Insulation

Now that everything that goes inside the wall cavities has been installed, it is time to fill those cavities with insulation.  We used several different types of cavity insulation in addition to the rigid EPS insulation that was installed on the exterior walls during framing.  The highest performance readily available type of insulation is closed-cell spray foam.  It provides over R6 per inch of thickness and also does a good job of air sealing.  However, it is the most expensive and also has environmental impacts due to the materials used in its manufacture.  Therefore, we used closed cell spray foam selectively in a few places where its properties would help the most.  Cellulose insulation is the most affordable and environmentally friendly common insulation product, so we used cellulose for the hangar/garage walls and for the attic spaces.  Cellulose is not recommended for basement walls.  Also, our insulation contractor was not comfortable installing cellulose in the walls that have exterior rigid foam.  Therefore, fiberglass insulation is used in the basement and exterior walls.

Closed cell spray foam is used in the rim joist areas and on top of the wall top plates in the attic.   Over the top plates, it is used for its air sealing capabilities.  The air barrier of the ceiling is a polyethylene sheet.  The air barrier at the walls is the OSB sheathing.  The spray foam connects these layers to one another to avoid air leakage between components.  The ceiling air barrier gets interrupted at interior walls, so spray foam is applied over the top plates of the interior walls to connect the ceilings of adjacent rooms and prevent air leakage through interior walls.  Some of the spray foam is applied before drywall installation and some of it will be done later.

Some rooms have vaulted ceilings.  In these rooms, access to the outside top plates will be difficult after the ceiling drywall is installed.  To get spray foam on these top plates, a piece of poly sheeting is installed and held in position by a temporary piece of OSB while the foam is applied.  The OSB gets removed before drywall is installed.  The grey baffles provide an air pathway from the soffit vents to the attic after the insulation gets installed.  Notice on the right of the picture, the spray foam installer had to create a psuedo top plate using some fiberglass batts in order to have a surface to spray against.

In the rim joists, the spray foam reduces heat leakage via the top surface of the concrete wall.  The air sealing properties also supplement the peal and stick air barrier on the outside of the rim joist to prevent air leakage.

The framed exterior walls in the basement are insulated with unfaced fiberglass batts.  The rigid EPS between these framed walls and the cement wall keeps the cavities warm enough to prevent condensation.

In the hangar and garage, cellulose is installed in the walls using the damp-spray method.  Enough water is added to the cellulose to make it stick.  Most of that water dries before the drywall is installed.  It can continue to dry later because the drywall and the OSB on the outside have some vapor permeability.

The insulation contractor was uncomfortable using damp-spray cellulose for the house walls because the rigid foam on the outside would prevent any drying toward the outside.  So, we used a blown-in fiberglass method.  Fabric is stapled to the studs.  Then, fiberglass is blown into each stud bay through holes in the fabric.

This picture of our stairwell shows the blown-in fiberglass process.  On the first floor, the fabric has been installed but the insulation has not yet been blown in.  On the second floor, the insulation material has been blown in.  When the drywall is installed, the fiberglass will get compressed.

This is the master bedroom with the walls and ceiling insulated.  For some reason, the contractor decided to staple a layer of polyethylene on the walls after blowing in the fiberglass.  That was removed before the drywall got installed.

Rough Electrical

Once all of the ductwork was completed, the electrician came to run the wiring.  Since much of the wire runs through exterior walls and the attic, the wiring must be finished before the insulation is installed.

The electric and gas meters were installed several months ago.  Since then, various contractors have been using a single temporary power circuit.  Unfortunately, the logical place for the meter on the outside of the house did not coincide with a logical place for the electrical panel on the inside of the house.  Consequently, we installed a split service, resulting in an extra exterior switch near the electric meter and a massive wiring bundle across the basement ceiling to the utility room where the electrical panels are located.

We have a "smart meter" that will send the utility our usage for every 15 minute interval.  It also sends our natural gas usage (we get both from Consumers Energy).  The box on top is an exterior switch.

Many of our decisions were based on things we plan to do in the future.  We plan to eventually get a natural gas powered generator, solar panels, and an plug-in electric vehicle.  In anticipation of eventually getting a generator, we decided to separate the large electrical demands that we would not need during a power outage.  We were surprised at how short our list ended up:

• air conditioner,
• range,
• dryer,
• central vacuum,
• a few lights and plug circuits,
• the 30 Amp circuit for the motorhome,
• the 220V circuit for a potential future plug-in vehicle, and
• at some point, inverters associated with solar panels

I guess we want to ensure that we won't be expected to do housework during a power outage.

