I have been talking about our house construction very much as if it is no different then a similar sized conventional house. This is true to a very large extent.

I occasionally refer to some product or method with additional technical information that differentiates our construction from a conventional “stick built house”.

I however generally stay away from too much hard technical data for fear of losing my family and friends as primary readers of this blog, preferring to provide anecdotal information instead, as to why we are doing things a little differently.

This difference is actually dictated by some very stringent MANDATORY technical requirements set out by the PASSIVHAUS Institute in Germany. The Canadian source for training and information is administered by the CANADIAN PASSIVE HOUSE INSTITUTE (CANPHI).

In a nutshell a passive house building is designed to be very comfortable and healthy while using vastly less energy than a similar conventional building irrespective of climate. We are talking a magnitude difference of at least 90% less energy.

While these requirements are not prescriptive in that they do not dictate exactly how to build your passive house – they are nevertheless stringent performance oriented requirements, which leave the actual construction methodology up to the individual builder to meet.

So what are these mandatory requirements and how does one calculate them in order to comply when designing a house for oneself?

AIRTIGHTNESS

Of no more than 0.6 ACH (air changes per hour measured at a pressure of 50 pascals) This is equivalent to having a 3”X5” index card sized hole representing the combined area of every crack within an average 2000sq.ft house under pressure by a 20 mile per hour wind.

Compared to a code complying stick built house which has at best an ACH of 6 to 10. A passive house is therefore 10 to 16 times tighter.

ANNUAL SPECIFIC HEAT (OR *COOLING) DEMAND

A maximum 15kWh/m2.a needed to provide space heating to 20 degrees Celsius

Compared to a code complying average Canadian house which has an energy consumption for heating of 137.2 kWh/(m²*yr) (43506 Btu/ft²*yr).or about 90% more.

*Cooling is for the most part not factored in most Canadian homes because of our colder climate)

SPECIFIC HEAT LOAD

10W/m2 Maximum peak power needed to maintain 20 degrees Celsius internally (when the outside temperature is minus 10 degrees Celsius)

ANNUAL SPECIFIC ENERGY DEMAND

120kWh/m2.a of primary energy – the energy consumed at source such as a gas well etc.

The above information is a lot to digest by itself, but it is absolutely necessary to understand if you want to build a house that will meet the Passive House requirements.

Before we begin it may be useful to use an analogy.

Let us say that we want to build a competitive race car – what are the fundamentals that we would want to ensure that we explore?

Weight: would likely be the first consideration. If it is light it will use less fuel, Weight distribution will be a major consideration as it will determine (neutral) handling, It will definitely handle better with less unsprung weight or mass, The power plant will be smaller since the overall weight is less and so on.

Strength: will be another major consideration but since weight is related to strength – some serious trade-offs will need to be made or expensive and exotic materials (carbon fibre, titanium) will need to be introduced.

Cost: money is always front and centre and will determine what is prioritized and what is compromised.

Planning and Testing: There has to be a methodology established right at the outset to accurately predict how this race car will perform, otherwise we will be constructing hundreds of prototypes at enormous cost to get it right.

Constructing a Passive House is no different – the parameters and criteria may be different but the fundamental principles are the same once we zero in on what is important:

Insulation or more accurately Thermal Management: In our northern climate we want to manage heat as effectively as possible. From simple physics we know that heat travels via conduction, convection or radiation. We therefore insulate the envelope as much as possible to prevent heat from escaping by using highly resistive materials thereby slowing down heat loss by conduction. The idea is to use as little supplementary heat to keep the house comfortable. Better resistive materials (insulation) will retain more of the expensive heat we use, however we need to ensure that there is no thermal bridging – places where inside heat is allowed to transfer to the outside by highly conductive materials, such as concrete, metal fasteners or even solid wood headers or studs. We use coatings on our glazing to prevent heat from escaping by radiation through our windows and we also make sure that heat does not leave our houses through convection by sealing the envelope and making it airtight.

Airtightness: Since we know that we lose as much as 40% – 50% of our heat through exfiltration/Infiltration regardless of the insulation value of the envelope, we need to ensure that the house is airtight.

Health and comfort: We need to ensure that there is an ample supply of fresh clean air in the house at all times for health and comfort now that we designed it to be built very tight. We therefore need a source of ventilation that can bring in fresh air that is pre-heated by the outgoing stale air. The exchange of heat between the incoming and outgoing air needs to be at least 80% or better. In addition we need to also expel the moisture built up in the stale inside air otherwise it will result in mildew or worse – mould. This requires a high efficiency Heat Recovery Ventilator (HRV)

Planning and Testing: Just like the race-car analogy, there has to be a methodology established right at the outset to accurately predict how this house will perform, otherwise we will be constructing hundreds of prototypes at enormous cost to get it right. Until fairly recently there was no real methodology to accurately predict how a residential building will perform before it is built. Before the PassivHaus Institute built the Passive House Planning Package (PHPP) software the industry relied on fairly unsophisticated rule of thumb “energy modelling software”.

