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diyfun
03-03-2012, 05:50 AM
My unfinished basement has a 87" ceiling height right now. I don't know I should use 1", 1.5" or 2" XPS foam on the floor? The whole basement floor plan will be 6mil poly + XPS foam + 23/32" T&G plywood + engineered wood floor.

dlarrivee
03-03-2012, 06:12 PM
Personal preference, how tall are the people who live there?

cacher_chick
03-03-2012, 08:02 PM
One thing to consider is that a standard door rough-in is 82-1/2 tall. Additional height will be required to install a standard casing around the opening.

diyfun
03-03-2012, 08:17 PM
Personal preference, how tall are the people who live there?

5'10" for now.

grahamW
03-03-2012, 08:41 PM
Can I ask the purpose of the poly? If your basement floor is allowing water up from beneath then you're likely going to have issues no matter what you do (IMHO).

I use ship-lapped, rigid foam insulation and use 2" on the walls and 1" on the floor. Glue to the walls & floor with the correcct adhesive and each seam should be tuck-taped, and spray foam used to fill any gaps around the edges. All rigid foam insulation is mould and mildew resistant and won't hold moisture, even if you have a flood in your basement. You can use mould-resistant drywall as well.

The goal of insulating in this manner is creating a thermal break between the air inside your basement and the air outside. It will eliminate any air movement behind the walls that could lead to condensation.

dlarrivee
03-03-2012, 11:40 PM
Can I ask the purpose of the poly? If your basement floor is allowing water up from beneath then you're likely going to have issues no matter what you do (IMHO).

I use ship-lapped, rigid foam insulation and use 2" on the walls and 1" on the floor. Glue to the walls & floor with the correcct adhesive and each seam should be tuck-taped, and spray foam used to fill any gaps around the edges. All rigid foam insulation is mould and mildew resistant and won't hold moisture, even if you have a flood in your basement. You can use mould-resistant drywall as well.

The goal of insulating in this manner is creating a thermal break between the air inside your basement and the air outside. It will eliminate any air movement behind the walls that could lead to condensation.

Mold only grows on organic materials, concrete, poly, foam, etc. etc. none of them support the growth of mold.

If your basement floods, having gimmicky drywall wont make a difference.

diyfun
03-04-2012, 07:00 AM
Can I ask the purpose of the poly? If your basement floor is allowing water up from beneath then you're likely going to have issues no matter what you do (IMHO).


The poly is to reduce moisture vapor from the ground and to prevent small amount of water from ground if any. But it will be bad if water is from inside (water pipe), I think.

In my case, that poly layer is for moisture only because I have added french drain inside my basement and outside grading has been addressed as well.

diyfun
03-04-2012, 07:05 AM
Mold only grows on organic materials, concrete, poly, foam, etc. etc. none of them support the growth of mold.

If your basement floods, having gimmicky drywall wont make a difference.

I plan to attach the drywall at least one inch above from the plywood. That means as long as there is no more than 1" water in my basement, the drywall will be safe. I have floor drain and french drain. I think my basement probably should be good enough.

LLigetfa
03-04-2012, 07:15 AM
If you need an interior weeping system, then you probably should have a gap as well. Something like dimpled plastic under the insulation, or skip the insulation and put in DRIcore. Insulation on the floor has little payback.

http://www.dricore.com/en/eIndex.aspx

diyfun
03-04-2012, 08:26 AM
If you need an interior weeping system, then you probably should have a gap as well. Something like dimpled plastic under the insulation, or skip the insulation and put in DRIcore. Insulation on the floor has little payback.

http://www.dricore.com/en/eIndex.aspx

We only get water in 100yr's storm and at that time the outside surface water was not handled properly. Normally there is no water issue and the sum pump basin is dry all seasons

dlarrivee
03-04-2012, 08:49 AM
Insulation on the floor has little payback.


I'm really getting fed up with all of the mis-information going on here...

LLigetfa
03-04-2012, 08:57 AM
I'm really getting fed up with all of the mis-information going on here...

PFFT! We are talking about a basement below grade were the temps are nothing like a room over the garage. Try some ROLAIDS®.

LLigetfa
03-04-2012, 09:07 AM
If there really was so much payback, you'd think the DRIcore engineers would be all over it and manufacture a version of their product with an inch or two of XPS sandwiched in it. DRIcore has an R value of 1.7 plus the engineered wood that is going on top of that. I don't know the degree days in the state of MA, but for sure less than ours. Summer cooling costs may even factor in.

dlarrivee
03-04-2012, 09:44 AM
You need to do some research outside of the Home Depot flyer my friend. The main reason DriCore engineers (you think they actually have engineers?), don't add 2" of XPS is COST...

It is already over priced and uses OSB instead of proper plywood, they wont sell a single 2'x2' tile if they double their price point again.

Oh and p.s., the other reason is because someone else already came out with such a product. Again, over priced.

http://www.ovrx.com/

I think it is hilarious that you figure it takes a team of engineers to glue 2 building materials together and come up with a marketing scheme.

