When it was time to schedule our blower door test we considered using Eco Achievers, but we only knew about them because they’ve worked extensively on projects for our original builder, Evolutionary Home Builders. We decided the potential awkwardness, or even a possible conflict of interest, wasn’t worth pursuing their services. An example of guilt-by-association I suppose, one that is probably unfounded but, nevertheless, the strong affiliation with our original builder made it difficult for us to reach out to them for help. They also hired one of Brandon’s former employees (this employee was nothing but nice and professional towards us as we were deciding to part ways with Brandon), which would’ve only added another layer of awkwardness to the situation.
Unsure how to proceed, I looked online and found Anthony from Building Energy Experts. He was able to come out and do a blower door test for us, helping me hunt down a couple of small leaks, so that we ended up at 0.34 ACH@50 for this initial test.
Here’s a Hammer and Hand video discussing the use of a blower door:
On a side note: all of the Hammer and Hand videos, along with their Best Practices Manual, were incredibly helpful as we tried to figure out all the Passive House details related to our build. It’s no exaggeration to say that without Hammer and Hand, the Green Building Advisor website, BSC, and 475 HPBS, our build would’ve been impossible to accomplish on our own. I owe an incredible debt of gratitude to all of these great resources who invest valuable time sharing such a wealth of information.
Below is a Hammer and Hand video noting the importance of properly detailing corners to avoid air leaks:
Because of this video, I sealed all of my corners for the windows and doors like this:
I also added some HF Sealant to the lower portion of the windows, since some air leakage showed up in this area with Anthony where components of the window itself come together in a seam.
The areas where components come together often need special attention.
Even with layers of redundancy in place, in the picture below there was a small air leak still present at the bottom plate – sub flooring connection. A coating of HF Sealant easily blocked it.
Once the stud bays were insulated (after most of the siding was up), the interior walls would eventually be covered with Intello (I’ll cover the details in a future post on interior insulation), adding yet another layer of redundancy for mitigating potential air intrusion.
Anthony didn’t have any previous experience with a Passive House build, so it occurred to me that it might be beneficial to reach out to Floris from 475 High Performance Building Supply (he had already done our WUFI analysis for us), and Mike Conners from Kenwood Property Development to see if there was someone locally who did. Mike is a Passive House builder in Chicago who had already helped me out with some Rockwool insulation when we came up short earlier in our project (the two GC’s we fired repeatedly struggled with basic math), and he was very nice to take the time to answer some other technical questions for me as well.
Steve would eventually make three trips to the house, doing an initial blower door test after the structure was weather-tight and all the necessary penetrations had been made through our air barrier, a second test after exterior continuous insulation was installed, and a final test after drywall was up to ensure there hadn’t been any increase in air leakage during the final stages of construction.
Following Passive House principles for our build, we also followed the same protocols for the blower door tests: Blower Door Protocol
With the structure under pressure from the blower door fan, Steve and I walked around the house while he used a small smoke machine in order to try and find any leaks that I could then seal up.
The gaskets around our windows and doors proved to be some of the weakest areas in the house although, comparatively speaking, it was inconsequential since the overall air tightness of the structure was fairly robust (favorite word of architects).
For instance, even though no substantial air leakage showed up around this kitchen door, during our first winter this same door eventually had ice form outside at the upper corner by the hinges, on the exposed surface of the gasket where the door meets the frame.
Much the same thing occurred around our front door as well, with the same solution — adjusting the hinges to get a tighter fit at the gasket between the door and the frame.
Steve was nice enough to go around and methodically check all the penetrations in the structure.
There was one area in the guest bathroom where the Intello ended up getting slightly wrinkled in a corner during installation. With Tescon Vana and some HF Sealant I was able to address it so nothing, thankfully, showed up during the smoke test.
After looking around on the main floor, Steve moved down into the basement.
The lids for the sump pit and the ejector pit were eventually sealed with duct seal putty and some Prosoco Air Dam.
Before the second blower door test, I was able to add some duct seal putty to the lids of the sump and ejector pits.
Below is a copy of Steve’s blower door test results, showing the information you can expect to receive with such a report:
For the last two tests Steve used a smaller duct blaster fan in order to try and get a more precise reading for air leakage.
Steve would be back two more times — once before drywall, and once after drywall — just to ensure we had no loss of air tightness develop in the interim stages of the build (especially after continuous exterior insulation with furring strips were installed).
