Insulating an enclosed porch

My wife and I just bought a house. It was built in the 80s and someone decided to section off half of the front porch and close it in with glass.

The floor is the deck boards of the porch. There are three exterior walls each with insulation and drywall on the inside and siding on the outside. The fourth wall is the front of the house. About 4' up there are 4 large (4'x6') panels of glass (picture a screened in porch but using glass).

The glass is not insulated. The room has a ceiling fan but no ventilation whatsoever besides the minimal ventilation from the floor. The room is pointless and poorly designed. Hot in the summer cold in the winter and always damp.

There is a door leading from the master bedroom into this room so I want to turn it into a closet.

My plan:

Rip out the glass. Wall up two sides. On the front facing sides I want to install two windows. So it will basically be an addition to the house.

Question:

What is the best way to insulate the floor? It was a porch so it's deck boards. Should I start from underneath or should I put down sub flooring and work up?

 

How about a few pics to see what w have to work with.

 

What type of deck boards, T&G or planks with gaps in between the boards?

btw - welcome to the forums! . . . . . http://www.doityourself.com/forum/el...your-post.html

 

What's underneath the floor, just dirt? Is the area under the floor open to the outside or closed off by...what? What sort of foundation supports all this?