So what data do I need to provide to enable me to meet the mandatory Passive House requirements?

(Or rather, what predictive tool do I use to determine the level of performance that will work for my house)

The GOOD news is that the PASSIVHAUS Institute has constructed an Excel based software package (Passive house Planning Package or PHPP Design Software) for a reasonable price of $260 – a bargain in my opinion – that enables one to enter all of the critical data required to test the design’s ability to meet Passive House requirements in real time.

The BAD news is that the software program is massively comprehensive, it is detailed to the nth degree, almost anal in its ability to ask for and gather the necessary information and it comes with a very, very steep learning curve. It needs to be fed every crumb of information about the design of your house, every component of your walls, their insulation values, type and thickness of sheathing, drywall, etc. etc.

The windows need to be described right down to the thickness of the frames, shadow lines, type of glass, u Values ug values. Their orientation, North, South East or West facing or degrees off the major cardinal axis, Are they inclined from the vertical? How high are the sills? Are they inset?

What are the areas of the specific walls, windows, basement slabs?

What are the volumes enclosed by the building envelope?

What appliances are you planning to use and their energy ratings?

The foundation walls, the slabs, stud spacing, thermal bridging, existing trees and their heights and shadows.

Roof overhangs and how they affect solar heat gain – it is like an intricate interrogation process rather than just data collection.

Where are you building? What is the climatic data – any microclimate information?

Some of the climatic data is built into the software – about 20 cities worth for Canada. This data inputing took me about a week of continuous work and the help of a trained Passive house consultant before I felt confident enough to start testing and changing components and assemblies. A lot of the input needs to be deciphered because it is either in Metric units or difficult to discern exactly what is required by the software programmers.

It also demands a lot of construction knowledge and experience. You need to be familiar and proficient with the latest building envelope design technologies. You will definitely need to get Help if you do not have the requisite knowledge base.

The PASSIVHAUS Institute has to be commended for building this software – it is truly a tremendous undertaking and a work of immense value. Future iterations can only get better.

It goes without saying that the design of one’s house has to be at a point where almost all of the technical design decisions have been considered and made in order to provide meaningful data to input into this software package. The design has to be ready for contract document preparation or at a level just before working drawings are started. Stated another way – finished design drawings are a must, but they need to be fluid enough to enable modification.

This brings us to what I would like to discuss and use as a small summary snapshot of what I am currently preoccupied with in my use of the PHPP software for our house. The table below shows the results of an optimized design, which meets Passive house requirements after all of the data has been inserted in the PHPP data fields. Remember this is but a small slice of the information available from the software package.

I wanted to demonstrate how the PHPP can be used to design the house to meet the Passive House standards or to a somewhat lesser arbitrary standard, while being aware of the implications of doing so. Or to undertake a simple cost benefit analysis.

You will notice that even though I meet the heating demand and heating load requirements with the optimal design, I am still a little shy of the Primary Energy target of 120 kWh/(m2a).

The next chart shows a lot more detail of the monthly and total annual heating demand calculated by the PHPP of 3630 kWh and by extension what it will cost me per year if I multiply the demand 3630 x *12 cents/kWh = $435.60

*12 cents/kWh is the average cost of electricity in Canada.

Now let us see what happens if I elect to change the parameters of my design slightly. The Revised scenario involves reducing the wall SIPs insulation by 50mm (2 inches) and substituting double glazed windows instead of using triple glazing. The cost reductions are based on actual quotes from my suppliers/manufacturers and represent real world costing and potential capital cost savings.

The actual capital cost savings are as follows:

Window glazing and window frame change: $11,600 savings

Reduction of SIP insulation by 50mm (2”): $10,200 savings

Total savings before taxes: $21,800

After entering the revised parameters the PHPP returns a new chart showing an increase in energy

requirements.

The next chart shows a lot more detail, including the monthly and total annual heating demand of 6052 kWh or what it will cost me per year if I multiply 6052 x 12 cents/kWh = $726.24

The annual savings between the two scenarios is $726.24 minus $435.60 = $290.64

It will therefore take me $21,800/$290.64 = 75 years to recoup my capital cost expenditure through the annual energy savings. I’m assuming I could invest the $21,800 in savings, and the yield would offset any future cost increases for a kWh of electricity.

My Economist friends can probably calculate this more accurately, however judging from their dismal record of predicting the economy up to this point – I doubt that.

THE BETTER WINDOWS AND INCREASED INSULATION IS NOT A VIABLE PROPOSITION BY ANY REASONABLE MEASURE AS FAR AS I CAN ASCERTAIN.

The PHPP is capable of demonstrating “what ifs” very quickly in real time before costly decisions are made on the site.

It is also very good at demonstrating the law of diminishing returns. (a point where more resources – better windows and insulation – do not neccesarily return an equivalent payback).

As an anecdote, it is the point where a passionate Audiophile gives up in despair because more money spent on equipment yields smaller and smaller improvements in sound quality. When regardless of spending more and more on improvements, he reaches a stage where his ears are no longer good enough to hear any further improvement in sound fidelity.