“And one more thing, Phil …”—the building inspector, who is a khaki-colored trench coat away from being a clone of my favorite TV super-sleuth, has a habit of dropping a request bomb as he heads toward the exit—“… You need to get a HERS rating for this renovation. Have a nice afternoon.” I am stunned. A HERS rating on a partial renovation of a poorly maintained wreck of a house? I take a breath, look around, and feel a giddiness begin to stir inside.
HERS stands for Home Energy Rating System, a nationally recognized index for rating the energy efficiency of a home. The only way to pass is to meet standards that are dramatically more stringent than this 1977 colonial would ever meet. In my area, this rating is not required for renovations—except at the discretion of the building inspector. In a typical renovation where a sizable portion of the house is untouched (about 20% of the interior was not gutted on this home), the chance of meeting the HERS standard is near zero. R-values of existing insulation are incalculable, and the required blower-door test would reveal dramatic breaches in the air barrier. This colonial was a sieve—not a premium, fine-mesh sieve, but a hole-ridden shell; critters and creepy-crawlers had set up shop in the attic, basement, crawlspace, and wall cavities.
However, this was not a typical renovation. Part of the budget had been directed at a deep energy retrofit. We were contracted to move insulation from ceiling joists to roof rafters and add a sweater of continuous exterior insulation with high-performance windows and doors and extended eaves. The job also included ventilation systems, pressure-balanced rainscreens, air-sealing, air-sealing, and more air-sealing. My growing giddiness at the inspector’s request came from being able to justify the cost of a blower-door test; I was itching to confirm how well we had sealed this 1977, hilltop sieve.
All the extensive and expensive details that a deep energy retrofit entailed were easily sold to my clients partway through the renovation. After discovering extensive rot, thriving infestations of bugs and four-legged critters, and massive insulation voids in the building envelope, we had a meeting. The husband, an accountant who understands return on investment, saw the value of the work I proposed. His wife agreed, focusing on the immediate and permanent eviction of all uninvited four- (and more-) legged tenants. I did my best dead-pan nod at my new directive and walked off, seemingly cool and collected while my internal building-science nerd did a happy dance and rubbed his hands together, with a stupid smile plastered across his face. We were ready to tackle an amazing challenge.
List of Priorities
I usually approach a deep energy retrofit using the following order of priorities (not of process) that I establish with clients to decide where to allocate funds until we run out of budget:
1. Air-sealing 2. High-performance insulation
3. High-performance doors and windows
4. Thermal decoupling
5. Recovery ventilation
6. Efficient heating and cooling distribution and equipment
I aim to execute each of these impeccably, but since open-wallet clients don’t seem to have my phone number yet, I pick my battles. Air-sealing is always nonnegotiable, and that’s where I’ll start for this article. Later in this series, I will cover the negotiable items and share more about the order of priorities, as well as what I have discovered gives the best bang for the buck.
In theory, air-sealing is quite simple: Keep the air in and out of your building. In practice, you have irregular-shaped geometry at a large scale, with a wide variety of penetrations: outlets and other wires, plumbing, vents, windows, doors, chimneys, access hatches, random holes made by negligence or beast, and the gap under the sill plate that is often as accessible as a popcorn hull between molars. In the field, the tools, materials, and methods are mostly simple to use; the tricky part comes in maintaining a high degree of impeccability and exercising patience.
Air-Sealing Tools
The tools we always depend on for air-sealing work include:
Good caulking gun, preferably one with an adjustable thrust ratio. The 24:1 to 12:1 settings are great for acoustical sealants that are very thick and heavy, while the lower setting of 12:1 is great for nearly any caulking job.
20-ounce sausage gun. We also use a 12:1-thrust-ratio caulk gun that takes large caulk sausages. Many professional sealants are sold in this format. Buy several extra tips as they may dry out between uses and need to be replaced.
Caulk sealing caps. Basically, a latex glove for your caulk tip. These make it easy to switch from one sealant to the next, while keeping sealants fresh the next time they’re needed.
Putty knives and scrapers. I like plastic body filler spreaders and a variety of metal putty knives. The most common sizes of putty knives we use are 1 inch and 1 1/2 inches wide, though occasionally we pull out the 3-inch.
Spray-foam sealant gun. A pro gun allows you to buy the pro-sized cans and not worry about the product drying up by the end of the day. I recommend buying a stock of plastic gun tips; they protect the gun and allow easy access to small gaps and cracks. Foam-gun cleaner is available in the same format as the foam; keep the gun clean between uses, and it will last for several jobs.
Tape roller. Pressure-sensitive tapes and peel-and-stick weather resistive barriers have revolutionized the industry. Having a set of small to large rollers is a must.
Rubber gloves and eye protection. On two occasions—once when a spray-foam can exploded and once when cleaner shot onto my assistant’s face—severe eye damage was averted by eye protection. In the case of the cleaner, the caustic material destroyed his plastic eyeglass lenses immediately. It was a good reminder to always proceed with caution.
Air-Sealing Materials
We regularly lean on a cornucopia of reliable materials, including:
Liquid sealants and foam sealants. On this project, we used six products: On exterior nail holes, between sheet goods, and at wall-to-masonry transitions, we used Zip Liquid Flash, mostly in the 20-ounce sausage format. Around windows and doors, we used Henry Moistop Sealant (also available in the 20-ounce format). On framing penetrations like rafter tails and on interior framing bays and voids, Sashco Big Stretch and Dap Extreme Stretch did the job. For interior pipe and electrical penetrations, we used 3M Fire Barrier Sealant. Under sill plates on newly framed or repaired areas, we used Auralex StopGap Acoustical Sealant. We also leaned on low- and high-expansion foam sealants to fill large gaps before applying a waterproof seal.
Weather-resistive barrier. Henry Blueskin VP 100 Self-Adhered Water Resistive Air Barrier Membrane. We used VP100, as it is waterproof and vapor open; much of the home needed to dry to the outside as tile, wallpaper, and millwork covered large portions of the interior. A peel-and-stick WRB, like Henry Blueskin, was ideal for steadfastly bonding irregular surfaces that the old house shell presented, where a staple-up WRB would be sloppy and hard to detail. Another desirable aspect of the Blueskin is the fact that fasteners self-seal when penetrating it. Our rainscreen install did not compromise the air/water-sealing strength of Henry Blueskin. Local availability was another factor: Henry products are a system with components like primer, caulk, and sealing tapes. Being able to dip into local stock is important.
Weather-barrier tapes including Blueskin WB, Vycor Plus, Zip Tape, and DuPont FlexWrap NF. We found that all these tapes adhered extremely well to the Henry Blueskin. We stayed with Zip Tape on the areas with Zip Sheathing, except the window sill pan—there we used a piece of clapboard siding to induce a slight pitch, over which we used Dupont FlexWrap NF. This is my go-to sill product, and it adhered extremely well to both the Zip and the Henry Blueskin. FlexWrap stays slightly wrinkled, allowing drainage channels under the lower flange of doors and windows.
The photos and captions in the slideshow above highlight the critical steps of bringing this home from a leaky sieve to 1.2 ACH50 (the building code requires 3 ACH50). The HERS inspector had never seen a home without an envelope of spray foam do so well. Though I wish we had done a blower door test on the front end of the project and knew the extent of the improvement, it’s great that the inspector gave us the imperative to test out, verifying that we had a tight shell in which to build the rest of the systems for this deep energy retrofit.
