Insulation Cheat Sheet Part 1

Selecting the right type of insulation is far more complicated that simply looking at a product’s R-value. It’s important to understand the entire long term impact of sourcing and using a particular insulation product. This means how and where the product is made, the ingredients, the waste generated during manufacturer and during installation, what happens at the end of its useful life, the R-value as tested, the R-value at extreme temperatures, the R-value long term as it ages, the vapor permeability, the air permeability, the resistance to water, the resistance to rodents and insects, the ease or difficulty in installation, the stability, the availability, and the cost. Rather than doing a deep dive, to make things easier we’ve summarized the most common insulation board products into this quick Insulation Cheat Sheet.



         extruded polystyrene

         closed cell / vapor impermeable

         typical blue or pink under names “Styrofoam” and “Foamular”

         R-5 / inch but loses R value as it ages.  actual R-4 / inch.

         suitable for below grade / underslab / comes in different densities

         blowing agent (currently used in US) has very high GWP and therefore should be avoided.

         High Availability / Low Initial Cost / High GWP

3 Primary Types of Foam Insulation

3 Primary Types of Foam Insulation



         expanded polystyrene

         semi closed cell / essentially vapor impermeable unless very thin

         typically white and made of tiny beads

         approx R-4 / inch

         suitable for below grade / underlab / comes in different densities

         blowing agent has fairly low GWP. 

         Readily Available / Low Initial Cost / Medium Low GWP



         expanded polystyrene with embedded graphite particles

         semi closed cell / essentially vapor impermeable unless very thin

         typically white and made of tiny beads

         approx R-4.5 / inch

         suitable for below grade / underlab / comes in different densities

         blowing agent has fairly low GWP. 

         Medium Availability / Low Medium Initial Cost / Medium Low GWP



         typically faced with foil or felt

         semi closed cell / vapor impermeable

         typically yellowish / off white with silver foil facing or black felt facing

         approx R-6 / inch but less R value at colder temps.  actual R-5 / inch.

         not suitable for below grade or underslab

         blowing agent has lowest GWP of rigid foams. 

most commonly use for commercial roof assemblies; used foam can sometimes be sourced.

         High Availability / Low Medium Initial Cost / Low GWP





         highly vapor permeable / hygrophobic (repels water)

         yellow gold color

         approx R-4 / inch.  maintains R value at cold temperatures

         now suitable for below grade or underslab

8lb per ft3 density / Roxul is most common manufacturer

         low GWP but uses steel mill byproduct / energy intensive

         Readily Available / Medium Cost / Low GWP



         highly vapor permeable / hygrophobic (repels water)

         can be used as exterior finish material if well protected

         approx R-4 / inch.  maintains R value at cold temperatures

         not suitable for below grade or underslab

         low GWP, from rapidly renewable resource,

imported from Portugal

         Medium Availability / Medium to High Cost / Low GWP




         highly vapor permeable / paraffin wax provides weather resistance

         doubles as WRB when used on walls

         approx R-3.5 / inch.  maintains R value at cold temperatures

         not suitable for below grade or underslab

         very low GWP but currently imported from Europe

         Medium Availability / Medium to High Cost / Very Low GWP


More Cheat Sheets coming. Check back soon or subscribe for updates.

Is it a Passive House?

We recently completed a new house that generally meets the criteria for Passive House but is not certified.  Can we call it a Passive House?

all photos by built photo

all photos by built photo

As more people gain awareness of Passive House, many projects claim to be similar to Passive House, using Passive House principals, almost Passive House, etc.  In Germany, Austria, and other European countries where PH is prevalent, it turns out that a majority of Passive House buildings are actually not certified (but have been modeled during design and blower door tested during construction).

modeling results from PHPP

modeling results from PHPP

Conceptually, Passive House buildings must be  superinsulated with high performance doors and windows, thermal bridge free, airtight, and mechanically ventilated with heat recovery,.  Technically, a Passive House must be modeled using special software (either PHPP or WUFI Passive) and meet criteria for Annual Heat Demand, Annual Cooling Demand (or heating or cooling load), Annual Primary Energy Demand (i.e. source energy), and Airtightness.  Certification generally involves a third-party review of the energy modeling, blower door testing to determine airtightness, and commissioning of the ventilation system.


