ext question for my cottage renovation....

The cottage is three season but i still want to apply some insulation. Wall and roof insulation are mainly to keep the building relatively cool in the summer. I'll try to use passive cooling as much as possible.

That said, I want to add a bit of insulation to the floor but i'm not sure which is my best option. Framing will be 2x10 or I-joists with underside max. 18" above grade. Framing sits on beams and metal post screw piles. I do not plan on using skirting around the structure so the underside of the structure will be exposed.

Choices that come to mind:
1. Insulate top of subfloor: e.g. 5/8 osb + 1.5" XPS insulation + 5/8" OSB on top of framing. Leave underside of framing exposed.
2. Insulate in between joist bays. Use rigid, batt, or spray-on foam and then cover underside with protective material.

My preferred option at the moment is option 1. It will solve the accessibility issue for installation and since there's no insulation under the cottage, critters will not be able to nest.

If I were to go with option 2, I'm not sure what is the best material to protect the underside of the cottage.
1. OSB
2. PT plywood
3. osb or plywood with steel hardware cloth
4. cement board
5. other

Anyone have any experience with insulating an exposed floor ?

If i go with option 1, is leaving the framing exposed a good idea? I don't think it should be an issue if kept dry and makes inspection easier.
If I go with option 2, what's the best material to use to cover the insulation and made sure animals can't burrow ?

Thanks

For your cottage insulation, option 1 sounds like a solid plan, especially with the idea of keeping critters out. Having that layer of XPS on top of the subfloor could make things easier to install and give you some good insulation without worrying about animals nesting underneath.

That being said, if you go with option 2 and insulate between the joists, I’d go with PT plywood or even cement board to cover the underside. Cement board is more durable and resistant to moisture, which could be handy with the open underside. When we were redoing our deck, we had some help from a hardscaping company Ottawa, and they recommended using cement board for areas exposed to the elements. It’s been holding up really well!