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Old 05-24-2012, 01:55 PM   #1
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basement humidity


Well still working on my basement... too many setbacks that have delayed it...

I have been watching the humidity levels in the basement now... in winter we average 30-45% in spring right now its in the mid 60's it has been raining a good bit, and pretty humid out... is this normal to expect? haven't watched it in the summer yet

there are no real "water leak" issues, it's 8" block walls, with a 9" slab (yes, 9 inch) under the slab is a pretty thich plastic vapor barrier then rough aggregate for a few inches at least (i only know this because of having to bore through it for the radon installation)

the walls are insulated internally with XPS foam then stud walls with unfaced fiberglass to R-19 I think it is

All basement cracks, gaps and possible air entrances where sealed up

the basement is 1500 sq ft finished, all below grade, except the top 3 corses of block

anything that can be done to keep the humidity down? I have a small dehumidifier but haven't really ran it much (one of those small stand up ones with a hose to run to a drain)

the basement has all the HVAC done, all apparently sized (according to the HVAC contractor), all duct work sealed up with mastic

basically the basement is air tight..

any suggestions on how I could perminatly keep this humidity level right? (below 55%) thanks!

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Old 05-24-2012, 04:05 PM   #2
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basement humidity


Post the specs for your humidifier.
That and what duty cycle it runs at will tell you how many grains of moisture per hour per 24 hr day you need to remove from your basement to get your 55% RH.

I guess I'd also be looking at the permeability level for basement walls like yours.

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Old 05-24-2012, 04:22 PM   #3
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Originally Posted by Yoyizit View Post
Post the specs for your humidifier.
That and what duty cycle it runs at will tell you how many grains of moisture per hour per 24 hr day you need to remove from your basement to get your 55% RH.

I guess I'd also be looking at the permeability level for basement walls like yours.
what specs do you need? I assume you meant dehumidifier? the humidifier is a Trane Fan blower whole home humidifier attached to the furnace directly... the dehumidifier I have in the basement is a

Frigidaire 70-Pint 2-Speed Dehumidifier going by lowes site the specs it lists are

Moisture Removal Pints/24 hours (Pints) 70.0
Continuous Run Yes
Drain Hose Connection Yes
Drain Hose Included No
Casters Yes
Washable Filter Yes
Bucket Full Indicator Yes
Side Discharge Yes
UL Listed Yes
CSA Listed No
ETL Listed No
ENERGY STAR Qualified Yes
Control Type Electronic
Fan Speeds 2.0
Reservoir Capacity (Gallons) 16.3
Warranty1 yr full /5 yr sealed system
Adjustable Humidistat Yes
Auto Shut-Off Yes
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Old 05-24-2012, 08:26 PM   #4
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I put the another 50 liter dehumidifier in a room that is 15 ft wide and 12 ft long 8ft high ceiling in the basement (completely finished space) humidify level was 64% within 1 hr it was down to 40%, obviously that worked great, but I need a solution for 1,500 sq ft across multiple rooms

the main room is 30x25 ft and right now its humidity level is 65% going to try it in there next and see how fast it changes
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Old 05-24-2012, 08:53 PM   #5
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Right now, it is 67 in my basement with 54% humidity, main floor is 71 with 49%. I would not say that yours is too high. If it was closer to the 70's, I would either run a dehumidifier or make sure that there is a cold air return in the basement along with a hvac vent, so that you can get the basement at around the same as the rest of the house.

You did not state what your basement temp is currently, what is it & how are you measuring humidity levels? If I go downstairs and look at the needle gauge on our thermometer down there, it will read higher than the remote sensor that is feeding the "weather station" upstairs, next to where I sit all of the time.
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Old 05-24-2012, 08:59 PM   #6
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Right now, it is 67 in my basement with 54% humidity, main floor is 71 with 49%. I would not say that yours is too high. If it was closer to the 70's, I would either run a dehumidifier or make sure that there is a cold air return in the basement along with a hvac vent, so that you can get the basement at around the same as the rest of the house.

You did not state what your basement temp is currently, what is it & how are you measuring humidity levels? If I go downstairs and look at the needle gauge on our thermometer down there, it will read higher than the remote sensor that is feeding the "weather station" upstairs, next to where I sit all of the time.
current temp in the main area is 65 degrees and 69% humidity (according to my monitor its been as high as 70% and as low as 55%) it of course goes up when its wet outside the most...

the room I just ran the dehumidifier in is now 72 degrees (little thing warms that space up!) and 40% humidity

just put the dehumidifier in the main space to see what it does...

was looking at maybe putting one of these in the furnace room

http://www.alpinehomeair.com/viewpro...ctID=453063166

then running two ducts into the main room to keep it lower humidity instead of doing a whole home situation, just a vent for in and a vent for out then a remote humidity controller for it in that room, since that room alone is about half the basement area
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Old 05-24-2012, 11:12 PM   #7
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My basement is up to 73% humidity at about 68 degrees. I'm not running any AC or heat or dehumidifier. I have no insulation on the 8" concrete block walls, nor is there any backplaster or waterproofing on the outside.

I want to excavate outside and repair as necessary, backplaster, then waterproof and put in 2" xps.

I still won't have a vapor barrier under the floor then, but I imagine it will help a lot. And insulating the band joist won't hurt me either.

I've been told that running a dehumidifier will cost as much to run as the AC.
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Old 05-24-2012, 11:24 PM   #8
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Also to add, if you are getting high humidity, and it is hot & humid outside, or just hot with low humidity, it helps to place insulation up in the rim joist bays. Basically place insulation around the perimeter where there is visible wood around the joist perimeter, even if it is R-13 fiberglass, it will help to keep the space more in line with the rest of the house. It also helps to seal any penetrations through the foundation above grade, so that you have no air leakage, along with any wire or pipe penetrations to the main floor.