Although we don't plan to install a generator right away, we prepared to eventually have one.  We divided our circuits into critical loads (in the left electrical panel) and other loads (in the right panel).  When the generator runs, the middle box will isolate all of the critical loads from the utility grid.

Instead of a single temprary power circuit, there are now a few.  Later in the construction process, after the drywall is installed, the electrician will return to hook up the light fixtures and plugs and connect all the dangling wires to circuit breakers in the panels.

HVAC 3 - Ventilation

Installing the ventilation system caused a several week delay.  For reasons I will discuss below, I insisted on installing a Renewaire ERV to provide ventilation.  Since the HVAC contractor doesn't handle Renewaire, he asked me to procure the unit.  Well before the unit was required, I found an online retailer that advertised carrying Renewaire and asked about delivery time.  They replied that a unit would arrive about a week after the order was placed.  I placed the order a couple weeks before it would be needed.  After a couple weeks, I contacted the retailer to ask why it had not yet arrived.  They said they had forwarded the order to Renewaire who would be shipping it directly.  After another week, I called Renewaire.  Renewaire had never received an order and said they had problems in the past with that retailer.  I cancelled the order and ordered it through another retailer that was recommended by Renewaire.  Just as the unit arrived, the weather turned hot.  The HVAC contractor spent the next week responding to service calls from people whose air conditioners weren't working.  Finally, three weeks after finishing the rest of the HVAC rough-in, the contractor was able to return and rough-in the ventilation system.

Rough electrical work was delayed until the ductwork for the ERV was completed so that the ductwork would not need to be routed around wiring.  I am glad they were done in that order because it was difficult to find a route for the ERV ductwork even without the wiring.  I downloaded the ERV installation instructions online and asked the HVAC contractor to do the ERV ductwork at the time of the other rough-in using these instructions.  That would have prevented the delay from cascading and delaying the entire project.  However, he was not willing to do that.

Why do we need a ventilation system?

Building science professionals bristle at the old saying that houses need to breathe.  However, they recognize the need for adequate ventilation and the need to avoid excessive ventilation.  Occupant activities within a house, such a breathing, cooking, etc. produce various types of pollutants.  Ventilation exchanges the polluted indoor air for less polluted outdoor air.  During much of the year, the incoming outdoor air must be conditioned which increases heating and cooling usage, so over-ventilating is a problem.  Traditionally, houses had enough random leaks to provide adequate ventilation.  Even with a leaky house, some force must push air through the holes.  In winter, a force called stack effect tends to pull air in through low holes and out through high holes.  In summer, the stack effect reverses.  Also, wind causes pressure differences around the house that pull air in through some holes and out through others.  Unfortunately, cold, hot, or windy weather does not necessarily occur at the times when ventilation is needed.  For a typical new construction house, the result is excessive ventilation sometimes and insufficient ventilation at other times.  For a leaky house, like many older homes, the result is slightly excessive ventilation sometimes and way too much at other times.  A mantra among building science professionals is "build tight and ventilate right."  The goal is to control the amount of ventilation, control which indoor air is expelled (since it is not equally polluted), and control where the incoming outdoor air is drawn from (since it is not equally fresh).

Why an ERV?

There are various methods of providing forced ventilation in houses.  Most houses have fans, such as bath fans or range hoods, to expel air during periodic activities that cause localized pollution.  One method to ensure adequate ventilation, called exhaust only ventilation, is to run a bath fan on a timer so that it runs a fraction of every hour.  Outdoor air then flows in through whatever holes exist in the enclosure.  This method provides control of the amount of ventilation and controls which air is expelled, but does not control what air comes in.  Another method, called supply ventilation, is based on having the furnace fan draw in some outside air through a dedicated duct.  This provides control of where the fresh  air comes from.  With a damper and appropriate controls, it also provides control of the amount of ventilation.  Air leaves through whatever holes exist.  This is the type of system that the HVAC contractor proposed although he did not plan to install the damper and controls.

The third type of ventilation system is a balanced ventilation system.  One fan brings air in through a dedicated duct while another fan expels the same quantity of air through another dedicated duct.  This provides control of the quantity, the source of the fresh air, and the source of the expelled air.  Additionally, there is an opportunity to run the incoming and outgoing airstreams through a heat exchanger to precondition the incoming air.  This reduces the heating and cooling energy use.  Systems that exchange only heat are called Heat Recovery Ventilators, or HRVs.  Some systems also transfer humidity between the airstreams.  These are called Enthalpy Recovery Ventilators or ERVs.  Since few people know what Enthalpy is, some vendors call them Energy Recovery Ventilators instead.

