Crawlspace condensation

[Bubbas Boys]

Any suggestions on how to keep my floor joists from condensating so much. I know that the issue is that we have a deep crawlspace and it is staying 55 degrees or so and the house is not heated yet and probably wont be this winter. Vents got closed and it was a mess,, dusty mold and subfloor was dripping. Lucky for me I got in there for no reason and found it. I of course opened the vents and the access hole and it is better with ventilation but still saw yesterday that where the subfloor meet and the joists is damp. I am freaking out about this since we just built the home this summer and am really not wanting issues already. Is this a big deal or am I overreacting? Wont have the money til spring for the furnace Thanks

[wharton]

I have built a ton of new homes on crawl spaces. Typically on wet clay, in the woods, and in a location with 45-80 inches of rainfall, and temps varying from -5 to 90* in a typical year. Bottom line is that the ONLY thing that really performs well here is a sealed, conditioned space.

Successful crawlspaces are built as follows:

1- No vents, ever!

Venting in the vast majority of case IS the source of failure. successful ventilation means a continuous flow of wind driven air, through the space. The air must be warm, preferably above 50*, or at least above freezing. The air must be dry, with less than 50% humidity, and lower that the atmospheric moisture in the space, or it will reach it's dew point and release all of it's moisture on cold surfaces of the crawl space.
The air must be driven by wind pressure, to drive excess moisture out of the space. This is typically pretty unlikely, as it assumes that wind will blow against an unobstructed foundation, and that the air will then pass through the space and exit unobstructed vents on the discharge side. This assumes that there are numerous vents along all sides of the space, and that no garages, decks, porches, shrubs etc.... are blocking the flow, pretty unlikely in real world conditions. It's fair to say that, in this area, optimal conditions to vent a crawl space exist less that 10% of the time, the other 90% is when the air is too hot, cold or wet to be of any value, and it is contributing to the problem, not curing it. Not only is the lack of optimal conditions an issue, but most existing crawls have about 1/4 of the vents they actually need to perform the unlikely miracle of effective, passive (no fans) ventilation.

2. Proper moisture resistant construction including waterproofing and footer drainage on the exterior of the wall, and crushed stone, plastic and a thin concrete slab on the floor of the space.

3. Proper grading and roof water diversion. The first ten feet surrounding the wall are critical. The area needs to be positively sloped to allow rain and snowmelt to flow well away from the foundation. Gutters are mandatory and leaders need to empty at least ten feet from the building.

4. Insulation. It goes on the inside of the foundation walls, NOT the floor. In our climate it's R-10 foam, either sheets or sprayed foam. The spray does a fantastic job of sealing the entire space, making it air and water tight.

5. Dehumidification. I run a 50 PT. unit, year round. It runs wide open for a few months while driving the moisture down from typically 90%+ until it stabilizes in the low 40% range. At that point it goes on a 12 HR timer, only running during the day. Contrary to some claims, by the time it is running sporadically, for 12 hrs a day, it makes very little difference in the electric bill.
6. Monitoring the space. I use a $20 indoor outdoor "weather station" with temperature and humidity readings. The indoor unit goes in the kitchen, or mud room, where the occupants are likely to actually look at the data on a regular basis. The 'outdoor probe" hangs in the crawl. This is critical, and I train my customers to keep an eye on the numbers from the crawl. If it is typically running in the 42-45% range and they call and ask why it's at 70%, I know something has failed. It may be a sump pump, or a dehumidifier, but it needs to be repaired immediately. When it comes to the health of the home, this is the best $20 you can spend.

I am sitting in a house I built this past summer. The crawl is spray foamed. Prior to gutters, proper grading and cranking up the dehumidifier, this place was in real trouble.
There was enough ground water pressure that it was pushing through the floor slab. The joists were horribly moldy, and the humidity level was well into the 90s. Upon completion it took two months of two dehumidifiers running wide open to get the level down below 50%. At that point the mold was gone, the moisture level settled into the low 40s, and one dehumidifier runs roughly 30% of the time. I have no heat source down there, and the space stays at an even temperature of 10* lower than the heated living space above.


As for your current, and hopefully temporary mess, you need to keep three things in mind. Humidity, temps and moisture control.

Humidity. Like I stated, there are going to be days when venting the crawl is going to really screw it up, and others when it will really help. Watch the weather, get a gauge and open and close the vents appropriately. I have made, quick, drastic improvements in conditions when the outside air was real dry, and I used a couple of box fans to stir the air under the floor, and one fan in the access hole, sucking wet air out.

Temp. you may be out of luck on this one. I frequently have crawls that are pretty nasty until the house is nearly finished, then I can start the final battle to keep the space dry and healthy. Dehumidifiers are the key, and some newer models work in pretty low temps. If you can seal the space and run one or two, you're going to see a huge improvement.

