One of the best perks of working in this community is the people you meet. I first bumped into Miwa Mori at our very first PHINZ conference back in 2015. Fast forward to a recent trip to Japan with my son, and I cheekily emailed to ask if we could stop by her home in Karuizawa-machi. I’m incredibly grateful she opened her door to us; it is a little slice of paradise.
You can immediately tell this isn’t her first rodeo. The home reflects the deep experience of designing many Passive House buildings. The attention to acoustics was particularly striking—it felt like a sanctuary.
As a mechanical engineer, I geeked out on the systems. It’s a complex but elegant setup designed to squeeze every drop out of renewable energy, using a pellet boiler and thermal solar collectors (with electric backup) to cover heating and hot water. Let’s not even mention my stab of jealousy on the auto-filling bathtub that stays hot for as long as you like.
But my absolute favorite detail was this window below. Miwa has integrated a Kumiko panel—traditional woodwork held together without glue or nails—right between the panes of the triple glazing. It produces lovely shadows and light, and because it’s sealed inside the unit, you never have to dust it. Genius.
The wall construction is a beast, achieving a U-value of 0.15 W/(m2K) (roughly R6.7). It’s a clever hybrid sandwich of blown wood fibre, phenolic foam, and glass wool in the service cavity. The detailing required to pull this off demands incredibly tight tolerances, but for the Japanese craftspeople involved, it posed no issue at all.
