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Trying to achieve Energy Star in an existing home

Danny Kelly | Posted in General Questions on

We are putting a small addition on the rear of a home and adding a second floor. We are reusing the entire floor system and subfloor which is diagonal 1×6. We are reusing about 75% of the exterior walls which are 2×4 with blackboard (or gyp board as it is called around here) and an existing brick veneer. The second floor and addition are obviously all new walls and floors – all roof is new. We are trying to seal the house up to achieve Energy Star. We are concerned that we may not be able to achieve this with all of the gaps in the existing floor. To offset the leakiness of the existing floors and to a lesser extent walls, we are planning on trying to make it up on the new areas and use the ADA.

We are thinking in order to seal the gaps in the subfloor we can use some type of housewrap, tape the seams and seal to the sole plates. Any suggestions on a particular product here. Do we think we can get decent results with this? The floor finish will be mostly hardwoods with some tile and carpet.

We are using fiberglass insulation so plan on air sealing at both the exterior sheathing and the interior at the Sheetrock. Any suggestions on a good product to use as our gaskets at top/bottom plates and around HVAC boots, etc.?

Due to budget constraints out of our control, doing a closed crawl and/or spray foam is not an option on this project. A few other random details – hot/humid, NC, traditional vented attic so our air barrier is at the ceiling, blown in fiberglass in ceiling, kraft faced batts in walls and floor system.

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  1. GBA Editor
    Martin Holladay | | #1

    1. The easiest way to provide an air barrier over a 1x6 subfloor is to install a layer of 1/2-inch plywood between the 1x6 and your finish flooring. If you're concerning about the change in elevation, 1/4-inch underlayment will work. Just be sure to install a bead of construction adhesive around the perimeter of each sheet of plywood before it goes down.

    2. Here's a source of gaskets used to install drywall for anyone following the Airtight Drywall Approach:
    Resource Conservation Technology
    2633 North Calvert Street
    Baltimore, MD 21218

    3. In North Carolina, building a vented crawl space because you can't afford a sealed crawl space is false economy. Repairing the mold damage in a vented crawl space is far more expensive than the small cost of the materials (poly to cover the dirt floor, and rigid insulation for the short walls) and labor to detail a closed crawl space. And you'll save the cost of the vents!

  2. Doug McEvers | | #2

    Martin's suggestion is a good one, I would re-fasten the 1 x 6 with screws to avoid a squeaky floor.

  3. user-659915 | | #3

    Martin is right. Sealing the crawl has one of the fastest ROI of all energy upgrades in a hot/humid climate and it will likely reduce the cost of your HVAC upgrade to service the addition. Doing a good job on the addition will not begin to compensate for leaks in the remainder of the house. If you can afford the addition, find a way to afford the sealed crawl!

  4. Danny Kelly | | #4

    Good idea Martin - sometimes the most obvious solution slips my mind. That not only will work better but will probably be easier to implement and will help level out our wavy existing floor too.

    Yes - I am very familiar with the research on closed crawls as Advanced Energy, who is one of the leaders on crawl space technology, is based right here in NC. I have read all of their papers and attended many seminars put on by them. We always explain the benefits of going to a closed crawl and the risks of a traditional vented crawl space. Unfortunately for us, the homeowner makes the final decision. Some just want to spend their money on their cabinets rather than their crawl and some some simply just do not believe us nor the research. I hear over and over that their house has has a vented crawl for 60 years with virtually no trouble. We even explain that it goes beyond mold in the crawl but IAQ, etc. We also explain how changing the house may chance the way it behaves - an addition and a second floor could increase the stack effect and maybe cause problems that were not there before. We do put language in our contract to protect us when they do not take our recommendations but it is still a hard sell. Doesn't help that all the architects specifiy a vented crawl on the plans during the bidding process so we rarely get much input until it is almost too late.

    The ADA process seems pretty simple if you take your time. Has anyone run into any issues that they didn't expect while implementing the process?

    Thanks for the tips guys.

  5. David Meiland | | #5

    Regarding air-sealing the floor assembly, what would the solution be if there is existing flooring already in place? My house has 1x8 diagonal board floor sheathing with 1x4 T&G fir flooring. The fir is 90 years old, in great shape, and it seems a shame to remove it to install an air barrier, but the house does have an astronomical ACH50, a lot of which I suspect is percolating up thru all those gaps. There is currently faced FG in the joist bays and the crawl is vented, which is all I've ever seen here in coastal WA. It has occurred to me to install foamboard under the joists with foam and tape around the edges, or possibly install something like Tyvek under the joists. Any other ideas?

  6. GBA Editor
    Martin Holladay | | #6

    Your best option would be to create a closed crawl space, with the air barrier at the crawl space walls and crawl space floor.

    Failing that, you can establish an air barrier at the floor by working from below. Your suggestion of installing foam board -- I would used foil-faced polyisocyanurate -- below the floor joists will work. Of course, tape all of the seams.

    You could also create an air barrier from below using closed-cell spray polyurethane foam. However, the fact that you have a vented crawl space leaves the bottoms of the joists at risk of mold and rot, unless the spray foam installer completely covers all the joist surfaces with foam. Considering the complexity and cost of this option, a sealed crawl space begins to make sense.

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