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Old 07-01-2011, 07:49 AM   #1
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crawl spaces are complicated


Hi to all, located in Idaho. My crawl space has fiberglass insulation between the joists, a 6 mil barrier and 2 small cross vents. As of yet the wood is dry. Only half of this space was finished this way until now. Can I expect problems with the exposed joist ends? If so what can I do? The house was built in the 1930s.

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Old 07-01-2011, 09:09 AM   #2
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crawl spaces are complicated


Is the vapor barrier located on the ground or on the bottom of the joists? What do you mean by exposed ends? Do you mean the edges between the fiberglass insulation?

The proper way to construct a floor system over a crawl space is to install a kraft-paper faced fiberglass batt insulation into the joist bays with the kraft paper facing tight against the floor sheathing. Code requires that the vapor barrier is on the warm side in winter. Once the insulation is fully installed then you should install an air barrier over the bottom of the joists. Tyvek is a good material for this, but anything that is an air barrier will work. DO NOT put a vapor barrier at the bottom of the joists as it will trap moisture in the floor deck and create mold. The air barrier is to stop the movement of air through the fiberglass insulation. Allowing air to circulate through the fiberglass reduces its effect R-value significantly. Think of adding the tyvek to your attic space to if you have exposed fiberglass. The 6-mill poly vapor barrier should be laid against grade and if possible protected by some kind of overlay if you access the space regularly. Having only two vents within the space should be adequate if they are free or dirt and debris and are located on opposite sides of the space to assist in a true cross-ventilation.

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Old 07-01-2011, 11:19 AM   #3
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Hi, Thanks for the advice,yes I did mean the edge of the joists sticking out past the figerglass and I have that install ed paper to the warm side.The 6 mil poly is on the ground.The tyvek sound like a very good idea! Do I just staple it to the edge of the joist and cover the whole insulated surface?,and is it ok to cover the vents in the winter?
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Old 07-01-2011, 11:55 AM   #4
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There; by doing that (putting up a Tyvek air barrier) you've gone and done what I mentioned in a previous post, about 'warming the joists'.
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Old 07-01-2011, 12:16 PM   #5
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Yes, staple the tyvek right to the bottom of the joists and tape around any pipe penetrations.

I would not cover the vents in the winter. You want to ensure that space is ventilated to dissipate moisture. Even though you have it on the floor and at the floor deck, there are still paths for moisture to enter the space.
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Old 07-01-2011, 01:43 PM   #6
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Quote:
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Yes, staple the tyvek right to the bottom of the joists and tape around any pipe penetrations.
I think I would use button cap nails & Tyvek tape, same as if you were installing Tyvek as a house wrap. Otherwise you destroy the Tyvek's capability as an air barrier.
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Old 07-01-2011, 02:31 PM   #7
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I was down double checking the insulation to see if any fell or some ajustment and realized I have a problem.With the joist bays now full of insulation there is no way I am going to get tyvek in place.There is only about 7" from the joist to the dirt.There is a channel on each side of the crawl space and I used the empty Joist bay to install insulation to the one next to it.I will need an army of mole people to pull this off.
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Old 07-01-2011, 04:29 PM   #8
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crawl spaces are complicated


littlecleo is right with the fasteners for the best installation.

As far as the 7" clearance, best of luck. Without seeing the space, I couldn't begin to give you an idea on how to tackle all that.
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Old 07-01-2011, 09:47 PM   #9
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My dad is a heating and AC man (and plumber and licensed electrician). When I asked him once about putting insulation between the joists he said that laying visqueen on the dirt and then insulating around the block was the way to go. My crawl space has a door off of the basement and he said to leave the door open so heat from the basement would circulate and warm the floor. Made a difference in my living room.
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Old 07-02-2011, 06:49 AM   #10
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Well would it be better to put the tyvek where I can and leave the rest?
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Old 07-02-2011, 07:19 AM   #11
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Tanya: nowadays, the tendency is to 'condition' crawl spaces i.e.bring them into the house envelope by opening doors, insulating the walls, closing off the vents (sometimes) and heating and/or cooling it just as you would all the other rooms of the house. There are a number of reasons for this; but mostly because now we insulate more than they did when the houses were built and that changes the airflow dynamics of the space. So, nowadays - and ideally - the walls and floor are insulated, air movement is controlled and there is no need for under-joist insulation. I think that's what you did with the resulting difference you feel in your living space above it...up here, we've been known to spray-foam the walls even - a costly but effective way of turning cold crawlspaces into warm areas...

pwa: you may be at the point where the law of diminishing returns applies, where you can only do so much before your time and effort may be more profitably spent elsewhere. Either way, I'd do as much as you can since you don't seem to have much of a problem now. I mean the point about warming the floor joists is good in theory and the Tyvek is one solution. But if you only have 7" headroom down there and to excavate that becomes a pain, well, you can only do so much. I'd cover as much of the ground as you can to reduce the moisture down there. And keep an eye on the ventilation.
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Old 07-02-2011, 08:01 AM   #12
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finally some good news,I thought I would be advised to start diging.AS much as you can sounds alot better than you better
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Old 07-02-2011, 08:14 AM   #13
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Oh yeah, I have some left over insulation,can I just lay that on top of my loose fill fiberglass in the atttic with the paper up. Thanks for all the advice
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Old 07-02-2011, 08:14 AM   #14
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One TV program I saw had a similar problem - but it was in Ontario...to excavate the crawl space meant a crew of four had to take off the floor above it (they were replacing it anyways) but they went the whole nine yards: insulating the walls with spray-foam, cover the floor, and close the vents. The crew admitted that excavating i.e swinging shovels and pick-axes between 16" joists and then digging out the earth by hand in 5 gallon buckets was really no fun at all.

But that's extreme. And no budget in mind...

Air infiltration is another big area of concern no matter what the climate; so air-sealing drafty windows and vents is another area where something like 40% of your energy losses can be effectively eliminated. A good place to look at as well.
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Old 07-02-2011, 08:21 AM   #15
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Yeah there not much fun to be had in my crawl space.While the energy savings will be nice I just hate to see somehting done half-ass,and try to do things right the first time.But sometimes theres only so much you can do.

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