Are cold feet giving you cold feet about winter weekends at the lake? If there’s no heated basement below, raised floors are usually as chilly as the wind between your piers. Insulation alone won’t make a floor barefoot friendly, but the right insulation can mean slippers are all you need.
Rigid Foam (Do this)
Sheets of 2″ extruded polystyrene foam over a subfloor make an excellent insulation option—if you’re planning a new finished floor anyway. Rigid foam (with 5/8″ plywood on top) is warm, solid, and vermin-proof, and it can support plywood without strapping. Anchor the foam and plywood to the joists with 4″ deck screws. Use 3/4″-thick spacers to create a gap between the foam sheets and walls, and use a can of spray foam insulation to fill the gap and prevent air leakage.
Spray Foam (Or this)
Closed-cell foam, sprayed onto the subfloor’s underside, makes sense if you’re not installing a new finished floor and if there’s enough room to work under the cottage. Nothing seals gaps and cracks like spray foam, so it blocks drafts as well as insulates. You’ll find spray-foam insulation contractors in some cottage communities, or you can use a portable spray-foam kit yourself. For best results, warm the contents to about 28℃, and spray onto surfaces warmer than 15℃.
Batt Insulation (Not this)
Familiarity is why stuffing batt insulation between floor joists is the most common strategy, but it has four significant drawbacks in this application: Batts don’t prevent heat loss very well when the wind whistles through them; mice love to nest in them; they can attract and hold moisture against floor framing; and they always jiggle downwards over time, falling out unless the joist bays are well packed and the batts are supported by plywood, another sheet material, or chicken wire.