Here’s some data on the 18th Ave Residence (as calculated per PHPP):

Treated Floor Area                2100 ft²

Annual Heat Demand           5.34 kBTU/ft²a

Heating Load                          2.92 BTU/ h ft²                                

Primary Energy                       29.5 kBTU/ ft² a

Site Energy                              11.1 kBTU/ ft² a

Airtightness                            .48 ach50

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main wall assembly

5/8″ gypboard

5 1/2″ wood studs w/ dens-pack cellulose

1/2″ plywood taped as air barrier

2″ rockwool exterior insulation

cedar rainscreen

R-value = 27

south wall assembly above windows

5/8″ gypboard

5 1/2″ wood studs w/ dens-pack cellulose

1/2″ plywood taped as air barrier

9 ½” TJI w/ dens-pack cellulose

½” plywood

cedar rainscreen

R value = 48

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basement wall assembly

veneer plaster

12″ Faswall blocks

1 1/2″ rockwool inserts

exterior cementitious skimcoat and waterproofing

R value = 21

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floor assembly

4″ slab on grade

10 mil vapor barrier

4″ EPS type II insulation

R value = 18

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main roof assembly

5/8” gypboard

1x4 wood furring

16” trusses w/ dens-pack cellulose

5/8” plywood taped as air barrier

4” min polyisocyanurate

½” protection board

TPO membrane roofing

R value = 78

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windows and doors

Euroclime Larch Windows and Doors w/ triple glazing

SHGC = .50

U value = 0.15 btu/hr ft² F

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Zehnder CA-350

heating / cooling

Mitsubishi Ductless Mini-Split (2 heads)

electric convection heaters for backup

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water heating

GE hybrid electric heat pump

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exterior shading

moveable wood screens

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So what do you think?  Is it a Passive House?

10 Mistakes When Designing an Energy Efficient Home

While they may be designed with the best of intentions, most so called energy efficient homes (and buildings of all types) designed and built today make many of the same mistakes:

1.  Focusing on Technology First

The simplest, most reliable, and most effective approach to energy efficiency is to focus first on the building envelope.  This means starting not with a more efficient furnace or water heater, or the addition of a photovoltaic solar array, but instead focusing on airtightness, minimizing thermal bridging, and providing thick continuous insulation.  Not only will you save energy and lower your utility bills, if done correctly you will be more comfortable and your building will be more durable.  Once you've made a great building envelope and significantly reduced your energy loads, technology can then be used on a more limited basis to complement your design.


2.  Focusing on Insulation before (or without) Air Sealing

Probably the single most effective strategy to achieving energy efficiency is to provide exceptional airtightness.  An airtight building minimizes energy losses (when heating or cooling), ensures even stable temperatures throughout a building, and prevents moisture laden air from entering the building assembly.  Exceptional airtightness starts with good design, and relies on proper execution of that design in the field.  A suitable ventilation strategy goes hand in hand with an airtight building.   Fresh air should come from an intentional controlled source (filtered fresh air rather than leaks in the building envelope) and the temperature be moderated; usually achieved by the use of a Heat Recovery Ventilator.


3.  Failing to do a Blower Door Test

This simple inexpensive test is the only way to determine the airtightness of a building.  A blower door is essentially a fan that is used to pressurize and depressurize a building to determine where there are leaks and how big.  Unfortunately very few buildings use a blower door test during construction.

4.  Ignoring Solar Orientation

While good design must respond to the immediate context, it's also important to recognize and respond appropriately to solar orientation.  If done correctly, the sun can be used effectively to help heat our buildings for free (assuming the climate and building type desires heating) without contributing to overheating.  Effective design means appropriately sizing glass area for different orientations and providing the right type of shading.

5.  Failing to do a Shading Study

Most sites are shaded at certain times of the year and day by buildings and trees.  It's important to correctly identify this information to predict the effect of shading on the building.  There are simple tools and software to provide this information.

