Ventilation and the Illusion of Efficiency

Since we’ve still got some cold weather and ice around, I wanted to make another post on the subject. When foam insulation is used in a cathedral ceiling application, we do not use ANY ventilation with the product. Many customers are very concerned at first because they’ve always been told that insulation has to be ventilated or they will get a bunch of ice and moisture damage. After we give a customer a proposal to insulate their home, their first response is often the following – I told my friend that you weren’t proposing any ventilation for my insulation and they said that would be a big mistake.

It would be a big mistake if we weren’t installing foam. Fiberglass has been extensively used in homes since the 1950s and it is still the most used insulation on the market. Since it was the only viable product to use for insulation prior to the advent of polystyrene and foam for installation in homes, we simply learned to live with its deficiencies. The most glaring deficiency in fiberglass and, to a lesser extent, cellulose, is that while it slows the transfer of energy from your house to the exterior, it still lets energy transfer at a torrid pace.

What that means is that heat (in winter) travels through the fiberglass and hits the underside of your roof, which does two things.

1.
It heats the underside of the roof to the point where the snow will melt and then reform as ice at your gutter.

2.
The moisture in the heated air condenses as it hits the cold roof. This moisture causes a number of problems, including mold.

The Building Code covers up these problems by requiring ventilation to carry heat and moisture laden air out of the house before it can cause these problems (Code does not require ventilation when foam is used). This is where the illusion comes in. Proud owners of brand new homes think that since they don’t have any ice on their roof, they must not have any heat loss. Think again. If the ventilation wasn’t there, they would see how bad fiberglass really works.

Take a look at this picture. This is a house that we actually insulated. The entire roofline has 6 inches of open cell foam sprayed to the underside except for the gable roof on the front, which is a cathedral we couldn’t access to insulate it. It is the only part of the roof that has fiberglass. Notice how it is the only part of the roof with no snow! The rest of the roof is full of snow and has NO VENTILATION.