The Final Layer

This weekend, we reached the final exterior layer of the building envelope: the siding! (In this case, “exterior” is considered as anything outboard of the framing.) We started the day by installing two perpendicular layers (1×3 & 1 x4) wood strapping over the continuous insulation and second layer of house wrap. The first layer was run vertically, spaced 16″ on center to align with the wall framing. We attached it by driving long screws through the strapping, outboard insulation, and sheathing and into the studs. Since our siding runs vertically, a layer of horizontal strapping was also needed. This was installed similarly to the first layer, but using even longer (7″) screws and countersinking the screw heads to create a flat surface for siding application. These two layers of strapping provide a solid attachment point to nail our siding to. The strapping creates an air gap between the siding and house wrap, so any water that manages to get behind the siding can drain freely downward; this air gap also encourages air circulation behind the siding, promoting further drying of any moisture in the assembly. This 3/4″ air space does unfortunately offer an inviting space for insects to congregate, and must be detailed to prevent curious critters from getting in. To this end, we placed a strip of Cor-A-Vent at the bottom of each bay between vertical strapping courses. Cor-A-Vent is a corrugated plastic product with one end wrapped in a screening filter fabric; it allows air to pass through, but not insects. With both layers of strapping installed, we were able to finish our day by putting up the first piece of vertical siding. Exciting!

So far the majority of our time has been focused on the various layers of the building envelope. The building envelope is what separates “inside” from “outside”. Good design and detailing of the building envelope is the most important passive design measure when it comes to minimizing building energy use and ensuring thermal comfort for building occupants. The Hygge House’s building envelope, when finished, will be made up of 9 separate layers: Drywall, Intello air/vapor control membrane, 2×6 wood framing (with dense pack cellulose insulation in the cavities), plywood sheathing, Mento house wrap, Gutex Multitherm wood fiber board insulation, another layer of house wrap, wood strapping, and finally vertical tongue & groove rough sawn wood siding! Each layer performs one or more of the essential building envelope functions: providing structural support, protecting components vulnerable to moisture from bulk water, providing an air and/or vapor barrier … and presenting an attractive finished surface to people inside and outside the building!

The first piece of siding-a momentous occasion!

This was the last weekend that the courses was officially in session. Since many members of the class are graduating and some have plans to leave the area this summer for jobs or travel, a celebration was in order for the last weekend we would all be at the build together. Kent and his wife, Lynn, generously provided us with lunch, and we all got to enjoy some great food on our lunch break while reflecting on our experiences of the build. Those of us who will be staying in the area over the summer will continue to work on the house on weekends until it’s ready to load onto a truck and travel to the Green River Festival. We’re no longer being graded on participation, but watching the project come together provides a strong incentive to keep showing up!

Ending the “official” part of the build on a high note.

Electrifying News!

On Friday, April 22, the Hygge House reached another major milestone: the completion of rough electrical work! Thanks to the technical expertise of Graham Electric of Haydenville, MA (with an assist from the DesignBuild student team), the house is one step closer to being equipped with all the comforts and conveniences of home. Yes, you can do a lot in terms of heating, cooling and lighting with passive strategies…but not everything! A system of wiring for distributing electricity to power appliances, HVAC equipment and lighting fixtures is essential for a modern house, and that is the focus of the rough electrical install phase.

Preparing for this phase requires a few per-requisites: first, all exterior framing and wall and roof sheathing must be complete; ideally, the house should be fully “dried in” with all windows and doors installed (we’ve decided to hold off on door installation to maintain easy access to the space so we can use it to store tools and materials, and to avoid potential damage to the glass doors.) Second, all interior walls which will contain wiring must be framed for this phase to proceed. The rough electrical work covers pulling wiring, mounting junction boxes for outlets and controls, and installation of the electrical panel (aka breaker box), grounding, and overhead service wire. It doesn’t include the installation of switches, outlets, or fixtures yet-that will happen after insulation and drywall! (So for now, our power supply is still dependent on extension cords.)
In this phase, it’s important to keep everything neat and labeled and to avoid kinking wires or damaging insulation on wires. Metal plates are installed over studs where wires run through them to prevent damage from stray fasteners during the finish phase.

Applying Visconn to Gutex


The rest of the weekend featured more Gutex installation and detailing. We used Visconn, a liquid-applied air barrier product, to seal the Gutex at the corners of the building. Visconn was also applied around the windows to provide an application surface for tape and for further air sealing. One more piece of exciting news from this weekend’s build: We got to enjoy a rare day of warm, sunny weather!