Why a Renewaire EV130?

This picture from the Renewaire website shows what is inside an EV130.  The tilted rectangular part on the left is the crossflow heat exchanger.  A single motor on the right drives two fans, one for the incoming airstream and one for the outgoing airstream.

There are many manufacturers of HRVs and ERVs.  They use a few different methods of transferring heat and, for ERVs, moisture between the airstreams.  They range widely in price and in heat and moisture transfer effectiveness.  One issue that comes up in cold climates is a tendency of outgoing warm moist air to form frost as it looses heat to the incoming air.  Manufacturers deal with this in various ways.  I chose a Renewaire ERV for the following reasons:

• The balance between price and efficiency fits my goals.
• Renewaire has been making ERVs for a long time.
• It prevents frost by tranferring enough moisture out of the outgoing airstream relative to how much heat is transferred out of the outgoing airstream, so no special defrost modes are required.
• Renewaire supports using the ERV to replace bathroom fans.

Experts disagree on exactly how to calculate the required amount of ventilation.  Several formulas are available.  The highest quantity using any of these formulas for our house is about 125 cfm, so I want a unit that will provide at least that much.  When replacing bathroom fans, Renewaire recommends at least 50 cfm per bathroom.  Since we have four bathrooms, I initially selected the EV200.  However, when I changed retailers, I was told that the EV130 would ship about a week sooner than the EV200, so I changed plans and decided to replace only some of the bath fans.

Installation

Renewaire supports several different ducting arrangements.  I elected to draw air from three of the four bathrooms and supply fresh air to the return air ductwork.  (The bathroom without a shower doesn't need a full 50 cfm).  A control next to the thermostat sets the percentage of each hour that the ERV will run.  A control in each of the bathrooms forces the ERV to run in circumstances in which a bathroom fan would be operated.

The ERV is mounted on the ceiling in the shop.  The insulated flex duct to the left connects to the outside air intake.  The duct to the right connects to the outside air exhaust.  The two that run between ceiling joists connect to the bathrooms and furnace return respectively.  (Insulated duct is not necessary for these last two, but that is what the installer used.)

Most of the ductwork from the bathrooms to the ERV is 6" rigid round or oval duct.

The air outlet and inlet are under the balcony in the back of the house.  They must be separated by at least 10'.  The other outlet near the ERV exhaust is the dryer vent.  

The bathrooms switches are wired with 24V wiring, so the electrical box has a divider to separate it from the 110V light switch.

Siding

The outside is looking more like a house as the siding is installed.  The siding is Hardie Board cement fiber siding, which will eventually be painted.

The front of the house with the siding installed.  The remaining areas will have brick.

A closer view of the dining room window.  The trim is wider than I was expecting but I like it,

The crew in the process of installing the siding on the back of the house.

The back of the house with the siding completed (and the balcony framed)

The crew working on the siding above the hangar door.

HVAC 2 - Ducts

Having settled on a central forced air furnace and air conditioner, ducts need to be installed to distribute the air throughout the house.  The conventional approach is to place supply registers on the floor under each window.  However, for low heating load homes, articles from NREL the Department of Energy, and Energy Star recommend compact duct system.  In a compact duct system, supply registers are located high on interior walls and blow the air across the ceiling toward the windows.  Attempting to apply this philosophy to our house runs into a problem - we have relatively few interior walls.  As I walked the house with the HVAC contractor to discuss duct placement, I learned that we have even fewer usable walls that I thought.  He explained that walls that are aligned with a floor joist are not accessible from below, so they are not suitable for ducts.  I wish I understood these constraints back when I was designing the floorplan.  For the most part, we ended up with registers under the windows.

We elected to set up three zones: first floor, second floor, and basement.  However, some rooms on the first floor will be part of the second floor zone.  That will make the heating loads of the zones closer to equal.  The office will tend to get solar heat gain from the window at the same times that the master bedroom on the second floor does, so it makes sense to have them in the same zone even though they are on different floors.

The duct system begins and ends at the furnace.  A MERV 13 filter is between the return duct on the right and the furnace.

One set of trunk ducts run from the furnace along the front side of the basement.  The duct on the right is the return trunk.  One of the ducts on the left supplies the first floor zone while the other serves the basement zone.  A shorter set of trunk ducts goes the opposite direction from the furnace to serve the second floor zone.

