Oh, hello! Yes, we’re still here. Apologies for the lack of new blog posts in the past year. You see, we became first-time parents and found ourselves woefully unable to do anything besides take care of our child. Turns out babies are an insane amount of work. More work than renovating a house to zero net energy, even!

Anyway, this is an extremely belated post about the renovation work we did in our attic. Better late than never…?

Here’s what our attic used to look like (back in 2016):

And now… our attic is completely transformed! Here’s what we did:

Removed old attic insulation (spoiler: we reused it later and put it all back in!) and old HVAC ducts.
Built a new wall between the (now vaulted) living room and the attic — called a “knee wall.”
Rewired the entire house, running new electrical lines through the attic.
Installed a mini split heat pump system (to provide energy efficient AC and heating).
Installed an energy recovery ventilator, or ERV (to ventilate the airtight house).
Ventilated the attic (to reduce moisture and heat buildup).
Insulated and air sealed the s*** out of the attic!

Since we’ve already written about some of these steps (see links above), this post will focus on the knee wall, the ERV, the attic ventilation, and the attic insulation.

KNEE WALL

Did you know that a short, non-structural wall between an attic and conditioned space is called a “knee wall”? Kind of a funny name.

Since we vaulted half the house (but not the whole thing) this meant that we ended up with a “half attic” set up. Chris constructed a new triangular knee wall where the attic ended and the living room ceiling began.

Chris decided to insulate the floor of the attic (as opposed to the ceiling), which meant that the knee wall had to be insulated as though it were an exterior wall. Jump down to the insulation section below to read about how we did that.

Below is a photo of the wall in the process of being insulated. Notice the living room on the left, the attic on the right.

Installing an ERV

What is an ERV and why did we need one? Let’s answer the latter question first.

Most buildings are not airtight — they have small gaps and holes and cracks in the walls, around windows and doors, etc. This means warm/cool air “leaks” in or out of the home, which is not good from an energy standpoint (you have to run the AC or heater more to compensate for the temperature change). One way to make a house more energy efficient is to air seal the building envelope, a.k.a. fill in all the gaps and cracks to minimize leakiness. This is what Chris painstakingly did for our house.

But — while air sealing helps solve one problem (wasting energy) it actually creates another: lack of ventilation. With an airtight building envelope, fresh outdoor air can’t come in and stale indoor air can’t go out. That means people in the house are at risk of breathing bad air (with high levels of carbon dioxide, harmful pollutants from cooking and/or off-gassing furniture, etc.). For health reasons, there needs to be a way to mechanically ventilate the house.

BUT (again)! If you put in a ventilation system and are constantly sucking air in from the outside, we are back to the original problem of energy waste. Pulling hot air into an air-conditioned house in the summertime can waste a lot of energy because the AC has to work harder (and vice versa in the wintertime for the furnace). So what can be done about this?

Enter the ERV! Which stands for energy recovery ventilator. An ERV is basically a ventilation device that brings in fresh outdoor air and spits out stale indoor air — but does so in a very energy efficient manner. The key is a heat exchanger (labeled 3 in the diagram below):

Source: https://www.pvhvac.com/blog/erv-or-ventilating-dehumidifier-which-is-better-for-georgia-homes

Basically, the ERV transfers heat between the incoming and outgoing air. So in the summer, hot air that is pulled into the house is able to “shed” some of its heat to the outgoing cool air. That means the hot air that enters the house is “pre-cooled,” and the AC doesn’t have to use as much energy to keep the house cool. The opposite happens in the winter: cold outdoor air is “pre-heated” as it comes in the house.

Genius!

Here are some photos of the ERV getting installed.

The ERV was hung and secured in the ceiling of a bedroom closet. Chris (with the help of our friend Wilson) then assembled rigid ducting for the incoming/outgoing air to flow through.

Below is Chris putting in one of the outdoor vents. This one sucks air from outside and brings it into the house.

Check out our maze of (insulated) ducts! Outdoor air was sucked in from outside and directed into the living room. Indoor air was sucked out from both bathrooms (the ERV system also served as our bathroom fans!) and exhausted outdoors.

Below is the brain (and also heart, I guess) of the ERV system, insulated and air sealed into place.

Thanks to the ERV, the inside of our home has fresh, filtered air 24/7. We love it.

Ventilating the Attic

It’s important to ventilate an unconditioned attic so that moisture has a way to dry out. Also, in hot climates (like where we live in Southern California), it means insanely hot air doesn’t build up in the attic and heat up the house.