Here are the final figures noting where we ended up:
We are well below Passive House requirements (both PHI and PHIUS), so there was a great sense of relief knowing that all the time and effort put into air sealing had paid off, giving us the tight shell we were looking for. Even so, it was still pretty exciting news, especially for a first build.
And here’s an interesting article by 475 HPBS regarding the debate over how air tightness is calculated for PHI vs. PHIUS projects, and the potential ramifications:
Our attic is designed mainly to hold our blown-in insulation (a future post will go over the details), as opposed to a place for running HVAC equipment, conduit for electric, or as a potential area for carving out additional storage space.
Nevertheless, in order to have access to our attic for future maintenance or repairs, I installed a well-insulated attic hatch in our master bedroom closet ceiling.
Following Passive House and Pretty Good House principles required trying to protect the thermal envelope, even in this relatively small area, in order to avoid what can be a notorious point of air leakage and heat loss (i.e., the stack effect).
There were two main products I considered using for this:
Because the Energy Guardian hatch is made out of rigid foam, I thought the Battic door was the better choice since it seemed like it would be a little sturdier and more durable. To be honest, once the product arrived and I unpacked it, I realized it was something I, or anyone with basic carpentry skills, could put together themselves (assuming you have the time).
Following the directions, I cut an X in the Intello on the ceiling between two roof trusses (and our 2×6 service core below each truss) in order to establish the opening for the Battic frame.
I folded the cut edges of Intello up into the attic for the two long sides of the Battic frame. For the two shorter sides of the Battic frame it was easier for air sealing to push the Intello down into the living area.
At this point I was able to screw the Battic frame into place.
Once the outside perimeter of the Battic frame had been air sealed to the Intello, the only place left for air infiltration was where the lid would meet the frame of the Battic hatch once it was installed (more on this later when I discuss my first blower door test).
There was some additional framing required, but it was just a couple of “headers” between the roof trusses to add structural integrity to the two shorter sides of the Battic frame.
Since we were using a significant amount of blown-in insulation in the attic, it made it necessary to build up the sides of the Battic frame in the attic with some plywood to get the top of the opening above where the insulation would eventually stop.
Here’s another view of the 3 sides of plywood installed:
The fourth and final side of plywood was installed just prior to blowing in the insulation — in the interim this made getting in and out of the attic much easier.
After a couple of practice attempts, it quickly became apparent that raising and removing the lid once in place, and fighting to get it back down into the master bedroom closet, wasn’t worth the trouble. Instead, I built a small bench in the attic next to the Battic frame so I could push the lid up above the level of blown-in insulation, this way it could have somewhere to safely sit while dealing with any issue in the attic.
It’s very easy to grab the lid off the bench and bring it back down into position while slowly walking down the ladder in the master bedroom closet to make the final connection/seal.
Although the installation process was fairly straightforward and headache free for the Battic product, if I had it to do over, I think I would have the attic access point on the exterior of the structure, for example, on the gable end of the house in the backyard.
Putting the access point above the air barrier would make meticulously air sealing the entry point for the attic less important, so keeping water out of the attic would be the main goal. An additional plywood buck would’ve been necessary, replicating what I did for our windows and doors (more on this later), but I think it still would’ve been the better option overall.
Putting the attic access on the exterior of the house would also mean avoiding an ugly hole somewhere in our drywalled ceiling. No matter how nicely trimmed out, these attic access points on the interior of a home never look right to me. We’ve tried to hide ours as much as possible by sticking it in our master bedroom closet, which has worked out well, but not having one at all on the interior of the house would make for a cleaner, better solution in my opinion.
If granted a do-over, I would also add a cat walk in the attic through the roof trusses. This would make getting to any point in the attic much easier to navigate. It would also help to avoid disturbing the blown-in insulation too much.
And here’s a photo of the bench in the attic, next to the opening for the Battic attic hatch, after the blown-in insulation was installed:
Sealing the Seams and Penetrations in Zip Sheathing
Note:This post will concentrate on the Zip sheathing itself, as it relates to seams and penetrations. I’ll address how I sealed around openings for windows and doors, along with our attic access hatch through the Intello on the ceiling in separate, future blog posts.