I would use Delta FL and plywood any day of the week over DriCore, and I would use XPS and plywood any day of the week over any xps+osb glue together crap.

dlarrivee
03-04-2012, 10:01 AM
For anyone out there listening LLigetfa also recommends MDF baseboards in basements with dampness issues.

I'll have to head over to Home Depot and ask the experts there, then report back on whether or not having a cold floor in a finished basement is a good idea.

LLigetfa
03-04-2012, 10:13 AM
Well.. if you think the Barricade® system you linked to supports your arguement, it falls way short. They claim 1% heat loss through the floor. Their product does not laminate two inches of XPS, not even one inch.

http://www.ovrx.com/subfloor-comparison.html

Don't get me started on engineers and marketeers. Maybe you could design something and then get Vince to pitch it for you. I hear he lost a lot of business after the hooker bit his lip.
http://www.celebtv.com/wp-content/uploads/2009/03/vince_shlomi_mug_shot.jpg

dlarrivee
03-04-2012, 11:15 AM
Like I mentioned I'm not fond of any of the 2' square products.

Dana
03-05-2012, 08:05 AM
My unfinished basement has a 87" ceiling height right now. I don't know I should use 1", 1.5" or 2" XPS foam on the floor? The whole basement floor plan will be 6mil poly + XPS foam + 23/32" T&G plywood + engineered wood floor.

Since you're not spanning 16" o.c. joists, there's no rationale for going with 23/32" plywood subfloor- XPS hard-sandwiched between even half-inch t&g sheathing for the sub-floor and a concrete slab has PLENTY of structural strength, and flexes far less than 23/32" plywood spanning joists. You don't want to go thinner than 7/16" though (for fastener retention reasons.)

There's an economic rationale for R5 (1") XPS on space heating savings (as well as a comfort rationale) in a MA climate zone & subsoil temp. There's a long term economic rationale for R7.5 (1.5"), but R10 only makes economic sense if

A: It's a DIY and you discount you fully discount the value of your labor

B: You use reclaimed XPS at 25-30% of virgin-stock costs

C: You are stuck only with very high space heating fuel options (propane, or oil, or >12 cent electricity & no heat pumps)

D: You are installing radiant floor to heat the place (in which case R12-R15 might even make sense.)

If you stagger the seams of the subflooring with that of the foam by at least a foot or so for least mechanical creepage you can just float the floor, using foam board construction adhesive between the foam & subfloor. If there's any detectable flex to it you can throw in a few tapcons through-screwed to the floor per panel of subfloor.

Dana
03-05-2012, 08:32 AM
PFFT! We are talking about a basement below grade were the temps are nothing like a room over the garage. Try some
ROLAIDS®.

Take it from some people who actually do the math:


http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones (http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones)

MA is US zone 5. (See the R recommendations in Table 2, p10, but read the first chapter to understand the rationale.)

See also: http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis

There's more to it than simply blocking ground moisture or heating season utility savings (but those all count too.) Putting real R-value between the subfloor and slab further reduces the mold & rot potential of the subfloor by increasing it's summertime temp to above the summertime dew point of the ventilation air. At MA outdoor summertime dew points R3 would be the minimum in central MA to mitigate summertime moisture accumulation and mold on the subfloor under a padded carpet finish floor (or area-rug over wood flooring), and the labor cost of putting down 1" or 1.5" is the same as for putting down 1/2-3/4". Without the under-floor R the mechanical dehumidification requirements to protect against mold are much higher than they would be otherwise.

nukeman
03-05-2012, 12:03 PM
One thing to remember is that you will probably have to do something with the basement stairs (probably for any of these options). Your last step will be too short, otherwise. Doors can also be an issue with the increased floor height.

dlarrivee
03-05-2012, 05:30 PM
Thank you Dana, our friend LLigetfa tends to spew his opinions out as fact.

LLigetfa
03-05-2012, 07:38 PM
Take it from some people who actually do the math:


http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones (http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones)

MA is US zone 5. (See the R recommendations in Table 2, p10, but read the first chapter to understand the rationale.)

See also: http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis

There's more to it than simply blocking ground moisture or heating season utility savings (but those all count too.) Putting real R-value between the subfloor and slab further reduces the mold & rot potential of the subfloor by increasing it's summertime temp to above the summertime dew point of the ventilation air. At MA outdoor summertime dew points R3 would be the minimum in central MA to mitigate summertime moisture accumulation and mold on the subfloor under a padded carpet finish floor (or area-rug over wood flooring), and the labor cost of putting down 1" or 1.5" is the same as for putting down 1/2-3/4". Without the under-floor R the mechanical dehumidification requirements to protect against mold are much higher than they would be otherwise.

I skimmed over both docs and didn't find anything compelling but I do agree that condensation could be an issue in high humidity with carpet if there is no dehumidification. The OP stated engineered wood. The approx. R2 of DRIcore + flooring seems to be adequate for many folks that don't have much headroom and the stairs could probably be easily modified to factor for it. The OP may not mind the low ceilings, but come time to resell, others might.

Around here, we pour our slabs over coarse stone and the air spaces somewhat reduce the conductivity to the soil if kept dry.

