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Old 10-16-2013, 09:21 AM
 
16 posts, read 44,086 times
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Hi all,

Read thru a lot in this forum and need to have some clarification.

If we put 15 Mil vapor barrier down, close the vents between Mar- Sept, run dehumidifier. And open the rest of the months, is this the right thing to do? It's about 2000 sq ft, how many of dehumidifier needed?

Currently, have 6 mil almost all covered. The crawl space dirt under the plastic is damp, not completely dry and not water, just sweating in the summer on the duct and A/C unit, a little mold here and there, all vent are open.

Anyone has this experience please share how you have handled.

Also need the tips for putting down the vapor barrier. What to use in the corner to stable it down and do I tape it on the concrete wall and bricks? Best way to work around on the concrete block posts?

Anyone knows someone would put down vapor barrier for reasonable charge?

Thanks!
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Old 10-16-2013, 09:25 AM
 
958 posts, read 1,590,220 times
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Quote:
Originally Posted by nc6588 View Post
Hi all,

Read thru a lot in this forum and need to have some clarification.

If we put 15 Mil vapor barrier down, close the vents between Mar- Sept, run dehumidifier. And open the rest of the months, is this the right thing to do? It's about 2000 sq ft, how many of dehumidifier needed?

Currently, have 6 mil almost all covered. The crawl space dirt under the plastic is damp, not completely dry and not water, just sweating in the summer on the duct and A/C unit, a little mold here and there, all vent are open.

Anyone has this experience please share how you have handled.

Also need the tips for putting down the vapor barrier. What to use in the corner to stable it down and do I tape it on the concrete wall and bricks? Best way to work around on the concrete block posts?

Anyone knows someone would put down vapor barrier for reasonable charge?

Thanks!
I used duct tape to fasten the plastic to the cinderblock foundation. None of it held. but it didn't matter for me. The amount of vapor that sneaks out throught the side is small compared to what was leaching up through the whole clay ground. I also run a dehumidifer.
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Old 10-16-2013, 10:35 AM
 
256 posts, read 340,364 times
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15 mil isn't necessary unless you frequently access your crawl space or use it for storage. You can get by with nylon reinforced 6 mil plastic. Attached the wall pieces first with two-sided butyl tape. It sticks well to the block as long as there's no dirt. You can further attached the wall pieces with foundation pins. After all wall pieces are in place, cut your floor pieces to size. Allow about a 12" overlap and tape the seams with a waterproof tape. Tyvek tape works. You don't have to, but you can anchor the floor piece with landscape fabric pins. Tape any holes you make with the tyvek tape.

If you close the vents, you'll probably need to run a dehumidifier to keep the humidity down. Remember, you'll also get some air leakage around your sill plate and rim joists if they aren't sealed. Also, why open the vents during the winter? Unless you have a furnace down there that requires combustion air, I don't see a need to do so.
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Old 10-16-2013, 11:00 AM
 
2,410 posts, read 6,721,522 times
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I've purchased tape and liner here:

Crawlspace Depot

The PE tape works well to seam the liner but the butyl tape is better to connect to masonry columns/walls.

The liners with a scrim layer are tougher than plain PE and resist tearing better.

They have a location in Greensboro, so shipping is fast.


Frank
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Old 10-16-2013, 12:30 PM
 
2,356 posts, read 2,478,901 times
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If you do not seal the rim/band joists (they have lots of holes from pipes and electrical wires) it will make dehumidification more difficult. They are also an access for cold air in the Winter.

One way
http://youtu.be/V5B5xytcz78
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Old 10-16-2013, 01:27 PM
 
Location: Cary
2,466 posts, read 2,827,781 times
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It's been years since I researched it, but there is no way I'd put down 6mil plastic as a vapor barrier. I remember reading the specs and decided that if I'm going to do the job myself then I was going to use 15mil Vapor block. may be overkill but I wanted to do the job just once and not every 10 years. The builder plastic was doing nothing after just a few years. Hopefully the 15mil stuff will last a long time. I think I paid about $550 for 2400 sq/ft and 3 rolls of the appropriate tape from a local concrete supply company.

Some basic DIY info:
Crawl Space Guru - Vapor-Barrier
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Old 10-16-2013, 02:20 PM
 
16 posts, read 44,086 times
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Thank you all for your help.

