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Old 06-11-2013, 08:49 PM   #1
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Basement insulation options


Hi all,

I am in the process of finishing my daylight basement in Maryland (zone 4). After reading building science for weeks and I confused on what would be my best option for insulation in the basement. I currently have an interior water management system with two sump pumps installed less than 3yrs ago. I also have a Santa Fe Compact 2 Dehumidifier to help with the humidity level now and it will stay once the basement is finished.

I planned on using either Thoroseal, SunnyDry or Xypex waterproof "paint", is this a good idea or not? Only reason I ask is because during a recent heavy rain storm in this area I noticed two corners that were lightly damp to the touch and would rather not have it ruin my basement after it is finished.

Below are my current options:

Option 1 (Traditional): 2" XPS glued to the cinder block with Tyvek taped seams, 2x4 framing, Roxul insulation and DensArmor Plus drywall
Option 2 (Spray Foam): 2" closed cell spray foam, 2x4 framing and DensArmor Plus drywall
Option 3 (Hybrid Spray Foam): 1" closed cell spray foam, 2x4 framing, Roxul insulation and DensArmor Plus drywall

For the record, I will not be using any type of poly sheeting either on the cold side or warm side.

Any help would be greatly appreciated!

-Geran

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Old 06-12-2013, 07:16 AM   #2
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Geran,

Option 1 is very good and will cost you the least.

Be sure to seal up the band joist locations and address the gutters and grading to help eliminate the water infiltration issues.

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Old 06-12-2013, 07:30 AM   #3
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Geran,

Option 1 is very good and will cost you the least.

Be sure to seal up the band joist locations and address the gutters and grading to help eliminate the water infiltration issues.
Thanks for the reply.

The band joist will be sealed by spray foam due to their location.

I will check on the gutters, after looking at it the next day. The gutters on that side of the house drain into the ground (probably catch basins) and I have a feeling they aren't sized properly. As for grading...the property already slopes away from the house on three sides and very slightly (less than 1/4') towards the front of the house (no water on that side in the basement).

So after fixing the gutters and grading would any of those waterproofing cements/paints be worthwhile?
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Old 06-12-2013, 07:40 AM   #4
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I have never seen them stop something that was coming into the home regardless.

Not sure they are worth it to that extent.
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Old 06-12-2013, 08:24 AM   #5
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I have never seen them stop something that was coming into the home regardless.

Not sure they are worth it to that extent.
Thanks for your help mate!
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Old 06-12-2013, 09:02 AM   #6
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I have never seen them stop something that was coming into the home regardless.
Even if they did... that doesn't stop the water from being there.
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Old 06-12-2013, 10:10 AM   #7
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Even if they did... that doesn't stop the water from being there.
So basically you're agreeing with Windows on Wash on that it isn't worth the extra expense?
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Old 06-12-2013, 04:20 PM   #8
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So basically you're agreeing with Windows on Wash on that it isn't worth the extra expense?
More. I'm saying that even if it did work it would just create other and possibly even more serious problems.
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Old 06-12-2013, 05:55 PM   #9
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More. I'm saying that even if it did work it would just create other and possibly even more serious problems.
Oh okay...thank you mate!
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Old 06-12-2013, 11:33 PM   #10
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The waterproofing paint-on material will force the exterior moisture (in the CMU) to dry either toward the mudsill/above-grade portion of the block (capillarity/air dry wicking) or downward (collecting/pooling) to the mortar joint between the CMU/footing- more likely to ingress per volume). IMO, don't use any- let the foamboard diffuse the moisture to dry to the inside (all surface of wall, not area concentrated) with the dehumidifier, or use thicker foam to raise the dew-point temp there so it will not condense, wetting the wood framing. For your local high/lows of Jan, Feb, Dec, average is 34.6*F; http://www.weather.com/weather/wxcli...ly/graph/20703

With that, at 68*F inside and R-15 Roxul + R-10XPS, the Delta T at inside foamboard is 48*F OR 49%Relative Humidity at grade/3' below grade.

Roxul + R-7.5 XPS = 44%RH dew point in cavity. With R-5 (1")XPS, dew-point is 40%RH and below.
R-15 Roxul + R-5 = R-20 or 95.5% efectively stopping heat flow; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

R-22.5 = 96%, R-25 = 97%. The Roxul meets minimum code below grade alone, the foamboard stops condensation; http://publicecodes.cyberregs.com/ic..._11_sec002.htm

Using Roxul+ R-2.5 (1/2")XPS gives 35%RH and you have a dehumid. to boot... glue the f.b. in 1'square grid patterns to stop air; http://joneakes.com/jons-fixit-database/743 be sure Rox is touching f.b. to stop convective loop-s there; https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ

Canned foam under f.b., tape/mastic seams, and fire-stop above at top plate to floor cavities and every 10' horizontally per code; http://publicecodes.cyberregs.com/ic...002_par017.htm

F.b. under PT bottom plate, not sill sealer for thermal/air/capillary break to cold earth; http://www.greenbuildingadvisor.com/...-building-code

And have fun knowing you are doing it correctly!