Windows & Insulation

This build weekend began with another significant milestone: window installation! Our 5 donated windows are a mix of flanged and nonflanged. These types of windows require different types of installation detailing. Flanged windows have (as the name suggests) an integrated nailing flange that runs all the way around the perimeter. When the window is installed, the back of this flange sits against the outside face of the sheathing. Nonflanged windows are attached to the window rough opening by nailing tabs integrated into their frames. Apart from this difference, the installation process for both window types is similar: first, the window opening is lined with a window buck made from ZipSystem sheathing, which is taped with Tescon Vana tape in the corners and around the intersection with the outside face of the sheathing for air sealing. Then, a piece of clapboard siding is nailed in the opening and covered with a layer of Extoseal Encors stretch tape to create a waterproof, slightly pitched sill pan. The tape is lapped over the edge of the window buck and sealed to the outside of the sheathing over the house wrap (for flanged windows) or outboard insulation (for nonflanged windows). This sill pan will drain out any water that may leak into the window, protecting the wall assembly. Another layer of Extoseal goes over the top of the window buck for additional protection from water. The window is then moved into place and centered in the rough opening. Next up is leveling, plumbing and squaring the window. After an initial check with a level, one corner (on the high side of the window) is tacked in place. Composite shims are inserted under the sill to level the window out, and the tab or flange in the opposite corner is nailed off. Next, the window is checked for plumb with a level, and checked for square by comparing diagonal measurements between opposite corners. Any necessary corrections are made by using a small flat bar to pry the window into place before it is fully nailed off. Flanged windows require a few additional details: a bead of acoustic sealant is applied to the back of the flange before install for air sealing, and after it’s nailed in place, the flange is taped over with Vana tape on the sides and top for air sealing and bulk water protection. A buck constructed from 2×4 rips is built around the window to provide a solid surface to butt the outboard insulation up to.

Flanged windows are the most common type used in American residential construction, but they have one major drawback: the nailing flange has to be nailed to the wall sheathing, restricting where they can be set relative to the depth of the wall assembly. This also means that the installation of the flanged windows must be completed before outboard insulation can be installed around them. For the nonflanged windows, on the other hand, the outboard insulation can be installed around the prepared rough openings with their ZipSystem window bucks before the windows are in place.

This created a fork in our critical path. While one team of students worked on window install, another team unwrapped the pallets of Gutex Multitherm that had been waiting under a giant tarp for the past few weeks. Gutex is an innovative insulation product made from wood fiber treated with paraffin to repel water. It has an R-value of 3.6 per inch of thickness; we used the 80mm (~3 1/8″) variety, contributing an R-value of 11.4 to our wall, and eliminating the thermal bridging effect of the wall framing. Gutex comes in board/sheet form similar to XPS, EPS or polyiso foam insulation and can be cut to size and attached with fasteners in the same way these products can. Unlike foam board insulation, it’s made from renewable resources and without CFCs or other environmentally damaging blowing agents. However, working with Gutex is not without its challenges. It’s approximately 3″ thick, which is greater than the maximum cut depth of a standard circular saw blade, and substantial enough that cutting it with hand tools is slow going. Our answer to this was to use a combination of tools: our trusty SawStop table saw for long rip cuts, and a jigsaw with a 6″ blade for shorter cuts and notches with square corners (for fitting around windows and doors.) It has tongue-and-groove edges to lock neighboring sheets of insulation together and prevent gapping, which is great from a performance standpoint but does require pieces to be installed in a specific orientation, limiting reuse opportunities for cutoffs. Not only do pieces need to be oriented correctly, the joints must be staggered between courses-and we also had to remember the 5″ wide removable strip of Gutex that covers the joint between building sections! Since Gutex is a European product, the sheet dimensions were based on the metric system, rather than corresponding to the standard multiples of inches and feet that American-made building products are based on. With all these installation constraints, the pile of scrap grew quickly. And so did the fluffy drifts of wood fiber produced from cutting the Gutex (which, in my experience, is still far preferable to the irritating by-products of working with rock wool or foam board!) The Gutex team made short work of installation, and by the end of the day the entire back wall and portions of the side walls were covered.

That’s a wrap, folks!

Progress may seem frustratingly slow at this phase compared to when we were raising multiple walls in a work day, but this is certainly not due to lack of motivation on our part – it’s just the nature of this phase of the build. Now that we are working on the upper section of the building, we are using staging as a work platform. This means a lot of climbing up and down, bringing any tools and materials we need along with us (and hopefully not forgetting anything on the ground!).

Setting up staging

We also continue to face the challenge of maintaining the continuity of the air barrier AND the ability of the house to be disassembled into two sections for transport. The finished HyggeHaus will have both an external air barrier (Solitex Mento 1000 House Wrap) and an internal air barrier (a layer of Intello Smart Membrane that will be applied upon completion of rough plumbing and electrical work.) One of the most important tools of the trade in this phase is surprisingly low-tech: the squeegee, a palm-sized square of plastic used to press down and smooth tape to get the best possible bond and seal with the substrate (the pressure activates the acrylic adhesive)..

