Insulation Investigation

We all know the benefits of insulation; the more insulation, the warmer your house will be right?  Well, that's true in a sense but not entirely.  The reason for this is various factors including insulating location, insulation type, rates of heat transfer of building materials, and wall and roof assemblies allowing for insulation access.

R-value is a term used when discussing the insulating value of a construction material.  It is defined as heat transfer per unit area, or a measure of thermal resistance.  The higher the R-value, the better your home will be to resist the warm inside air to move toward the colder outside air (vice versa in warm climates).  With that said, R-values are not "etched in stone".  For example, damp fiberglass insulation has a lower R-value than its dry counterpart and R-values change in different temperatures or if wind is applied to the equation.  Certain insulations such as closed-cell polystyrene foam have a higher R-value per inch (~6.5) versus fiberglass fibers (~3.5), not to mention their air sealing characteristics.  Laboratory measurements are always different than the real-world performance.

One must think of R-value as it relates to the entire system; the wall, roof or floor for example.  Thermal bridging and the conductance of warm air to cold air (to be discussed later) can drastically decrease what you may think is a super R-value wall.  Let's say I have a 2x8 stud wall placed 16" on center.  These stud walls extend from the inside to the outside of the structure, essentially bridging one space to the other.  Despite filling the voids between the studs with closed-cell spray polystyrene foam (~R-6.5/inch, 6.5x7.5"=R-49!) the whole wall r-value is considerably less because of the combination of the poor R-value of the wood (~R-1.5/inch) and it's poor u-value (the rate of heat transfer-inverse of the R-value).

Another consideration is the location of insulation.  The chimney effect or stack effect is the natural movement of more buoyant warm air rising and as a result pulling in cold air inward from below.  Having more insulation in your roof (whether unvented or vented) as well as in the slab can significantly increase your home's performance.  When talking about the slab that tends to be much colder then the surrounding air above, warm air will travel downward in the direction of the cold, essentially "robbing" the home of heat.  Yes, it makes the slab warmer, but is not keeping the warm air where it should be.

Another location to look at are the sill plates or rim joists, top plates, and truss/wall junctions; anywhere there are two building structures coming together.  These areas are often ignored in building construction and tend to be the areas where up to 25% of heat loss is occurring in your home.  Paying attention to these areas in the design and building of the home can save significantly on heating costs.

As we progress with the building a specific design, I will go through insulating in much more detail.

Clever air sealing assessment

In addition to the ever important blower door test, use a fog machine to expose leaks from the outside of your home.  Reverse the fan to pressurize the house rather than depressurize which is what a blower-door test does.  Place a cheap fog machine in the house, stand outside and watch (hopefully not) the fog seep out of the undiscovered openings.  Do this before the drywall is hung.

Duluth, MN, passive house example

A passive solar home in Duluth, Minnesota

This above link describes a passive solar home constructed in 2009 in Duluth, Minnesota.  I like the concepts of the house and their thought process but think that it could have been less expensive to build and slightly more efficient using a few different methods.

1. Spray EPS foam walls with 4'x8' foam sheets to break the thermal bridge and/or with offset 2x6 wall studs.  Less labor intensive too.  
2. Instead of foam-cut sheets to fit between the floor joists, again use spray foam to offer a better R-value while make for a more airtight section.  Again, less labor intensive.
3. As they mentioned, at least 10% of the floor space to be high performance windows on the south facing elevation, instead of their claimed 8-9%.     
4. The article doesn't go into detail about the air sealing around the window frames.  Taping in this area is a must.

Important to note:  Duluth, MN, yearly heating degree days are very similar to Fort Kent.  Approximately 8,000 for Duluth versus 8,300 for Fort Kent.

Solar PV versus solar thermal?

The following is an insightful article comparing solar pv (solar panels) to solar thermal (evacuated tubing) systems to heat your domestic hot water.

GreenBuilding Advisor-Solar PV vs. Solar Thermal

This and other information that I have collected is pointing me more in the direction of heating both my home and domestic hot water with solar PV, not solar thermal; its simplicity paired with a super efficient heat-pump water heater or electric-resistance water heater would foreseeably make for a less complicated, more hassle-free, higher efficiency system.  

Passivhaus defined

                                         Copyright 2011 G O Logic

The Passivhaus movement was developed by Swedish professor Bo Adamson and German professor Wolfgang Feist in 1988.  They developed a realistic method of building using super efficient materials and efficient concepts that saves 80-90% of home heating costs as compared to conventional new home construction.  The first passive house was built in Germany in 1991, now with about 25,000 houses worldwide.  Passivhaus is now the world standard in energy efficient construction regardless of climate and location.  For a house to be considered "passive" it must incorporate specific building characteristics including the majority of heating from the sun, a super insulated and airtight shell and mechanical air ventilation to achieve a specific volume/hour of air exchange.  To be considered "passivhaus certified" (not to be confused with net-zero homes) the heating load must not exceed 15 kWh/m2 per year.  The Passivhaus Institute certifies building products which meet or exceed their efficiency standards.  Additionally, they have developed a powerful software called PHPP (passive house planning package), a highly accurate energy modeling tool used to calculate the energy requirements of any structure (accuracy of +/- 0.5 kWh).

Eight Building Principles (all to be explained further in future posts) 

1. Super Insulation: significantly reduces heat transfer between the inside and outside of the home.  High R-values (conversely, low U-values) resist the flow of heat down the temperature gradient.  Not only are walls and ceilings considered, but at the ground level and windows as well.  

2. Super Airtight Envelope: very simple-if air is allowed to move back and forth, heat is lost.  At least 40% of a home's heat is lost through ventilation (ie. leaks) even in new construction!  But doesn't a house need to "breathe"?  Sure it does, but I want to know exactly where it is breathing.

