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  1. #1
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    Default What to do in a crawl space

    I recently moved into a new house...NEW to me but built in 1953. Its a ranch, but at one end there are two shallow steps that lead into two bedrooms and a bath. My question pertains to what is beneath that, I have a full basement under most of the house but where those stairs are the full basement stops and there is a crawl beyond that...As of right now the crawl has a plastic vapor barrier on top of what looks to be a dirt floor.The plastic is stapled to a very old wooden frame, but the wood is so old that it is rotten and falling apart...

    Question 1. Should I remove everything and build a new frame? do I need a wooden frame? can I just cover the dirt with plastic and be done with it?
    The ceiling of this crawl is insulated but the walls and floor are not, there are also two metal grates(vents) which let an enormous amount of cold air into this area.
    Question 2. Can I close off these vents or will that lead to mold growth..Reason I ask is with this area beneath the bedrooms they are constantly cold.
    Thanks to anyone that can lead me in the right direction, Ryan.

  2. #2
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    Default Re: What to do in a crawl space

    Ryan,

    1- No you don't need the wood framing.

    2- The plastic is there to reduce (not eliminate) vapor transmission from the soil to the air above.

    3- The vents are there to reduce the vapor content. You do need those. Since this space is not heated, you should never close the vents. The opposite is true; the more venting the better.

    4- Covering with dirt will help protect the plastic, but will hold moisture like a giant sponge. You want less moisture down there, not more.

    5- If this space makes the bedrooms cold, then increase the insulation and vapor barrier at the underside of the floor.

  3. #3
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    Default Re: What to do in a crawl space

    Quote Originally Posted by HoustonRemodeler View Post
    Ryan,
    No you don't need the wood framing.
    Nor do you want it near the ground where termites might see it as a free lunch and continue eating!


    The vents are there to reduce the vapor content. You do need those. Since this space is not heated, you should never close the vents. The opposite is true; the more venting the better.
    This is not always a 'given'. Here in the upstate of SC, unless a crawlspace has a lot of moisture many folks in the know close the vents during the cold months and it does no harm while helping keep the floors a bit warmer. We open them in the spring and leave them that way till winter comes again. If you try this, be sure to keep a check on dampness in the crawlspace and if it seems to increase it, then leave the vents open.

    If you don't live where high atmospheric humidity is the norm, one cheap way to monitor crawlspace dampness is to put an unopened box of baking soda upright on a high spot near the middle of the crawlspace, then cut it open and check it a month later. If it's still basically a powder, you're dry. If it's slightly caked in the lower quarter but basically powder above you're OK. If it's all somewhat caked, you're moist, and it it's all caked solid or totally soggy then you've got problems. The very bottom 1/2 inch will probably be caked hard or mushy regardless as it will draw some moisture from ground contact on the plastic vapor barrier . Disregard that and analyze the rest. Baking soda is benign and does not attract insects so don't substitute another powder which may not have these properties. This will give you a general idea of what's going on.

    Phil
    Last edited by Mastercarpentry; 12-10-2013 at 09:46 AM.

  4. #4
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    Default Re: What to do in a crawl space

    Back in my former home of Chicago, such crawl spaces were normally sealed and treated as part of the contiguous basement. Heated air from the furnace was allowed to enter this area. Often, the floor would have a concrete floor and became useful storage.

    Out here in Portland, Oregon, the crawl spaces are vented to the exterior and normally left open. The floor above is insulated. During cold spells, the vents are closed to conserve heat, as the water pipes are down there. We are presently having temps down in the teens and I made a point of going around and closeing them all to avoid problems. Come more seasonal temps, i.e. above freezing, I open them up to avoid moisture problems. There is merely a 6 mil plastic over the earth. In areas with high water tables, people will frequently have sump pumps to keep it dry down there.

  5. #5
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    Default Re: What to do in a crawl space

    Thanks for the replies...One more question, why would you leave the floor DIRT? The crawl on the other side of the house has a concrete floor.

