Crawlspace Insulation Issues

[Unregistered]

I saw in some previous thread that styrofoaming the exterior walls of the crawlspace is a better choice than insulating between floor joists. I started digging around the net and opened a can of worms.

I was wondering what would be the best method for my place. It's a 950 sq ft 1952 single story pier and beam. The "skirt" is basically stucco on lathe (1/2" or so thick), vented and has two access doors, dirt floor, plumbing/electrical exposed. I'm in Austin, TX.

What's my ideal combination of plastic lining, insulation/styrofoam, venting, etc, etc?

Thanks much!

[Wgoodrich]

Per the IRC Austin Tx has a 1500 to 2000 heating degree days. Crawl space requires an R5 in that area per the IRC. This is a much thinner insulation value than we have in my area.

Check for styrofoam insulation board rated with an R5 value then scoop the dirt away from your skirting then cut the board to fit tight from dirt to floor joist then shove into place making a tight fit board to board and dirt floor to ceiling. Then shove the dirt against the styrofoam board to hold in place. Then use torn pieces of fiberglass insulation shoved between the floor joist ends to seal that area also. Lay a bisquine sheeting on the dirt floor first for a vapor barrier as required.

COPIED SECTION 2003 IRC;

N1102.1.7 Crawl space walls. Where the floor above the
crawl space is uninsulated, insulation shall be installed on
crawl spacewallswhen the crawl space is not vented to out-
side air. The required R-value in Table N1102.1 shall be ap-
plied inside of the crawl spacewall, downward from the sill
plate to the exterior finished grade level and then vertically
and/or horizontally for at least an additional 24 inches (610
mm). The exposed earth in all crawl space foundations shall
be coveredwith a continuous vapor retarder having amaxi-
mum permeance rating of 1.0 perm [(57 mg)/(s · m2 · Pa)],
when tested in accordance with ASTM E 96.

COMMENT:

Eastern Texas has a heavy termite concern with a slight to moderate termite concern for western Texas splitting the state almost in half east to west per the IRC. When installing styrofoam per the IRC only those area with VERY heavy termite concern need further protection with styrofoam installation. The installation you discribe should not be a concern for extra precautions per the IRC concerning termites and your styrofoam insulation.

HOpe this helps

Wg

[Unregistered]

outstanding...thanks a load! what's a good resource for this quantity/type of styrofoam? i'm not familiar with the r value of the 4X8 sheets you can find at the big box stores, and the only white styrofoam insulation i've seen at said stores are packs for metal garage door insulating. i'm sure there's a better place than going to michael's or hobby lobby and ordering some god-awful quantity.

thanks again.

[suemarkp]

You need to look at home improvement stores (home depot, lowes, large hardware stores) and not craft stores, as craft foam may be too flammable. Usually its in the insulation section stacked up high. But it may be outside in their storage yard. Ask if you can't find it and see if they can order some for you. The R value varies based on the exact plastic formulation used, but is around R4 to R7 per inch. So 1.5" sheets would be plenty and maybe even 1" sheets.

[Unregistered]

flammable and expensive and all hell, i'd expect. a couple more things....IRC section quoted refers to crawlspace NOT vented to outside. mine is. any change to the suggestions? also, as far as securing the foam to the perimeter, would you actually fasten it to structure, or is the displaced soil the sole means necessary?

[mdshunk]

Generally the soil is all that holds the styrofoam. If there are some pieces that are of special concern, they sell a screw/washer assembly that is specifically for attaching foam board to concrete. The washer is a quite large plastic washer, and the screw most closely resembles a Tapcon screw.

[suemarkp]

Insulating a vented space seems self defeating. The previous owner of my house did the same thing in the attic -- insulation between the rafter spaces, but you can see daylight every 10 feet through the soffit vents in the floor. Doesn't make much sense!

If you close off the crawl space vents in winter, then insulating would make sense. But perhaps that area was not designed to be closed off without venting?? You can keep it vented and insulate the floor (and any ductwork down there too). Whether you should seal off and insulate a vented crawl space depends on local conditions (temp & humidity). You may be OK if you vent in summer and close off in winter.

[Unregistered]

I would insulate the floor bottom, between the joists. Vapor barrier towards living space. Box frame around any plumbing or heating so you can insulate those from the cold side as well. I would also install a minimum 6 mil. poly vapor barrier on the dirt floor, regardless of venting.

