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How To Apply Insulation From Below In Crawlspace

 
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Old 12-17-2015, 07:49 AM   #1
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How To Apply Insulation From Below In Crawlspace


Hi. I have applied fiberglass insulation between floor joist from below in a crawlspace (2' oc). I stapled the paper lip onto the joists while laying on the ground facing up. Now, 6 months later I get a call saying that the insulation is falling down. Sure enough, in many places the staples have ripped through the paper which got soft in the moist crawlspace.

I made the wrong assumption that the paper facing on fiberglass insulation is made to last forever even in moist conditions. Can anyone suggest how to save this job? I thought about nailing it with nails with big plastic washers. Certainly an improvement but I would still have to rely that the paper lip holds over the years.

Any suggestions are much appreciated. Thank you
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Old 12-17-2015, 08:03 AM   #2
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Re: How To Apply Insulation From Below In Crawlspace


Ain't gravity a biatch?
#1 - using FG insulation like this, it must come in contact with the sub floor, if it doesn't it needs to be supported by foam panels
#2 - they make these nice little wire supports to help hold the insulation up - preferably unfaced

As for saving it - probably not going to happen
Is the floor covered in plastic to help prevent moisture from coming in?

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Old 12-17-2015, 08:05 AM   #3
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Re: How To Apply Insulation From Below In Crawlspace


I have seen chicken wire or lath used to hold it in place. And the paper ,vapor barrier , should go up against the floor. Although most time it is done like you did because it is easier to do at the time.
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Old 12-17-2015, 09:39 AM   #4
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Re: How To Apply Insulation From Below In Crawlspace


Tear it all out and insulate the stem walls with a fire retardant fiberglass blanket. Let the heat from the ground radiate up.
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Old 12-17-2015, 11:37 AM   #5
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Re: How To Apply Insulation From Below In Crawlspace


Where are you located?

To do it like the pros do: staple twine to the joists. Zig-zag back and forth every 12" or so.

Don't use paper faced in crawlspaces, and definitely don't have the paper facing down. If the insulation isn't tight to the subfloor, at least block the cold at the rim joist by curling it up. Otherwise that cold air runs all the way through the joist above the insulation.
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Old 12-17-2015, 11:40 AM   #6
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Re: How To Apply Insulation From Below In Crawlspace


Like to are saying above, because, most importantly, exposed paper is a fire hazard.
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Old 12-17-2015, 11:44 AM   #7
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Re: How To Apply Insulation From Below In Crawlspace


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Originally Posted by BarryP View Post
Tear it all out and insulate the stem walls with a fire retardant fiberglass blanket. Let the heat from the ground radiate up.
Some places don't have ground heat

I'm from Fairbanks, Alaska. I think the average ground temp is 31 degrees.
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Old 12-17-2015, 01:15 PM   #8
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Re: How To Apply Insulation From Below In Crawlspace


Thanks for the suggestions. I am in Washington state and radiant floor heating tubes are connected to the sub floor from below. Thus the need for insulation. Thanks again
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Old 12-17-2015, 01:18 PM   #9
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Re: How To Apply Insulation From Below In Crawlspace


Then, wrap the stem wall instead of packing the floor joists. Ground temps in an insulated crawl space will not go below freezing.
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Old 12-17-2015, 03:50 PM   #10
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Re: How To Apply Insulation From Below In Crawlspace


Quote:
Originally Posted by Kempfe View Post
Thanks for the suggestions. I am in Washington state and radiant floor heating tubes are connected to the sub floor from below. Thus the need for insulation. Thanks again
Not that I am an expert on radiant heat...but it is my favorite type of heating

Did you leave an air gap between the insulation and the piping?

If it were me I would leave the current insulation and put a foam board underneath like RMax then tape the seams and foam or tape the edges. The thicker the better in my book, but at least 1.5" for strength, although 2" would be better. Rmax is considered a thermal break, but you might want to check the local building codes for fire. Drywall over anything that has a flame too. The sheets will also insulate the joists creating more of a thermal break. Radiant needs all the help it can get like aluminum dispersion plates.

This is the Rmax insulation commonly available at the box stores. There are other brands...Therma-something or another.
http://www.rmax.com/products/wall-pr...hermasheath-3/

The moisture problem needs to be addressed too. A dehumidifier at the least. Enclosing the crawl space and insulating is probably the best option. If there is water intrusion some french drains might be needed.

If I am wrong on any of it, someone please correct me.
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Old 12-17-2015, 04:27 PM   #11
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Re: How To Apply Insulation From Below In Crawlspace


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Thanks for the suggestions. I am in Washington state and radiant floor heating tubes are connected to the sub floor from below. Thus the need for insulation. Thanks again
Ahh ha, then in this case you do want an air space, and I'd respectfully disagree with BarryP and say that you do want insulation in the joist spaces, or you'll pump a lot of heat into the ground. Radiant heat goes in all directions. Best is a rigid foil faced insulation a couple inches below the tubes, and you can install fiberglass below that.

I've heated a few homes in Fairbanks Alaska this way (-50 degree winter temps) with great success, though tubes in a thermal mass are much better.
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Last edited by Golden view; 12-17-2015 at 04:43 PM.
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Old 12-17-2015, 04:34 PM   #12
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Re: How To Apply Insulation From Below In Crawlspace


Golden view has a legitimate point and it is merely a preference.

I like to keep the mechanicals exposed (less condensation, easy to find leaks)

Otherwise it is a preference with me.

When it comes to insulating the floor under, I would do a R30 minimal. Get 24" tiger claws.

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