For my inaugural blog post, I wanted to share some information about the green building strategies and high performance envelope details for my home office building for Madrona Building Solutions. It was an enlightening process for me doing the design/build and I thought I would share what went well and what we learned from this project.
Design and Performance Goals
Prior to construction, my wife Annie and I spent a fair bit of time in the design phase. Our initial goal was to build an ADU with an apartment upstairs and shop/studio downstairs. However, permitting challenges and budget constraints led us towards skipping the ADU and just building a heated studio building where we could have a home office along with heated storage, a home gym, and a workshop space for woodworking projects. We settled on a 14′ x 20′ footprint, slab on grade foundation, advanced framing (studs spaced 24″ o.c. to allow more insulation) and a shed style roof with two skylights. From an energy standpoint, our home is Net Zero Certified, meaning it is all electric (no natural gas hookup) and produces more energy than it consumes, so we wanted to make sure that we had enough solar power produced to cover the Studio building as well. Our other performance goals were to have a robust building envelope that would stand the test of time and to utilize as many natural and nontoxic materials as possible with low embodied carbon. We wanted it to be a pleasant space to spend some time in with appealing finish layers and lots of natural lighting.
We started constructing the building in March 2020 right as the COVID-19 pandemic was emerging. While I faced some challenges with building during the pandemic such as supply shortages and managing subcontractors and inspections during lockdown, it also provided an opportunity for outdoor, socially distanced work and always having something to do while stuck at home. I hired subs for excavation and concrete work and pretty soon had a solid foundation to start framing. I framed the building with a carpenter friend who has framed many homes in the past. We framed the walls on the ground and were able to lift them in place with the two of us, except for the 11′ tall West wall with a double door framed out where we had to recruit some neighbors to help lift it in place like a good old fashioned barn raising. After two weeks, we finished installing the sheathing and I would be finishing construction solo from this point out.
Building Envelope Details
The building envelope consists of the all the components of the exterior shell that helps maintain a dry and heated indoor space (roof components, housewrap, flashing, insulation, air sealing components, etc.). It should provide protection from the rain and cold (comfort), good indoor air quality, building durability and energy efficiency. While it can be a challenge to figure out what steps to do when during construction, when building in the rainy Northwest climate, there is always a rush to get the building weathered in – to have a waterproof roof covering and weather resistant barrier on the exterior walls, so typically weatherproofing details will come next after framing.
Roof – Getting a waterproof roof covering was my initial focus. For the roofing underlayment, I used a continuous layer of Henry BlueSkin High Temp Roof Underlayment across the whole roof, providing a secondary waterproof layer and covered the roof with standing seam metal roofing. Metal roofing is great in that it provides a long service life (up to 50 years) and doesn’t contain all the chemical runoff in asphalt shingles, so it could be used for rainwater catchment (future project). This was my first time installing metal roofing and it was mainly straightforward, except for all the metal folding and cutting for the flashing around the skylights.
Exterior Walls – For the exterior walls, the air barrier layer was to be at the wall sheathing, so I started air sealing by caulking the gap between plywood panels. I then used Henry Blueskin VP100 as the weather resistant barrier (“WRB”). This type of WRB serves not only as rain barrier, it also can be an airtight layer that still allows vapor to pass through, keeping the wall cavities dry. As opposed to a mechanically fastened WRB like Tyvek, Blueskin is self-adhered meaning it doesn’t require thousands of little holes from staples to install. However, it is a bit trickier to install – kind of like putting a giant sticker all around the building. The next outside layer was the rainscreen. This layer allows a drainage plane behind the siding so that wind driven rain that gets behind the siding will be able to drain away from the building. It consists of diagonal wooden furring strips which the wood siding will attach to along with Cor-a-vent SV-5 strips on the top and bottom to allow moisture to drain away and preventing insects from getting behind the siding.
Interior – After the building was weathered in, I next focused on the interior. I have an electrician friend who was able to help me dig a trench to bury service wires, install a subpanel and get everything wired up in the studio. Then I focused on insulating the building. I used Roxul Comfortbatt mineral wool insulation for the interior walls and sloped ceiling. Mineral wool is mostly natural product formed from volcanic rock, which is melted and spun into “wool” and bound together by different resins and oils. It is non combustible and water resistant – it doesn’t loose it’s thermal effectiveness and doesn’t rot or promote fungal growth if it were to get wet. Because mineral wool is dense and firm, it is easier to conform to the dimensions of a stud cavity and achieve a secure fit versus fiberglass batts.
Finish Layers – I chose to use Tongue and Groove Western Red Cedar as a siding product. While there are certainly impacts to our local forests from harvesting cedar, it has lower embodied carbon than other siding products like fiber cement or vinyl. Cedar is naturally rot resistant, but its longevity can be improved with a Japanese technique called Shou sugi ban, which involves charring the cedar before installing it on the building. For my building, I gave it a light char with a propane torch, being careful not to set the narrow groove on fire. I then scraped the char residue off, gave it a light sanding and applied a stain to seal the wood. This process should provide added durability along with a unique look. For the interior, I chose to use prefinished plywood over drywall for the finish layer due to it being easier to install as a DIY owner-builder, but also it has added strength which is great for creative storage solutions. For the floors, I wanted a durable layer without requiring added products, so I simply polished the concrete slab and applied a stain and sealer. For the heating system in a small, tightly-sealed space I didn’t need anything fancy so I simply installed a plug-in electrical panel heater from Heating Green. For ventilation I went with a sidewall exhaust fan along with a fresh air inlet that can be opened and closed.
Closing Thoughts – Overall I was really happy how this project turned out. By building it myself I was able to save quite a lot over hiring a GC while learning about the new construction process with first hand experience. After a winter spent working in the Studio, I was able to stay quite comfortable. With the radiant heating panel positioned over my desk, I can run it at a lower operating temperature while still feeling warm enought being close to it. On warm days, the building stays cool passively. If I had the budget, a couple things I would do differently in the future would be to shoot for Passive House certification with mineral wool rigid exterior insulation, and a small heat pump unit with integrated heat recovery ventilator (HRV) like this one from Innova.