TheKlunk, we do have Goodman HVAC unit(2 yrs old) in the crawl space.

When furnace is running, do we need to keep all the vents open? How many of the 70 pint Home Depot dehumidifiers are needed for 2000 sq ft crawl space?

Thanks.
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Old 10-16-2013, 02:26 PM
 
Location: Cary
2,466 posts, read 2,827,781 times
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The dehumidifiers should show sq/ft recommendations. Note that there is probably a Y-drain in the crawl space that you can tap into for drainage. A 20 gallon plastic tub can work until you get the drainage squared away. You'll just have to empty it by buckets.
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Old 10-16-2013, 04:13 PM
 
Location: Near Falls Lake
2,300 posts, read 1,676,833 times
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Let's think about this for a minute! Do you really have an existing problem such as mold, mildew, water intrusion or deterioration or have you been doing a lot of reading and decided this is what you want to do? in the event you have an issue what is your budget for repair?

If your problem is high humidity in the crawlspace and that's very common here, what I am telling you will work perfectly fine and not bust the budget! If you have water intrusion issues that is a horse of a different color and needs to be addressed. 6-mil vapor barrier is perfectly fine to prevent moisture from migrating into the structure above. Is it as strong as thicker 10,15,20 mil barriers-of course not but unless you are living down there (and most people don't) the thicker vapor barriers (although nice) are overkill. If you plan on staying in your house for 30 years then installing the thicker barrier would be preferred. However, for the most part,the 6-mil will serve the purpose at significant cost savings. Mine is 20 years old and still looks good. Install the barrier over 100% of the surface area making sure to overlap the joints-secure and tape if you like but it is not really a huge deal if you don't. I've been in thousands of crawlspaces and running the barrier up the wall gains you very little and serves to potentially obscure other issues. Install a properly sized dehumidifier with a drain (recommend using a pvc pipe to the exterior or into a sump and out). Set the dehumidifier to somewhere around 45% plus or minus a little. It will run when it needs to run and shutoff when it needs to be off. If you have mold on the wood structural members no is the time to remediate. This can be done a few ways and I'm certain there are plenty of posts that describe the methods just keep in mind, bleach is NOT the right product! If you have a gas furnace combustion air will need attention. Failure to do so can/will create a carbon monoxide issue. I'm not a fan of sealing the band and I've never seen it as much of an issue with a properly sized dehumidifier. Sealing it may obscure view from those pesky termites!

All this being said, let me share with you an experience I had today with a "sealed/conditioned" crawl space that was done by one of the largest contractors in the area. The contractor in question charged over 10k for this repair (which was in Chapel Hill). This house had water and humidity issues. A "French Drain" was installed on the interior of the crawlspace into a sump-ok. However, they didn't fix the significantly negative soil grade around the perimeter that was directing water toward the structure nor did they bother to extend the gutters away from the house. The downspouts just terminated right at the foundation. By the way, the exterior grade was very easy to get to and would not have been difficult to fix properly. Insulation under the floor was missing at random locations throughout, the drain for the dehumidifier was a garden hose (not pvc) that ran uphill, there was mold on the floor joists and girders everywhere with no evidence of any attempt at remediation. A 20-amp breaker was installed in the panel with improper sized wiring (14 gauge) and the dehumidifier was installed with an old extension cord into a non ground fault protected circuit. The lesson here: Choose your contractor carefully-this particular one does a very nice, slick presentation unfortunately the work was very slipshod. When it comes to this type of work, the highest price doesn't necessarily get you the best quality.
For anyone who wants to know who the contractor is you can PM me.
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Old 10-16-2013, 05:22 PM
 
Location: Cary
2,466 posts, read 2,827,781 times
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As a person that hates spiders, yeah...I'll opt for the 15mil stuff so that I don't have to do it again.

The points about water intrusion are very good. When i redid my crawlspace I also re-sloped my soil near the foundation and ran tubes from my downspouts under my mulch and to the front of my house where it drains down my lawn away from the house. I also installed gutter guards that have done a great job in keeping leaves and pine needles from clogging my drains. This has helped keep the foundation area much drier than before.
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