I want to build a deck, and am considering building a screened porch or maybe a sun room on it. If I want to make it a four-season sun-room, what do I need to do to the deck to make it properly insulating?

 

You usually leave a 16# nail space between decking boards on an open deck, but if you're going to cover it, butt the boards tightly against each other.
Use 16" centers for the decking joists for "floor" strength, and so that you can put insulation batts easily between them.
Put the vapor barrier up toward the "heated" space.
Good luck!
Mike

 

Thanks for the advice. But what do I put under the rafters to hold the batting up? Will the fiberglass hold up to the elements? And, if I am butting the deck boards against each other, can I just use pressure treated plywood instead and put some outdoor carpet on top?

 

Insulation batts are held up under flooring by "tiger claws", which are just pointed pieces of stiff wire that stick across between the joists.
As long as the insulation doesn't get wet, it will do fine. Do not install any insulation until the sunroom is completely dried in.
Floors are usually a subfloor and then a flooring layer. In most floors, it would be 3/4" plywood subfloor with 5/8" plywood or underlayment over that.
You can use one layer of p-t plywood instead of decking in this instance, if you choose, but use 3/4". You may need to add purlines between the joists at the seams for support since you won't have a subfloor.
Use Liquid Nails on top of the joists and galvanized screws to put it down with to prevent squeaking, and then add the indoor/outdoor carpeting.
Good Luck!
Mike

 

HI,
A couple of suggestions. Use tounge and groove 3/4" P-T
plywood, and if possible put some fiberglass screen on the underside with another covering of 1/4" hardware cloth over it
if it is close to the ground. The screen will keep out a lot of bugs and the screen will help keep wildlife or pets from tearing up the fiberglass screen.
good luck,
Trent