We used Zip sheathing as our WRB (weather resistant barrier — sometimes it’s referred to as a water-resistant barrier) based largely on Hammer and Hand projects:
As the 7/16″ Zip sheathing went up, I taped most of the seams with Pro Clima’s 3″ Tescon Vana tape (available at 475 HPBS), but also their Contega tape(6″ wide), which I used mainly for outside corners and larger seams in the Zip (mainly where the horizontal seam in the Zip transitioned from the exterior walls of 2×6 framing to the roof trusses — shown in a photo later in this post).
My wife and daughter also cut up the Tescon Vana tape into small pieces in order to cover all the nail and screw holes in the Zip sheathing.
The nail holes were initially sealed with HF Sealant, also available from 475 HPBS, thus giving them double coverage — this was discussed earlier, here:
And here’s a good video discussing the Zip sheathing and its benefits (and its place in the evolution of building science):
If I had it to do over, I think I might be tempted to use 1/2″ exterior grade plywood as my sheathing (there are any number of WRB options these days). This would be sealed on the exterior side with either a liquid membrane, like Prosoco’s Cat 5, or a peel-n-stick tape like Henry’s Blue Skin, or even another 475 HPBS product Solitex Mento 1000.
The Zip sheathing works, and the exterior green skin held up nicely during construction, even as it sat exposed for nearly 10 months after we fired our GC’s and struggled to keep the project moving forward. Nevertheless, it is little more than glorified OSB, which comes with certain inherent weaknesses.
Matt Risinger does an excellent job of delineating the cost/benefits of using either OSB or CDX plywood as a sheathing material:
View of the West facade with Tescon Vana tape, along with the black Contega tape at larger seams (e.g. where the walls meet the roof trusses) and outside corners.
Once the Zip was fully installed, it was readily apparent that some of the seams, especially near the base of the first floor where a horizontal seam ran around the entire structure, would need to be tightened up.
Here’s a view looking down on one of these areas where the Zip sheathing did not sit flat against the framing members:
Using a 1×4 in each stud bay, I was able to pull the seam in the Zip sheathing together. It wasn’t always perfect, but the difference was visibly significant and in most areas well worth the effort.
Placing a 1×4 into position over the seam in the Zip, I would drive a couple of screws towards the exterior.
Once securely attached from the interior, I went outside and drove several screws into the Zip, both above and below the seam in the Zip, to pull the seam tight to the 1×4. At that point, I could go back inside and remove the two screws that were driven towards the exterior.
In addition to air sealing the exterior side of the Zip sheathing, I also invested some time in air sealing the interior side of the Zip as well. Below is a long view of several stud bays with 1×4’s installed, but before air sealing gaps around the 1×4’s and lower areas of the stud bays with HF Sealant.
Long view after applying the HF Sealant:
Close-up of the interior side of the Zip sheathing meeting a 2×6 framing member in a stud bay after applying a thick bead of HF Sealant:
Close-up of lower area of a stud bay after air sealing with the HF Sealant (it transitions from a light to darker green as it dries):
I held off on using the HF Sealant at the wall sill plate/subfloor connection until just prior to installing the Intello on the walls since this area constantly attracts dirt and debris.
Sealing on the interior side with HF Sealant, even between vertical framing members, means that even if there are any weaknesses in either the Zip sheathing or the Tescon Vana tape at these points, air won’t find an easy way in, since it will be blocked from the interior side as well (there won’t be a difference in air pressure to help the outdoor air make its way indoors).
This kind of redundancy in air sealing should give the house long-term protection against air leaks, thereby aiding the long-term durability of the structure, as well as making it a much more comfortable environment to live in.
I also spent some time on the roof trusses, sealing around nails, the top plates of the exterior walls, and the many Zip-framing member connections in what will eventually be the attic.
This had less to do with air sealing and more to do with preventing any potential water intrusion since this area is technically above our ceiling air barrier (the Intello), which is detailed here:
This proved helpful when explaining to the various subs how to help me protect the air barrier — especially when it came time to drill holes through the Zip sheathing. Of particular importance was making holes closer to the center of a stud bay, as opposed to hugging a corner or side of one of the 2×6 framing members. A hole cut too close to a stud or a roof truss is much harder to properly air seal.
In effect, any time a sub had to make a penetration through the air barrier we discussed the details, and once the cut was made I immediately air sealed the penetration both on the exterior and interior side.