Problem with high humidity is, that you give mold & mildew spores part of the equation to survive downstairs or in the crawl space. First, get the house sealed with DAP foam for exterior placed outlets & switch boxes, seal any holes from attic to the basement, any penetrations, get good air flow to help keep the space conditioned, you should be good to go. Even if you do not place XPS on the foundation walls, getting the air sealing done along with insulation the Rim joist spaces helps.
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Old 05-25-2012, 07:50 AM   #9
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Originally Posted by gregzoll View Post
Also to add, if you are getting high humidity, and it is hot & humid outside, or just hot with low humidity, it helps to place insulation up in the rim joist bays. Basically place insulation around the perimeter where there is visible wood around the joist perimeter, even if it is R-13 fiberglass, it will help to keep the space more in line with the rest of the house. It also helps to seal any penetrations through the foundation above grade, so that you have no air leakage, along with any wire or pipe penetrations to the main floor.

Problem with high humidity is, that you give mold & mildew spores part of the equation to survive downstairs or in the crawl space. First, get the house sealed with DAP foam for exterior placed outlets & switch boxes, seal any holes from attic to the basement, any penetrations, get good air flow to help keep the space conditioned, you should be good to go. Even if you do not place XPS on the foundation walls, getting the air sealing done along with insulation the Rim joist spaces helps.

Like I said in my original post, my basement has been completely sealed and insulated

All rim joists where filled with XPS foam, sealed around the foam perimiter then stuffed the remaining space with R-30 unfaced fiberglass, all openings and cracks where sprayfoamed. all walls where XPS foamed with R-5, seams taped with housewrap tape, then stud walls built infront of it, and filledwith R-13 fiberglass unfaced.. all rooms are conditioned with returns and supplies

with all this the humidity is still up to 69% and there is no noticable water infiltration when the walls where bare (before the XPS went up)

so this is still a problem and why I am looking at putting a basement only dehumidification system in.

anyone do something like with the aprilair system I posted above? just two 8" duct runs to a main room? now a whole home system.. the rest of the house stays fine
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Old 05-25-2012, 08:32 AM   #10
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What I'm saying is that your vapor/thermal barrier isn't doing the job. Did you install it or someone else? Did you see the installation? There are only 6 sides that the problem can be coming from, and if you are confident about your walls, that leaves the floor and ceiling or a faulty humidistat.

I think it is much easier and effective to put the envelope on the outside of the building.
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Old 05-25-2012, 09:22 AM   #11
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Originally Posted by cleveman View Post
What I'm saying is that your vapor/thermal barrier isn't doing the job. Did you install it or someone else? Did you see the installation? There are only 6 sides that the problem can be coming from, and if you are confident about your walls, that leaves the floor and ceiling or a faulty humidistat.

I think it is much easier and effective to put the envelope on the outside of the building.
the vapor barrier below the slab was of course done when the houe was built, I didn't own it at the time, I only could tell what was there due to the radon system install


the interior XPS I did myself, its all glued to the wall, taped with housewrap tape, all caps expanding foam sealed, its pretty much a continious seal from the floor to the top of the rim joist with XPS

now, outside I have no clue what exists, it appears it's just your standard block wall with the black tar sealant over the block then a gravel backfill and I think perferated pipe around the perimiter, because we have an outside sump right next to the foundation that goes downabout 10 ft with black HDPE pipe going into it which I assume is the foundation drainage to be pumped higher up to the storm water system

I don't think its a humidistat issue either, because I have three of them right now down there, one on the portable dehumidifier, the HVAC one and a little battery powered one and they are all within 1% of each other

the fact there is a humidity problem doesnt suprise me, as our house is at the lowest point a foot below the water table apparently... the negibors said when it was built the hole in the ground would just fill up wioth water and they had to run pumps constantly to keep it dry until the slab was poured then the issue "stopped"
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Old 05-25-2012, 04:47 PM   #12
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Wow.

The fact that the hole was wet when dug shouldn't matter too much. You are basically living in a bucket in the water. As long as the bucket is water-tight, you should stay dry. If the bucket is insulated, you should not have any condensation.

If you slab isn't sweaty, you have me stumped.

By the way, I traveled out to that nursery in Indiana, PA in 2005 to pick up a bunch of trees. Nice country.
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Old 05-25-2012, 05:10 PM   #13
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Wow.

The fact that the hole was wet when dug shouldn't matter too much. You are basically living in a bucket in the water. As long as the bucket is water-tight, you should stay dry. If the bucket is insulated, you should not have any condensation.

If you slab isn't sweaty, you have me stumped.

By the way, I traveled out to that nursery in Indiana, PA in 2005 to pick up a bunch of trees. Nice country.
yeah, I am stumped also... walls are dry, floors are dry... no air flow due to being sealed up even had a blower door test done on the house and the basement had no real air infiltration


and yep, lots of nurserys out here, a few big ones too
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Old 05-25-2012, 08:55 PM   #14
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Ducted whole house/area dehumidifier.
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Old 05-25-2012, 09:05 PM   #15
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Ducted whole house/area dehumidifier.
yeah, that's where I was leaning towards... have you ever worked with Aprilaire whole home dehumidifiers? Been trying to get some info on them, the two local dealers put them in (trane and lennox dealers) but I could probably do that myself not to hard going by the manuals.. expensive little things, but probably worth it for the basement

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