EHH week 22: PV rack

The Eastside Harvest House is aiming to be a net-zero energy building.  That means that it will generate on site at least 100% of the energy it uses on site.  All the energy the homeowners use for heating, hot water, air conditioning, lighting, cooking, fans, pumps, computers—everything—is expected to be 15,500 kWh (kilowatt hours) for a whole year. 

 

To generate that much electricity, they need to install a 17 kW (kilowatt) PV (photovoltaic) system.  A fixed 1 kW PV array tilted at a near optimum 25 degree angle from the horizontal and facing due south generates about 980 kWh annually in the Seattle area, even with our notoriously cloudy weather. 

 

That means we need a 60 foot long by 24 foot tall array.  We can’t use the roof of the house or garage because they face the wrong direction, aren’t steep enough, and are too small.  So the solar contractor built a custom rack from steel pipe.  It runs over the garage and is partly supported by the garage roof.  The rest lands on concrete footings on the ground, each at a different height which required precise lengths of pipe.

 

The rack made use of standard pipe fittings to make it relatively easy to weld together in the shop and then assemble with bolts in the field.  It is powdercoated black to stand up to the weather and look sleek.  A structural engineer made sure it can resist strong winds trying to send the PV panels into the neighbor’s yard.

EHH week 21: vegetable garden

The Eastside Harvest House has devoted a significant part of its 1 acre lot to raised bed vegetable gardens and an adjacent fruit orchard.  The design of these beds changed from 30 rectangular beds boxed in by cedar timbers to 5 terraces retained by stone walls for greater flexibility in crop arrangement. 

 

The terraces step down the 9% natural grade of the site.  The dry stack stone came direct from Iron Mountain quarry in nearby Granite Falls.

 

Besides a green thumb, the key to a successful garden is soil preparation.  The landscape installer, Northwest Bloom, did a great job.  Balancing cut and fill, they used lightweight equipment for the rough grading and machine tilled the dirt to a depth of 12 inches, to assure drainage.  Over top an 18 inch layer of “three way” (loam, sand, compost) mix was brought in, then top dressed with a 2 inch layer of certified organic worm castings from Yelm.

 

To protect the compost over the winter of 2011/2012, a cover crop called Austrian pea was planted and then covered with temporary plastic horticultural sheeting to prevent erosion and nutrient leaching.  In a few weeks the sheeting will be removed when the cover crop gets established.  Planting will take place in the spring of 2012. 

EHH week 20: air sealing

To build a net zero energy house it is essential to reduce air leakage to the bare minimum.  Doing so requires a comprehensive effort by the contractors to fill every gap between the heated inside and the outside.  Typical problem areas are at electrical outlets, light fixtures and switches, pipes and ducts, around windows and doors, and at wall intersections.  For this house, we used a combination of spray polyurethane foam and caulk to seal all these gaps.

 

During design, the architects determined the boundary of the air barrier surrounding the whole house.  At the walls and floor overhangs it is the plywood sheathing, which had all its joints covered with black butyl tape.  At the floor and foundation it is the concrete slab and walls.  And at the roof it is the sloped gypsum board ceiling, which had a dozen light fixtures hung from it that were enclosed in a special airtight plastic box.

 

To confirm air tightness, a device called a blower door is used to depressurize the interior to 50 pascals.  The blower fan is trying to suck outside air in, which can be felt by the test technician using a damp hand and an infrared camera.  A gap as small as that between two uneven pieces of wood is significant.

 

Our specs targeted 2.0 ACH50 (two air changes per hour at 50 pascals) as an ambitious maximum, but the team wanted to get much lower.  Our first blower door test achieved 1.6 ACH50, which is a terrific result.

EHH week 19: concrete floor polishing

The interior concrete floors have cured long enough that they are ready for polishing.  A heavy machine fitted with diamond tipped blades (reminds me of an electric shaving razor) makes several passes over the concrete surface.  Its job is to remove the “cream,” the uppermost 1/8 of an inch or so of cement that forms the skin of the cured concrete. 

 

Removing the cream exposes the pea gravel aggregate which gives the finished surface a lovely “salt and pepper” appearance.  The trick is to remove just enough to expose the aggregate without overdoing it so that the salt and pepper look gets too chunky.

