from Maggie in Shorewood, WI:
#506
I have a 1920's bungalow that does not currently have any exterior wall insulation. I started researching which type would be appropriate for my home and came across several discussions that advised against insulating the walls. Since the walls do not have an existing vapor barrier, adding insulation without a vapor barrier could lead to moisture problems within the wall. What is your opinion? Would a closed cell spray in insulation solve this problem? Additionally I have heard that the payback doesn't make sense because the cost can be $2,000-$3,000 and depends on the existing conditions you might only save $160 a year, which would equate to over a 10 year payback? Do you have any thoughts on this? I always strive to do what is best for my house and the environment.
Done properly, insulating equates to energy savings.
The “vapor barrier” on the exterior wall issue can easily be addressed with the proper application of what is known as vapor barrier paint. Keep in mind the term, vapor barrier, is somewhat of a misnomer… the older term "vapor barrier" is still used even though it may inaccurately imply that the material stops all of the moisture transfer. Since most building materials allow some water vapor to diffuse through it to some degree, the term "vapor diffusion retarder” is more accurate. Most building materials have a perm rating. Any material with a rating of more than 0.1 perm is considered a vapor retarder. Any material with a rating of 0.1 perm or less is considered a vapor barrier (also known as a Class I vapor retarder). Vapor barriers are materials that are vapor impermeable.
With regards to using a closed cell spray in insulation… that would indicate to me that you have stripped (or plan to strip) the lath and plaster (common in homes of 1920’s construction) on the exterior walls and have exposed the stud cavities. If that is the case, you could insulate the cavities with a closed cell spray in insulation to achieve high R-value (R-6 per inch) and superior air sealing. Using a closed cell spray in insulation would also address the vapor “barrier” issue you mentioned. If you do expose the stud cavities, you open the door for many other possibilities for air sealing and insulating (i.e. dense-packing with dry cellulose or short fiber fiberglass, damp-sprayed cellulose, low density spray foam, or high density fiberglass batts).
I strongly disagree with advising against insulating the exterior walls (cavities). Properly done, the inside wall surfaces become much warmer in the winter, air leakage is reduced, and thermal performance is enhanced. That equates to energy savings and improved comfort all year.
The energy savings can be calculated. Once calculated, it would be a simple matter of determining the time period for the energy savings to equal (and surpass) the initial expenditure. In addition to the on-going energy savings, there are currently federal tax credits for installing insulation measures. To learn the details regarding federal tax credits, I would suggest visiting the ENERGY STAR (R) Web site or the Tax Incentives Assistant Project Web site. These Web sites have information that consumers and businesses need to make use of the federal income tax incentives for energy efficient products and technologies.
One of the best ways to help calculate potential savings would be to have a home energy evaluation conducted on your home by a consultant partnering with Home Performance with ENERGY STAR®. This computer-based evaluation would take into consideration the above mentioned parameters (and others) to calculate savings and payback information for installing conservation measures such as attic insulation and dense-packed cellulose for your sidewalls. You may also be eligible for Cash-Back Rewards from Focus on Energy for sidewall insulation. Please visit focusonenergy.com/incentives for the latest incentives and requirements, as Focus offers are subject to change.
Published Thursday, October 08, 2009