Zone dampers are installed in each supply duct where it connects to the furnace plenum.  There are four zone dampers, but two of them will be wired to open and close at the same time such that there are only three zones.

This shows a return duct and a supply duct routed through an interior wall on the first floor to the master bathroom on the second floor.  Most of the return ducts are created by closing off a stud bay.  Some articles advise against this practice, but the reasons seem most applicable to ducts located outside of conditioned space.  Return ducts formed this way must be on interior walls.  The supply ducts use oval metal duct within a stud bay.  It is better to route supply ducts through interior walls, but we were forced to use exterior walls in some locations.  Fortunately, even in those locations, the ducts are still inside of the rigid foam insulation.

This is the only usable interior wall on the second floor, so the return ducts from the master bedroom and master closet had to be placed in this wall.  The PVC pipe in the other stud bay is a radon vent from the sump pump to the roof.  We don't have any reason to suspect a radon problem, but adding a radon vent later if radon is detected would be much more expensive than now.

Finding a place for the supply duct for the master bathroom was particularly challenging.  Wall registers are preferred in rooms like bathrooms that get wet floors.  Due to the structure under this room, there was no way to route ducts from the basement into any of the walls of this room.  After much head scratching, we concluded that the tub base was a viable option.

The kitchen, at least, was straight forward.  The supply duct will be under the sink in the island.

Lots of things compete for space along the basement ceiling.  Two supply trunk ducts are on the right.  The two parallel PVC pipes are the combustion air and vent for the furnace.  The PVC pipe on the left side of the black beam carries water away from the sump pump.  The two round ducts are supply ducts for the powder room and the basement ceiling respectively.  The red and blue PEX tubing are hot and cold water lines to the powder room and the guest bathroom.  The PVC pipe running parallel to the joists is the powder room sink drain.  The black pipe is the natural gas supply to the furnace.  That small white tube is, uh, I guess I would have to trace that one.

HVAC 1 - Heating and Cooling Equipment

Warning: This is another of my more technical posts.  There are no pretty pictures.

This post addresses two parts of the HVAC system, the Heating and the Air Conditioning.  The other part of HVAC, Ventilation, will be addressed in another post.

In Michigan, most people install a natural gas forced air furnace and air conditioning.  Those willing to spend money on a premium system consider radiant floor heating.  However, highly insulated houses have some differences from typical houses which can change what types of heating a cooling systems are appropriate.  Homes which take insulation and air tightness to extremes, such as those that conform to the Passivehaus standard, usually end up with different types of heating and cooling systems, such as one or two mini-split ductless heat pumps.  In terms of insulation, this house falls into a middle ground between typical houses and Passivehaus houses.  So, it wasn’t obvious whether our systems should be like typical houses, like Passivehaus houses, or some other choice.  (Well, maybe it would have been obvious to someone with less tendency than me to over-think these things.)

Highly insulated houses have a much lower heating demand than typical houses.  Why wouldn’t they just use smaller versions of same types of systems that typical houses use?

•  Mainstream HVAC equipment manufacturers don’t attempt to serve the highly insulated house market.  The range of equipment sizes offered is based on typical house heating loads.  In fact, most equipment installed in typical houses is considerably oversized.
•  Distributing heat is easier in a highly insulated house since the heat is not escaping as quickly.  That opens up some possibilities.  However, the warm floor feeling that many people like about radiant floor heating would not be so noticeable in a highly insulated house.
•  People interested in net-zero homes prefer all-electric systems, which can be supplied by PV panels.
• Ironically, spending more for highly efficient equipment is less likely to pay off in a low load home.  People who have spent extra money for insulation may want to recoup some of that by spending less on heating and cooling equipment.

For any type of equipment, the first step is to calculate the design heating and cooling loads.  The heating load includes heat lost through walls, windows, ceiling, etc. due to conduction and also heat lost due to air leakage and forced ventilation.  For my location, the design heating load is calculated at 7 degrees F.  Although the temperature gets colder than this, it rarely stays colder than this for long periods.  The design heating load ignores various internal heat gains like solar gain through the windows, use of the fireplace, appliances, and people.  These heat gains, and the thermal mass of the house and contents, sustain the inside temperature when the outside temperature drops below the design temperature.  Also, the equipment is usually sized at least a little larger than the design heating load.  The design heating load came out to 34,000 btu/hr.  The design cooling load, which is calculated at 88 F, came out at 18,000 btu/hr.  Design cooling load does include some internal gains.