By sealing each hole in the Zip on both sides, again I hope it ensures the long-term durability of the overall structure. The main argument for this strategy assumes the exterior side of the sheathing will face more extreme temperatures, and fluctuations in humidity, and presumably even wind-drive rain if/when it gets past the siding and 4″ of Roxul insulation, putting it at greater risk of failure (especially in the long term). By taking the time to air seal the interior side, it just gives the overall air barrier, and therefore the structure, a better chance at avoiding air and water intrusion (that’s the goal anyway).
For air sealing I used a mix of tapes, HF sealant (later even some Prosoco products), EPDM Roflex gaskets, and duct seal.
The penetrations for electric service were my first go at using the Roflex gaskets:
The smaller diameter Roflex gasket comes with its own Tescon Vana tape, which makes installation straightforward.
Exterior view of electric Meter air sealed with gaskets and Tescon Vana tape:
Once sealed on the exterior side, I went inside to seal the penetrations for a second time:
It was a big moment when the electric panel went in:
The installation of our solar panels required air sealing two penetrations — one through the Intello on the ceiling on the inside of the structure, along with one exterior penetration through the Zip:
Details regarding the installation of our Solar array can be found here:
We also had two frost-free hose bibs, or sill cocks, installed, which also required gaskets on the exterior and interior sides of the Zip sheathing.
One of the big advantages a Roflex gasket has over using a sealant like the green HF Sealant, or Prosoco’s Joint and Seam, is the pipe can be moved in and out even after air sealing, which is especially helpful for installing siding later.
We left the sill cocks loose (unconnected to water supply line inside the house), allowing the siding guys to adjust in and out for a more precise fit of the charred cedar siding.
Below is an example of what conduit through the Zip sheathing looks like before it gets a gasket and some tape:
And here’s the conduit after the gasket and some tape:
Note the extended length of the conduit, anticipating our 4″ of Roxul covering the Zip, 2-layers of furring strips (vertical then horizontal — for vertically oriented siding), and the eventual charred cedar siding.
The photo below shows the penetrations, along with multiple lines of conduit, for our eventual ductless mini-split Mitsubishi heat pump system. The empty hole will be our disconnect for the heat pump. I’ll go into the details of our ductless mini-split system in a future post.
Same series of conduit pipes after gaskets and being connected to the compressor outside:
In addition to the conduit for electrical hook-up, the Mitsubishi heat pump system required a separate penetration for running the refrigerant lines to the compressor:
After discussing it with Mike from Compass Heating and Air, who did our ductless mini-split installation, we decided to use a 4″ section of PVC plumbing pipe as our “conduit” for running the refrigerant lines from the interior of the structure to the outside:
After the PVC was passed through the hole in the Zip, we added a 2×4 underneath it to give it some added stability, along with the usual gasket and tape for air sealing around the PVC pipe:
Once the refrigerant lines were passed through the PVC pipe, it was clear that some additional air sealing was required.
I filled the gaps around the refrigerant lines from the interior and exterior sides with duct seal. Before stuffing in the duct seal at either end of the PVC pipe, I added bits of Roxul Comfortboard 80 into the pipe to try and give added R-value to the interior of the PVC pipe (hoping to prevent any possible condensation from forming inside the pipe).
Duct seal proved especially helpful at air sealing multiple weak points in the structure —areas that would’ve been difficult or impossible to air seal with just tape, gaskets, or sealants:
Once the interior was taken care of, I was able to address the exterior side of the PVC pipe:
Again, note that the PVC pipe is extended out in preparation for the layers of exterior insulation, furring strips, and siding:
And here’s a view of the same area after the siding was installed (I’ll go into the many details regarding the installation of the exterior insulation, furring strips, and siding in a future post):
Additional areas where the duct seal proved to be invaluable:
Conduit for the water meter in the basement (only the interior is shown below, but the conduit was air sealed with duct seal on the exterior end as well):
And here’s the same conduit for the water meter as it leaves the house on the first floor:
I also had to address the disconnect boxes for our solar array and our heat pump. For instance, here’s our solar disconnect box when it’s open:
And here it is after removing the pull out switch, revealing an air leak:
Close-up of the conduit:
An even closer look:
And here it is after being air sealed with the duct seal:
I did the same air sealing for the Mitsubishi heat pump disconnect box:
Close-up of the conduit sealed with the duct seal:
During my initial blower door test (more on that later), some air movement around the main panel in the basement was detected, so when the electrician came back we added duct seal to the main pipe entering the house (it had already been sealed from the exterior side with duct seal):
Besides the penetrations in the Zip sheathing, there were other penetrations through the Intello (our air barrier on the ceiling) that had to be addressed as well. These areas were air sealed with the same set of products as the Zip.