 

Once the removal step is complete, polishing begins with successively finer grit, just like sanding a piece of wood.  The final grit for this project is 400, which we feel is not too shiny but still lets you see into the depth of the concrete, so to speak.  Before polishing the main floor, the contractor did a test patch to the satisfaction of architect and homeowner so everyone agreed on the look we were targeting.

 

As part of the polishing, a densifier is added to essentially fill in the pores of the concrete so it is resistant to water and stains.  The polished floor was then covered with protection boards for the duration of construction.  Just before turning the finished house over to the homeowners, the protection will be removed and one last densifier coat will be applied.  They will look gorgeous!

EHH week 18: metal roofing

The form of the roof for this house was driven by several factors.  Preference for a modern aesthetic dictated that it be flat with a shallow slope, which made it easy to stay under the 25 foot height limit.  We sloped it all to one side of the house, so the interior ceilings rise towards the western view and so the rain water all flows to the other side to simplify collection.  The exception to the main slope is on the street side, where we sloped the roof up in the middle to mark the entry on the front of the house.

 

For roofing material, we chose standing seam steel, prefinished with Kynar, one of only two types of roofing suitable for potable rainwater.  The other type is TPO, a white membrane roofing.  Because of the shallow 1:12 pitch, these standing seams needed to be crimped upon installation, rather than just snapped in place the way they are connected on steeper roofs.  To assure weathertightness, a high temperature underlayment covers the entire roof, a second layer of protection from the incessant Seattle area rain.

 

The color of the roofing is a nice steely gray called “preweathered zinc,” though it is important to note that it is not actual zinc metal but instead a PVDF “paint.”  True zinc would leach off the roofing and sully both the drinking water and the irrigation water.  And of course our roofing color has a Solar Reflective Index of 34, so that it reflects unwanted summer heat.

EHH week 17: resilient design

Most houses are totally dependent on municipal utilities for power and water, what a friend of mine calls “life support.”  Cut the utilities, and the occupants are left to freeze in the dark while their food rots. 

 

A major goal for Harvest House’s owners is to be able to withstand all nature’s calamities in their house.  In the Seattle area these include earthquakes, floods, and wind.  In December 2006, a wind storm left over 1 million without power, some for as long as 5 days. 

 

This house was designed by the structural engineer, Harriott Smith Valentine, to the strength of a critical facility, like a hospital or an airport control tower.  The building is superinsulated, has a root cellar to store food, and has four huge tanks in the basement to store rainwater.  Without any operating equipment, the occupants will have shelter, warmth, food, and water. 

 

Factor in its solar energy systems, and this house can enable its occupants to live in complete comfort for at least 3 weeks.  With both photovoltaic (solar electric) panels and solar hot water tubes, which are backed up by batteries and a propane generator, the lights will glow, the refrigerator will stay cold, the oven can warm, the heat will flow, and the water will be potable.  By rationing their usage of electricity, they could live independently for many months.

 

With climate change ratcheting up the frequency and intensity of storms and droughts, there is a growing interest in what Alex Wilson calls Resilient Homes.  Alex and Jerelyn Wilson of Building Green visited Eastside Harvest House in October 2011.

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 15: continuous exterior insulation

The big problem with insulating stud walls is…the studs.  Wood only insulates to R-1 per inch of thickness, while most insulation used in wood stud walls is more like R-3.5 per inch.  So every 24 inches we have a stud that lets out 3.5 times as much heat as the insulation next to it.  These passages for heat to escape are called thermal bridges.  They reduce a 2x6 at 24” stud wall with R-21 insulation from a potential R-23 wall (including all the material layers) to an effective R-20.5 wall, an 11% reduction.  If the studs are spaced closer at 16” it is even worse, an effective R-19.4 wall, a 16% reduction.

 

In order to reduce thermal bridges in the walls of the Eastside Harvest House, we decided to wrap them in rigid foam insulation.  At 2 inches thick, the foam adds another R-9 to the wall, for a potential R-32.  Significantly, the wrapped wall is an effective R-30, only a 7% reduction and one and a half times as good as the effective R-20.5 of the unwrapped wall.

 

Rigid foam is plastic resin foamed with a gas that can contribute to global warming. The worst offender in this regard is XPS (extruded polystyrene, often colored pink or blue or green) which is foamed with a greenhouse gas over 2000 times worse than CO2, the major climate change gas.  We used EPS (expanded polystyrene, usually white) instead which is foamed with pentane, only 3 times worse than CO2.

