Adding Insulation Behind the Walls of a Kyoto Machiya (Matsugasaki, Part 2)

Location: Matsugasaki, Kyoto | Work: Wall insulation | Series: Matsugasaki Machiya Renovation, Part 2

1. What the Owner Asked

The owner's request was simple: "Put insulation in wherever it can go." Older Kyoto houses were built with almost no insulation at all. Winters inside a machiya can be colder than outside feels, and summers are humid. For an owner coming from a country where insulated walls are standard, this is usually the first thing they want fixed.

2. What Was Behind the Walls

The interior walls of this house were finished with thin decorative plywood panels (kesho-beniya in Japanese), a very common finish in houses renovated during the 1960s to 1980s. You can see the original wood-grain panel still in place on the left of the photo below. These panels are only a few millimeters thick and sit directly on the wall framing, with an empty cavity behind them.

That empty cavity is both the problem and the opportunity. It is why the house is cold, and it is exactly where insulation can be fitted without changing the room size.

3. What We Did

• Removed the plywood panels to expose the wall framing.
• Checked the framing and the back of the exterior wall for moisture or damage while it was open.
• Fitted glass wool insulation batts between the studs, cut to fill each bay without gaps, with the vapor-barrier facing toward the room.
• Closed the wall with new boards ready for the final finish.

[IMAGE 1: Glass wool insulation fitted between the wall framing, with the original plywood panel still visible on the left]

4. What "Wherever It Can Go" Means in Practice

In a machiya, not every wall can take insulation. Some walls are traditional earthen walls (tsuchikabe) with no cavity. Some are shared with the neighboring house. Some are too thin. So we go room by room and insulate every wall that has a cavity, and tell the owner clearly which walls could not be done and why. The result is not a fully sealed modern house, but the difference in comfort is immediate, especially in rooms that get winter wind.

FAQ

Is it worth insulating only some of the walls?

Yes. Every insulated wall reduces heat loss in that room. Combined with interior windows and floor insulation, partial wall insulation makes an old house noticeably easier to heat.

Do you need to remove the walls to insulate?

For plywood-panel walls, yes, and it is the right moment to do it, because the panels are usually being replaced during renovation anyway.

More From This Renovation

Read the other stages of this project in the Matsugasaki Machiya Renovation series. Planning to make an older Kyoto house warmer? Contact Tsuji House and we will tell you what is possible in your house.