Replies

1. 
   Guest_ | Apr 09, 2000 04:53am | #1

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   Yes , the 6 mil plastic is neccessary, we keep it down with clean mason's sand...

   what is your heating system?...if you're running ductwork thru the crawl space then i would insulate the exterior walls with 3" of PerformGuard foam with a cement board bonded to it for flame spread..

   install your vents to conform with code..but plan on blocking the vents so you don't introduce moist air into the crawl space....

   Mike

1. 
   Guest_ | Apr 09, 2000 02:07pm | #2

   *For the vapor barrier, the thicker the better - if for no other reason it's more likely to stay in place. Use plenty of overlap (2' - 3'). Don't bother covering it, but weight it down in strategic places with bricks (not wood off cuts - appetizers for termites.)I used unfaced FG: with the right width, you can just roll it out horizontally and lean it against the walls.I don't like to see the interior surface covered with a moisture barrier: I've seen some homes with rot in the sill plates where they wrapped the plastic up to the sill plates.Condition the crawl, as Mike mentioned, & block them vents (your inspector might require them, but he wouldn't come by later.)Some folks argue conditioning the crawl wastes energy. OTOH, at least in winter, a warm crawl = warm floors = warm feet = warm people = lower thermostat settings.I haven't seen any conditioned crawls with moisture pronblems (mold or rot) even where there was significant water lying on the plastic.Bob

1. 
   Guest_ | Apr 09, 2000 04:10pm | #3

   *Hi There,Because this will be a new construction, you may want to consider all your options with this space.One item you may want to consider installing is a concrete floor, even in your "crawl space".It increases dramatically on the usefulness of your space. With a moisture barrier over granular material, proper drainage and topped off with a 3" concrete slab you will have a healthier environment and an increased storage for seasonal items that normally crowd your garage or workshop with.It also adds to the value of your home for a small investment.Just food for thought.Gabe

1. 
   Guest_ | Apr 09, 2000 04:38pm | #4

   *Bill,

   Around here we use the term "rat slab" to describe what Gabe suggests. It is either 3 or 4" thick and does make a big difference. This would be poured over a 6 mil poly and stone, it would also be a good idea to extend this poly up the sides of the foundation wall to the sill plate. You could embed the poly in a water proof mastic spread on the foundation walls.

   If you plan on putting a wood floor over this space, you will really need to "manage" the moisture coming into this space. You might want to install R.F.I.B. in between the joist bays and caulk all the joints.

   View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle

1. 
   Guest_ | Apr 09, 2000 08:30pm | #5

   *Joe mentioned: <>There's no right or wrong here, but I recommend against extending the poly up to the sill plate.As a home inspector, I see a lot of crawls, some (not many) with plastic up to the sill plates. Sometimes, there's mold under the plastic right up to the top of the plastic, sometimes rot. It's not likely, esp with PT sill plates, but it demonstrates that the moisture builds up behind the plastic. (I haven't kept track of how many were block and how many poured.)Of course, you're going to keep your sill plate well above grade, maintain positive grading away from the house and use good downspout extensions or tiles, which will minimize moisture in the foundation, so it's not worth going to the mat over.I do like the idea of the rat slab.Bob

2. 
   Guest_ | Apr 09, 2000 08:47pm | #6

   *Bob,

   One good thing about cyber space is unless you chance your name to "." you will most likely be able to quote someone exactly. Its clear you have not.

   I said. . . "This would be poured over a 6 mil poly and stone, it would also be a good idea to extend this poly up the sides of the foundation wall to the sill plate. You could embed the poly in a water proof mastic spread on the foundation walls." I haven't seen much mold growing in the mastic have you? Also, I haven't seen much rot in a concrete or block foundation have you?So, if you wish to comment on any statement I make, please make sure I made it and you quoted it correctly.

   View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle

2. 
   Bill_Harbstreet | Apr 10, 2000 04:59am | #7

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   Thanks for the information. Do you mean to "block" the vents year round? I was under the impression that you wanted air flow in the summer and a "closed" crawl space in the winter? Am I wrong? What do you think? Thanks

3. 
   Guest_ | Apr 10, 2000 05:32am | #8

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   Bill

   Codes haven't caught up with it yet, and you wil get opinions to support what you said, but venting an enclosed crawl space that has had
   b all
   the attention to detail looked after to mitigate moisture, ranges from redundant to just plain dumb. Why would you want to go to all kinds of effort to draw warm humid air into a cool dry place and thereby cause condensation, when you can leave the humid air outside with no extra effort at all??????

   -pm

1. 
   Guest_ | Apr 10, 2000 12:32pm | #9

   *Joe,The part I left out, <> is imaterial to the issue I'm raising.The concern I have is that if you seal the inner wall of the crawl foundation, you _might_ get "rising damp", i.e., moisture wicking up the foundation and getting into the framing. The waterproof mastic part raises the identical issue.Is it likely? Probably not. Can reasonable people disagree on this issue? Of course.Bob

1. 
   Guest_ | Apr 10, 2000 12:54pm | #10

   *Bob,

   My post is not about reasonable people disagreeing, its about being quoted correctly.