3. Thermal Bridging: a thermal break is needing to separate the cold to hot surfaces.  The best insulated wall in the world will transfer heat if thermal bridging is not considered.

4. Heat Recovery: 90% of the heat from the air that mechanically moved out of the house is recovered and brought back into the house. The energy transfer is reversed in the summer, keeping the house cool.

5. Mechanical Ventilation: related with #3.  Because the house is virtually airtight, it needs to breathe to maintain proper humidity levels.  New super high efficient air exchange units (that recover the heat-see above) move the entire home's volume of air in a number of hours, replacing it with fresh outside air and virtually uses no electricity to do so.

6. Highly Insulated Windows: one of the building criteria that people think they are achieving but in fact are not.  There are many window companies that provide surprisingly high R-values (upwards of R-12), unfortunately none of which are manufactured here in the United States.  Certain Energy Star certified windows insulate well (for a limited lifespan-more on this later) but do not let enough solar heat through the glass to provide the necessary heating from the sun.  This is not to mention specific glazing and frame insulation options.  

7. Energy Modeling: using the PHPP modeling software, the efficiency of a design can be calculated before it's built with astounding accuracy.  Prediction of energy usage is a vital component in the design process.

8. Passive Solar Gains: amazing to me to see new homes facing completely the wrong way or having too many windows on the northern exposure.  The home requires many insulated windows on the south facing side and limited windows on the west and north sides.  Conversely, avoiding overheating in the summer with planned shading/overhangs.          

Solar site planning

For a passive solar home to receive the intended ~40% of a home's heat from the sun, proper positioning is crucial.  Solar azimuth angle, solar elevation angle and hour angle based on our latitude and time of year need to be determined for the site of the home.

Below is a map of the path and solar rays for winter solstice, December 21, the day with the least amount of sunlight.  If our home can receive the maximum amount of sun on this day, we can assume the remainder of the year will provide more than enough sunlight for effecting solar heating.

  
Here is another solar diagram which shows the solar elevation angle corresponding to the solar azimuth and hour on that same day.

At noon, when the time of the day when the sun is at its peak (in this case 19.06 degrees), the azimuth angle is 186.6 degrees.  This means we need to orient the southern facing elevation perpendicular to this heading to receive the most direct sunlight on the day with the least amount of sun.  

Here is another chart that represents the same data in a different way.

Here is an example of the opposite solar calendar; summer solstice on June 21st, the most daylight of the year.  Notice the dramatic difference of the angle of elevation and time of day of rise and set as compared to December 21.

The solar azimuth at noon changes to 193.3 degrees.  As stated above, our south facing elevation facing 186.6 (based on December 21 solar geometry) will not be directly perpendicular to the house at this time of year which is advantageous on keeping the house cooler.

Aside from eyeballing this data while at the lot, I have not applied these measurements to the site itself.  I will be using an inclinometer to determine solar light based on the time of day on December 21 and hopefully get at least 9-3pm sun.  Fingers crossed. 
  

Site planning

A lot of thought and consideration has been made regarding where exactly we want our house. Making a decision has been based upon a number of factors including land availability, site access, location from work/school, scenic views, road length, utility installation costs and price.  As our our entire design idea is based upon passive solar, geography, placement and sun availability had to be one of the biggest priorities.   

As a passive solar house costs ~15-25% more as compared to a traditional build, we needed to take into consideration the extraneous costs associated with the site(s) to stay within our budget.  Of the two sites available, one was perfect for a passive solar home, allowing for unobstructed sun from at least 9am-3pm (in the winter) which is necessary to provide sufficient solar heating for a home.  It had magnificient views (although our orientation would not be looking at it) but its lack of tree cover from the west and north made it exposed, with the winter wind buffeting and trying to penetrate our building envelop.  It turns out that our driveway at this site would have been too costly and time consuming to maintain in the winter.  As it was located in a field it would have been ~1,400 feet long with 2 steep sections, clearing drifting snow would have required a large and very costly compact tractor (upwards of ~$40K).  It was also about 4 miles away from town on a busy road; not a far commute by any means but a challenge once the kids got older and had the option and independence of biking to town/school and being with friends.  Moreover, installation of utility poles would have cost at least $6K (and potentially much more by the time we build as prices will be increasing substantially in the near future as our local utility company adopts Bangor Hydro pricing ).  Lastly, ledge would not have allowed for a basement which we wanted for a garage, work shop and storage. 

The second site is about 1 mile from the center of town and offers a slightly shorter and more gradual climb from the main road.  The road will end up being about 200 feet shorter but most importantly it will be protected from the wind so that snow drifts won't be an issue.  It is a heavily wooded lot but will be harvested to allow for the maximum sun exposure.  The amount of clearing is still being determined.  I'm thinking about harvesting several trees on the lot to make into beams for the great room.  They are mostly hardwood, consisting of yellow birch, beech and maple species.  We estimate the tree harvesting from the road and the lot will pay for the ground work and road construction.  Getting electrical lines will be much less expensive than the first site.  Currently, Maine Public Service Company provides the first 300 feet for free and then charges $6.22 per foot.  Our house location would be approximately 350-400 feet from the nearest utility pole, making it substantially cheaper than the first site.   

Below is the proposed road.  Its length is ~1,100 feet with a steep early decent from the main road, leveling off towards a stream and a gradual rise to the home site.

Below is the proposed utility line from my father's existing pole near his garage.  Its length is ~370 feet.

One thing that has remained constant throughout our site determination is our home's orientation to take in the most sun possible during the winter months.  190-195 degrees is required for our south facing windows.

More on sun geometry coming up.