DIY Piano Soundproof Room Construction [Plan] [Subfloor] ~Converting an 8-Tatami Japanese-Style Room into a Floating Floor Soundproof Room~

Soundproof Room Construction 2024 Begins

I am taking on the challenge of building a DIY piano soundproof room. I will not be asking a professional contractor for help; I will build everything by myself. This is my third time building a soundproof room, and I want to give it my all, using my past experience and know-how, thinking of this as the final soundproof room of my life.

Renovation Plan

This is the plan for this soundproof room construction. I will renovate an 8-tatami Japanese-style room into a piano soundproof room. The building is a reinforced concrete (RC) detached house. The windows are already double-glazed.

Instead of installing a box-type soundproof room inside the room, I will build an original soundproof room that fits the shape of this room. The space that used to be the closet will be incorporated into the soundproof room, and the door opening space and the alcove will become the anteroom (sound lock) for the soundproof room.

I will be putting in a grand piano, but I am aiming for a size that allows for an ensemble with a piano, violin, and cello. Since the piano will be brought in from the balcony side, the sliding window will become a 'quadruple sash'.

Floating Floor Structure (Concept)

The soundproof room I am building this time is a floating floor type, where another room is built inside the existing room, with an air layer in between. In the diagram below, the black frame is the existing room, and the green frame is the soundproof room. The yellow part is the floating floor structure.

The inner soundproof room does not touch the ceiling or walls of the existing room, and it is structured as if it is floating inside the room due to the floating floor structure. Since it cannot actually float, I will apply a structure to the floor that blocks vibrations to break the transmission of vibrations and sound.

Since the building is an RC detached house, it can be said that the conditions are better than those of an apartment or a wooden house.

10-Layer, Approximately 14 cm Thick Floating Floor Structure (Dry Method)

There are two methods for floating floors: the 'wet method' which uses concrete, and the 'dry method' which does not. Since large-scale construction involving pouring concrete is difficult for DIY, I will use the dry method.

A state where the floor is floating on water is the ideal structure for not transmitting sound, but since that is almost impossible in reality, I will use cushioning materials such as 'high-density glass wool' to create a structure that breaks the connection between the foundation floor and the soundproof room floor.

I will be layering several materials like a mille-feuille, but this time I decided to build it with the structure shown in the diagram below, thinking it through myself and utilizing the materials I have on hand. It is 10 layers and about 14 cm thick.

I actually wanted to stack about 20 cm, but due to the ceiling height, this was realistic.

Compared to commercially available soundproof rooms like Yamaha's Avitecs, I think the floor is about twice as thick.

The floor work is tougher than I thought... (with photos)

Well, with the planning out of the way, I will introduce the actual construction process with photos. First, here is the state after removing the tatami mats.

Once the tatami mats were removed, the plywood subfloor (rough floor) appeared. I considered placing the soundproof room on top of this as is, but there are some soft spots, and I have a lingering concern about what exactly is underneath.

A hollow space under the floor can also cause box resonance, and this floor is structurally connected to the walls. I decided to take the plunge and tear it all out to redo it. I will expose the concrete slab and start over.

I have listed the tasks to be done.

1. Observe and understand what is actually under the floor

2. Clean up debris under the floor

3. Decouple the floor from the walls ← Important

4. Reinforce the floor joists

5. Level the floor joists

6. Fill the space under the floor with glass wool to eliminate hollow areas

7. Install plywood subflooring

It's daunting...

Let's go for it all at once.

Demolishing the closet

The area that used to be a closet will be incorporated into the soundproof room, but since it needs to be at the same height (level) as the other areas, I will demolish it. There were some areas with mold, so I am removing it root and branch.

Concrete slab exposed

When the plywood was removed, the concrete slab was exposed. The joists were spaced at 45 cm intervals.

I found a pack of Hi-Lite cigarettes under the floor.

These are the square timbers I purchased.

Leveling the joists

I carefully level each joist one by one by placing shims underneath or planing the surface.

Edge isolation

I am isolating the walls from the floor. I have filled the gaps with 96K glass wool. This ensures the soundproof room absorbs its own vibrations without transferring them to the walls.

Glass wool filling

I am reinforcing the joists and filling the space under the floor with glass wool. By eliminating the hollow space under the floor, I prevent the drum effect (resonance). Since it is glass wool, it should also act as insulation.

Subflooring with plywood

I am installing the plywood subfloor in a staggered pattern.

It feels great to work with brand-new materials.

The walls and floor are isolated from each other.

I could look at this subfloor forever.

Even though I'm thinking this might be enough for the floor, this is actually just the start of the real soundproof room construction.

The sound insulation sheets were applied promptly, and we are moving on to the next task.

Continued)
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