rain garden

EHH week 16: rain garden excavation

As everyone knows, it rains in the Seattle area.  We get 37 inches in an average year, but once in a while we will get an inch in a single day.  In May 2011, Seattle got 1.78 inches over two days!  All that water has to go somewhere.

 

The Harvest House site is a wonderful piece of property (see blog 1), but its major defect is that there is no stormwater outlet pipe and the soils do not percolate particularly well.  So the civil engineer, springline design, designed a rain garden to collect and then gradually percolate the rain.

 

A rain garden is an open pit into which rain flows from the impervious surfaces on the site (see blog 10).  The bottom of the pit is filled with 18 inches of special soil designed to hold water like a sponge.  That soil is then planted with marsh plants.

 

When it rains, first the “sponge” gets soaked, then water will pool up to the rim of the pit.  Over a few days the water will gradually both evaporate and infiltrate into the ground below the rain garden.  The sloping site at this project required a series of 5 terraced pits, each with a concrete dam to hold back the ponded water.  The lowest pond is expected to never overflow its rim.

 

The excavation for this rain garden is huge, but the landscaper will spread the dirt pile around the rest of the site so we don’t need to export any off site.

EHH week 10: storm drainage

Before we started construction, the site was a fairly uniform slope down 9% to the west.  The new house foundation was installed across most of the width of the site, set into the slope.  Because the foundation acts like a big barrier to the downward flow of water, we need to pipe the rain around the house to avoid a wet basement.

 

Rain will fall on four major surfaces: the house roof, the PV panels over the garage, the autocourt, and the landscaped yard.  The house roof water will be harvested for reuse inside, so it is routed into big rain tanks.  But the rest of the rain must be directed to a new raingarden just downhill from the house.  The purpose of the raingarden is to collect and then slowly infiltrate all that rain so it does not flow off the site.

 

The task this week is to install the buried piping, all of which flows to a single catch basin (concrete box) at the uphill end of the rain garden.  A backhoe digs the trenches and then the black polyethylene piping is installed.  The contractors carefully set the slope of the pipe to assure positive drainage.  The trench is then filled with gravel to bed the piping before being covered with dirt and plants.  Where the pipe bends underground, vertical pipes called cleanouts stick up to allow for future maintenance.

EHH week 01: about Eastside Harvest House

Welcome to Eastside Harvest House, a new home designed to harvest food, sun, and rain on site.

A Kirkland couple seeking to build their new home had three main criteria for their site: ample space for an edible garden, room for elderly parents to live comfortably and share their home, and enjoying a sweeping view of Lake Washington and the Olympic Mountains.  They found a 1 acre dream site in the heart of Kirkland, largely undeveloped, with sweeping views of lake and mountains to the west.  The house is a 5 minute walk to grocery stores, coffee shops, retail, and restaurants.  There is a bus stop right at the street with service every 15 minutes to Kirkland, Bellevue, or Seattle, enabling car-free living.

The site will boast an abundant 6500 square foot garden for the owners to grow their own fruits and vegetables.  Irrigation will be provided by a subsurface drip system to irrigate two dozen raised beds, a dozen fruit trees, and numerous edible berry bushes.  A basement root cellar will store the garden bounty and ample kitchen counter space will enable home canning in season for personal use or to give as homemade gifts.

This 3500 square foot single-family residence will be divided into two suites, each with its own kitchen.  The master suite will group the living, dining, and kitchen in one great room with a master bedroom and bath, a guest bedroom and bath, his and hers offices, and an exercise room.  The private in-law suite will have a smaller great room, with two bedrooms and one bath.

The floor plan allows for long term flexibility depending on the occupants.  The wall dividing the great rooms is structurally designed to allow connection as one single dwelling, perfect for a large family with the in law suite becoming the children’s wing.  But the wall can subsequently be divided again in the future to suit two smaller families.

The house will be one story over a full daylight basement to fit it into the gently sloping site.  An elegant stair will connect the two levels.  However, all the principal rooms in both suites are located on the main floor flush with driveway grade to allow for accessibility for elderly parents now, and the middle aged owners in the future.  Bathrooms are designed with aging in place in mind, with curb-less showers, comfort height toilets, and grab bars.

This house has ambitious ecological goals, targeting LEED for Homes Platinum and Built Green 5 Star certifications.  100% of stormwater will be captured and infiltrated on site in a 2200 cubic foot rain garden.  Rainwater from the metal roof will be collected in four cisterns in the basement totaling 12,000 gallons.  Filtration and UV sterilization will allow the homeowners to use the rainwater for potable purposes in addition to toilet flushing, laundry, and irrigation.  This is the first residence in King County to be permitted to drink its rainwater.  The project anticipates net zero energy, supplying 100% of its own power with a 17kW photovoltaic array and 30 evacuated solar hot water tubes.

The Eastside Harvest House is a truly functional, beautiful, and sustainable addition to the vibrant community of Kirkland.

Project statistics
Location: Kirkland, Washington
Lot size:  41019 square feet (almost 1 acre)
Number of units: 1 dwelling unit with attached mother in law suite
Total gross square footage: 4400 gross square feet (3570 conditioned)

Project Team
Client: (confidential)
Architect: VELOCIPEDE architects inc
Contractor: Model Remodel LLC
Civil engineer: springline design, LLC
Landscape architect: Outdoor Studio
Structural engineer: Harriott Smith Valentine Engineers, Inc.
Mechanical engineer: Ecotope, Inc.
Solar designer: Solterra Systems, Inc.
Surveyor: Pacific Geomatic Services, Inc.
Geotechnical engineer: Geotech Consultants, Inc.
Arborist: Urban Forestry Services, Inc.

 

EHH week 30: rain garden

The rain garden is complete.  Its job is to collect all the stormwater from the site (see Week 16 blog) and allow it to gradually disperse.  During a storm, rain enters at the top and as upper pools fill, they spill over to lower ones in a controlled manner through a notch in the top of each concrete wall.  The entire rain garden can hold 90,000 gallons of water, which is a lot of rain.

 

Once full, the pools then gradually empty by either percolating down into the earth or evaporating up into the sky.  As the wetland plants in the rain garden mature they will help speed the rate of emptying.

 

The landscape contractor managed to redistribute all the dirt from the rain garden excavation.  So the project has not had to export any dirt, which is a success ecologically and economically.

 

Rain gardens are becoming more common in the greater Seattle area.  They have been used at shopping center parking lots and along the sides of residential streets.  For sites with restricted areas, buried detention pipes are a better solution.  But for sites with enough footprint area, I really like the way that rain gardens make visible the process of stormwater collection and dispersion.  They are miniature versions of nature’s hydrological cycle.

Smart design begins here.