Vented to unvented crawl space

blinkySeptember 13, 2013

I have a split level with 600 sq. ft. crawl, all below ground with no mechanicals. Crawl is accessed inside through the utility room. I have two proposals to remove the present fiberglass insulation and poly on the floor, clean and kill the mold. Both companies want to replace the poly and run it up the cinder block wall, leaving a space to see termites in future. One company quotes insulating the wall with eps called Boraform, the other insulating between the floor joist using fiberglass in plastic but the vapor barrier on just one side. I have read where it's best to insulate the wall but I am hesitant because on occasion the lower block gets wet from very heavy rain and be blocked behind the insulation. I am also concerned that the hardwood floors will be colder than they are now and noisy. Both would block the vents and add a dehumidifier. Any advise anyone could give me on which method would be better in my situation would be greatly appreciated.

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Any company still installing fiberglass in plastic between the floor joists in a crawl space hasn't a clue.

The most energy efficient unvented crawl leaves the joists uninsulated but insulates the walls and includes a ground cover.

However, no amount of insulation will correct water seeping into a crawl from poor exterior drainage that leaves the block walls wet. That will have to be corrected from the exterior by redirecting water and/or waterproofing the foundation wall. In any case, eps or xps (extruded polystyrene) will be unaffected by the moisture and are good choices for insulating material.

A dehumidifier may be necessary for keeping humidity levels below 50% relative humidity (RH).

Two other considerations are:

1) the provision for air change in the crawl; depending on leakage may not be sufficient. (See here for further info.)

2) if radon gas is present in your area, you may add an exhaust fan system under the ground cover. (See previous link for info.)

Here is a link that might be useful: Building Science Corp. on crawlspace Insulation

This post was edited by worthy on Sat, Sep 14, 13 at 12:40

    Bookmark   September 14, 2013 at 8:16AM
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This post was edited by worthy on Sat, Sep 14, 13 at 8:33

    Bookmark   September 14, 2013 at 8:20AM
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Many thanks Worthy, I appreciate you taking time to reply, gives me the info I need to make the right decision and hopefully help someone who may read your post...

    Bookmark   September 14, 2013 at 10:14PM
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Blinky, I have a split level (tri-level) with a crawl space underneath the entry level. Up until recently I have had no idea how to get into the crawl space. There was a deck on the backside of the house that I had removed this past summer and there is a tiny window in a well that I didn't know was there. The window is a slider that when open cannot possibly be big enough for an adult to fit through. There has to be another way in. The split side of the house is semi-finished on the lower part. I use as a basement. It has drywall but the floors are unfinished. I'm wondering if there might be a crawl space entry from the basement that has been covered by drywall.

Can you tell me where your utility room crawlspace entry is in relation to the stairs? I don't want to just start poking holes in my drywall but I need to find a real entry to my crawlspace soon so I'm hoping split level foundations are similar everywhere. I can't tell you how many evenings I have spent looking for information on where the crawl space entry might be in my house.

    Bookmark   November 23, 2013 at 8:16PM
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My basement level is the same level as the crawlspace floor so the entrance to the crawl is in the utility room on the basement level inside the house. It's about 4 feet from the back wall of the house. I can't imagine somebody dry walling over the access door but anything is possible. Maybe there was an outside entrance that was back filled to level an area for the deck.
Good luck!

    Bookmark   November 30, 2013 at 8:37PM
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Thanks Blinky. I wouldn't have believed anyone would build a deck over an unsealed window well either, but they did. So anything is possible.

Unfortunately 4 feet from my back wall is where a toilet sits in my downstairs bathroom so no way it is there. If there is an entrance from the basement then it has to be under one of the stairwells or closer to the front of the house. I'm on a heavily sloped lot so I'm pretty sure I'm going to find close to that same slope in the crawlspace. It just makes sense that there would be an opening inside the basement. I guess I get to drill a few holes...

    Bookmark   December 1, 2013 at 6:18PM
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Ran across this today, don't know if this applies to your home but might explain why you may not have an access door.

    Bookmark   December 2, 2013 at 8:54PM
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Thanks Blinky. I appreciate that you took the time to try to help me out! Fortunately my house is your average 3 level split with one side split with the living/dining/kitchen to the side over the crawl space. Somebody ran cabling and water over to the fridge so surely that was since the house was built about 50 years ago. I haven't yet begun drilling holes. I took a closer look at the window that looks to be too small an opening for a crawlspace and have decided that in the spring I will have the window removed and a removable door built for it so at least if I have to I can poke my head in and look around from the inside to see if I can see another entrance that has been covered. If not, I'll have to start getting slimmer so I can fit through the window. :)

    Bookmark   December 11, 2013 at 9:31PM
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You might want to give this product a look.

It can be a part of the solution, perhaps

    Bookmark   January 4, 2014 at 11:23AM
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