Over insulate basement?

braverichard

Hmmm... your explanation actually implies the opposite of what you said. Since cold air can hold less moisture than warm air (which is true), then the humidity in the basement which is colder should less not more than that on the main floor.

High Gear

If I understand right you built a straight wall ground up over your half exposure ?

Then in front of the framed portion you stuffed full of ins.and then added a vapor barrier.

Holy overkill.

The above ground framed portion should be 2x6 and already insulated to probably r19 or better depending on what they used.

The "vapor barrier" is the house wrap ( which is really a vapor retarder so your walls will "breathe").

I believe using the 6mm vapor barrier on the interior is a big mistake.

The walls need to breath.

Higher humidity is probably from the concrete wicking some moisture from the earth ( normal).

I believe basement moisture should be under 50% with these type walls ( foam/glass) according to building science ( less chance for mold to develop)

You may wish to use a dehumidifier in the basement along with the A/C as needed.

If its not hot enough to cycle the A/C much then the dehumidifier picks up the slack.

Money may be better spent on acoustical tile ect. rather than fiberglass as far as sound reduction goes ( ceiling )

If you have lots of carpeting upstairs you may not have any noise issues , hardwood/ceramic floors yes.

I see no advantage to ceiling insulation from an efficiency standpoint when the basement is living space.

VelvetFoot

If you have high humidity summer air from the outside getting down to the cooler place, with no A/C, I would think the air in that cooler place's relative humidity would get even higher and would condense on cool surfaces.

braverichard

Actually you're wrong on several counts...
-My above ground portion is framed by 2 x 4 and was stuffed with faced R-13. I removed the "faces" and replaced them with a continuous sheet of 6mm vapor barrier. House wrap is not a vapor barrier. It is a water barrier but moisture/water vapor can still go in and out of it so the wall breaths through it.

-I didn't state that I put a vapor barrier over the fiberglass on top of the foam insulation on the below grade portion. Just fiberglass, no vapor barrier on it because the foam insulation is a vapor barrier itself.

-Soundproofing-wise, don't sweat it. I'm doing many more things to soundproof the ceiling, including using much thicker drywall to add mass (a total of 1-1/4" thickness), decoupling the ceiling from the joists using clips and hat channels and then using a sound dampening chemical between the drywall. For what I am doing, adding fiberglass in the joist cavity is absolutely essential to achieve complete results. (see http://www.soundproofingcompany.com/...oise_ceilings/ )

The moisture must be coming from the concrete floor which isn't sealed. I sure hope so. I'm doing a lot of different things here to ensure that I won't need a dehumidifier. Looks like I am pretty close to getting to 50%, I'll probably be there once the floor is sealed. It makes much better financial sense to spend a little more now with a one time cost than to just do a "contractor grade" basement finish with an on-going cost (electricity for dehumidifier).

High Gear

OK gotcha !

Sounds like ya got it all figured out.

Many exposures around here use 2x6 on the basement level ,hence R19 or in

my case BIB insulation at R23 ( I'm further north ).

I'd tell ya more but I just remembered I have to organize my sock drawer.

braverichard

I actually furred out some of my walls so I could get R-19 in them. I honestly believe they should just do all walls with 2 x 6s for additional insulation. R-19 traps 72% more heat than R-13, it would easily pay for itself in no time. Oh well, builders have their structural engineers design stuff to just meet code, never to exceed it. When I had my house built I couldn't even get them to make changes and pay more. They simply wouldn't do it due to the additional costs of submitting new plans to the city, etc.

High Gear

http://www.buildingscience.com/resou...r_barriers.htm

Type in Vapor in the search bar and look for






Research Reports

RR-0410: Vapor Barriers and Wall Design


You may want to read this article from the above link.



As energy prices climb you'll probably see less stick and more SIP & ICF

I'll bet plenty of builders would jump though hoops to please you in this economic climate.

jogr

Why would you insulate between the floors? Since you want both floors the same temperature the insulation serves no purpose.

Edit: Sorry, I didn't see the second page. I see yo're doing the insulation between floors for sound.

jogr

Richard, If your relative humidity upstairs is 41% at 74 F and your downstairs temp is 68 F then the downstairs relative humidity will be 50%. That difference is not due to moisture coming from the floor or walls. It's strictly a temperature effect.

Hopefully your builder used poly under the slab to prevent moisture coming through it. So while you might be getting some moisture through the slab please be aware that as long as you have the basement cooler than the upstairs then it will be a higher relative humidity. There is no reason that your basement should be a different temperature than the upstairs. Any difference in temp is entirely due to inadequate balancing of your heating/cooling system. Fix that and you may find the relative humidity upstairs is the same as downstairs.

braverichard

Well I don't believe my builder used a vapor barrier under the slab. I have yet to ask, but a house from the same builder just got a flooded basement last week (their sump pump after barely keeping up with the torrential rains we have been getting lately finally burnt out and they had no backup) and the owner of the house said they could literally see watter bubbling up from the basement slab. If it is confirmed to not have the barrier then I'll have to use a concrete sealer on it.

The game hasn't been called with respect to my house, for one thing, I have air returns open in the basement but the supplies are closed for now. I'll know how things are for sure once the construction is complete.

As for temperature differences and balancing, I don't believe a perfectly balanced system is attainable. While I can stop heat from rising from the basement up to the floor above using fiberglass, I can't stop cold air from the main floor from sinking into the basement. So the basement will always stay colder unless I am adding some heat to it, no matter how much I run the fan which circulates the air in the entire house between both levels. The aim is to have a very small temperature difference, say 2 F instead of 7 F.

Gary in WA

"I didn't state that I put a vapor barrier over the fiberglass on top of the foam insulation on the below grade portion. Just fiberglass, no vapor barrier on it because the foam insulation is a vapor barrier itself." ---- only if it is 8" thick or more.

http://www.buildingscience.com/docum...ecommendations

http://www.buildingscience.com/docum...gs?full_view=1

http://www.quadlock.com/technical_li...Insulation.pdf

Did they use a sill-sealer? http://www.greenbuildingadvisor.com/...-building-code

Be safe, Gary

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jklingel

•• Not to diverge, but ICFs? Maybe in warmer places. SIPs? Pretty expensive to get a good R-value, IMO. But, they are fast and thin.