Insulation, Radiant and Vapor Barriers - Insulating a sunroom

We have a sunroom in the house we purchased a couple of years ago. It is similar to this Solid cathedral roof sunroom or patio enclosure with vinyl cladding (http://www.fourseasonssunrooms.com/Products/vinyl_sunroom_ultra_solid_cathedral.aspx)

The difference is that it was put on top of an existing deck so sits about 9 feet aboce the ground. If you are under the sunroom they enclose the roof with plywood, but there is no insulation. The windows are the double paned low e windows, and they provide great insulation. However the room will get really hot or really cold from the floor. In the winter if I hit the heater on, the room heats up but if you sit on the floor you can feel the cold seeping through the carpet.

I have a feeling that pulling the ply off, adding insulation, and then sealing it up will immensely help the room. I need advice on what to use. Batts, spray foam, cellulose? What about a vapor barrier? What R value?

I know very little about insulation, but think this is a do it yourself job.

Hi Dishiki, you are correct that it should help a lot. If you use rigid foam or spray on foam it will seal and insulate at the same time. A couple of inches should be all you need in GA. If you stop any air leakage that will prevent any concerns about vapor/moisture movement. Many lumber yards and box stores (or online) sell small kits to do the spraying yourself. If you use rigid, cut to fit tight and use can foam to seal any gaps.

GL
Bud

Thanks Bud for the response.


My joists are 2x8. If I were to use either spray or foam boards, how much of each cavity should I fill? Is 2 inches enough in the North GA climate, or should I fill the whole cavity?

Also, I'm not sure I am following you on a vapor/moisture barrier. So if I have from top down--subfloor/joists and insulation/plywood--where do I put vapor barrier? Do I put it between joists and insulation and the ply or do I put it in between the joists before I put in insulation, or do I do both?

Thanks again for your help.

Sorry Bud, misread about vapor barrier. By stopping air leakages, what exactly do you mean and how do I go about doing that? Thanks

Vapor barriers have two primary concerns, cold climates and air conditioning. The issue is moisture laden air coming in contact with cooler surfaces. IE in the winter a warm house with 50% relative humidity (RH) might deposit moisture inside a wall if it hits a surface below 30 degrees. (just numbers for the example) Like a glass of ice tea setting on your coffee table, the water condenses out rapidly. During ac months, the warm moist air from outside can be pulled into a wall or floor cavity and come in contact with cooler surfaces created by the ac. Both of these conditions deal with the movement of air, thus block the air flow and the primary concerns are gone. The other issues with VB's is moisture through materials like wood, but if I understand correctly, your sun room is up in the air, eliminating any contact with concrete or soils.

The general rule for VB's is to place them on the warm side of the insulated cavity and in the same plane as the air barrier (plywood, sheetrock, yada). In the north that is inside. In the deep south that is outside. So what do we do for all the homes in the middle? Decide on the primary consideration, ac or heat and favor the VB to that side. More correctly, use a vapor retarder (link below) that will allow some movement of moisture as needed.

If you select foil faced foam, the foil is a strong VB. Pink, Blue or some spray foams have a higher permeability.

If it were my deck/sun room, I would apply 2" of rigid directly under the sub-floor, reinstall the lower plywood, and omit the vapor barrier so that the cavity below will be allowed to breathe. If you choose to add more insulation, even better ($). A complete fill would be overkill but not a problem.

I find the primary issue with overhanging sections of homes or areas built over unheated crawl spaces to be the convection of warm air up and out of the upper portions of the house. That air that exits must be replaced, resulting in cold air being pulled into the lower portions of the house, in your case the floor area. Once you block the air leakage, the required r=value goes way down. I'm not real familiar with GA, but 2 to 4 inches of foam should be plenty (R=10 to R=20 plus say 4 for all of the other surfaces and materials.

There, can I have dinner now :).

Bud
Energy Savers: Vapor Barriers or Vapor Diffusion Retarders (http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11810)