Question

We have inadequate wall insulation. What is the best approach to insulate our walls?

Asked by Valerie Upton
Knoxville, TN

Our was home built in 1946.  We have plaster walls and aluminum siding.

Answer

Michael Holcomb

Answered by Michael Holcomb

Byron Center, MI

Alliance for Environmental Sustainability (Headquarters)

November 2, 2011

Valerie,

Thank you for your question concerning wall insulation. In 1946 very little consideration was given to insulation in your climate zone (6b). I suppose the same could be said about a cold-weather state like Michigan so do not take it personally or harbor any ill-will towards the builder. It’s just the way things were done back then.

There are a variety of mitigating circumstances that will need to be considered before selecting an insulation product.

  • I’ll list options and provide information to help you make an informed decision.
  • I don’t sell insulation so my bias is based on building science and over 20,000 residential inspections over 30 years as an energy auditor.

Pour in Place Foam

Sold under a variety of trade names, pour-in-place foam is getting more press lately.

I recently saw a television commercial showing the process. They poured the material into a Plexiglas covered test wall. The wall had three stud cavities: one with fiberglass blanket insulation, one empty and one with wiring and electrical fixture boxes. In each case there were large voids after the foam was poured in place. I figured that if that’s the best installation they can do in a test wall it would only be worse in a real world situation.

I would consider using this material:

  • if you had a third-party Infrared evaluation completed before installing the foam and
  • a follow-up after the foam was installed with a guarantee from the installing contractor that they would correct any voids and warrant against shrinkage and/or material degradation within the wall cavity over time.

Blown-in-Fiberglass

Insulasafe III by Certainteed is a quality insulation material designed for blowing into cavities under pressure.

A 2” x 4” wall cavity can achieve values ranging from R-13 to R-15 using this material. I would urge you to go for the higher R-value because it is put in at a higher density which reduces convective air movement within the wall cavity on cold winter days/nights.

Achieving a high density necessary to reduce convection within the insulation may result in plaster damage on the interior side if pressures exceed what can be handled by 70-year-old plaster.

Cellulose Insulation

Cellulose is a recycled newsprint product. It has a higher density that fiberglass so it reduces convection as well as conduction. Contractors still need to control the installation pressure to prevent plaster damage but it is less likely to be a problem with cellulose than fiberglass.

Cellulose is a green product (keeps all those old newspapers out of the landfill).

Cellulose insulation manufacturers add chemicals to the pulverized newsprint to make it rodent, insect, mold and fire resistant. Use a product that uses borates rather than aluminum sulphates to reduce the potential for oxidation of metal (nails, fixtures) in the wall cavities.

I recommend that you insist on stabilized cellulose because there is less dust involved when installing it – and believe me you will have places where the product gets into your home.

If you have tubs, showers or fireplaces on outside walls the contractor may need to open the wall to install a thermal barrier to the studs to keep the insulation in place and prevent convective air movement.

Check your electrical wiring

Before hiring an insulation contractor have an electrician evaluate your electrical wiring to make sure that it can be safely encapsulated in insulation.

Some older wiring may need to be replaced before you can insulate to reduce the potential of creating a fire hazard. Knob and tube wiring and aluminum wiring are candidates for replacement.

Quality of the installation is paramount

Insulation contractors will remove rows of your aluminum siding and drill a series of holes in the sheathing to allow them to blow insulation into each wall stud cavity. There will be some cavities that may be too narrow to inject insulation but they should be kept to a minimum.

It would be prudent to hire an Infrared technologist to evaluate the finished product to determine the quality of the installation. Some insulation contractors may offer this service as part of their quality control process. I would not advise you to hire an independent specialist if the installing contractor is willing to provide you with enough quality IR images so you can judge the installation yourself. As a side note, the quantity of insulation is not as important as the quality of the material and the installation. 

Consider air sealing the attic floor

Many clients have expressed concern when they did not receive the cost reductions they expected when insulating their exterior walls.

Since heat rises it makes sense to stop air from passing through your ceiling into the attic. This can only be done by air sealing the attic floor since fibrous insulation will not effectively stop upward convection in an open cavity like an attic.

Choosing an insulation contractor

Your local Better business Bureau will have a list of Accredited Insulation contractors. This is a great place to start in identifying a qualified contractor.

Since many states do not license insulation contractors your risk may be higher of getting a poor quality contractor if you base your purchasing
decision on low bidder.

Make sure the contractor you select has (active) general liability insurance, workman’s compensation and warrants his work.

Asking questions and checking references is an important task in hiring qualified contractors. Do your homework.

 

For more information:

Read "I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?" a Q&A answered by Alex Georgiou.

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