Insulation, Radiant and Vapor Barriers - Adding Insulation Below Floor (and in Attic) Of Older House - Vapor Barrier Needed?

Hello,
I have recently moved into a new one story house which was built in 1948 and has no insulation below the floor. There is no basement, but there is a crawl-space of about 3 feet. It has a very small amount of insulation in the attic, a couple of inches probably. The house in upstate South Carolina. I haven't ever installed insulation and I've got a few questions. I thank you in advance for any advice that you can give me.

I plan on installing some insulation between the floor joists (above the crawl-space) and in the attic as well. I've talked to a few people about the best way to do this and I'm a little confused about the need for a vapor barrier.

I was told to use kraft faced R-19 with the paper facing the floor for the insulation between the floor joists. I was also told to lay down some 6-mil poly on the dirt in the crawl-space to act as a vapor barrier. Do I need this poly or not?

For the attic I was told to use R-30 and to lay it down on top of the small layer of existing insulation. Would I use faced or unfaced insulation for that? I assume that if I just laid it on top of the existing insulation then I would use unfaced right? I'm wondering if it might be better to pull the existing insulation out and lay the new insulation down in it's place.

Thanks for any help.

Yes you need poly on the ground as a vapor barrier. Because of your climate you should also be concerned about dampness from humid air. Many people are closing off the vents and using a de-himidafire (spelling) in there crawlspace.
Do a web search for... crawlspace ... I saw a artical from the NC building dept on how to do insulate and damp proof a crawlspace in NC. Your close enough it should help.
Good luck
Ollie

Thanks for the advice. I will look up that article about damp-proofing.

So, R-19 faced for under the floor, and R-30 faced for the attic is what I should use? With the faced side facing torwards the house in each case?

If I use faced insulation in the attic then do I need to pull out the existing insulation so that the faced side lays directly on the wood?

Sorry for all the dumb questions.

Adding unfaced insulation to the attic should be appropriate. Before then, it is a good idea to lift up the existing insulation and caulk & tape all joints & penetrations, as this can represent a great deal of heat loss in cold conditions.

Adding insulation to the floor joists will make your flooring more sensitive to condensation. Poly on the floor will reduce the amount of humidity coming from the soil. Poly on the underside of the insulation is a two-edged sword. I'd be more comfortable using an air barrier insulation there, to eliminate the need for a vapor barrier.

Enclosed crawlspaces require substantial investment in mechanical equipment in order to manage humidity issues. They should be reserved for crawlspaces with HAVC equipment in them.

Adding insulation to the floor joists will make your flooring more sensitive to condensation. Poly on the floor will reduce the amount of humidity coming from the soil. Poly on the underside of the insulation is a two-edged sword. I'd be more comfortable using an air barrier insulation there, to eliminate the need for a vapor barrier.


Are you saying that I should think about using unfaced insulation between the floor joists? I'm not sure what you mean by "air barrier insualtion". Thanks

All dirt floor crawlspaces should be covered with 6 mil visqueen (plastic). You can roll it out and put bricks on top to keep it down. You can use either faced or unfaced R-19 in between the floor joists. If you use faced, the facing should be against the subfloor. You can use wire insulation supports to hold it up. Try not to jam the insulation in the joist cavity, this will lessen the R value. If you can afford it, I would recommend the foam spray insulation which will eliminate all air penetration into the house. Also, the crawl space should be well ventilated. Lack of air circulation is a major cause of mold growth.
For the attic, if you install fiberglass over existing fiberglass it must be unfaced. If you remove the existing you can install faced or unfaced. If using faced the facing should be down (touching the drywall)
If you remove the existing, you should caulk or foam spray all penetrations or openings to the living area. Stopping air penetration is just as important as insulating
Minimum--- R-19 in floors, R-30 in attics