Gary
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Old 06-13-2013, 05:49 PM   #11
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Quote:
Originally Posted by Gary in WA View Post
The waterproofing paint-on material will force the exterior moisture (in the CMU) to dry either toward the mudsill/above-grade portion of the block (capillarity/air dry wicking) or downward (collecting/pooling) to the mortar joint between the CMU/footing- more likely to ingress per volume). IMO, don't use any- let the foamboard diffuse the moisture to dry to the inside (all surface of wall, not area concentrated) with the dehumidifier, or use thicker foam to raise the dew-point temp there so it will not condense, wetting the wood framing. For your local high/lows of Jan, Feb, Dec, average is 34.6*F; http://www.weather.com/weather/wxcli...ly/graph/20703

With that, at 68*F inside and R-15 Roxul + R-10XPS, the Delta T at inside foamboard is 48*F OR 49%Relative Humidity at grade/3' below grade.

Roxul + R-7.5 XPS = 44%RH dew point in cavity. With R-5 (1")XPS, dew-point is 40%RH and below.
R-15 Roxul + R-5 = R-20 or 95.5% efectively stopping heat flow; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

R-22.5 = 96%, R-25 = 97%. The Roxul meets minimum code below grade alone, the foamboard stops condensation; http://publicecodes.cyberregs.com/ic..._11_sec002.htm

Using Roxul+ R-2.5 (1/2")XPS gives 35%RH and you have a dehumid. to boot... glue the f.b. in 1'square grid patterns to stop air; http://joneakes.com/jons-fixit-database/743 be sure Rox is touching f.b. to stop convective loop-s there; https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ

Canned foam under f.b., tape/mastic seams, and fire-stop above at top plate to floor cavities and every 10' horizontally per code; http://publicecodes.cyberregs.com/ic...002_par017.htm

F.b. under PT bottom plate, not sill sealer for thermal/air/capillary break to cold earth; http://www.greenbuildingadvisor.com/...-building-code

And have fun knowing you are doing it correctly!

Gary
Hi Gary,

Thank you for such a detailed reply and explaining a ton. I do have some questions though...

1. Do I want a higher or lower relative humidity? I'm guessing higher. Also from buildingscience, they recommend 2" F.B. (R-10) with R-15 insulation.
2. When you say 1' square grid pattern, do you mean something like this?
3. Why should the Roxul be right up against the FB instead of away from it by a inch or less? Also would this mean that the wood framing would need to be against the F.B. as well?
4. What do you mean by a fire-stop above at the top plate? I was planning on using Roxul as insulation in the floor cavities with resilient channels to help with noise...would this be sufficient?

That's all I have for now and I definitely want to do it correctly the first time so your information has been extremely helpful.

Thanks,
Geran
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Old 06-15-2013, 12:04 PM   #12
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So just to clarify is 1/2" xps sufficient if you plan on using R15 roxul?
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Old 06-15-2013, 02:46 PM   #13
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"1. Do I want a higher or lower relative humidity? I'm guessing higher. Also from buildingscience, they recommend 2" F.B. (R-10) with R-15 insulation.-------------------- lower is better... you can use 2"XPS if you want. The thicker foam boards are mainly to control the dew-point in the cavity (depending on exterior temps per location); stopping/reducing condensation that is harmful to wood framing and f.g. insulation R-value when wet.

2. When you say 1' square grid pattern, do you mean something like this?------------------- No, that would one of the least effective ways to stop room air between the f.b./concrete where it will condense with temp. differences. Glue an inch or so around perimeter, then grid pattern (12" or so, wide/high) to limit any air (that you missed a hole/crack in the taping of seams or ADA the drywall or 1" f.b. under the p.t. bottom plate for the air/thermal/capillary break) to condense.

3. Why should the Roxul be right up against the FB instead of away from it by a inch or less? Also would this mean that the wood framing would need to be against the F.B. as well?-------------- the wood framing can have a gap, though it helps hold the f.b. in place. The insulation cannot; Read only middle column pp.3 under "Vapor retarders in basement" about "vertical airspace"; from; https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ

4. What do you mean by a fire-stop above at the top plate? I was planning on using Roxul as insulation in the floor cavities with resilient channels to help with noise...would this be sufficient?"--------------- any gap between top plate of new frame wall and old wall top plate/mudsill requires fire-blocking, not just draft-stopping to keep vertical wall separate from horizontal ceiling; Post #21, 22--- read the whole 9 yards ....;How to fireblock framing

We have an excellent sound-pro here, I'll PM him for you... Ted White.