Before renovation, our attic was ventilated with eave vents (little screens located where the lower roof meets the walls), gable vents (vents in the walls near the pointy part of the roof), and whirlybird wind turbines (round silver spinny things on the roof). The idea was for cool air to come in through the lower eave vents and for hot air to escape through the higher gable vents and whirlybirds.

In our renovated attic, we improved upon this by increasing the number of eave vents (from every 4-5 rafter bays to every rafter bay) and replacing the gable vents and whirlybirds with a ridge vent (a vent that runs along the entire ridge of the roof). So now air can flow in and out much more freely.

Here’s Chris and our friend German installing the ridge vent over the attic.

We didn’t take a close-up photo of the attic ridge vent installation, so below is one from way back when Chris was installing a ridge vent over the vaulted living room. Not technically the attic, but the ridge vent is the same.

He cut a slit along the ridge of the roof and put that black corrugated plastic thing on top, which allows air to flow out from inside the attic. Then he covered it on top with ridge shingles.

When it came to the eave vents, Chris was faced with an interesting challenge. He planned to cover the floor of the attic with a thick layer (about 14 inches) of insulation, but this would effectively block the eave vents. So what did he do?

Check out his drawings (especially the two on the bottom):

Chris decided to install rigid foam baffles (chute-like things) for each eave vent to give air a “tunnel” pathway through the insulation. The easiest way to explain this is through photos.

First, he cut out the blocking for each rafter bay. Then he constructed U-shaped chutes (a.k.a. baffles) made out of rigid foam insulation and installed them in each bay.

Since the chutes are made out of rigid foam, they provide insulation properties as well. This is good because in the small, tight corners of the attic, there’s not much space to put any insulation in. Having rigid foam chutes ensures that we are still insulating the corners of the attic as much as we can.

View from outside:

View from inside the attic (not the same location — this spot only had 2 chutes installed at the time):

So air from outside travels up the chutes and into the attic. As you’ll see in the completed attic photos below, the chutes are long enough stick out above the fluffy insulation.

It should be noted that installing these baffles was a pain in the ass. Squeezing yourself in the tight corners of a hot, dusty attic is NOT fun. Just ask our friend Wilson.

Here’s Wilson diligently air sealing the vent chutes and jamming triangular pieces of rigid foam (which had to be cut by hand, along with every piece of rigid foam in the baffle assembly) into the back corners to provide additional insulation.

You’re our hero, Wilson.

The last step was to cap off the rafter bays. We did this by re-installing blocking, but leaving a 1-inch gap at the top to put in venting slits (stacked strips of corrugated plastic). These thin white strips at the top of each rafter bay is where air flows in and up the chutes.

Insulating and Air Sealing

After completing installation of the new attic systems — the ERV, the ventilation, plus the mini split heat pump — it was time to insulate and air seal everything and call it done!

As mentioned above, Chris decided to put the insulation on the floor of the attic, which meant that the knee wall was effectively an exterior wall and also needed to be insulated. Chris filled the bays of the knee wall with 3 inches of rock wool, and then covered that with 3 inches of continuous rigid foam (he estimates this assembly to have an insulation value of about R27). Then he air sealed it as much as he could with canned spray foam (see this earlier post for why air sealing is so important).

Here’s a photo of the final, insulated knee wall from the attic side. One thing about attic construction is that it doesn’t really have to look good (few people will ever see it) — it just has to be functional. So yay for mismatching insulation boards. The differing faces may not not ideal, but it’s the foam we had available.

Notice in the foreground of the photo the shiny, insulated ducts of our mini split heat pump system. We made sure all the ducts in the attic (HVAC, ERV) were air sealed with mastic and wrapped with duct insulation. This is to save energy (by minimizing loss of heat/coolth) but also to keep condensation from building up on the outside of the ducts which would lead to moisture/mold problems in the attic.

As for the floor of the attic — this was the really interesting part! Chris decided to reuse the original fiberglass attic insulation (which was installed in… are you ready? 1983! When Reagan was president.). This basically meant sucking up the old insulation from the attic floor with a giant vacuum thing, putting it all in bags, storing said bags until the attic was renovated, and then blowing the insulation back onto the attic floor.

P.S. If you haven’t read our earlier post about “The Big Suck” (I just came up with that name, haha), you really should here (scroll to the bottom half of the post). It was epic. As a taste, here’s a video of Chris sucking away with the giant vacuum (a dust collector).

