Total Construction Duration to date

Thursday, 13 June 2013

Do energy targets of Passivhaus make sense and will they pay back during the lifespan of the dwelling?

I have been discussing the payback periods of Über high levels of insulation and high R value windows on LinkedIn and thought I would share my thoughts with you and possibly promote a discussion.  My comments on LinkedIn started after one participant wrote “PS: BTW, why are we talking about this in the PH forum? Aren't we all allergic to any heating other than auxiliary heaters?”.  This was a topic asking for advice on whether it made more sense to install an Air Source Heat Pump or a High Efficiency Furnace on a home that currently had an oil furnace at the end of its service life.  The dwelling of concern was not a Passivhaus, but the poster felt that the expertise of the Canadian Passive House Institute forum may be beneficial to his decision.

I commented that I felt the jury was still out on the need for a heating system in a Passivhaus design for our climate, and that in most examples I have reviewed the only way it has ‘worked’ to not have a ‘real’ heating system (many designs incorporate a hydronic or electrical resistive heating coil in the dwellings ventilation air ducts to provide ‘auxiliary’ heat), is when the occupants were willing to accept significantly lower temperatures (<+ 65°F) during cold days and nights, which is just not going to be acceptable for most occupants in North America.  But the PH Program uses the claim that a normal heating plant is not needed as a way to justify spending the extra money on extreme amounts of insulation, which in many regions will never have a reasonable chance of payback throughout the life span of the dwelling.

If you accept that some form of heating plant will be required, but through increased insulation and better windows, that plant can be substantially downside, logic would say that the smaller plant will save you money and allow for the extra expense on the insulation and windows needed to reduce your heat load and downsize your equipment.  See the circle hear.  Well logic unfortunately has nothing to do with the pricing of consumer goods.  Pricing has nothing to do with the actual cost to make an item and everything to do with how badly does the consumer want it and what are they willing to pay.  Because the average North American consumer lives in a McMansion and has a bajillion gigawatt heating plant, there is very little demand for small 10-15K BTU units that are needed in a very energy efficient home.  The result is that they cost a lot MORE than the much larger units installed in the ‘average’ homes.  So not only are you spending a lot more money on windows and insulation, you now have to triple your HVAC budget even though you are getting less.

Another poster then suggested reducing the heating load by first “renovating to Passive House-Retrofit standard with R60 Wall, R90 Roof and R50 under-slab insulation, replacing your windows with R19 Ecoglass and PH doors”.

How long of a payback is and will be acceptable to most homeowners/buyers? Does R50/60/90 (slab/wall/roof) EVER make sense in the vast majority of climates around the globe? Are windows really able to reach a R20 thermal efficiency for the total assembly?

This then lead to a new discussion topic about windows, the claims by window manufacturers (in this case EcoGlass claiming a R20 window), and the general payback metrics of the Passivhaus program and what makes sense. 

In my travels I have generally been exposed to three trains of thought when discussing the Passivhaus program; those that have drank the full pitcher of Cool-Aid and take everything at face value and run with it, those that completely dismiss the program’s claims (these tend to be people who do not believe in Global Warming or the need to reduce energy use or our carbon footprint) and often call the practitioners of the program charlatans, and finally those that can see the value in a program like Passivhaus and see the building science wisdom in many of the program’s concepts but also feel the program may go too far down the energy reduction path.

I fall squarely into the last category.   I believe we are having a detrimental effect on the environment and need to make changes in how we build and live.  Yes I plan to build a ‘close to PH’ dwelling.  I believe that PH has the right focus when designing a dwelling, unlike LEED/Built Green/or other ‘green flavours’ of the year, that are more focused on the small to minor contributions that reduce the carbon footprint, and not ensuring the elephants in the room like heat load and thermal bridging are first looked after.  How many times have we seen a LEED Platinum building with 60-80% glazing and wondered how could that building possible be energy efficient and good for the environment? 

