Howell Lofts goes to market this week. The first public open house will be Sunday, January 29th from 1- 4pm. Howell Lofts looms large for us for a number of reasons. Notably, it is the first new housing project that we’ve completed since the bottom fell out of the market three years ago. It is our first project to use some of the new parking flexibility of the new multi-family codes, which helped provide a more pedestrian friendly street presence for the project. It is also our first project designed for Built Green 5-star, the highest level of certification available through that program, and one of only ten homes in King County built to this level of performance in 2011. Howell Lofts will be a significant test for how well the current home sales market will reward an ambitious green project and how it will respond to our unconventional parking solution.
The neighbors, however, were not thrilled to hear of our plans for providing less than 1 parking stall for each unit, as this would put pressure on the already over-subscribed street parking in the area. To resolve the issue, we approached the Union Gospel Mission next door and made a deal to lease some surplus spaces in their parking lot. In the end, we got the building design that we wanted, the neighbors got our cars off the street, and UGM gets income to help with their mission.
The project is laid out with the units facing south onto Howell street. Large windows are grouped along this south façade to capture natural light and passive solar gains in the winter. The large trees we preserved provide shading in the summer. The homes have about twice the amount of glazing as a typical home, and most of the windows are operable in order to provide good ventilation in the summer. In addition, the stairways are designed with open risers to facilitate vertical airflow & allow for convection currents to pull out hot air in the daytime & push down cool air for nighttime flushing.
The limited space on the site required layouts with a very compact (20’x20’) footprint. We designed the units with a split level entry and a switchback stair so that minimal space was given over to hallways and entry circulation. While the footprints are relatively small, the zoning allowed us one more story than a typical townhouse project, so in the end we got units that are quite generous. Each unit has 3br/2.5ba and a rooftop deck.
One of the biggest challenges that we faced is that 5 star projects have to meet an energy performance 30% better than what is required by code. Moreover, since the energy code baseline is based on an assumption that the project has significantly less glazing than we were using, we had a lot catching up to do. We used very high performance windows and a premium insulation package, which got us part of the way there. Air leakage, it turns out, is actually the biggest source of energy loss, and it can be hard to eliminate because the sources of leakage are so manifold and dispersed. To help tighten up the envelope we used Knauf Ecoseal, a form of sprayed caulking that gets applied to every joint in the framing and seam of the plywood. A blower door test at the end of framing helped us find little cracks before the building cavities got closed up.
Window U Value = 0.18. The blue color is the Knauf Ecoseal
Tight building envelopes make for great energy performance but also create a couple new challenges. Leakage is bad from an energy standpoint, but air exchange is necessary for healthy interior environments, so we needed to provide a supplemental mechanical ventilation system. Each unit is outfitted with a heat recovery unit that brings in a constant supply of fresh air. Exhaust air is run through a heat exchanger that transfers the outgoing heat to the incoming air, retaining about 80% of the heat energy.
|Rainscreen battens ventilate behind the siding|
Another challenge is that conventional residential siding systems aren’t particularly watertight. Over time a fair amount of water gets behind the siding. In a conventional building that moisture often gets dried out by all of the heat leaking out of the building. Energy efficient buildings don’t lose as much heat, so they can’t depend on interior heat loss to make up for deficiencies in the building envelope. With this issue in mind, we design all of our new projects with a rainscreen siding system. Rainscreens create a cavity between the siding and the building paper. Openings are provided at the top & bottom of the wall to ventilate the cavity and dry out any moisture that gets behind the siding.
Civil Engineer: Brian Darrow, Blueline Group
- Triple Glazed Windows, oriented for passive solar gain in the winter, shaded by trees in the summer, have a U-Value of 0.2, about twice as efficient as a typical window.
- BIB insulation package provides complete fill of cavities providing much higher performance than conventional batt insulation.
- Airtight construction methods including sprayed sealants at the framing level and airtight drywall reduce air infiltration to about 20% of what is seen in a typical project. Project has been blower door tested to confirm energy performance.
- Fresh air intake and exhaust provided by a Heat Recovery Ventilator, which strips the exhaust air of its heat and transfers energy to the incoming fresh air. The HRV system retains about 80% of the heat that would otherwise be exhausted to the outdoors.
- Super-high efficiency on-demand boiler and domestic hot water supply heat on an as-needed basis, preventing energy losses from storage tanks.
- TED 5000C Energy monitor allows real time monitoring of energy use and tracks use over time.
- Overall energy performance is modeled at 30% better than energy code (rated HERS 70).
- Low VOC paints, floor finishes, cabinet finishes, insulation, sealants.
- No added formaldehyde in interior millwork including cabinets, trim, plywood.
- Heat recovery ventilator provides a constant supply of fresh air.
- No carpet. Flooring is entirely tile and concrete.
- Radiant floor hydronic heating system. Ahh.
- Stairwells with open risers and operable windows create a stack effect to increase natural ventilation in warm weather.
- A rainscreen cladding system provides a ventilated cavity between the siding and the building paper to increase the longevity of the exterior finishes and protect the structural framing against long term moisture intrusion.
- Commercial grade TPO membrane roof with standing seam sheet metal parapet caps.
- Exterior fiberglass entry doors with integral sill pans.
- Recycled countertops, tile, pavers, fencing, drywall, steel, concrete.
- Open space is entirely pervious pavers and drought tolerant landscaping.
- Rain barrels provide for rainwater capture.
- Low flow faucets and showers reduce consumption by 30%.
- The existing house on the site was saved and remodeled.
- An existing garage on the site was deconstructed & substantially recycled.
- Two large specimen trees were preserved and made into project features. The tree canopies provide summer shading for the south facing windows and the rooftop decks.
- Parking for the project was provided partly by leasing spaces from the Union Gospel Mission next door, freeing up the open land for pedestrian courtyards instead of parking stalls.
- All units feature rooftops decks, providing much needed private open space with expansive views of Lake Washington.