Finishing the underside of a Perm

[Chumba]

So I bought a perm last spring. Apprently the previous owner never covered over the bottom, so I intend to insulate and finish this weekend. Is marine grade needed for the plywood? and if so, any tips on cheapest place to buy? Otherwise any tips I should know before I dive in? plan is to head up to isle with a couple saws and get it done in a few hours this weekend.

[Hawg]

That seems like overkill to me, I've had plain exterior plywood on the bottom of my house for over 10 years with no problem. Remember if you get water in from the top floor and it sits trapped inside you're going to get rot.

[Lip_Ripper Guy]

I assume you are replacing the flooring plywood. I have used Advantech in 3 houses. Available at Lowes for under $30/sheet.

Best bet is to spray foam the underside, but you can also use pink or blue sheets and seal everything with Great Stuff.

[Chumba]

So it sound like the main thing is to make sure everything is sealed up good?