep moisture away from the house structure where it can do damage.