Dana
03-06-2012, 08:55 AM
The OP did specify engineered wood, but the likelihood of throw-rugs/area rugs being used at some point in the future, especially on an uninsulated slab with maritime zone-damp soil with a subsoil temp of ~9C (like this poster's location) is quite high, and would a mold hazard at MA type summertime dew points. He also lives in a 30-50% higher-than-US-average-cost natural-gas & electricity market, which makes the economic rationale on the space heating end more compelling than in some other places.

Insulated slabs aren't necessarily the best investment for every retrofit, but IIRC code-min for new construction is now R10 subslab in Maine (which is probably warmer than where you live.) If the goal is to lower the energy use profile every time the house is remodeled or upgraded, skipping the foam now makes upgrading it in future cost-prohibitive. The high-R home rule of thumb for this area is R-10/20/40/60 or sub-slab/foundation-wall/above-grade-whole-wall/attic-roof R values. (With air sealing and not-too-many & better grade windows houses built to that prescriptive standard would likely meet the Canadian R-2000 (http://oee.nrcan.gc.ca/residential/new-homes/r-2000/standard/16118) standard in most of Ontario too.) Code minimums are about half that (or less), but building only to code minimum on new housing is crap, IMHO. The comfort factor of code x 1.5 and air sealing to <2ACH/50 is enough of a payback in itself for the people living there, even if there's no margin in it on resale value. (Better to spend the money on the granite counters and the 6 sidespray marble master-bath shower if the intent is to flip it in 5 years, eh? ;-) )

In a well designed home the cost of going code-min x 1.5 can be relatively cost-neutral using an iterative design process, using best-value materials & techniques to attain those whole-assembly R values, and applying the savings on the reduced cost of the smaller-simpler mechanicals to the R values. Clearly using 5" of 2lb foam cavity fill to raise the whole-wall R of a 2x6 studwall from R14 using fiber insulation to R17 isn't going to cut it in a present-value analysis of the utility savings any energy market. But adding 1-1.5" of 2lb foam to the exterior of a cellulose filled 2x6 wall for a whole wall R in the R20+ range would in most markets, as would taking it to the R25-R30 range with 3-4" of exterior EPS at ~$1/R/square meter in colder climates. The combined annual mortgage + utility payments for tight code-min x 1.5 homes in cold climates is usually lower than a code-min home, if some care was taken on how the whole-assembly R values were achieved. (Code min walls in MA are R20-2x6 or R13 2x4 + R5 exterior foam, either of which comes in at about R15-ish for a whole wall assembly. Foundation walls are required to be at least R15 if continuous foam, or R19 if open-cell in 2x6 studwall, again about R15-ish. Taking that to R20-25 isn't a huge stretch or huge expense.)

Slabs are required by code in my area to be poured over coarse stone primarily for the capillary break against ground moisture, not the paltry insulation value of the air spaces although it does add about R1-R2 if you go deep enough. But the porosity of the stone and the foundation backfill can in some cases create surprisingly significant air leaks at slab penetrations, notably sumps, which may require air-tight lids for homes to meet even IRC2012 air tightness levels.

mhmmofro
03-11-2012, 02:58 PM
I have no real comment on payback time etc. . .
I am diy not a pro.

I used 1/2 inch xps then a double layer of 1/2 ply over that for comfort and i love it. We use the basement as a tv / play room and are often sitting on the floor. It way more comfortable for both temp and softness compared to every other finished basement i have ever been in.

I went with 1/2 because i was concerned with height issues. I am rite at 7ft. I think they say 1/2 is r3 so its not a great temperature difference but its a heck of a lot better then sitting on carpet on cement.

mark

Dana
03-12-2012, 02:15 PM
R2.5-R3 is plenty for mold-protection in a Staten Island climate, and is a HUGE improvement in comfort. Your total sub-finish stackup including the R value of the ply is about R4. You'd able to feel the difference between R3foam and R7.5 though.

diyfun
04-03-2012, 06:57 PM
I used 1/2 inch xps then a double layer of 1/2 ply over that for comfort and i love it. We use the basement as a tv / play room and are often sitting on the floor. It way more comfortable for both temp and softness compared to every other finished basement i have ever been in.
mark

why not use 1" XPS + one layer 1/2" ply which is the same thickness as the 1/2" XPS + two layers of 1/2" ply? I assume the "ply" means plywood.

Dana
04-04-2012, 07:05 AM
why not use 1" XPS + one layer 1/2" ply which is the same thickness as the 1/2" XPS + two layers of 1/2" ply? I assume the "ply" means plywood.


I suspect they mhmmofro assumed more than 1/2" of plywood was necessary for the sub-floor, which it WOULD be were it spanning joists, but not if fully supported by XPS & slab. As long as 1/2" fastener penetration is sufficient mechanical retention the finish floor (usually is), 1" XPS with half-inch subfloor is fine. Half-inch plywood or OSB on an XPS/slab base flexes less than 3/4" plywood on 16" o.c. joists, so the nail/staple loosening forces are already lower.