6.  Specifying the Wrong Type of Glass

Windows (and doors) are one of the most important components of a building.  They provide views, daylight, ventilation, and have a huge impact on the experience of a place.  The selection of windows and glass can be complicated and overwhelming, and selecting the wrong glass can have huge consequences.  The right windows and glass can mean exceptional comfort and performance, and can make a building sing.

7.  Ignoring Material Sourcing and Impact

In the quest to make an energy efficient building, it's important to have a complete understanding about the source and impact of our material selections.  Many so called high efficiency materials actually have a much larger negative impact on the environment than the benefit they provide. 

8.  Not Setting Proper Goals

Without setting proper goals at the outset, it can be easy to compromise when facing a challenge during the process (there are many).  While rating systems and certifications aren't always perfect, they can help to appropriately guide a project in the face of adversity.

9.  Failing to do an Energy Model

Without a real energy model, it's all just guesswork.  The best way to understand the effect of design decisions is to have an energy model as part of the design process.  Effectively used an energy model can be another tool used as part of the design process.

10.  Forgetting about the Architecture

It could be argued that a beautiful architectural space that is thermally uncomfortable and not energy efficient does not make great Architecture.  Likewise, the focus can't be on energy efficiency alone.  The challenge is to create beautiful spaces that are thermally comfortable and energy efficient - less than that can no longer be acceptable.


clean energy

i received an email a couple of weeks ago alerting us that our PV array was generating less energy than typical, and that the system should be inspected.  this is one of the benefits of leasing a PV system.  after a quick climb to the upper roof the problem was obvious - the sedum from the green roof had grown up and over the base of most of the panels.  while in hindsight it may have been better to mount the panels higher above the roof, in less than 30 minutes the sedum was cleared off and away from the panels and they were washed clean.  later this fall i will prune back the sedum and again check in on the array. IMG_0002







is it working?

after more than 2 years living in skidmore passivhaus, i'm frequently asked is it working?  let's take a look at the numbers from the last year: IMG_6877

it's interesting to compare our actual annual consumption to the predicted consumption per the PHPP model.  this project was modeled in PHPP 2007, and there has been some criticism in the passive house community suggesting that the German default values for electrical consumption built into PHPP are far too low for the US culture.  (PHIUS has gone so far as to radically change the default values for electrical consumption).  given the data on our project, i'm not so sure there is a problem.

Site Energy Actual v Predicted

occupant behavior of course plays a significant role in energy consumption, and there are a number of conditions to note for this building.  PHPP assumes 4 occupants for a house of this size, when in reality there are only 2 of us (plus 1 dog and 2 cats) which should result in lower overall energy consumption.  with fewer occupants, there will be lower internal gains which presumably would increase slightly the heating demand and heat load.  Because we both work from home much of the week with computers and other devices running all day, it could be assumed that while there are only 2 of us, our consumption includes both home and work and would therefore be higher.  I also should note (somewhat sheepishly) that we have 3 cables boxes that stay on all the time, including one DVR, which draw a steady amount of electricity and generate some heat.  This is all somewhat anecdotal, but it shows the inherent complexity in accurately predicting energy consumption.

an annual summary of our site electricity consumption and site energy production (from our roof mounted 4.32 kW array) shows that we generated 82% of the electricity we consumed.

Site Electricity v Produced

an annual summary of our site energy consumption (gas and electric) and site energy production shows that we generated 49% of the total energy we consumed.

Site Energy v Produced

a monthly summary of our site energy consumption (gas and electric) and site energy production (from our roof mounted 4.32 kW array) shows the large deficit during the winter months as expected.  more efficient equipment for our space heat and hot water would certainly help to offset some of this deficit.  while a larger PV array would get us closer to net zero on an annual basis, it wouldn't solve this deficit and demonstrates one of the problems with an approach that focuses solely on annual net zero energy.  elrond burrell has written an excellent blog post covering this topic.

Monthly Site Energy

a monthly summary of our annual gas and electric bills demonstrates our consistently low monthly utility costs.  our average monthly cost for both gas and electricity over the last year was $36.53.