For example, in addition to the conduit for solar through the Intello, we also had to air seal conduit for electric service to the attic (for a light and switch in the attic), in addition to the the penetrations for radon and plumbing waste vents, some of which are shown below:
Another view of this vent pipe after air sealing, this time from below:
Here is one of the vents that our first, incompetent plumber installed too close to one of the 2×6’s used to establish our service core:
Here’s the same area after applying the Tescon Vana tape:
Below is another vent pipe incorrectly installed too close to a 2×6. This one was even more challenging to air seal properly. After the gasket and Tescon Vana, I added the green HF sealant as insurance against air leaks, both for now and in the future.
We also had to air seal the penetrations for our Zehnder Comfo-Air 350 ERV ventilation unit. I’ll go into the details of the actual installation later, but here are some photos of the penetrations through the Zip sheathing and how we addressed making them air tight:
We followed the same process — Roflex gasket and Tescon Vana tape — for the exterior side of the Zehnder Comfo pipe:
And here’s a picture of both supply and exhaust pipes for the Zehnder:
During my initial blower door test some air movement around the sump pit was detected.
The sump pump discharge pipe also needed to be air sealed on both sides of the Zip:
Some air movement around the ejector pit was also detected, so I used duct seal to try and block it.
For low voltage — in our case, a cable TV/Internet connection — we found a utility box at Lowe’s (also available at Home Depot and Amazon), and combined it with conduit to transition from the exterior to the interior. The diameter of the conduit is large enough to allow wires for other utilities/services to pass through as well, if necessary, in the future.
An engineer from Comcast-Xfinity visited the site back in the summer, and he gave me the go-ahead for using this box/conduit set-up:
Hopefully this inventory of penetrations will prove helpful to someone in the planning stages of their own “air tight” build. It always helps seeing how other people do things — in particular, the strategies they employ and the specific products they use.
Seeing these real world examples of air sealing around the many penetrations in a structure will hopefully give others the confidence to come up with their own plan of attack for building an airtight structure.
Once the wall assembly details were figured out, and our ceiling set-up detailed, the transition between the two became the next challenge. In other words, how to carry the air barrier over the top of our exterior walls.
Using a waterproof peel-and-stick membrane to wrap over the top of the wall (going from exterior sheathing — in our case 7/16″ Zip sheathing — to interior side of the top plates) seemed like the easiest way to maintain a continuous air barrier at the wall-to-roof junction. The membrane would also have a nice air sealing gasket effect after the trusses were set in place.
I also found this excellent Hammer and Hand video on YouTube (one of their many helpful videos):
Also, by being able to carry the Zip sheathing up above the top plate of the wall, hugging the bottom of the trusses, meant our 4″ of Roxul Comfortboard 80 over the Zip sheathing would rise above the top of our walls, so that thermally we would be protected going from the exterior walls to the attic, which will be filled with 24″ of blown-in cellulose — making our thermal envelope continuous for the whole house: under the basement slab – exterior of foundation – exterior walls – attic (except for one small gap at the footing-slab-foundation wall connection, which I talk about in a separate post: Foundation Details).
A high R-value wall meets up with a high R-value attic, with no thermal bridging, making our thermal layers continuous. When this is combined with an equally air-tight structure, conditioned air cannot easily escape — resulting in a significantly lower energy demand for heating and cooling (and therefore lower utility bills), and added comfort for the occupants.
I tried using rolls of conventional peel-and-stick window flashing membrane, purchased from Home Depot and Mendards, but they performed poorly, even in unseasonably warm temperatures for February in Chicago.
I then switched to Grace Ice and Water Shield, normally used as a roofing underlayment along the first 3-6′ of roof edge.
Since it came on a long roll about 4′ wide, my wife and I cut it down to a series of strips that could more easily be applied to the wall-top plate connection.
While the sun was out, the Grace membrane worked fairly well, especially when pressure was applied with a J-Roller.