Of course, before blowing any of the old insulation back in, we had to air seal the attic floor. Chris did this by using a blower door to pressurize the living space (suck air into the house) to find all the gaps where he could feel (or see with an infrared camera) air leaking into the attic, and sealing them up with rigid foam, spray foam, and caulking. Tedious work.

Something else Chris decided to do before putting in the insulation was to relocate the attic hatch. It was originally in the ceiling of our hallway, which meant you would enter the attic by poking your head through the attic floor (see the photo of me at the beginning of this post). But since Chris wanted the attic floor to be as airtight as possible, that wouldn’t really work. So we sealed up the original hatch and put in a new one in the exterior gable wall.

Now the only way to get in/out of the attic is through the outside of the house with a ladder. Pretty quirky! Looks like a floating door.

One final thing that needed to be done before the insulation was blown back in (I know, so many things! That’s how we felt) was to figure out a way to maneuver around a future attic where the entire floor would be covered in a thick layer of loose, fluffy insulation. The answer? A catwalk that hangs from the rafters:

At long last, the day has arrived — time to put the old insulation back in!

Yes that’s right, let’s completely bury the brand new, beautiful mini split and ERV systems that Chris painstakingly installed in 14 inches of old, dusty fiberglass from the ‘80s so it’s all never to be seen again. Woot!

Here are some of the bags of fiberglass insulation, ready to be blown back into the attic. In total we had about 40 bags of this stuff.

Chris rigged the dust collector (the giant vacuum thing that he used to remove the insulation to begin with) to blow instead of suck. Wilson fed the dust-collector-turned-insulation-blower from below…

And Chris was in the attic above, spraying the insulation onto the attic floor.

It’s hard to describe just how disgusting and unpleasant this job was. Please imagine loose, fluffy fiberglass insulation that has been sitting in an attic since 1983. Envision how dusty it becomes after 30+ years. Anyway, now imagine putting this stuff in a machine and then SPRAYING IT EVERYWHERE. Like, holding the spray nozzle in your hands and blowing this stuff into the air and having it fall all around you while you’re in a dark, enclosed attic.

I mean, wow. Look at this dirty, grey snow. And look at the dusty haze hanging in the air.

Unsurprisingly, there are no photos or videos of Chris doing this heroic (insane?) work — I was not going into that dusty s*** storm. But here’s a photo of when I convinced Chris to poke his head out of the hatch during one of his breaks.

My husband is in there somewhere, I think.

Chris protected as many facial orifices as he could — wearing a professional grade respirator as well as eye goggles. But every exposed surface of his body was covered in fine dusty fiberglass fuzz. Look at all the stuff clinging to his arm hair (doesn’t help that he was also sweating)! It was in his hair, in his ears, in his shorts. It was bananas.

Luckily, it was finished in one day. And… it worked! Ta da.

(Please note the rigid foam ventilation chutes jutting out of the insulation. Just as planned!)

Pre-renovation, this insulation was about 5 inches thick on the attic floor — but that was when there was an attic over the entire house. Now (since we vaulted the living room, dining room, and kitchen), the size of the attic is much smaller so the insulation is thicker — about 14 inches thick. Chris estimates this to have an insulation value of about R35. (Note: Chris wishes this could have been a little higher — something closer to the R46 in the vaulted ceiling.)

Here are a couple guys at the end a LONG day — exhausted, dusty, shower-needing, but proud. Well done, Chris and Wilson!

Here’s a panoramic photo of the attic just before insulation:

And after!

Now, to be perfectly honest, Chris isn’t sure if it was worth all the trouble to reuse the fiberglass. Sure, we didn’t have to buy new insulation. We also saved money by doing it all ourselves. And we minimized waste by not throwing away functional insulation. But, it was TONS of work that took many weeks (a professional company would only need a couple days). While 30-year-old fiberglass insulates fine, it probably still doesn’t perform as well as new insulation. And well, it’s just kind of filthy and unattractive.

It sure was an achievement though, and a story we’ll tell for the rest of our lives.

Fun fact: The attic by far was the part of the house that was renovated over the longest period of time. Chris worked on it on and off throughout the whole house project, sometimes not touching it for months. Removing and bagging the insulation was the first thing we did in the attic (back in April 2016) and putting the insulation back in was the last thing (in October 2019). So the photos you see in this post span over 3 years’ time. 😮

Thanks for reading!