Monthly Bills

note that for most of the year we pay our electricity provider the minimum monthly charge even though we are generating more electricity than we are using.  our only gas appliance is our hot water heater, and a significant portion of our small monthly gas bill is for fees and taxes regardless of our consumption.  if we were to change our gas water heater to electric even without a change in energy consumption, our monthly utility cost would be even lower by eliminating the minimum gas charges.

aside from reducing our CO2 emissions and our consistently tiny utility bills, we're staying extremely comfortable year round - warm in the winter while barely using our heating system, and cool in the summer without any air conditioning.  so the answer is unequivocally yes, it is definitely working.



form factor and passivhaus

HH front render It is well known that compactness is an important aspect of a well designed and cost effective Passivhaus as it has a considerable impact on the overall heat demand.  Having now modeled a number of projects in PHPP (Passive House Planning Package), I decided to do a quick comparison of the ratio of envelope to floor area (known as the form factor) as well as the average R-value of the entire envelope.  Here are a few examples:


envelope to treated floor area:  3.8

average R-value:  39.4



envelope to treated floor area:  3.7

average R-value:  29.7


18th Ave Residence

envelope to treated floor area: 3.2

average R-value:  24.1


Haig Haus

envelope to treated floor area:  2.7

average R-value:  25.9


Ankeny Apts

envelope to treated floor area:  1.5

average R-value:  19.7


While there are many variables at play that make each project distinct, it is clear that form factor has a huge impact.  Remember boxy can be beautiful!



help wanted

In Situ Architecture is looking for some part-time contract help. Excellent rendering and graphics skills a must.  Interest in low energy building and passivhaus is helpful.  If you are interested please email a brief description of yourself with a few examples of your best work. Info at insituarchitecture dot net

passivhaus heating

really this post should be titled: "selecting a heating system for a small passivhaus in portland oregon"

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with an extremely low heating load, a passivhaus makes most typical residential heating systems unnecessary and unsuitable in terms of size and cost (this includes gas forced air furnace, ground source heat pump, and hydronic radiant heating).  for skidmore passivhaus (1965 sf house /1680 sf treated floor area), the peak heating load per PHPP was estimated to be 5,657 btu/hr (at a design temperature of 32deg F).  as an example, a small wood stove might produce about 20-30,000 btu/hr when running hot, far too much from a single point source in a passivhaus.  in addition, providing fresh air for combustion and sealing all the penetrations creates complications, plus we frequently have no burn restrictions during our coldest winter days.  a very small gas furnace still produces about 30,000 btu/hr, and delivers warm air at a higher velocity than is really comfortable.  both systems could easily overheat a small passivhaus and each have their pros and cons. while gas here is still cheap and the electric grid nationwide is pretty dirty, most of our electricity in the northwest is generated by hydro and is clean and generally considered renewable.

so for our small passivhaus in portland, we considered the following all electric options:

Electric Resistance Heating


  • very low first cost and simple to install (under $1k installed)
  • easy to zone and control individually
  • no maintenance
  • silent (radiant or convection type)
  • ok aesthetic (not great though)


  • inefficient compared to heat pump (COP 1)
  • difficult to meet PH with all electric energy sources
  • not great aesthetic


Ductless Mini Split Heat Pump


  • high efficiency (COP 3:1 or greater)
  • ability to provide cooling
  • variety of sizes starting at around 9000 btu/hr


  • higher first cost (roughly $4k - $5k installed for 1 head with 1 outdoor unit)
  • requires open plan / poor distribution to closed rooms
  • difficult to zone (add roughly $2k for additional head)
  • fairly unpleasing aesthetic (add $500 for slightly better looking floor mounted head)
  • often requires some electric resistance heating as supplement
  • ability to provide cooling means increased energy consumption (if cooling used)

ductless head

floor mounted


Ducted Mini Split Heat Pump


  • high efficiency (slightly less than ductless mini split)
  • ability to provide cooling
  • pleasing aesthetic / discreet (concealed ductwork)
  • good distribution (ductwork required)
  • variety of sizes starting at around 9000 btu/hr