Unfortunately, the sun and warmer temperatures didn’t stick around long enough for me to finish.
When the weather went gray and cold again, we started to use a heat gun to warm up the Grace membrane, which had turned stiff and nearly useless in the cold.
After wasting a lot of time and effort trying to pre-heat the Grace membrane before installing it, I finally relented and switched to the much more expensive (but also much more effective) Extoseal Encors tape from Pro Clima. Where the Grace membrane lost virtually all of its stickiness, the Extoseal Encors stuck easily and consistently, with the J-Roller just helping it to lay flatter and more securely.
It was a case of trying to be penny wise but ending up pound foolish. Looking back, I would gladly pay an extra $300 in materials to have those hours of frustration back (including the time it took to run to the store and buy the heat gun, which turned out to be ineffective anyway).
After finishing sealing the Zip sheathing-top plate connection on all the outside perimeter walls over the weekend, it was time for the trusses to be installed.
Zach asked me to stand by the front door rough opening and give the crane operator hand signals. It was a fun way to watch the roof take shape.
Once the trusses neared the front door, Zach could signal the crane operator himself, so I was able to get some shots from just outside the construction fence.
Once the trusses were on, and the guys had a chance to install the final top row of Zip sheathing (up to the bottom of the trusses on the exterior side of the wall), I could move inside to seal all the connections from the interior.
Top of Wall (Interior)
Because of the cold, the Grace membrane was beginning to lift at the edges in certain spots, so just to make sure it had a nice long-term seal, I went around the perimeter of the house and used a layer of Tescon Vana (3″ wide) tape to seal the edge of the Grace membrane.
The picture below shows all the connections involved: top of Zip sheathing meeting the roof trusses and the top plate of the outside wall:
We had to wait for shingles for quite some time. First we had to fire our GC’s, and then I had to find a roofer and a plumber (to make penetrations through the roof before the shingles went on). But before the plumber could even start, I had to get the Intello installed on the ceiling. And even before that, I had to figure out the insulation baffles, which I’ll talk about in a separate post.
It took awhile to find a roofer since they would have to make three separate trips for a relatively small job. The first trip was just to set down the Grace Ice and Water Shield at the edges of the roof, along with a synthetic roof underlayment (the consensus was that typical roofing felt wouldn’t hold up to long term exposure). As it turned out, it took weeks before the plumbers made their penetrations through the roof sheathing (literally the day the roofers showed up — a long, horrible story in and of itself that I’ll save for later).
The second trip out was to install the shingles on the roof of the house, while the third trip to install shingles on the garage roof could only happen after the Roxul on the exterior of our Zip sheathing was installed (in order to make a proper sealed connection between the wall of the house and the garage roof).
There weren’t many roofers willing to work with our unique Passive House sequencing, but Peterson Roofing was kind enough to take it on.
Unfortunately, the day after the guys installed the Grace membrane and the synthetic underlayment, we had a cold, blustery day. Once the wind grabbed the Grace membrane, the membrane rolled up on itself, turning it into a real mess.
Because of our recent past bad experiences with general contractors, I just assumed I was on my own, so I spent a couple of hours putting down new layers of the Grace membrane. When Peterson roofing found out, they were shocked I did it myself, and assured me I could’ve called them and they would’ve come back out. We were so used to people not following through, that low expectations meant it didn’t even occur to me to call them.
We initially were going to use Certainteed’s Landmark TL shingle, which mimics a cedar shake shingle profile, but Armando from Midwest Roofing Supplyin Schaumburg, Illinois was kind enough to take the time to walk me through the options available, and explained that because our roofline isn’t steep, only the neighbors from their second story windows would get to appreciate the effect. He recommended we save some money, while not giving up on quality or durability, and go with the Landmark Pro product.
The shingles went on quickly since we have a relatively small and simple roof. In addition to the aesthetic leap the shingles made on the appearance of the structure, it also meant I didn’t have to go around cleaning up the subfloor every time it rained.
Although the synthetic underlayment worked pretty well at keeping the rain out, if there was significant wind combined with rain, the water easily found its way under the underlayment where it could then drip and fall on the subflooring below — pretty depressing showing up to the job site after a hard rain knowing I was going to spend the first hour just cleaning up and looking for leaks.
After they cut the opening for the ridge vent, but before it was installed, I managed to get this shot from inside: