One of our neighbors recently asked in a local FB Group the following question…

Q&A: Is anyone familiar with “air sealing” an attic? Is the investment worth it? Any recommendations for companies that are good and reputable? Thanks So much!

In this blog article, we will geek out on all things attic insulation and take a deep dive into what goes into the thought process when designing an attic space. Two approaches can be discussed when using the phrase "air-sealing an attic." Whether we are talking about maintaining a vented attic but air sealing to create an air control layer between the attic and the living space, or whether we are talking about converting the attic into an unvented space bringing it into the conditioned space of the home.

METHOD A:

Generally speaking, when we talk about Air-Sealing an attic, we want to close ALL of the penetrations from the top floor of your house into the attic space. This is generally done in preparation for adding additional blown-in insulation.

This means applying sealant around all electrical junction boxes in the ceiling for light fixtures, checking recessed lights for rating compliance and potentially installing and sealing a dome over them, checking any bath-exhaust fans and dryer vents that exhaust through the attic, and typically adding one-way check valves to the bath exhaust fans. Sometimes we can upgrade exterior dryer vent covers for better protection as well. Depending on how your sheetrock was installed, it may be necessary to also air seal the tops of any wall plates where drywall meets the stud wall and the attic joist or truss system. We also need to look for wire penetrations in the top wall plates, though most modern-built homes had that fire-caulked before the appropriate inspections.

The goal is to "reduce air exchanges per hour" between your home's inside, conditioned air and the unconditioned exterior air. We also want to look at your basement foundation sill plate and rim joists and possibly seal those areas. All of this can help reduce the stack effect, warm air rising, and pulling exterior cold air into the lower levels of your home.

Code in PA is that new construction homes must pass a blower door test with a score of 3 Air Changes per hour or less. If you want to get passive house certified, it's something less than 1 ACH... (maybe 0.7 ?). Please don't quote me on the numbers.

Houses built 25 years ago, with vinyl siding and no house-wrap or water-resistant barrier, can't come close to a score of 3 air changes per hour or less. So if you plan to have your siding and windows replaced, there are LOTS of ways we can improve the energy efficiency of your home with back-damming and air-sealing the windows and doors, rather than simply shoving the jambs full of pink fluffy stuff. That's old school, and we now have new, better, more energy-efficient techniques that also better protect your home, should you ever have a "leak" in the future, by creating a safe path to daylight for that water, down and around the outside of the rough opening, to a waterproof pan, and out to light. We cover this topic more thoroughly in a different playlist on our YT Channel. This video from Joe Lstiburek is also beneficial for understanding the concepts of connecting the water control layer and air control layer of the wall to the water control layer and air control layer of the window… (starting at 30:28) and also here in his Joe Lstiburek's description of the perfect wall and how we integrate windows and doors.

METHOD B:

Alternatively, air-sealing an attic can also mean bringing the attic into the house's conditioned space by moving the thermal layer up to the underside of the roof deck. Many homes have an HVAC system in the attic, the ducts can leak, and they are subject to the ambient temp of the attic. Why would we put a heater in the coldest space in the house and expect it to work? And why would we put an air conditioner in the hottest room in the house and expect it to be efficient? Modern builders are now including the attic inside the thermal layer of the home so that HVAC equipment is now inside the conditioned space. There can be challenges if this is done wrong, which will lead to the premature failure of the roof deck.

Joe Lstiburek is the Father of Modern Building science. In this video, he walks us through air-tightness in home construction and how the standards were developed. Including how they came up with the 3 ACH code, he also explains more about including the attic in the conditioned space.

We have a video from a home build where the air-sealing is being done, another showing the HVAC in conditioned space,

Matt Risinger discusses some of the pros and cons in this video on Unvented + Unconditioned Attics.

The Build Show explains how moisture can condense up at the roof peak and how to address that possibility with Joe Lstiburek.

And to your question of whether it's worth it, the clients from our "Insulation is Sexy" video playlist (LINK) said they saw Tremendous energy savings in the first 12 months. They may recoup their investment in these upgrades in about 2-1/2 years.

Our clients, who we recently did a complete exterior renovation with new siding and windows, have a full-frontal assault of wind from the west at the top of the hill. Their remark was the house is quieter, and they don't feel the drafts blowing through anymore when the wind picks up. Comfort is important.

There are ways to bring the attic into the home's conditioned space and maintain an air channel to allow intake air to enter the soffits and exit at the ridge vent. This is true unless you are in certain types of Cape Cod homes where the second-floor roof becomes a second-floor wall. There isn't a good spot to install the air intake vents. We do have new products available that allow you to incorporate intake vents into a roof deck to achieve the airflow we would typically get from the soffit vents.

AirVent.com has an "air vent university" tab, and their 30-minute class walks you through the high points of intake and exhaust to prevent ice damming. Factors to consider as one designs a plan to retrofit an attic and bring it into the conditioned space.

Here's some info on Ice Damming and an example where the crew at This Old House brought an attic into the home's conditioned space. The only thing I don't like about their method is that there is no airflow under the roof deck, and this method could BAKE the shingles and cause them to fail prematurely.

Suppose you leave the attic unconditioned and seal the penetration's from the upper level, through the drywall, into the attic and possibly add insulation to the ceiling of the upper level of your home. Those measures significantly reduce the chances of ice damming if you have proper soffit vent intake and ridge vent exhaust.

Gable vents are next to useless compared to continuous shingle over ridge vent and soffit vents and should be boarded over, so we aren't mixing vent types. We don't like turbines or power fans either as they throw off the balance of the convection system and typically pull in exterior air from the closest area (likely the ridge vent) rather than from the soffits, disrupting the airflow that is supposed to be keeping the underside of your roof deck the same temperature as the outside air.

Another neighbor commented and asked: "I thought air changes of less than 5/hour leads to a sickly house."

Now, I'm not entirely up to speed on all the specifics of the passive house standards. My general understanding is that when you get down to one or two air changes per hour, then you have to put in an air exchange unit (Link to the HRV vs. ERV blog 3) which brings in outside air, filters it, dehumidifies it & and sips it into the house. The other important factor when building a tight place has proper dehumidification inside. And you have to get your exterior cladding right so that you don't have a moisture drive. It all comes down to correctly understanding the permeability of the materials and the thermodynamics involved.

If you're looking to build a much more energy-efficient house, you'll want to make sure that the architecture used is a speed in these areas. We can also connect with a certified passive house consultant who can assist in the process.

I understand that including a properly sized ERV or HRV in a tight Passive House is essential to combat the problems commonly referred to as "Sick House Syndrome," especially if you are building to sub 1 Air change per hour passive house standards.

I'm not recommending any specific brand or model of ERV, but here's an example of a unit.

In Chester County, we are in climate zone 4.

The 2021 IECC Building Code states in R402.4.1.3 Leakage Rate. The building or dwelling shall have an air leakage rate not exceeding 5.0 air changes per hour in climate zones 1, 2, and 3 and 3.0 air changes per hour in climate zones 3 through 8. In Chester County, all new construction has to pass a blower door test with a score of 3 ACH or less.

So, if your desired ACH is 5.0... I would not recommend buying a new construction home that has to be built to the current 3 ACH code standard today... or if you do, plan on finding ways to make it leak air after you purchase it.