# Crawlspace insulation



## TheRambler (Jan 1, 2015)

Howdy folks, looking for some advice on insulating my crawlspace. I crawled down there yesterday and found to my surprise that only about 60% of it is insulated. The insulation that is there is fiberglass batts between the floor joists. Under my stove room, there is no insulation at all, crawlspace area of about 15x20 give or take a bit under this room. This area is probably 3/4 of the total area in the crawlspace that currently has no insulation.

I also found lots of random areas in the attic areas where sections of batts are missing, maybe 10% of the total attic area that is accessible has missing batts. Seems like wherever they ran elec wiring or plumbing there Is no insulation.

For the crawlspace, its a tight area, install of anything will be a big pita. So I was thinking about using reflectix and stapling it to the joists. According to their website this would provide r-16 installed in this manne, which is much better than 0. This would also be cost effective and installation easier I think. I have about 2ft to 2 1/2ft in most areas with some places 3ft or maybe a little over of overhead clearance...aka lots of belly crawling

For the attic I plan to replace the missing batts with fiberglass batts.

Is the reflectix worth doing, or should I just suck it up and go with batts down in the crawlspace?

TIA for any and all advice


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## woodgeek (Jan 1, 2015)

Do a lot of research before you do anything, 

Yup, many workers in attics pull batts out of the way and DONT put them back.  Sucks.  In my house they also like to walk on the rigid ducts, and break all the seams, doubling my heating bill until I got it fixed.

In random order...
--think about attic airsealing (before insulating)
--think about sealing and insulating your crawlspace around the edges (rather than the floor) and putting a membrane over the crawl floor to keep soil smell/gases out of your house.
--reflectix is junk.  Give it a miss.


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## TheRambler (Jan 1, 2015)

The floor of the crawlspace is concrete slab, I assume the membrane would be only for a dirt floor? I will definitely be doing lots of research before doing anything. Most of the ceilings in my house are cathedral so really no way to do sealing up there without opening up the roof I assume. I have access to the attic area above the 3 bedrooms and the kitchen area, and to most of the basement. Is there a good resource to look at in regards to attic airsealing? Other than around light fixtures etc, what else should I be looking for?


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## woodgeek (Jan 1, 2015)

I would just google "house airsealing" and sift through the info.

If you are cathedralized, you are either all set there, or there is not much you can do.  

With a slab under the crawl, I would def seal and insulate the perimeter rather than doing the floor overhead.  Is it dry down there?


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## TheRambler (Jan 1, 2015)

Yes its dry, have not seen any evidence of water intrusion either.


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## begreen (Jan 1, 2015)

Our crawlspace is insulated around the interior perimeter. Works great. It never gets below 60F now. This warmed up our floors and it keeps a warmer ambient around the insulated forced air ducts. The vent covers come off in summer.


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## woodgeek (Jan 1, 2015)

If you do the perimeter, you will have to decide to vent or not to vent in the sumer.  If you use central AC a lot in the summer, you might keep it sealed to the outside, but vented to the interior, e.g. with a (small) branch duct from the CAC.


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## semipro (Jan 1, 2015)

Are there any pipes, ducts, or mechanical systems in your crawlspace? 
If not then insulation and sealing at the floor joists may still be a good option though I realize space is tight.

If you insulate the crawlspace perimeter and condition the space via CAC I'd be concerned that water may still enter the crawlspace through the concrete slab.  It will unless the slab has a water barrier like poly sheet under it.  I'm talking water vapor here not liquid water. A simple masonry sealer may take care of that though. 

Spend some time reading at Energy Vanguard, Building Science Corp and Greenbuildingadvisor, among others, would be a good start.


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## woodgeek (Jan 1, 2015)

If there is CAC down there duct leakage would presumably be sufficient to keep it ventilated.  LIke the masonry sealing idea.


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## begreen (Jan 1, 2015)

Yes, we have a heavy poly sheet covering our crawlspace dirt floor. There is no sealing of the masonry walls, the foamboard is glued directly to it. After 8 yrs there is no sign of any mold or other problems, but we have dry summers with lower humidity than the east coast.


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## TheRambler (Jan 1, 2015)

The crawlspace does have several C/AC/forced air heat ducts running through the space, as well as a few water lines, and the septic plumbing where it all meets and exits.


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## semipro (Jan 1, 2015)

Then sealing the crawlspace slab and sealing/insulating the walls is probably your best option.  BuildingScience.com has some good articles on how this is best done.  If you don't want to do it yourself there are companies that specialize in that sort of thing.

This is very good article on the subject but a bit dated.  I believe they have more recent related publications. http://www.buildingscience.com/docu...w-light-in-crawlspaces/?searchterm=crawlspace


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## semipro (Jan 1, 2015)

woodgeek said:


> If there is CAC down there duct leakage would presumably be sufficient to keep it ventilated.


Good point and one I hadn't considered.  All that would then be needed is some small return vent between the crawlspace and conditioned living area.


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## valuman (Jan 3, 2015)

I'm not a building energy engineer, but I'd sure recommend having someone spray those crawl space walls and rim joists with closed cell foam. Both air sealing and insulation will be reliable that way.


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## FTG-05 (Jan 3, 2015)

When we built our Madison, AL house in 1994, I had R-19 insulation installed in the floor joists.  In 2012, most of that insulation was just home building crap for rats, full of moisture and a good portion of it falling out from between the joists.  I had it all pulled and it far better for it.

The latest info is to not insulate the floor joists in houses with a crawl space, no "ventilation" and very heavy visqueen/plastic on the ground to prevent moisture intrusion.  That's basically what we did and the house and crawl space became much dryer.

I used a lot of that Reflectix in my Madison house in the attic.  Made the attic space much cooler and therefore my house a lot cooler.  I'll be installing a bunch of it in my new house this spring well before the summer temps hit.

Good luck,


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## semipro (Jan 3, 2015)

FTG-05 said:


> The latest info is to not insulate the floor joists in houses with a crawl space, no "ventilation" and very heavy visqueen/plastic on the ground to prevent moisture intrusion.


All good as long as you seal/insulate the crawlspace walls and rim joist areas and provide some ventilation between crawl space and living space. 



FTG-05 said:


> I used a lot of that Reflectix in my Madison house in the attic. Made the attic space much cooler and therefore my house a lot cooler. I'll be installing a bunch of it in my new house this spring well before the summer temps hit.


If you want a radiant barrier you're better off installing one, not bubble wrap with a reflective coating.  The claims made by this company on their R-values are questionable at best.


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## woodgeek (Jan 3, 2015)

Conventional wisdom is radiant barriers for attic cooling are not cost effective north of the mason-dixon line.


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