Building a dwelling that has reduced thermal load achieved by increased insulation, reduced thermal bridging, increased air tightness, reduced window glazing with the glazing present having higher insulating value or better solar gain harvesting, utilizing south solar gain when available, and of course correct ventilation (all the fundamental building stones of the Passivhaus system) just makes sense from a building science and energy reduction point of view. 

And concentrating on your insulation and air tightness as the first and highest priorities also makes common sense, because you will most likely never get another chance to address these components during the life of that dwelling due to their inaccessibility.   So it makes sense to concentrate more of the available funds to maximizing the efficiency of these soon to be inaccessible components and calculating the optimal insulation levels based on a full life of the building cycle (20, 30, 50, 100 years?).  Components like windows and heating plants are far less important to optimize during the initial construction, when working with a limited budget (a reality for all except a select few), because both will need to be, and most importantly can easily be, replaced or upgraded in 15-20 years at the end of their service life.

But I agree with many, that the PH program goes far too far up the pendulum in its goal to reduce the energy load on a dwelling, to a point of drastically diminishing returns that are not acceptable or practical for most in North America and in my view, may actually be increasing the building’s footprint on this planet (incorporating embodied energy in a dwelling that will never be offset with energy savings).

I also feel that so often the costs to build to PH standards are grossly misstated.  I often see figures of +10% to +20% as the premium to build to the standard.  In reality it is usually at LEAST 2 – 2.5 times the cost of a house built to building code minimums.  I have seen several examples of houses built in cities in my region for under $100/sqft over the last year or two (for a 3500 – 4000 sq ft dwelling).  These are house designs that do not utilize an architect or building envelope engineer on the team, and often have only minimal structural engineering input because they are generally optimized to meet the BC Building Code’s Part 9 prescriptive rules.  They still have fancy kitchens with gas stoves and granite countertops, a gas furnace or boiler, crown mouldings, and fancy paint schemes. They however usually incorporate PVC or vinyl windows of dubious quality (R2 max and air leaky like a sieve), code min insulation levels, and no air tightness to speak of.  The types of houses build by a majority of developers/builders in the majority of cities in my region (The only City’s that buck that trend in my area are the west side of Vancouver and North and West Vancouver).   A PH on the other hand requires the use of all the specialists (for one, because no Municipal inspector is going to take responsibility for the design and you have to have an engineer sign off on every aspect of the design).  Now you are looking at $200+ per sq ft to build minimum and that is if all the rest is par with a code min dwelling.  But clients who entertain a PH typically also still want all the bells and whistles including custom cabinets, media rooms, and home automation, and so on with the costs quickly escalating to $350/built sq ft or higher.  I am often directed to the stats for countries like Germany where a PH represents at least 25% or more of all new house builds.  There is a very good reason; a builder gets a huge government grant to build to the standard, the size of the grant reportedly offsets that bulk of the added expense to build to the program.

My final concern about the program is that it is not even possible in so many locations.  In order to meet the energy targets and not have a requirement for insane levels of insulation, a Passivhaus relies on solar heat gain (SHGC) to provide a large portion of your heat during the sunny winter days and shoulder month seasons.  This is obviously only possible if you have an unobstructed view of the sun (and of course have Sun) on your south elevation.  In an urban environment, this probably represents less than 10% of the available build opportunities which make the program quite elitist and limited in its ability to apply on mass.
I value the work that the Passivhaus community has done around the world and applaud there tenacity for building quality homes. I however personally would much rather see the energy use requirements lowered 20-30% and applied on mass to all new construction by means of building code requirements.  Only then will we truly make a difference in the carbon emissions and fossil fuel outputs of our society and substantially reduce our dependence on fossil fuels in North America.  Fortunately, I live in a Province that is leading Canada if not North America down this path with its new requirements for ever increasing insulation, ensuring for the first time that doors and skylights have to meet the same minimum air tightness requirements as windows, and hopefully really soon, will require an air tightness demonstration that meets a minimum level at the end of construction.

As always, thanks for reading and I look forward to your comments.

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