Insulating a crawl space

[SteveHebert]

I need some help here.

We finished building the house last year and have been trying to do all of the "tomorrow" projects since then. One of the big areas that we have concerns with is the crawl space. Some say no vapor barrier on the dirt while others say yes. Some say no vents while others say yes. I have been doing some research on this but am not confident in my findings. I grew up in VT where cold damp basements were common. We did not have the humidity issues we have here though so most of the basement issues were of minimal concerns there.

Here is what we have:

The house is on a crawl space that averages 12" at the short end and 40" at the tall end. There are 14 vents around the foundation that I keep open in the summer and close in the winter. We have a big moisture issue that has been measured in the house (sub floor) at 14% or so. That was discovered after the Pergo floor was ruined of course.

I have covered the clay with white sand and then with a 6 mil plastic. I over lapped all of the seems and used landscape fabric stakes to hold it down.

The pipes are not insulated. The crawl space has a steel door that is not insulated.

I am thinking about insulating the walls of the crawl space by draping 6 mil plastic from the rim joist and then draping batt insulation from that all the way around. I am even contemplating keeping the vents closed all year and insulating that area as well as the area above the rim joist to the floor joist. If I do all of that, I will not insulate the sub floor.

I even considered pouring a thin layer (2") of concrete over the existing 6 mil plastic.

My big concern is the cold floor in the winter months and the moisture content. I will be putting down a wood floor and do not want to have the issues we have with this Pergo.

Any help is appreciated.

Steve

[dixieoutlaw]

Steve,
You certainly need the vapor barrier. It keeps a lot of the moisture down. You also need vents. Recommend the ones that are automatic. They have a spring on them much like an old choke spring on a carburetor that closes and opens according so some unknown temp (actually know to the builders, but not me). They are not very expensive, and you don't have to worry about did you close them or not. If you have that much moisture under the house, you may want to investigate some type of ventilation system for you subfloor area. By trapping that moisture under the subfloor you will be creating a long term problem with mildew and rot of your floor joist.
If you ever go crawl under some old houses that were built using large rocks as the foundation stones and little else and on underpinning, you will most likely find the old subfloor timbers are as good as the day they were put down because they had good cross ventilation.
Have been under several houses which have poor ventilation and lots of moisture and they all have crap growing on the lumber. Of course all this moisture lends itself to a healthy environment for our subterranean termites.
Because of aesthetic values now we want our brick or what ever to continue all the way to the ground and this is killing some house as we build up the ground around the underpinning and force water(moisture) to the lower ground under the house. There are massive class action suits against builders who use drivit and carry it all the way to the ground. The instructions say to stop at least 6" above ground level. This is to keep out moisture and the inherent path for termites.

Might want to check out someone who knows about the possibility of adding a second vapor barrier stapled directly to the floor joist. There are different schools of thought where adding insulation to the subflooring ever pays off in energy savings and I would say no in the area you live in.

another thing to consider may be to investigate and make sure the water from you roof line is going away from the house and not under the subfloor. This may be happening on your uphill side where the subfloor is only 12".

Dang, think I am trying for a pair of socks next year.

Gary

[Vance]

I agree with Gary (well pretty much any way..please don't hold that against me). You most definitely need the vapor barrier and I use the plastic as you have. Normally that should be enough protection with the vents open in summer and closed in winter (provided you are sitting on a spring or something) I doubt the insulation along the walls of the crawl space will be of any real value either. Insulating between the floor joists may help block some moisture if it is protected by a layer of plastic along the bottom edge of the joists encapsulating it. However I would suggest insulating all your plumbing if you do. There is a good bit of heat transfer from the house through that floor into the crawl space.
As Gary stated it would be a good idea to make sure you are not getting any unwanted water in around the foundation aggravating the problem. Bare in mind, I am no expert here. I do need typing practice though...

[TomGilbert]

Steve,
You certainly need the vapor barrier. It keeps a lot of the moisture down. You also need vents. Recommend the ones that are automatic. They have a spring on them much like an old choke spring on a carburetor that closes and opens according so some unknown temp (actually know to the builders, but not me). They are not very expensive, and you don't have to worry about did you close them or not. If you have that much moisture under the house, you may want to investigate some type of ventilation system for you subfloor area. By trapping that moisture under the subfloor you will be creating a long term problem with mildew and rot of your floor joist.
If you ever go crawl under some old houses that were built using large rocks as the foundation stones and little else and on underpinning, you will most likely find the old subfloor timbers are as good as the day they were put down because they had good cross ventilation.
Have been under several houses which have poor ventilation and lots of moisture and they all have crap growing on the lumber. Of course all this moisture lends itself to a healthy environment for our subterranean termites.
Because of aesthetic values now we want our brick or what ever to continue all the way to the ground and this is killing some house as we build up the ground around the underpinning and force water(moisture) to the lower ground under the house. There are massive class action suits against builders who use drivit and carry it all the way to the ground. The instructions say to stop at least 6" above ground level. This is to keep out moisture and the inherent path for termites.

Might want to check out someone who knows about the possibility of adding a second vapor barrier stapled directly to the floor joist. There are different schools of thought where adding insulation to the subflooring ever pays off in energy savings and I would say no in the area you live in.

another thing to consider may be to investigate and make sure the water from you roof line is going away from the house and not under the subfloor. This may be happening on your uphill side where the subfloor is only 12".

Dang, think I am trying for a pair of socks next year.

Gary

Gary is a guru. He is right about everything. I would add that the auto vents like the old chokes quit working over time. WHen its real cold Dec,Jan,Feb I cut and place styrofoam wallboard pieces over my vents.
The aluminum matches the Airstream.

[SSummers]

Doug Rye is an architect from Arkansas who writes a monthly column for the Alabama Living magazine (Alabama Electric Co-op magazine). He advocates sealing up the crawl space, just like it was a basement. He insists that if you treat it like a basement, just shorter, that you won't have any problems. This includes a good vapor barrier on the ground, and closing all vents. As I remember, he also advocates insulating the walls (rigid foam insulation board).

His website is www.dougrye.com

Sabrina

[SteveHebert]

Thanks for the link Sabrina. I have read that same treatment elsewhere. That is where the concrete cap over the dirt idea came into play. I have some deep thinking to do here.

Steve

[dixieoutlaw]

Sabrina,
I don't dispute this guys analysis if you want to treat your crawl space as a basement. One can certainly waterproof a basement, but it should be done at the time of construction and this includes the walls -the crawl space walls in Steve's case. It is much more difficult to apply this waterproofing after construction.
I believe Steve's original question was on insulating his crawl space and whether or not to use a vapor barrier. Short of totally waterproofing the crawl space and making it a mini basement, I stand by my original suggestions.
I think Steve needs to determine where his moisture is coming from and I suspect it is coming from outside of the crawl space because of proor drainage.
I had a house in NC with a 1/3 basement. The previous owners had done some wonderful landscaping including building up flower beds on the side of the house where the basement was; however, they did not provide a method for all the water from the roofline to exit the flower beds. Over the years this water finally defeated the water barrier on the basement walls and cost me extensive pains and dollars to rectify. Bottom line water has to have a place to go and it will take the path of least resistance.

Gary