Ed May from BLDGTYP– a design-build firm from Brooklyn – stopped by our offices to discuss the experience he had building an almost Passive House cabin in WI. They have documented this project very well in their project blog – with great images, 3d details and gorgeous pictures (all images in this post are BLDGTYP’s). To share the experiences, I invited Ed for an interview to get some specific feedback regarding the construction of this cabin, of course with a focus on the Pro Clima membranes and tapes they had used for air-tightness and vapor control on both the interior and exterior (exterior to be featured in part 2 of this case study)
FKB: How did you plan and sequence your airtight construction?
EM: This was the second project that we were working towards airtight construction with a goal of 0.6ACH50. The first was the Empowerhouse when we were at Parsons. Therefore we knew how we wanted to approach the airtight construction of this project and the support and feedback 475 provided helped us get a very good blowerdoor result. We used the red-lined drawings and lessons learned in that project – we have a dedicated interior airbarrier that is as simple and straight as possible and is not interrupted by structural elements. It consist of the floor (taped OSB), walls and roof (INTELLO membrane/tape). There is a small mechanical room in the crawlspace that is also included, this caused additional taping around floor joist, etc. Which made making that space airtight much more time consuming.
FKB: How many blowerdoortests did you do?
EM: We only ended up doing one blowerdoortest at the end of construction. We originally had planned to do 2-3 tests, but as we were running out of time, we never did a preliminary test. This made us quite nervous. So it was great to get a result of 178cfm and 0.45ACH50 in our first attempt (kitchen exhaust not taped (with closed electronic damper), HRV ducts taped). This showed that our careful planning, detailing and diligent application of membranes and tapes paid off. Especially the sequencing, by putting INTELLO strips up before building interior walls / ledger boards really contributed to this. We were also impressed by how well it held up while being exposed (note: recommended direct UV exposure should be limited to 2 weeks)
FKB: What was your experience with installing the interior airtight/smart vapor retarder INTELLO Plus?
EM: The staple gun (Surebonder 9600) you recommended was affordable and worked well – it never jammed. This allowed us to install the membrane very fast – it took only a few trials to set the compressor to the right pressure to get the staples to sit flush with the membrane and made stapling parallel to the studs very easy (as the installation manual recommends). It was definitely much faster than stapling it with a hand stapler as we did for the small strips behind interior walls (see 1st photo).
FKB: How did this dense packing of cellulose behind the INTELLO Plus work out, I heard you did it yourself.
EM: Yes, we did it ourselves because the bids came in really to high for the time it would take them to install it (3-4 days). So we decided to do it ourselves – also as a learning experience. Since the machine we rented wasn’t super powerful, we had to restrict its output flow to get the 3.5lbs per cubic foot density. This of course slowed us down and we spend 7 days blowing cellulose, which was a little long – all in all we used 800 bags of cellulose to fill the double stud walls to 3.5″. Working with a less strong machine also meant we needed to cut some air-release holes in the INTELLO so we could get the right density in. Which did mean we had to seal those holes later with TESCON VANA or UNITAPE Patches.
Blowing cellulose behind the translucent INTELLO was great, as you were able to see and feel and gauge the progress from the pillowing of the membrane – besides counting the bags – this feature enabled us to check the density of the dense packed insulation (See this blogpost about densepacking behind INTELLO)
FKB: 3/4″ battens you used aren’t deep enough to fit outlet boxes/form a service cavity and normal drywall screws could puncture the membrane behind it. Why did you opt to use that size.
EM: Because all of the plumbing, services etc are located in interior walls, so there were only a few outlets that needed to be located in exterior walls we chose not to use a full depth service cavity. We used KAFLEX gaskets to seal around wires, used a pair of airtight outlet boxes and sealed all the pipes (HRV, sewer, plumbing, exhaust) with ROFLEX gaskets that were taped back to airtight materials.
The 3/4″ battens, 16″ o.c. on the interior did hold back the INTELLO Plus very well (see photo above). We didn’t have any issues with bulging of the membrane beyond these battens and/or difficulty getting the pine boards to sit flush with the battens. The 16″ spacing worked well and together with the parallel staple direction (noted above), I am confident that we never popped a single staple while dense-packing. However to prevent the nails that we used to secure nail the pine boards to the battens to make airleaks, we had to use shorter nails than normal so they wouldn’t puncture the airtight membrane. (Note: In projects with more outlets in the wall, or that use drywall, 475 recommends a 1.5″ deep service cavity, that can be used for services, can be insulated and one doesn’t have to worry about any nails/screws puncturing the INTELLO).
FKB: What was your experience with taping the windows?
EM: We planned taping the windows carefully. We cut back the entire opening out of the INTELLO. This then gave us a big sheet that we could then use to make strips- these strips were used to make an airtight connection from the membrane on interior of the wall to the frame of the window. We cut the sides first and then had sufficient
membrane left for the top and bottom. The taping was pretty straight forward. Flat seams were taped with TESCON Vana, all corners with TESCON Profil. This tape made it very easy to create nice and tight corners with its two release papers. Pre-folding this tape and starting the release paper by folding it – before applying the tape – and making pre-made tape corners (see this blog post), had the desired effect: no leaks around our windows during the blowerdoor test, as the infrared camera proofed.
FKB: What could still be improved in regards to the airseal of the building?
EM: The doors in the mechanical room in the crawl space that lead to the portion of the crawlspace that we didn’t airseal weren’t installed yet during the blowerdoor test. We expect that once those are installed that our blowerdoor numbers will improve. Furthermore, we could have reduced the airtightness by 4cfm – this was the extra leakage caused thought the damper of the kitchen exhaust. After we removed the temporary airseal on the exterior of this pipe, the blowerdoor went from 174cfm to 178cfm. We were actually presently surprised by how well the damper sealed (when depressurized), but for a real Passive House replacing it with a recirculating hood which would made the house even tighter.
Editor’s note: This is a condensed version of the conversation. Comments have been paraphrased and edited for clarity and continuity.
- BLDGTYP interview 2/2 – Exterior WRB/airseal and rainscreen details
- Foam-Free Wall Assembly Guidelines by Climate Zone
- INTELLO Plus: airtight in the lab for ASTM 2178 and onsite