Sealing Attic Floor Pits

Dropped ceilings in closets are seen in an attic, as floor pits. Photos here, with corrective action, are of a home built in 1953. Attic air is freely admitted to walls the full height of rooms below, amplifying the ceiling-area heat loss or gain, by an order of magnitude. Let's try the math here, on that order of magnitude. Numbers in play are represented by L and W, the dimensions of the ceiling, and H, the below room height. I see that the influence of closet interior walls is debateable where the door is normally closed. Figure the amplified area as 2* (L + W) *H, where L = 46, W = 31 and H = 96. 2* (L + W) *H = 103 sq ft. LW = 9.9 sq ft. The amplification factor is 10.4. If insulating 9.9 sq ft saves $7/ yr, the larger saving is $73/ yr.

 

Carry the argument of an order-of magnitude multiplier a bit further. For this closet, if the door were left open, the area exposed to attic-room temperature difference increases by the interior side-wall area below the drop. The larger amplification factor is 13.5. The smaller amplification factor, (2* (L + W) *H) / LW, is a minimum for home situations. I imagine home situations where the minimum is larger than 10.4. How about a long, deep wall used as a ventilation chase? Ten ft long, a foot deep. The amplification factor for a one-floor 8-ft chase is 17.6. If the chase runs down two floors, 16-ft, the amplification factor is 35.

I argue to my rebates manager, that pit closure is far more important than air sealing opportunities in an attic floor. Pits are often overlooked or are improperly fixed when found. Old insulation may be draped over a pit, merely hiding it, with slight impediment to air flow driven by the temperature gradients. A loose-fill installer will almost never know of the neglect. There are no incentives to pick up that old, dirty insulation to find and fix pits or other problems, in practice. In my area the testing trade, Home Performance, is promoted by a fifty percent of cost rebate for air sealing work if that achieves quite-large drop of infiltration, 300 cfm or more under test conditions. That is absolutely unhelpful here. The problems are not made detectable by blower-door conditions of pull from the attic. A pit doesn't contribute to infiltration.

My closure of the pit employs half-inch drywall pulled up to floor joists, and edge-sealed with spray foam, or better, my flexible grout which I offer for free with easy conditions, as a sample. I prefer GP Densarmor fiberglass-faced drywall, kept as scrap from my closet projects. Screw a length of 2x4 under the drywall for lifting and anchoring. Sandwich the drywall with another 2x4. I shape Densarmor edges with a Shurform plane. Ordinary drywall is too brittle, and paper facing resists trimming of edges.

This relatively simple pit closure took more than an hour of actual performance. With an extra trip it is far more costly to an installer, if not known in advance and rewarded through a contract. If a contract change must be argued or if the worker is somehow detached from responsibility, a proper fix is not mere due diligence. It is unlikely to happen.

This home was like a test lab for pit sealing. A rare opportunity, yet daunting since problems were detected upon bidding. Daunting since more time would be spent in the attic in summertime heat. Daunting since pulling drywall up under floor joists requires more than a bit of cleverness.

There were three more pit areas, one including a dropped ceiling over a bathtub; another a long wall with dead volume associated with a grand fireplace; and another very simple at a dropped ceiling over the home entry. That at the fireplace involved working in extremely cramped overhead, out to an outside wall, and had six hours of actual performance. Multiple visits dealt with rerun of interfering wires. All of these problems were happily hidden, until I pulled up nice-looking insulation.

I challenge Energy Trust of Oregon, and other rebate organizations, to do a better job of serving and protecting Utility consumers. All stuations that invite being overlooked, should be specifically reported by weatherization contractors, to secure diligence rebates. I ask for a new rebate program, where reported pit closure qualifies rebate-times-ten for involved floor area. All diligence rebates should be presented for public examination and learning. This reward approach is consistent with the fact that some pits are large enough that pit walls could be insulated instead of making a difficult but fall-protective cover. The alternative reward of fifty percent of repair cost is of comparable size, and would work if the conflicted tie to reward those invested in Home Performance, were removed. Keeping the tie here is absurd, yet that is the dogged position of Energy Trust of Oregon. Keeping the tie is a grave disservice to homeowners. While I owned a blower door, modestly invested in Home Performance, I NEVER found a problem not more-readily detected by simple observation. I never found a home without a great excess of infiltration, to be dealt with by progressive and obvious measures such as window replacement. Tests taught nothing.

Here is related comment upon feedback to focus on unique and interesting opportunities, and to raise the state of the art in weatherization. At the last Energy Trust Trade Ally meeting I attended, I shouted out that blower door testing for unique purposes should be rewarded directly to the contractor, a token amount of $50, if he offers a report of why and what learned for PUBLIC DISCLOSURE. A family of public reports would raise the state of the art among contractors nationwide, would inform the DIY public, and would sell Home Performance services. We all need to better imagine the situations where blower door and/ or infrared thermography testing profits the homeowner. The situations may be uncommon.