The first option I considered was a ground source heat pump (sometimes called a geothermal heat pump).  Instead of creating heat by burning fuel, a heat pump moves heat that already exists.  To move a btu of heat from a cold place to a warm place requires energy but, if the temperature difference is small enough, it requires less than a btu of energy.  The advantage of a ground source heat pump is that the heat is being moved from the ground which, in theory, is a constant, moderate temperature.  The heat is extracted from the ground by fluid that flows through buried tubes.  In summer, the same process is used to transfer heat into the ground to provide air conditioning.  Unfortunately, heat transfer from solid ground is not very efficient.  A lot of tube must be buried to transfer enough heat, which gets expensive.  Even then, the temperature of the dirt near the tubes is not constant due to the heat being extracted.  I was dissuaded by a number of articles on Green Building Advisor that found that the extra efficiency of a ground source heat pump relative to a modern air source heat pump is not worth the additional cost.

That takes me to the next option I considered – mini-split heat pumps.  These move heat from the outside air.  Traditionally, air source heat pumps have been out of favor in cold climates because the capacity and efficiency declines when the outside temperature gets lower.  However, technical advances have made them a practical cold climate alternative.  A ductless mini-split provides the conditioned air directly to the room as opposed to blowing air through ducts.  This improves efficiency but requires equipment on the wall which raises an aesthetic concern.  Another issue is how well the heat is distributed from these units to other rooms.  A ducted mini-split can serve several rooms though a small duct network.  Ducted units give up a little of the efficiency but improve heat distribution.  One thing that builders of super-insulated houses like about mini-splits is that they are available in small capacities – as low as 6000 btu/hr.  They use electricity instead of natural gas which is great if you want to use PV panels to achieve net zero.  In Michigan, however, electricity is much more expensive than natural gas.

A related option is an air-to-water heat pump, such as the Chilltrix system.  Whereas a mini-split relies on refrigerant lines between the outdoor unit and the indoor unit, an air-to-water heat pump retains all of the refrigerant within the outdoor unit.  The heat is transferred between indoor and outdoor units by water lines.  This enables smaller indoor units.  Other than this distinction, the advantages and disadvantages of air-to-water heat pumps are similar to those of mini-split heat pumps.

Eventually, a fuel price comparison convinced me that a natural gas solution made more sense than an electric solution.  Some builders of low load homes have taken advantage of relatively low natural gas prices by installing a combination space heating and domestic hot water system (sometimes called a combi-system).  Domestic hot water is supplied by an efficient natural gas water heater, such as an HTP Phoenix Light Duty.  Hot water is circulated through coils in a hydronic air handler to provide space heating.  Trying to get local contractors to quote and install a combi-system proved difficult.

In the end, I decided on a conventional natural gas furnace.  The smallest size most companies offer in most models, including their modulating models, is 60,000 btu/hr.  (An exception is a Canadian company called Dettson that sells modulating furnaces starting at 15,000 btu/hr.  I ended up ruling out this option due to unfamiliarity to local contractors.)  However, some two-stage high efficiency furnaces are available with an input capacity of 40,000 btu/hr.  The output capacity is 25,000 btu/hr on low stage and 39,000 btu/hr on high stage which is a good match for the house’s heating load.  The smallest available air conditioning unit is 1 ½ tons which is a good match for the cooling load.

The British say that Americans can be counted on to do the right thing, but only after they have tried everything else.  I guess I am willing adopt the conventional solution, but only after I have ruled out all other possibilities.

Basement, Garage, and Hangar floors

Once the plumbing under the basement floor was in place, the concrete could be poured.

In preparation for pouring the concrete basement floor, a layer of  plastic vapor barrier is placed followed by a 2" layer of high density EPS foam.

This shows the basement floor shortly after the concrete is poured.  The high density EPS extends a few inches up the sides to slow heat conduction from the floor to the concrete walls.

The garage and hangar floors did not need to wait on plumbing, but did need to wait for conditions to dry up a bit.  The garage floor slopes slightly toward the garage door while the hangar floor slopes slightly toward the hangar door.

A vapor barrier is placed under the garage and hangar concrete floor,  A chalk line on the wall indicates the level of the top surface of the concrete.  Rebar ties the floor into the basement wall. 

This shows the garage floor in the middle of the pouring process, while waiting for another truck to bring enough concrete to finish this section.

The hangar floor was poured in two sections on different days.  The two sections will be the same color after a few more days.