Can you omit insulation on the botton half of a basement wall?

[Mike from NH]

Can you omit the fiberglass insulation on the bottom half a basement wall below the frost line? There is 1 1/2" rigid foam floor to ceiling, a 2x4 wall in front on the rfi and r-13 FB in the stud bays. My thought was omit the fiberglass insulation up about 3-4' so if theres water it will not wick. Secondly use Den Armor dywall for the first sheet (to the floor) as its bullet proof, then use XP or Humidtek everywhere else. So the top half will have an r-21 and bottom r-7. There will be hollow wall cavidy should there be a flood without the water behind. So all you'd have to do is cut 1/2" holes to extract the water behind. The DAP and RFI stays intact and no demo needed...thoughts?

[BigLou80]

Mike,
I could be wrong but I think the ridgid may meet code all by it self.
If you are going to omit half of the fiberglass you might as well leave all of it.

The only way the fiber glass is going to be woth having is if you install some sort of blocking half way up to stop the air from moving with in the stud cavity

[Mike from NH]

Hey Lou is "80" the year you were born or the amout of years we'll be f'ed after obama is done? Crap that slipped out.. Hows west mass? I hear Springfield is real hit with a ton of foreclosures...

The potental client framed, insulated and will hang it. I'm just taping. But thinking if he skipped the FB below the frost line that he'd be safe if he got a flood with 12'' or more of water in the basment. In which case use the DAP as it will withstand a flood and there would be no need to open a wall to remove FB... Otherwise I say use regular drywall and when it floods it all gets ripped out and replaced.

[MClark]

I would suggest to the client that they spend their money on work to eliminate the potential flooding problem. Why build something with the thought of making it easy to fix after it floods?

Well,...... maybe you'd want to sugar-coat it a little more than I did.

Matthew Clark

[ThingOfBeauty]

IMHO 12" of water will mean restoration will be pretty complex, there's not much that will make that situation more manageable.
Keeping stuff 1" above the floor, or even a couple more, can be very helpful though. Many 'floods' just barely cover the floor, if the rock is down on the slab it wicks up.
In my basement I used plywood strips, held up 1" and running to 1/2" below the top of the base. Then put rock from there up. But I think you get almost all the benefit from just the first inch off the floor.
In my experience, fiberglass doesn't wick water up very well. But drywall and studs do. I think I'd just run the FG all the way down. That will be the least of your worries if you get a lot of water in there. In my experience, when you get any more than a tiny amount of water, you need to remove the base & drywall to get air into the cavity anyway.
On the other hand, FG batts installed in studs with a space on the back (between studs & foamboard) aren't going to do a heck of a lot of insulating. (If the studs are tight to the foam they will do a lot more. If there's a gap, there will be a lot of convection behind the FG, negating a lot of its insulating value.)
One thing I'll try next time is using blueboard strips under the plates. Then even the wood is up out of the puddle. Learned that from Building Science.
Tell me more about the Dens Armor, I'm interested in it but haven't had the chance to try it. Is it permeable? Does it paint up as nice as the GP guys claim at the shows?
Sounds like you have a nice project going there. It feels warm just thinking about standing in front of all that foam board.

[mrd999]

The Building Science Corporation described half wall insulation as "the fastest and most cost effective way to provide insulation" in this paper:
http://www.eere.energy.gov/buildings...s/db/35017.pdf
See page 12, figures 11 & 12.

So sure, you can omit the bottom half of insulation. But, their example uses foil-faced isocyanurate, and their designs consider vapor transmission in addition to thermal protection.

I'd expect moisture to always come from the earth, so a vapor barrier between the wall and the batt insulation would deter batt moisture. However, if there's no vapor barrier at the top of the wall, and it can breathe to the exterior, I'd leave that upper portion of the wall without a vapor barrier so any trapped moisture in the batts could find its way out.

You could mix and match rigid insulation, using foil-faced iso or XPS to deter vapor behind the batts and EPS to allow more vapor penetration at the top and bottom.
Check Table 1, page 8 on the following link for permeance of various rigid insulations:
http://www.buildingscience.com/docum...ting-sheathing
The insulation manufacturer should provide values.

[mrd999]

Ah, but you already have the foam and wall in place. Find out the permeance of the foam insulation. If it breathes, you could place faced batts with the facing toward the exterior. This will deter batt moisture, as long as vapor can escape at the bottom and/or top. Bottom to interior, top to exterior, as per the previous links.

I understand you're concerned with flood protection, but if that's a real concern, then moisture will need to be addressed too.

[Bill Robinson]

Notwithstanding our political comment you might consider wet flood proofing.
Follow the guidelines using FEMA's Flood Damage Resistant Material guidelines.

Bill R

[BigLou80]

Mike,
80 was the year I was born. Things are good down here I am finally catching up with my back log of work. Springfield has been hit hard but its full of low income after all the factories closed in the 70's & 80's so what do you really expect ?

[JayNos]

Check out exactly how it will effect the insulation with this: www.pprbd.org/plancheck/Heatcalcpublic-v2.xls
Pike's Peak makes you submit a Heat Loss Plan...actually a great way to see where you can save the most energy with insulation.

[gary robertson]

check your code first you may not be able to use fiberglass in the first place.
our code dose not allow use of fiberglass below top of floor joist.

[Mike from NH]

This was a job that the h/o did everything, and wanted me to do just the taping. It was inspected and drywall ready. He inquired about drywall options, like green board vs. grey board and purple. Since he had r-13 figerglass insulation in addition to r-7.5 1.5" rigid foam, I said go with grey board. If there's a flood plan on the 1st 4" will be gone. Because the FB will wick water. Then I thought if he just used the FB insulation to the frost line and left the stud bay empty, he could use DAP Dens Armor Plus drywall. Which is flood proof drywall. Drill a few hole to extract any water between the RFI and the back of the DAP and he's golden.

[Roger P]

80% of the heat loss in a basement occurs in the top 4 feet of the wall.

Is the fiberglass insulation in full contact with the foam board?
Leaving an air space between the fiberglass and foam will allow convection currents to set up reducing the effectiveness of the insulation. Install draftstopping at the bottom of the fiberglass and no vapor retarder (other than kraft paper or membrain(R)).
You said that this has already passed inspection so I assume that there is fireblocking at the top plate.
The exterior soil adds R5 to the theoretical value of the wall insulation below grade.