Salis Ali

I think the key distinction is that the gravel inside the room isn’t necessarily there to collect water coming sideways from the perimeter trench. It’s mainly providing a capillary break and a drainage layer beneath the floor.

If the soil underneath is damp, moisture can move upward through the soil by capillary action. A layer of clean, washed gravel with minimal fines interrupts that movement because the larger voids don’t pull water upward as readily. That’s why the “washed” part matters.

I’d be more concerned about getting the overall floor assembly right than trying to make the perimeter gravel somehow drain the entire room. Good site drainage, compacted/native soil, clean coarse gravel, and a properly installed vapor barrier each serve different purposes.

For Hokkaido, I’d also think carefully about frost and seasonal moisture. If Yoshida-san knows the local soil and has built similar foundations there successfully, his experience is worth considering, but I’d want to understand exactly what the vapor barrier is intended to protect against and where it sits in the floor assembly.

And yes, I’d avoid putting carpet directly over a potentially moisture-prone floor. A floor finish that can tolerate some seasonal moisture is a safer choice.

That’s a great example of how even a really small pond can change the whole garden ecosystem. The toads are probably doing a lot of the slug control for you, especially once they realized the pond was a reliable place to hang around.

I also like the reuse of the old sand filter rather than buying a purpose-built pond. One thing I’d watch is keeping some shallow areas or rocks where the toads and tadpoles can easily get in and out. It’s pretty amazing how quickly wildlife finds even a tiny water source.

Definitely seems like a much cheaper solution than constantly fighting slugs.

I’d definitely reuse it before trying to recycle it. Clean EPS foam can work surprisingly well as insulation, especially around sheds, workshops, cold frames, or other places where you’re not worried about appearances.

For larger pieces, you can cut them to fit between framing or use them as a lightweight filler in projects where the foam won’t be exposed to heat, sunlight, or chewing animals. Smaller pieces can also be useful for packing fragile items you’re storing or transporting.

One thing I’d avoid is burning it or putting it somewhere it can break down into little foam beads and spread everywhere. If you have a lot of it, I’d probably set aside the clean, usable sheets and treat the odd-shaped scraps as a separate problem.