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AeroBarrier on Existing House

Jon S | Posted in General Questions on

I recently purchased a two-story house with a large basement and ventilated attic.  The basement is 1500 sq ft, the first floor is 2450 sq ft, and the second floor is 1500 sq ft.  The house is located in Zone 4A.  Walls are R-19 and I will top off the attic to R-49 or R-60.  I installed new HVAC to replace 30+ year old equipment (16.5 Seer A/C w/97% furnace).  I am also upgrading the natural draft water heater to a heat pump.   I am getting bids for solar to offset energy usage.

An energy audit revealed a 7.8 ACH50.  I received a quote for AeroBarrier for about $7,500 (before a local rebate of $1500).  I like the idea of reducing drafts and pests, while also saving energy.  Conservatively, I expect a final result of 5 ACH50, with an optimistic goal of 3 ACH50.   To accomplish the air sealing, I will need to prepare the house and cover all horizontal services.  Fortunately, since the house is still under renovation, we do not have all that many possessions inside.  But, it’s still gonna be a few days of work to cover the floors, furniture, and fixtures.

From an economic and environmental perspective, I believe I can offset the air sealing with solar (please correct me if I am wrong).  So, ultimately, I need to ask the most offending question on this forum: Is it worth it?  Will the proposed air sealing amount appreciably increase comfort and/or have any effect on pests?  And, if not, can you help me spend $6,000 on something better?

Thanks for the wealth of information you all provide.

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Replies

  1. Andrew C | | #1

    Not a pro, but I did stay at a La Quinta inn...
    I haven't had Aerobarrier quoted, but I would be surprised if they can't go from 7.8 ACH50 to a lot better than 3.0. I would aim for 1.5 ACH. Of course, most of us live in places that have a lot more than 3.0 ACH50 leakage and would be happy with that.

    Note that with a relatively tight house, you now need mechanical ventilation. That should be in your plans/budget. You may want to get the ventilation system installed before you do the air sealing and insulating, as you're probably going to add some penetrations to your house to install the ventilation.

    I'm not sure about payback in terms of $, but with air sealing and an added layer of blown cellulose insulation in the attic, your house should be quieter and more comfortable, and have better air quality with ventilation system. That's worth a lot IMO.

    1. Jon S | | #3

      Thanks Andrew. I was thinking the same thing. I was hoping to get below 3, but I was cautioned against hoping for that result. Seems like you learned a lot at the La Quinta.

  2. Expert Member
    Kohta Ueno | | #2

    Given the ventilated attic, I would consider a "Step Zero" priority to air seal the attic floor--in particular, before you add supplemental attic insulation, and make your job harder. The job involves excavating insulation at all wall top plates, electrical penetrations, wet walls, etc., and creating a robust air barrier with sealant/caulk, expanding foam, spray foam, rigid board foam, or other materials. Depending on your attic construction, this can have some significant improvements. Some basics here:

    GM-1001: Attic Air Sealing Guide and Details
    https://www.buildingscience.com/documents/guides-and-manuals/gm-attic-air-sealing-guide/view

    Also, an outstanding Fine Homebuilding article on this topic from back in the 1990s (still very relevant):

    Fixing a Cold, Drafty House
    Forget about weatherstripping doors and windows. Sealing and insulating the attic are the keys to lower heating bills and a more comfortable house.
    https://www.finehomebuilding.com/1996/11/01/fixing-a-cold-drafty-house

    No idea if you were considering the work yourself--it's dirty and uncomfortable but not difficult. If you want to pay people to do it, the search term is a "weatherization contractor." Also, insulation contractors may also do this work.

    1. Jon S | | #4

      Kohta, thanks for the resources. I'm always surprised to see how much good building science was available in the 90s and how much was ignored. I was on the fence about this step, but after your response, I will consider it essential.

      I was under the assumption that AeroBarrier would seal the conditioned space from the attic and negate the need for additional sealing at the penetrations between the 2nd floor and attic. Do you believe that AeroBarrier would accomplish the goal of sealing the attic floor? If so, that would help justify its cost (and help avoid me getting dirty or hiring a pro).

      Thanks for the info.

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