  6. #6
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    Default Re: What to do in a crawl space

    The simple answer is money. If it doesn't need to be spent then why do it? Dirt crawlspace floors are usually no problem, so the money goes elsewhere. And simply concreting them doesn't always fix moisture issues down there either- sometimes it just makes for a longer-duration pool for water to stay in which aggravates the moisture problem.

    Encapsulated crawlspaces are becoming the 'rage' these days but usually have a negative cost-benefit ratio and they can introduce other problems such as a space for radon to collect in if there's any leakage in the sealing system. Usually the best system is a ventilated crawlspace with floors and utilities insulated as needed. Otherwise you might as well build on a slab.

    Phil

  7. #7
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    Default Re: What to do in a crawl space

    Thanks for that explanation, so what would be the best thing to do in this space... Should I just replace the plastic on the floor (it has ripped because of the wood framing rotting away) and then re-insulate in between the rafters...what should I use to do this..R-30 or should I go thicker, and will the faced insulation be the way to go or should I get unfaced and cover the bottom with plastic. One more question, what thickness should the plastic be, is 6mil enough or do I need something thicker? Sorry for all the questions but I'm clueless as to what to do with this space.
    Thanks, Ryan

  8. #8
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    Default Re: What to do in a crawl space

    Ryan,

    1- it helps if you number your questions

    2- yes

    3- thicker is better as long as it remains fluffy

    4- The vapor barrier goes toward the side with the most heat year long

    5- I'd put the plastic under the joists if that's the climate you're in. Tyvek would be a good substitute as its harder to rip.

    6- 6 mils is plenty

  9. #9
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    Default Re: What to do in a crawl space

    You've got 2 things going on here: Handling any moisture in the crawlspace, and insulating the floor above it. They do interact to some degree, but can be addressed separately with good results.

    I don't like a sealed vapor barrier (tyvek or poly) up against floor joists because if any moisture happens to get into the system (condensation, water leaks from plumbing or spills from above) they that will retain the water causing rot or allowing mold to grow there. Better for it to be open where you can easily see any problems before they get big, or to use a plastic mesh netting for this purpose. A 6mil vapor barrier on the ground should be enough but heavier will last longer. If after this basic approach you still have moisture problems then you're looking at needing more ventilation, a more water-tight ground covering (could be concrete), or encapsulation of the crawlspace.

    The fiberglass insulation needs to fill the spaces- don't short yourself at the ends. If it has a paper vapor barrier, that belongs on top towards the conditioned space when used over a crawlspace for the reasons noted above. You should look for unsealed openings, especially at the rim joist (outer edges) and where wires, pipes, etc enter the walls. One of the problems with insulating floors is that the bottoms of the joists are usually not well insulated, often completely exposed below. While wood is a pretty good insulator, there is still some thermal transfer going on like this. Rather than having them exposed you can apply strips of rigid foam to cover them, making those an inch or two wider on either side. If you put these up first, then install the fiberglass batts with mesh to hold those in place over those strips, that's about all you're going to get a good cost-to-benefit ratio for (unless you live in the Arctic).

    The benefit of this approach is that the house will still 'breathe' and no excessive moisture will be happening underneath, plus if there are ever any water problems in the house you can pinpoint them by looking where the fiberglass is trying to get through the mesh- it will dangle and look 'shaggy'. Floors will always be cooler than the room, but they shouldn't be downright cold.

    Phil

  10. #10
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    Default Re: What to do in a crawl space

    Back in the Mid-50's in Chicago, there was a large builder who was building low priced entry homes. He used a rather unique method of sealing the crawl space tightly and then using a down draft furnace to presurize the entire space. When a vent was needed for the rooms above, a hole was cut and a vent dropped in. It seemed like a clever idea and if the crawl space were insulated and really tightened against air leeks, should be a viable way to heat a ranch home.
    For sure, the floor would always be foot warm. The money saved on metal ducting would counter the sealing and insulation neccessary. I am not sure this would be a great system for air conditioning. It would be darned cold down in tha crawl space and cold air does not like to rise. Great place for an old fashioned root cellar though!

    The Romans did something similar. They would have open fires in a basement chamber and the flue would travel back and forth under the floors, warming them.

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