EHH week 14: concrete floor topping

The finished floor upstairs will be a polished concrete topping.  At just 2 inches thick, the concrete has pea gravel aggregate and is reinforced with steel mesh.  It was pumped into the house, then screeded and troweled to a smooth, flat surface.  Flat is crucial for the floor polishing to look good.

 

The subfloor is red!  The color comes from a waterproof coating sprayed over the entire plywood subfloor.  Since concrete is wet at first, we did not want all that water to soak the plywood that Model Remodel so carefully protected from rain all summer.  The coating also acts as a bond breaker, allowing the concrete to shrink and move independently of the plywood.

 

Since the finished floor will be “cast in concrete” it was crucial to lay out all the floor penetrations before the concrete is poured.  Items like electrical outlets, heating grilles, and some plumbing pipes were blocked out to the precise size of each recessed item.

 

The pour was done in two halves on two different days with a “cold” joint between.  After the concrete had hardened, control joints were saw cut into the surface using a wet saw and a vacuum to limit dust.  These joints are intended to control the surface cracks as the concrete dries so they fall in nice straight rectangular lines, instead of unsightly jagged cracks.  Both these joints will be filled with caulk to match the color of the concrete once it is polished.

 

A week after pour day, still no cracks!

EHH week 13: window spray test

If you have ever driven past a building wrapped in a tent, then you have seen the sad result when rain gets into the exterior of a building.  Eastside Harvest house aims to last for a century or more, so it has to be really good at keeping rain out.

 

Fortunately, a couple decades of studying rain intrusion failures have increased professional understanding of what does not work, and of what does.  We consulted a building scientist for this house because they have developed details at windows and other wall penetrations that effectively keep rain outside where it belongs.  And then we tested the first window installation to make sure we were right.

 

The test, ASTM E1105, is essentially an artificial rain storm.  An array of sprinkler heads sprayed water on the outside of the window at the rate of 5 gallons per hour per square foot.  Inside, a fan combined with a plastic sheet tried to suck the water in through any gaps, simulating wind-driven rain. 

 

The pressure gauge read 0.397 inches of water column, equivalent to 100 pascals, which is twice the pressure that we will be using later to test the whole house for air leaks.  The torture test lasted 15 minutes and if there was no sign of water inside, then the window passed.

 

It passed!

EHH week 12: view from house

The walls are framed and the rough window openings are all in place.  Now we can walk around inside and get a physical sense of the interior space.  And we get our first real look at the actual view out the main windows. 

 

The main great room (living, dining, and kitchen in one room) and the mother in law great room both have large windows with clerestories (a second row of upper windows) plus corner windows.  All these windows admit lots of daylight even on cloudy days.  And they afford a panoramic view over the lake to the mountains beyond, capturing one of the main assets of the site.

 

I have to say, the view is pretty spectacular!

EHH week 11: roof venting

The roof of this house is one large plane tipped up to the western view.  This shape allows us to stay under the 25 foot height limit (not easy to do with a two story house) and simplifies rainwater collection because everything flows towards one side of the house.

 

Because we are superinsulating, we are using the full depth of the roof joists for blown-in insulation.  Well, all except the upper 1-1/2 inches which must remain void to ventilate the roof.  This 1-1/2 inches allows air to carry away any vapor that condenses into water on the underside of the sheathing.  Without the ventilation space, the roof structure would rot.

 

The ventilation space must run continuously from the eave at the low end to the eave at the high end in every single joist bay.  I like to think of an ant crawling on the underside of the plywood from one edge of the roof to the other. 

 

Trouble is, seismic design wants to have the roof sheathing fully nailed at its perimeter to the tops of the exterior walls.  On this house, we solved the issue with semicircular holes in the perimeter blocking that allow nails between the holes.  At the rakes (the sloping sides of the roof) we had to lower the required cross blocking to avoid blocking the air passage.  And at the one part of the roof that is overframed, we drilled over 100 holes through the lower sheathing to let air pass up and out.

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 09: advanced framing

Houses are usually built from wood, a lot of wood.  For this project, we decided to employ the Advanced Framing method to reduce the amount of wood we used.  The idea is to use just enough lumber for a strong structure, but no more.  This way we save on lumber cost, cut down fewer trees, and as a bonus get more insulation in our walls and ceilings.