OR

block off the vents and insulate the walls and the rim joist (between the floor joist) I would then also still cover the dirt floor with the 6 mil. poly vapor barrier. The vapor barrier should be overlapped at the seams by at least 2 ft. and weighted down in spots around the perimeter. If you roll out the floor vapor barrier first, it will make insulating the walls a cleaner job. (As in, not rolling around in the dirt)

I would myself opt for #2

[Unregistered]

thanks to all of you. this is precisely what i found when sifting through the net...options upon options. only consistent detail i found was to cover the dirt with plastic. i read that styrofoaming the perimeter was good for the summer, but you'd still have cold floors in the winter (did i mention i have hardwood floors?). insulating the joists spaces seems to make a bit more sense, but would take plenty more work and $$$. i guess ultimately what i'm looking for is the most efficient means for the money. maybe down the road i can invest more.

thanks again.

[Wgoodrich]

The venting is not a concern in the crawl space. In my area we hit 10 below often. The venting if not closed in winter and open in summer during hte winter the popes will freeze even if insulated due to the flow of freezing air through that crawl.

Venting is required for a crawl space. The wording is for concern of venting being able to be closed in teh winter. The vents in this area are most often auto closing crawl space wall vents that open at a certain temp and close at a certain temp automatically. This way if we hit a moist warm indian summer the vents then open and help dry out the crawl during those warm days even in the winter. This is really not a concern though. Many just close the vents same as you close a heating duct vent by pushing a lever on each vent closing in fall and opening in spring.

Now is you want better insulation when you install your styrofoam on the perimeter walls of the crawl you must cut out the styrofoam for the vents in the wall. Save those squares of styrofoam and in late winter shove those pieces of styrofoam from the outside into the vent recesses of the wall. Removing these styrofoam plugs again in the spring and store in garage or attic for next winter. Not required but nice for warm walls.

I have the above in my home and my floors are warm. Remember for effeciency insulate your heat ducts.

As the building inspector I often get complaints about floor insulated crawl spaces. While the Code allows the perimeter or the floor area to be insulated the insulation of the floor makes the crawl space colder thus causing many more frozen pipes as well as increased heat loss of heat ducts in cold area crawl spaces trying to tranfer heat from furnace to the far end of your home.

MY preference after watching this done for 35 years in my area [winters extreme cold about 15 below to average 10 degree winters.

Never install a double vapor barrier. If you install your vapor barrier such as plastic on earth then do not add a vapor barrier on the floor. This would be a moisture trap making your crawl space look like white clouds of mold to build due to moisture trapped. The most moisture comes from teh earth. In this area almost all crawl floors are with bisquine plastic sheets and perimeter of crawl insulated. One exception is manufactured home brought in with floors alread insulated. Many of these have cause frozen pipes in the crawl prompting many to remove that insulation and install perimeter insulation for an even non freezing crawl area. Warm floors seem to be present if you maintain stagnent air in the crawl in the winter by closing your vents.

Just my thoughts.

Wg

[Unregistered]

Hello, I was wondering if someone can help me with my crawlspace insulation installation. I have a mobile home and have built an addition that is 26" above the ground (the ground has a 4" limestone base). This addition is 540 sq. feet and the builder didn't install a vapour barrier (usually it would be installed between the floor joists and the osb board). I live in Winnipeg, Manitoba and the winters here can go to -35 degrees celcius and summers to + 30's with average rainfall. The area will have an insulated skirting with an R value of around 15. It will not be heated. How do I go about insulating the floor joists (I am looking to get an R 40 value in the end). Should I install a thermoflex (which has a built in vp) in between the floor joists then R 40 fiberglass insulation? (the joists are 2 x 12 on 16" centers) or should I install the batts first and then put the thermoflex along the joists and perhaps a heavier vb on the ground? I appreciate any of your comments. The heating ducts will be going in soon (in between the joists and across the joists) and I want to insulate and vb the floor area properly. Thank you... C.

[Wgoodrich]

You are way up north, wow.

Insulating your floor will invite freezing your plumbing and heat loss on heat ducts.

I would install insulated heat duct insulated from the inside of the ducts. Then I would insulate the crawl walls using styrofoam board using the highest R value you can find then using plastic covered fiberglass layering to add up your R value installing from next to the inside of the wall with styrofoam then the fiberglass plastic covered layered inside that. I would suggest no less than R 25 for your area. This will make the floors warm but also maintain non freezing of water pipes less heat loss of your heat ducts and general warmer longer lasting installation.

Just my opinion

Wg