Ask the Architect

The lowdown on insulation


Q. We want to re-insulate our house before winter while we renovate, and aren’t sure about which type to use. The costs seem to be very different between fiberglass and foam. What would you suggest we use, and why? Are there any other less costly choices?

A. Insulation, of all building materials, has the highest return on investment when you consider the installation and material cost compared with the savings over the rest of the life of the building. Every second of every day, your building or home is losing temperature to the outside environment, heating up in the summer and cooling down in the winter, at constant expense, so resisting that loss of temperature and money should be a high priority in the design and selection of materials. Choose the best material and have it installed correctly.

The best choice is closed-cell foam, which has the highest return on investment and the highest initial cost but is worth every penny. Closed-cell foam is a complete cavity-filling barrier with the highest resistance to temperature changes. But it also does what other insulators cannot: It is a vapor retarder and resister.

The two biggest problems buildings face are water and movement, and closed-cell foam is an excellent choice to resist both, because it adds rigidity to the walls and roof while slowing or stopping moisture. Open-cell foam is less costly, but can collect and hold moisture like a sponge does. Fiberglass not only does not expand to completely fill the floor, wall and roof cavities, it also collapses when wet. The only place I would use fiberglass, given a financial choice not to, would be in buildings that need to be stripped due to regular flooding, since foam would be hard to remove in a repair or remediation. With fiberglass insulation you must leave an air space to the outside of the insulation so that air can freely flow to carry moisture away, a sure sign that the cavities continuously have humidity, just like the outside air.

From a cost perspective, you can look at the issue two different ways. Do you want to save money in one day and pay more the rest of the building’s life, or do you want to make the investment to save the money on rising utility costs for the rest of your life in the building? I reduced the insulation in an energy analysis for a home in the spring, when the client got a quote of $16,000 for closed-cell foam. We are now required to do formal energy analysis on each project, so working the numbers and using some creative changes with more resistive window and door ratings, which adds some cost, we were able to use closed-cell foam and save the owner around $8,000. In 10 to 12 years, all those savings will begin to reverse themselves as utility prices rise and continuous temperature is lost. Good luck!

© 2021 Monte Leeper.  Readers are encouraged to send questions to, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.


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