Attics & Crawl Spaces

Attics and crawls are not appendages but integral organs of the system

December 29, 2015
January/February 2016
A version of this article appears in the January/February 2016 issue of Home Energy Magazine.
Click here to read more articles about Building Envelope

I had a client who spent $3,800 restoring an old O’Keefe & Merritt stove, $3,000 on a retrofit 1950s fridge, and $2,200 on a porcelain sink from England. When I suggested that he allow us to clean out the attic and the crawl space, do some air sealing, and insulate, he said, “No, it’s not that expensive to heat this place.” He pointed to a small electric heater by his desk. “I just sit close to this and wear a sweater in the morning and then it gets warm after a while.”

Attics and crawl spaces are left in darkness, waiting for some worker to put his or her suit and mask on and fix a leak, or plug some holes, or reset the rattraps.

I like cellulose because rodents do not like cellulose. This R-48 cellulose makes for a healthy house. (Terry Nordbye)

Attics and crawl spaces are the hidden integral part of the house that you don’t live in. Behind these closed doors are the forgotten and ignored orphans of building performance and design. That’s me in the photo. (Terry Nordbye)

The author, left, and Sebastian take a tea break from a nasty attic. (Terry Nordbye)

Here is a semi-conditioned unvented crawl space I did seven years ago. I do annual inspections to make sure it is still a healthy space: no mold, no condensation, no bad odors. This house is fully unplugged from the ground temperatures. (Note: In my climate zone 3, insulation is not required on the side pony walls.) (Terry Nordbye)

Here I had to climb over $20,000 worth of clothing to get into the only access to the attic of a $6 million house in Silicon Valley. (Terry Nordbye)

Original attic access of this 2,000-ft2 ranch house was in a walk-in closet in the master bedroom. From that access hole we were expected to shlep through the house and take out all the old insulation, air seal, and blow in new R-42 cellulose. Here we cut a hole in the garage ceiling and another into the rake wall of the house, left of opening. This will remain as the work access for the life of the building. (Terry Nordbye)

This new access hole, easily accessible from the roof, also serves as a vent. (Terry Nordbye)

Most of my 35 years of contracting has been in custom new homes and retrofit work. I am a trained cabinetmaker as well. My crew and I have been selecting to do the nasty work of attics and crawls because I realized that is where we must do our best work if we really care about reducing carbon loads in our buildings. I want to figure out how to do them better and faster.

Attics and crawls are indeed the low-hanging fruit on the path to achieving better indoor air quality, greater thermal comfort, and lower heating and cooling demands. So why don’t we gladly throw money at them in our endeavors to fix up a house? Is it because they are hidden, dark, smelly, toxic places we would rather ignore? Attics and crawls are like dirty underwear that no one really likes to talk about.

Even if you can convince an architect or a homeowner to spend some money on an attic or a crawl space, your next big, and perhaps bigger, challenge would be to find a worker who was trained and willing to do honorable work in these often hellholes.

To understand thermal bridging, vapor drive, hydrology, convection loops, pathways for air leakage, radiant barriers, stack effect, and condensation, and to incorporate that understanding into a favorable design, requires a great deal of skill and attention to detail.

And to have what it takes to execute these practices requires the skill level of a worker who would rather be inside the house doing the built-in library or the granite countertops. More often than not, it is the unskilled worker who is sent up or down to do skilled and demanding work.

Beliefs and Controversies

Radiant barriers are sold that are said to reduce heat gain by 5–10%. That percentage comes from the manufacturer’s claim. Radiant barriers work differently in different climates (better in hot ones), and differently depending on the occupants’ lifestyle. Their efficiency is greatly reduced over time by dust particles settling on the reflective coating.

To vent or not to vent? Without any scientific evidence, venting attics just turned up in the building codes. There is no conclusive evidence that attics need to be vented. A well air- sealed and insulated attic will not radiate heat into the living space below. Long ago, Building America concluded that unvented crawl spaces greatly outperform vented crawl spaces (see “Crawlspaces Do Double Duty,” HE Special Issue ’05, p. 32). So why do we continue to vent? The danger of an unvented crawl space is that if it does not have a bombproof vapor barrier at ground soil level, the health of the house can be at risk.

I do not suggest that you buck your local building codes, but do consider questioning authority and doing your homework.

In a fully conditioned crawl space the house is plugged into the ground. The stem walls or pony walls are properly insulated, in this case, with two-part foam. The crawl space breathes with the house, not randomly with the outdoors through foundation vents. In this case, a heat recovery ventilator (HRV) brings in fresh air and takes out stale air.


Part of the hellhole charm of crawl spaces and attics is the typical access hole. Workers are expected to drag their tools and materials through the house maze and enter through holes often little bigger than shoulder width. This house assembly feature is usually a concept of the designer or architect.

Whenever possible, I create new and or permanent access holes into the crawl space or attic.

Now for a couple of case studies.

Case Study #1: The Brookness House

The house in this first case study is located in Inverness, California. This is in climate zone 3, a mild temperate climate with a long dry season. The site of the house is a cooler and shaded valley, with winter frost up to four months of the year.

We bumped up the R-values in the attic and used R-25 in the floors. We used triple-pane, multilock windows and doors to compensate for the low R-value and the untouched 2 x 4 walls. We got rid of all the combustion appliances except the kitchen range. The first blower door clocked in at 16 ACH50. Because there was no money in the budget for an HRV, I stopped air sealing the house at 2.5 ACH50 to let it breathe/leak on its own. Someday if the exterior siding gets replaced, the house can be made tighter and will require an HRV.

Case Study #2: The Coast House

Jeremy Walker’s wife had to move out of their newly purchased house on the California coast because something in the house was making her ill. Jeremy called me in to do an inspection and figure out how to solve the problem. After a half an hour visual tour of the grounds and house, nothing particularly bad jumped out at me. I entered the crawl space and it was obvious.

We removed about 10 yards of surface soil, terraced out the contours, ran 10-mil plastic wall to wall, and then put up the pressure-treated retaining walls. The cardboard runners are to protect the 10-mil plastic from traffic. On top of the broom-finished dirt floor is Tyvek, to keep the duct from puncturing the 10-mil plastic above. All the concrete walls were twice coated with a waterproofing compound. Overnight, this work transformed the air quality of the house.

Good work often depends on good access. Designers and architects have left us construction workers with these ridiculous working situations. As retrofit workers, the best we can do is to create better access for current and future work.

Terry Nordbye is the owner of The Practical House and has been a general building contractor in Northern California for 35 years. He specializes in Passive House and high-performance envelopes.

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