The basic strategy is to install studs and joists at 24” spacing instead of the usual 16” spacing.  Additionally, extra studs called trimmers and cripples are eliminated where they can be.  Finally, we make sure that all cavities between the framing can be accessed from inside by the insulators so we don’t end up with any cold spots.  Sometimes in Advanced Framing the double plate at the top of the walls is just a single plate, but on this house aiming for extra seismic strength, we went with a double top plate.

The key to advanced framing is to stack roof joists over walls studs over floor trusses, all at 24” spacing.  That way the weight of the building gets transferred efficiently straight down to the foundation.  Windows and doors will interrupt this vertical path, and then headers are installed.  But the headers are sized individually depending on the specific load on each, rather than just using one standard oversized header at every opening.

 

EHH week 08: HVAC precon

This house will be heated (and sometimes cooled) by air running through ducts out to each of the rooms and back from some of the rooms.  There are actually quite a lot of ducts in this house, and the trick is routing them through the structure so they stay hidden above the ceiling or inside the walls.  Easier said than done.

Anticipating this common design problem, VELOCIPEDE made a 3D model of all the ducts to assure there was a viable route from central mechanical room to perimeter windows.  Then once the main floor was framed, the architect, mechanical engineer, general contractor, and HVAC contractor spent a couple hours at the site spotting the route of each and every duct.

This on-site planning effort is called a “precon” for preconstruction meeting.  We considered not just the ducts, but also the plumbing pipe routes, structural obstacles, and architectural niceties like centering grilles below windows.  There were (as there always are) a few problems that we had to work out in the precon.  For example, we had to change four 8” ducts serving the great room to three 9” ducts to better fit in the available joist bays.

Then we marked the chosen routes and grille locations right on the structure for the subcontractor to follow at install.  A couple hours of planning effort should avoid problems and make things go smoothly later on.  Remarkably, duct layout is usually left to the installers to figure out the day they arrive on site with a truckload of ducts and fittings.

 

EHH week 07: rain battles

Rain in July?  Is there no way to avoid rain in the greater Seattle area?

The project schedule was carefully planned to have wood framing occur in the driest months of the year, July and August.  But “summer” 2011 has been surprisingly rainy, including a whopper of a thunderstorm on 18 July 2011.

Fortunately, Model Remodel is on top of things.  Lumber waiting to be installed is wrapped with tarps and up off the ground.  Lumber that has been installed is protected with tarps.  And if rain does get on the floor deck or concrete slab, then the contractors use squeegees to push the puddles away and fans to blow dry things out.  Fortunately, most morning drizzles are followed by sunny afternoons, so drying usually occurs the same day.  Still, nail heads show telltale rust indicating they have gotten wet.

We really wanted to keep the lumber dry to avoid any mold problems later.  Under a microscope, wood is like a bundle of straws and they wick water and tenaciously hold onto it.  I like to think of framing in the rain as wearing a cotton T-shirt in the rain.  Both get wet and must be actively dried out or they will mold.

It will be a relief to get the roof on this building to help keep the weather out.

 

EHH week 06: sustainably harvested wood

The carpenters have begun!  We are rising out of the dirt and starting wood framing.  So let’s talk about wood.  Thinking of trees as just a source of wood is not seeing the forest for the trees.  

Trees are a key element of a forest ecosystem, and standard logging practice is brutal to that ecosystem.  Forests provide animal habitat, stabilize soil slopes, buffer rain runoff, transpire water back to the atmosphere, shade the surface of the earth, convert carbon dioxide into oxygen, and reduce the heat island effect.  Clearcut stump fields do none of those.

Back in 1993 an organization called the Forest Stewardship Council was formed to change forest management.  Somewhat akin to organic certification for vegetables, FSC certification assures that the wood used in a building project came from a forest that is both a healthy ecosystem and can continue to produce timber indefinitely.  FSC means no clearcuts, no old growth, is third party certified, and has a chain of custody to track the lumber from forest to construction site.

All the wood material in Northwest Harvest House, all 100%, is FSC certified as well as formaldehyde free.   We got the dimensional lumber (2x6s) from Gray Lumber and the engineered lumber (I-joists) from RedBuilt.  The homeowners paid a small premium for FSC certified material.  The upcharge was worth it to them because they wish to support healthy forests.  Think of it like a donation to the Sierra Club.

