Now people are stopping to stare. I overhear a passing child call it the Lego Block House, and the parent chuckles. Several passerby’s comment that they don’t like the look of that ugly green siding. Almost nobody recognizes it for what it is. It’s CavityRock insulation – an exterior rated stone wool batt made by Roxul.

Cavity Rock


  • Non-combustible stone wool insulation with melting point of approximately 1177°C (2150°F)
  • Fire resistant due to its high melting temperature
  • Water and moisture resistant; does not absorb moisture to maintain insulating value
  • Chemically inert
  • Does not rot, promote mildew, fungi, or bacteria
  • Made from natural and recycled materials

Now the unique and unusual products are on display and this doesn’t look like every other house anymore. Every time I visit the job site someone has stopped in to ask questions. There are a lot of quizzical eyebrows and I find two very different groups of people.

The first group is mistrustful. This is definitely something different and certainly not like the way things are usually done around here. This might be some sort of scam. “Why insulate on the outside like that? Haven’t stud walls and fiberglass batts worked perfectly well for decades? If it’s air-tight don’t you have to open the windows to breathe?” Early failures of air-tight homes cast a negative shadow on these modern principals which have excellently controlled fresh air exchanges.

The second group is fascinated. “Is there really no furnace or baseboard heaters going in? How do you know it will work? How much does all that cost? What’s it made out of?” We know the technical answers, but this is our first Passive House and we have to trust in the science at this point.

The questions are endless and we all enjoy talking it through. We ask both groups about their heating bills and we hear quite a range between $1500 – $3500 annually. Then we tell them this house is modelled to need as little as $100 to heat for an entire year.

Most people walk away thinking we might all be a bit nuts. But at least a few people run straight home to google “Passive House”.

Read Part 1: an up and coming neighbourhood

Read Part 2: science makes sense