Using a squeegee to press Vana tape into the corner of a window buck

On the lower section of the house, the Mento functions as the primary air barrier, due to the high likelihood of the Intello being compromised by occupant activities such as driving nails in the wall to hang pictures. On the upper section, the primary air barrier is the interior layer of Intello, which is applied to the underside of the roof trusses (see image below). This unusual arrangement allows us to avoid having to wrap the Mento up and over the top of the sheathing to join with the interior air barrier, and then setting the trusses on top of it (difficult and also highly likely to damage the Mento in the process). However, it does require an extra level of detail when sheathing the gable ends. A continuous bead of acoustic sealant is applied along the bottom chord of the truss to prevent air leakage between the truss and sheathing. Although the Mento is not needed as an air barrier above this level, we still applied it all the way up to the roof where it functions as the Drainage Plane protecting the sheathing and inboard wall assembly from bulk water.

Drawing by Lia Douillet

At the joint between sections, the air barrier is split and taped to the sheathing on either side of the joint. This will be covered with a third piece of tape to provide continuity, and the joint will eventually be covered by a removable piece of trim backed with Gutex Multitherm insulation. When it’s time to move the house, the trim will be removed, the tape over the joint cut, and the LVLs unbolted. The house will then be disassembled into two parts, moved, and then reassembled in reverse order (applying a new piece of tape over the joint to maintain continuity.) The Intello will be detailed in a similar way.

Mento wrap taping details

We got our first chance to work with Intello this weekend while doing some preparations for rough plumbing installation. The rough plumbing phase will include installing the shower stall, which when installed will block access to the wall behind it. To prepare, we filled the stud bays with mineral wool insulation and applied a layer of Intello over the framing.

Preparing for shower stall installation.

Up next: Rough plumbing, window installation, and applying outboard insulation (~3″ layer of Gutex Multitherm, a wood fiber board product treated with paraffin to resist moisture.) Onward!

Spring(ish) Break(ish)!

To make up for time lost to the predictably unpredictable New England weather, the HyggeHaus team held 3 build days over Spring Break week.

This week’s build focused on finishing interior framing, sheathing the lower section of the house, taping the CDX sheathing, prepping for roof and window installation, and installation and air sealing of a Weather Resistant Barrier (WRB).

Applying weather resistant barrier: a team effort.

Two ongoing design challenges for us as we wrap up the framing phase have been the interior loft layout and the question of installing a clerestory window near the high point of the shed roof to bring more daylight into the interior. Both aspects of the design are complicated by uncertainty over the final siting and orientation of the house, meaning we have to plan a design that can work for two opposite shed roof orientations. This is a challenge for the loft design, since the water heater we planned to install in the loft area must be located near the high point of the roof to have adequate clearance. We solved this by framing two access hatches into the loft and then laying the subfloor over both; this gives the option of installing the water heater on either side of the loft while maximizing available loft space, and the subfloor over the corresponding access hatch will be cut out to provide access to the space when the building reaches its final destination. We used the framed and decked loft as a working platform to prep for the roof installation.

The shed roof’s structural components will be wooden trusses, which will rest on a short knee wall of 2x6s with an LVL bottom plate at the peak, and directly on an LVL plate at its low point. The LVL plates will provide added strength and stiffness to the roof assembly when the building is disassembled into separate roof and body sections for transport. The lower LVL plate rest on top of the lower wall’s LVL top plates; both extend past the plane of the walls on the interior to provide an attachment point where the two sections of the house will be bolted together. The idea of adding a clerestory window to the upper section of wall below the roof was challenged by the difficulty of finding a location that would still work if the roof was rotated 180 degrees. Eventually, we decided that the existing windows and doors would provide enough natural light that the clerestory window idea wasn’t worth pursuing further. 

Our short-term goal is to get the house “dried in” as soon as possible; to that end, part of the team devoted a significant chunk of time to prepping windows for installation. Our collection of 7 donated windows got a fresh coat (or 3) of black paint, to harmonize with the warm gray paint color we picked for the siding. The WRB membrane we used was Solitex Mento 100. This durable, fabric-like product which was detailed with both Tescon Vanna and Ectoseal Encors. When details with the window and door connections are completed the entirety will act as the primary air barrier, preventing air leakage through the building envelope and the accompanying unwanted heat gain/loss., reducing the chance of condensation within the wall assembly, and is the drainage plane for the vertical surfaces of the building.

To work effectively, this weather resistant barrier must be detailed properly; this includes allowing sufficient overlap between courses, lapping to the weather, minimizing stapling in the field (creates holes), avoiding bunching or wrinkling of the membrane, and taping at joints. The taping process, as we found out, has its own learning curve. The challenge is to apply the tape without wrinkling it, wandering off the line, or having the tape stick to itself — easier said than done! But for the purpose of building a high-performance home, every minute we spend getting these details right really does make a difference. 

Spring Break Timelapse