The drywall you picked is only 10 perms rather than 50 perms for regular, is it worth the added expense, possibility of slowing vapor from diffusing through unhampered, (need to research that more). http://www.gp.com/build/DocumentView...elementid=6496

Gary
PS. Brian, the foamboard thickness changes with Zones (location), just as above-grade walls. As far as controlling condensation (dew-point), basement walls require about 1/2 as much R-value due the concrete wall protection from the elements (wind, rain, etc.) so one could possibly use the standards per code; R-2.75 for Zone 4, though it's best to figure on graph per city. http://www.buildingscience.com/docum...r-requirements

Note; for a 2x4 wall only, in his case, a 2x6 requires thicker foam because heat is stopped with mass fibrous insulation between f.b./room;http://www.buildingscience.com/docum...nsulation/view That is the reason I always suggest 2" XPS on any rim joist- due to the cavity insulation (fiberglass, rock wool, etc.) between the rim and the heat source as in a basement -- more fibrous mass, thicker foam as the temp there is closer to outside temps). There is always some diffusion through the foamboard (unless $$$$$ thick) at the rim; last paragraph; http://www.buildingfoundation.umn.ed...oistphenom.htm
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Old 06-15-2013, 03:49 PM   #14
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Regarding soundproofing efforts- standard fiberglass will work as well as anything, regardless of price. Extensive data to support this, so I'd go with whatever is cheapest. R19 is fine.

I would never suggest Resilient Channel (RC-1 or RC-2). Underperforms in the lower frequencies and easily short circuited. Consider a low cost clip & channel assembly to decouple. Then as much drywall as you can deal with. Double 5/8" is great.
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Old 06-15-2013, 09:01 PM   #15
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Originally Posted by Gary in WA View Post
"1. Do I want a higher or lower relative humidity? I'm guessing higher. Also from buildingscience, they recommend 2" F.B. (R-10) with R-15 insulation.-------------------- lower is better... you can use 2"XPS if you want. The thicker foam boards are mainly to control the dew-point in the cavity (depending on exterior temps per location); stopping/reducing condensation that is harmful to wood framing and f.g. insulation R-value when wet.
Thanks for letting me know that lower RH is better so that means the .5" F.B. with Roxul will be sufficient enough with my dehumidifier. If I can't find .5" then I'll go for .75" or 1".

Quote:
Originally Posted by Gary in WA View Post
2. When you say 1' square grid pattern, do you mean something like this?------------------- No, that would one of the least effective ways to stop room air between the f.b./concrete where it will condense with temp. differences. Glue an inch or so around perimeter, then grid pattern (12" or so, wide/high) to limit any air (that you missed a hole/crack in the taping of seams or ADA the drywall or 1" f.b. under the p.t. bottom plate for the air/thermal/capillary break) to condense.
That's good to know...this is the first time I heard about doing a grid pattern like that behind foam board. I will be using spray foam around all the edges of the f.b., tuck taping each joint and putting 1" f.b. under the p.t. bottom plate with the grid pattern too.

Quote:
Originally Posted by Gary in WA View Post
3. Why should the Roxul be right up against the FB instead of away from it by a inch or less? Also would this mean that the wood framing would need to be against the F.B. as well?-------------- the wood framing can have a gap, though it helps hold the f.b. in place. The insulation cannot; Read only middle column pp.3 under "Vapor retarders in basement" about "vertical airspace"; from; https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ
Makes sense to me. The gap in the framing would be in the front of the insulation right behind the drywall...is that okay?

Quote:
Originally Posted by Gary in WA View Post
4. What do you mean by a fire-stop above at the top plate? I was planning on using Roxul as insulation in the floor cavities with resilient channels to help with noise...would this be sufficient?"--------------- any gap between top plate of new frame wall and old wall top plate/mudsill requires fire-blocking, not just draft-stopping to keep vertical wall separate from horizontal ceiling; Post #21, 22--- read the whole 9 yards ....;How to fireblock framing

We have an excellent sound-pro here, I'll PM him for you... Ted White.

The drywall you picked is only 10 perms rather than 50 perms for regular, is it worth the added expense, possibility of slowing vapor from diffusing through unhampered, (need to research that more). http://www.gp.com/build/DocumentView...elementid=6496

Gary
I will do more research on this as well as the drywall (I would prefer to have mold/mildew resistant drywall just for the extra assurance but if it is pointless then regular drywall will suffice). I will be using latex paint to help as a vapor retarder so maybe regular paper based drywall will be fine...thoughts?

I will definitely have some questions for Mr. White when I get to my home theater setup.

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