 

EHH week 05: avoiding pressure treated lumber

Part 2 of the quest to avoid toxic chemicals in this project (see week 4 for part 1).  Get ready for some acronyms.

Chemicals to keep wood from rotting, called PT for “pressure treated,” are by their very nature not “natural.”  I mean, wood in nature is supposed to rot.  But nobody wants rotting wood in a house.  So the wood treatment industry injects toxic chemicals into the cells of PT wood to prevent rot.

For decades, CCA (chromium copper arsenic) was used for PT.  But under pressure from the EPA (Environmental Protection Agency), CCA was phased out as of 2004.  Alas, there are still thousands of playgrounds with arsenic wood in this country.

Replacing CCA are ACQ (ammonium copper quaternary) and CA (copper azole). While the chromium and arsenic are gone, the copper remains.  And unfortunately it leaches out of the wood over time.  Copper is toxic to aquatic life if, or should I say when, it gets into the water.  So it is best to avoid PT lumber altogether.

The two most common places for PT lumber in a house are the mudsills and exterior decks.  The best way to deter rot is to keep wood dry.  Not an easy task in the rainy Pacific Northwest.  But we figured out how to do it.

Mudsills are the pieces of wood immediately on top of the concrete foundation wall.  Concrete in contact with the earth is always damp, and the moisture rots this critical piece of wood.  For this house, we isolated the mudsills from the concrete with an adhesive rubber membrane so no PT chemicals are needed.  

The exterior decks of the Northwest Harvest House are made of naturally rot resistant wood decking (ipe).  Supporting the decking is framing made of steel, so no PT lumber was necessary.

We did have to compromise when the electrical utility insisted on pressure treated lumber for the temporary power post, the only stick of PT lumber in the project.

 

EHH week 04: avoiding PVC

To reduce the toxicity of our work, we are systematically avoiding materials that are considered to be harmful to humans and the environment.  We even oiled the concrete forms with olive oil instead of the typical diesel oil.  It is surprising, and sad, how common these toxic chemicals are in buildings and it takes a lot of diligence to avoid them.  This post is a story of mostly victories but also a defeat.

PVC (polyvinyl chloride) is a plastic used to make many, many products because it is cheap and durable.  But its manufacture generates chemicals such as dioxins, pthalates, lead, mercury, and vinyl chloride monomer that cause cancer, harm the nervous system, and damage reproduction.  Worse, most of these chemicals are PBTs (persistent bioaccumulative toxins).  PBTs never seem to go away, and are now found in the breast milk of humans worldwide, and even in the tissues of polar bears and penguins.

We have worked hard to find PVC-free alternatives, starting with the site utilities.  The underslab plumbing pipe is ABS, the footing drain pipe is CPEP (polyethylene), and the sanitary sewer pipe is cast iron.  In all cases, the subcontractors arrived at the job site with PVC in their trucks, and Model Remodel had to send them back for an alternative.

We did end up using PVC for buried conduit, however.  The only legal alternatives are galvanized steel, which the electric utility rejected, or HDPE, which would have delayed the project for 6 weeks.

 

EHH week 03: foundation

The lower floor of the new house will be a concrete box, with full height foundation walls on all four sides.  These walls will be exposed, so the concrete subcontractor had to take extra care to layout the form boards and the snap tie spacing.  They did a beautiful job!  Amazingly, the long diagonals are only 1/16” different, meaning it is perfectly square.  The tall downhill wall is flat and plumb, a real work of art.

We are building this house from recycled materials.  The steel rebar is 100% recycled steel.  Under the slab on grade, instead of gravel we are using 100% recycled glass, called “cullet.”  It comes from the local curbside recycling bins that collect glass bottles.  The concrete wall has a brown dimpled drainage mat on the inside, made from 60% recycled HDPE.

The concrete mix contains blast furnace slag, a waste product from smelting iron into steel.  The slag has the added benefit of reducing the Portland cement from a typical 5-1/2 sacks per cubic yard (517 pounds) to only 2-1/2 sacks (235 pounds) without a loss in strength or durability.  Manufacturing 1 ton of Portland cement requires 6 million BTU of energy, so we are reducing our energy consumption before the house is even operational.