Published on June 30th, 2016 | by Henri


Improving insulation on a 1960s ranch

Q.  I find myself with a question that I cannot get to the bottom of, so I am turning to you  for your opinion and guidance.

I live in central New Jersey and have a ranch style home that was built in the late 1960s. Recently I have been approached by two different contractors touting the energy savings benefits of making my attic space unvented by closing the ridge vents in the roof, removing the attic fan and closing the resulting hole and spraying the rafters (underside of the roof deck) with 5″ of open cell spray foam insulation, as well as sealing off the soffit vents with this same spray. They also proposed 2.25″ of closed cell spray foam insulation on my basement sill plates.

They claim that this will significantly reduce air infiltration into my home and save loads of energy but I am concerned about what might happen to my rafters, sheathing and asphalt roof shingles by cutting off the air circulation in the attic.

I have been unable to find any independent information regarding this procedure although I have found quite a few articles on the internet about creating an unvented attic by using this spray foam technique, unfortunately all of these articles are by contractors that provide this service or by spray foam manufacturers.

What are your thoughts on this process and would you recommend it for my climate?

A.  Creating a hot roof by spraying closed-cell foam underneath the roof deck has been used and suggested for certain conditions, such as in cathedral ceilings where adequate ventilation is difficult — if not impossible — to provide. In these particular roofs, fiberglass insulation is not usually the best to use.

Open-cell insulation is not acceptable for this use, as the open-cell structure allows moisture penetration, which may result in condensation on the underside of the roof sheathing with potential structural damage. You are right to be concerned about this procedure.

The shortcomings of hot roofs, where there is a standard attic, are that the attic becomes a conditioned space, adding to the volume to be heated or air-conditioned for no good reason, and it causes the roof shingles to cook, reducing their life expectancy and voiding any warranty remaining, however poor roof warranties are in general.

But there is something missing in the equation. Did these contractors conduct a thorough assessment of the air infiltration of your house by means of a blower-door test accompanied with infrared thermography? If not, they are selling you a job you may not need, although a 1960s house is likely to need energy efficiency improvements, which the tests mentioned would point out.

However, you must also keep in mind that air sealing the house may bring about a dangerous problem. Houses built before the new energy standards changed the way houses are built count on the many cracks and crevices to provide the needed air for combustion appliances.

If all these cracks and crevices are sealed and no fresh air is provided for a gas-or oil-fired heating system and water heater, the demand for make up air will be satisfied by drawing air through these appliances’ chimneys, bringing carbon monoxide in the living spaces.

How much insulation is between the floor joists of the attic? What type of insulation is there?

If you have minimal insulation on the attic’s floor, adding 8-inches of blown cellulose may also solve the air-infiltration problem — if you do have such a problem — but make sure that the insulators protect your soffit vents with baffles, as you do not want those blocked off. They are essential to proper ventilation in combination with the ridge vent.

This would be far less expensive than foaming the roof deck, and it would preserve the ventilation you have – not a bad thing to have to help cool the attic and the roof shingles in the summer and help dissipate winter moisture.

Attic fans are not desirable as they seldom have the adequate free net ventilation area (NFVA) in the attic to satisfy their CFM requirements. As a result, they rob conditioned air from the living space through any and all cracks available between the living space and the attic, causing an increase in heat and air-conditioning costs.

As to the basement sill plates, their suggestion is good, but, again, there are less expensive ways to control air infiltration in this location. Caulking of the joint between the masonry foundation and the wood sill plate would take care of this problem, and fitting 2-inch thick rigid foam against the rim joist between the floor joists, with the foam’s perimeter caulked, will take care of making this weak band more energy-efficient.

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