   I totally disagree with you regarding your wood "imaterial". The issue is to prevent moisture into the crawl space. Your concern about moisture "wicking" up the foundation wall would take place in any case with or without the poly in a concrete or block wall.

   By not having the poly on the wall you have a real chance of moisture migrating into the crawl space from the concrete or block wall. The amount of moisture your walls absorb is a function of how well the outside of the foundation wall was water proofed. Also, if you take the proper steps to "break" the connection between foundation and framing you will greatly decrease your chances of moisture reaching your framing.

   The issue once again was to prevent moisture coming into the crawl space so that moisture will not wreak havoc with his wood floors.

   View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle

1. 
   Guest_ | Apr 10, 2000 05:48pm | #11

   *As an alternative to bringing the poly up to the sill plate, I'm considering lining my footing trenchs with some type vapor barrier BEFORE pouring, and letting this extend about 4 ft. into the crawlspace, and then lapping the crawlspace barrier over the top of it, sealed with double-sided tape. I will also bring the "footing barrier" up the outside of the foundation wall so it will be between the foundation and the french drain that I'm installing along the back footing (there's a hill sloping down to the house that I just can't afford to eliminate and the backside is wide -- 66 ft). I will put waterproofing on the outside of the foundation, but to just above ground level. I'm also putting a french drain INSIDE the crawlspace at the front of the house (downhill side) to take away any groundwater that may make it into the crawlspace. I will install the vents as suggested (then block them), insulate the inside of the foundation walls with foam board, and put in a register with a shutoff damper so I'll have the "option" of conditioning the space if needed. An "active" humidity meter will be very cheap in the near future (if not already) so it seems reasonable to just monitor the humidity at some point.My thinking is, keep the foundation (footings, block, sills) as dry as possible, keep the water out of the crawlspace if at all possible, provide a means of exit for any subsurface water that manages to get in, use a sealed vapor barrier to keep it out of the house, maintain the crawlspace at a fairly constant temperature and humidity (will vary some with the season) to minimize the expansion/contraction of the flooring, use the crawlspace as a "thermal buffer" effective in winter (warmer than the outside air) or summer (cooler than the outside air). Since the crawlspace is essentially sealed, I will test for radon on a periodic basis.I also like the idea of a "rat slab" but will have to run the numbers on it. (Sounds like a lot of trouble but I will be in this house for the the rest of my life and I'm putting lots of hardwood over it.

1. 
   Guest_ | Apr 10, 2000 06:12pm | #12

   *Joe,What do you recommend to "break the connection between foundation and framing" ??

2. 
   Guest_ | Apr 10, 2000 08:18pm | #13

   *

   If you were paying attention to any of the go-zillion discussions on moisture/venting/insulation you'd know what I was referring to. I like to use combination of sill sealer bug shield and sill sealer to create what I believe to be a very effective moisture break between the top of the foundation and the sill plate. Try it. . . you'll like it. . .

   View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle

3. 
   Guest_ | Apr 10, 2000 08:45pm | #14

   *Joe, I can honestly say I've never run across anyone quite like you.... thanks for the info.

4. 
   Guest_ | Apr 11, 2000 05:15am | #15

   *CrustyRefering to my thread on i House Inspector Liabilitythe rotted mudsill I referred to had been installed over exterior tentest fibreboard( Black Joe, Thermax) as a sill sealer. Strips were placed over the top row of block. It turned out to be a very effective wick/sponge for groundwater, and the weight of the building crushed it once it was soaked, causing the rims to tip in places.-pm

5. 
   Guest_ | Apr 11, 2000 12:26pm | #16

   *Crusty:>The same question arose recently: here's some info I posted there:http://webx.taunton.com/WebX?127@@.ee6b303Bob

6. 
   Guest_ | Apr 11, 2000 03:20pm | #17

   *Bob, I posted that question; was trying to pickup a little more feedback here, as well as offer some additional ideas/thoughts. I think the good info you posted is at Bob Walker "Vapor Barrier Under Footings ???" 3/29/00 2:45am

4. 
   Bill_Harbstreet | Apr 11, 2000 03:20pm | #18

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   We are building a house in the Kansas City, Mo area this summer. About 1/3 will be basement and 2/3 crawl space with concrete walls. Can anyone recommend to me the best treatment for the crawl space? It will be vented and access through the shared basement wall. The basement will have a sump pump. I have heard about laying down 6 mil plastic with "buckshot" size rock (easy on the knees?)on top. We will have carpet and wood floor over the crawl space on top of 3/4" t&g OSB. Is the plastic necessary? Can or should I insulate and if so do I use faced or unfaced insulation. All comments will be appreicated.