Moisture control. Proper grading is critical. If the initial backfill has settled, and allows water to pool against the wall, the game is over. I have seen foundations on existing homes go from horrible to great when the grading and gutters were properly repaired.
The other thing is the floor. As a minimum you need to have a sheet of plastic on the dirt, even if it's only temporary.

Sealed, conditioned, dehumidified crawl spaces are nothing new. The first spray foam retrofits were done is this area in the 1960s. They work extraordinarily well, when done with a little bit of care. They can really stand out as being a huge improvement given the fact that the vast majority of old school, vented crawl spaces in these parts are nothing but absolute failures. Good luck

[Tarheel]

Bubbas Boys, been there done that and got the t shirt. It's no fun and games either. When I built my house 7 years ago no one in our rural county knew any different about vents etc. It's the law, you gotta have vents.......or so they thought. I had been here may be 6 months and the first service on the central a/c was free so they came out to check over everything when they found my mess! Water leaking from the floor joist, furnace duct work etc. They told me that I need to condition my crawl space and they would send me the info to study. Well I sure wish there had been a "wharton" in my life back then. The information he just gave you is spot on.

After lots of research I went back and insulated, put 2 layers of plastic down and up the side of the walls, covered around all the pillars and sealed all the joints after making large overlaps. Sealed the foundation plate and sealed up all the vents. Then went and added a 50 pint dehumidifier and set it for 45% and let it rock for about 2 weeks. When it finally got dried out I suited up in protective clothing and mask and sprayed the seals with a bleach solution to kill any mold that might be hiding.

When all that was done I was able to add a timer to the dehumidifier and run it during the day in the summer from about 8 to 8 for a total of 12 hours a day. During the winter I just cut it off. I wish I had a picture of it but my crawl space is a lot nicer than houses I've been in. You could actually live under there it's so nice. I really wished I would of done more research on climate controlled crawl spaces before I built. It would of been much cheaper to have done it to start with. I actually think my power bill has been reduced by conditioning my crawl space.

I wish you luck, IMHO it's the only way to go!

[wharton]

Thanks Tarheel.

Two things I forgot to add. First, taking care of yourself. Mold is under- respected as a potentially nasty health issue. I didn't take enough care earlier in my career, and now I have pretty serious respiratory allergies. Don't know if it's cause and effect, but months of working in moldy, wet crawl spaces probably didn't help. Best protection would be a disposable Tyvek suit and a proper respirator.

Bleach. Bleach is nasty stuff. I have used a ton of it, and still spray it with a small pump sprayer, when dealing with this issue. Clorox brand is far more effective than generic for some reason, and Clorox brand "Splash-less" is some crazy, half jellied stuff that will NOT work in a pump sprayer. That said, it isn't very effective on totally eliminating the problem, it will beat it into submission, but it will reoccur, in the same areas, as soon as conditions are right. It is also toxic and really something that you don't need to be breathing or soaking in. Just saying, but keep in mind I have done it far too often, LOL. There are other products that are spray applied and supposedly far more effective, and less toxic, they are also exponentially more expensive, so I haven't used any myself. Good luck.

[Tarheel]

Originally Posted by wharton

Thanks Tarheel.

Two things I forgot to add. First, taking care of yourself. Mold is under- respected as a potentially nasty health issue. I didn't take enough care earlier in my career, and now I have pretty serious respiratory allergies. Don't know if it's cause and effect, but months of working in moldy, wet crawl spaces probably didn't help. Best protection would be a disposable Tyvek suit and a proper respirator.

Bleach. Bleach is nasty stuff. I have used a ton of it, and still spray it with a small pump sprayer, when dealing with this issue. Clorox brand is far more effective than generic for some reason, and Clorox brand "Splash-less" is some crazy, half jellied stuff that will NOT work in a pump sprayer. That said, it isn't very effective on totally eliminating the problem, it will beat it into submission, but it will reoccur, in the same areas, as soon as conditions are right. It is also toxic and really something that you don't need to be breathing or soaking in. Just saying, but keep in mind I have done it far too often, LOL. There are other products that are spray applied and supposedly far more effective, and less toxic, they are also exponentially more expensive, so I haven't used any myself. Good luck.

Glad you caught that for me, Yes DO NOT use bleach unless you have special breathing apparatus especially in a confined space. I did have a sealed mask with fresh air (retired fireman) to use. Mold & bleach will make you very sick and I suggest you get a professional if you don't have the proper gear.

[cindy71]

I am also having problems crawl space holding water. My home is old so sometime in the past they closed up around the pillars. I am thinking about opening it back up. What do you think?