Harrison Architects
http://www.harrisonarchitects.com

Green Roof Workshop

Kirkland, WA, 2003

Our goal was to make a simple, modern workshop outbuilding to be used for hobby cabinetmaking and appropriately reverent storage and display of our client's vintage Mercedes 230SL convertible.

The idea of a planted roof came up early in the design process. By setting the floor level low and digging the building partly into the site, and sloping the roof up and away from the neighbors yard and planting it, we minimized the visual impact of the new structure, as well as accruing all the environmental and aesthetic benefits that come with a blooming roof.

The planted roof is part of the Northwest EcoBuilding Guild-organized and King County-sponsored Green Roof Project, intended to document and publicize the ecological benefits of residential green roofs. American Hydrotech donated their green roof system, Snyder Roofing, a certified American Hydrotech green roof installer, installed the roof membrane and drainage layer, and Guild volunteers helped with the installation of plant materials. Please visit the Guild's web site (www.ecobuilding.org) for continuing updates on the study.

The American Hydrotech green roof system is typically used on large commercial roofs of over 10,000 square feet. At around $15 per square foot installed, it is more expensive than many homeowners can afford. It does come with a warranty like any other roofing material, which is a major advantage. We followed the manufacturer's recommendations and details to the letter, in order to have a “control” green roof system against which to judge the performance of the less expensive experimental systems of the Green Roof Project. (For example, the American Hydrotech details called for a border of gravel around all edges of the roof that on a larger roof would be less noticeable.)

The planted roof did not fare well in the drought of 2003. A housesitter misunderstood the watering regime, and most plants on the roof withered. It was replanted in spring of 2004, but plantings on the roof are still not as well established as one would hope. We are not yet able give definitive reasons for this. The monitoring which was to provide empirical data on the roofs of the Guild's Green Roof Project has yet to be implemented.

An excellent cabinetmaker, our client was able to provide much of the finish work on the interior, as well as fabricating the large wood and polycarbonate exterior doors. His work was beautifully consistent with the environmental goals of the project. At our request, Jim provided us with a list:

• Free standing workbench; made by J. Sproull; birds-eye maple with walnut inlays
• Workbench along and attached to south wall; reclaimed bowling alley lane;
• Second Use Building Building Materials (SUBM); southern yellow pine, shelving in south west corner: cut off sections of above bowling alley material
• Blue cabinets along south wall (supports workbench), reclaimed kitchen cabinets SUBM; painted to match floor color
• Blue Credenza along south wall; reclaimed from an architects office SUBM; painted to match floor color
• Metal drawers; reclaimed from school science display cabinet;
• Shelving to support metal drawers: reclaimed from neighborhood
• Shaker peg border; reclaimed high school bleachers SUBM; ripped to width for use
• Table saw out-feed table support; reclaimed basketball backboard support; local neighborhood kid
• Bathroom door: reclaimed door for owner's residence
• Drill press stand: reclaimed cabinet; painted to match floor color and set on rollers
• South wall Madrona door handles: reclaimed windfall; owner's woodlot
• Rolling cabinet located on east wall; reclamined display cabinet from school (left original color)
• Metal cabinet on east wall over sink (first aid cabinet); reclaimed medical office cabinet SUBM (left original color)
• Misc. wood thin stock storage bin (southeast corner): wooden barrel clothes washer circa ?; unknown origin

As with all of our projects, this one incorporates a number of green features spread evenly across the categories of settlement ecology, energy conservation, resource conservation and healthy building.

settlement ecology

• “extensive” (thin) planted roof reduces run-off and urban heat island effect, provides habitat for birds, insects and delicate plants
• siting of the building on the lot was done carefully to preserve root system of a 36” diameter mature Douglas fir, as well as other trees, and to fit into landscape architect's plans
• new paving is semi-pervious gravel (Grase-Pave proved too expensive.)
  

energy conservation

• infrared “on-demand” heating system heats people & objects rather than air
• insulation exceeds code requirements for this type of building
• extensive daylighting (translucent clerestory around entire building)
• T-5 high-output fluorescent lamps with electronic ballasts

resource conservation

• full line job-site recycling
• source reduction through simple design;
• advanced framing
• full modules for fiber-cement panel siding
• structural sheathing used as interior finish
• detailing to eliminate trim.
• 43% fly ash in concrete
• blown-in cellulose (recycled newsprint) insulation in walls
• engineered lumber for roof framing
• about 80% FSC-certified wood (everything that was available)

a healthier life

• natural ventilation through stack effect
• additional mechanical ventilation for use during cabinet finishing (although our client uses low-toxic finishes)
• elimination of unnecessary finishes
• where finishes are required, low toxic paints, caulking, concrete finish, etc. were used.

lessons learned…

• Advanced framing combined with visible alignments (through clerestory, and siding joint lines) proved challenging for the framer.
• What looks like a simple siding system turned out to be quite complicated. Each 4x8 sheet of HardiPanel had to be trimmed 1” in horizontal dimension to allow for 1/2” flashing reveal and still stay on module with framing-not as fast and easy as we intended.
• When everything is on module and visible, even things like plumbing stack locations need to be detailed and dimensioned.
• Placing structural sheathing on the interior side of studs (and placing HardiPanel directly over building paper on the outside) conserved material, but required special sequencing for subcontractors.
• Small infrared heaters spec'd were not available soon enough. The supplier substituted much larger units for the same price. These take up quite a bit more visual space in the ceiling than the specified units would have.
• In our next green roof projects we will provide dedicated access to the roof.
• RHA would have preferred more yellow in the green paint to blend more with the fir trees...but the color used matched the trim on the house.