  • higher first cost (roughly $7k installed)
  • requires space to locate concealed unit and run ductwork
  • ability to provide cooling means increased energy consumption (if cooling used)

ducted minisplit

Heating Skidmore Passivhaus

at skidmore passivhaus we elected to use electric resistance wall mounted heaters.   in our climate mechanical cooling seems like an unnecessary and wasteful luxury, and we frankly did not want it at all.  instead we opted for operable exterior shades on the large south facing windows to significantly reduce summer heat gain.  combined with well placed operable windows + doors and a nice amount of exposed thermal mass, the house stays extremely comfortable even during the hottest days of the summer.

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although the improved efficiency of a heat pump was (and still is) extremely appealing, we struggled with the significant additional cost, the appearance of the ductless heads, and the difficulty in zoning.  for the money saved installing the electric resistance heaters (we spent under $1k total) we were able to install a decent sized roof mounted solar PV array.  had we not built to passivhaus, we would not have considered this approach.


we installed a total of 4 individual convection heaters made by Convectair ranging from 1250 watts - 1750 watts each.  these convection heaters don't have a fan so they are completely silent.  while there is an option to connect the heaters and control them from a single programmable thermostat, we opted to keep them individually controlled for maximum flexibility.  without the programmable thermostat we have to adjust each heater daily, but this has simply become part of our routine and works for us because of our unpredictable schedules.

skid plans

because the plan is organized essentially as a one bedroom house with a separate wing with individual work spaces, an electric heater in each work space allows for simple control as separate zones.  the open living room has one heater, while the remaining heater is in the master bedroom upstairs.  because the house is so tight and well insulated, a number of rooms don't have any heating source yet remain perfectly comfortable including the pantry, 'breezeway', main floor bathroom, and upstairs walk in closet.  the kitchen, entry, and dining room are open to the living room and served by the living room heater.  the master bathroom has only an electric radiant mat under the tile floor.

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our total system approaches 20,000 btu/hr (5750 watts x 3.413 btu/hr/watt), but it is distributed throughout the house and we rarely have all of the units running at the same time.  after our first winter, the house stayed extremely comfortable as expected with only a few degrees variation between the warmest and coolest rooms.  during our record cold weather this winter (almost 3 weeks with lows dipping into the teens and cloudy snowy skies for much of it) the living room heater struggled a bit to raise the temperature very quickly when setback at night.  in hindsight that heater was probably undersized considering that it serves a huge portion of the house - the 2 story living room (with large areas of glass and lots of mass), dining room, kitchen, entry, breezeway, and pantry.  we are considering adding a small additional heater to the living room area just for those extreme cases.


while many may question our decision to use electric resistance heat and a PV array, for our super low load passivhaus and particular situation it seemed to make sense.  overall we are pleased with the system although it is definitely not sophisticated, super efficient, nor great looking.  while we don't have individual data loggers installed yet to track electricity used for heating specifically and to monitor indoor temp and humidity, we will be posting general information about our overall energy consumption this summer documenting our first year of living in the house.  hopefully we will begin logging data for year two.

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we'd love to hear your thoughts, suggestions, corrections, etc. as we continue to ponder appropriate systems for some of our new projects currently in design.



skidmore passivhaus

there's quite a bit of excitement in the air surrounding our skidmore passivhaus.  in addition to officially receiving passivhaus certification (PHIUS +), the house was awarded an earth advantage platinum rating and energy star northwest certified. back in early october the house was featured on the aia portland's design matters tour of exceptional homes, and was the only passivhaus on the tour.

a few weeks ago a 4.32kW PV system was installed on the upper roof which is expected to help the house approach net zero energy use.

inhabitat just featured the house on their website, and portland monthly magazine was on site this week to photograph the house for an upcoming issue.

we're also excited to present a handful of new photos completed by local architectural photographer jeremy bittermann.

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drop us a line if you have questions, want to learn more, or just to say something nice.

you can also follow us on twitter @insituarch

check back for more updates soon.