Cinder block finishing interior walls in Florida???


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Old 09-10-14, 08:44 PM
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Cinder block finishing interior walls in Florida???

I love to research online vs just asking. I learn so much when do....my point...I can not seem to find what is needed. (Researched for hours!!)

We live in NW Florida. (Hot and humid!)

Getting ready to finish lower part of home. Which is cider block on a slab. The exterior....the front of house (south side) has vinyl siding...then osb board....then cinder block.
The back of house (north side) has vinyl siding....house wrap....osb board.....cinder block.

Interior issue? Have already framed in walls with treated 2x4's ....16" centered.
My plan was to install a radiant barrier with staples and foil tape. This will cause an air gap between the drywall and barrier.....and an air gap between the cinder block and radiant barrier.
Of course this would also be a vapor barrier.

My concern is that this will cause condensation between the barrier and cinder block?
I just read that that foam board (insulation board) should be glued to cinder block and then the drywall be attached to the foam board so ther is NO air gap.

I guess if my first choice above will work....great!
If NOT, how would you or what is the best way to finish the walls?

(We get a lot of moisture in the air because we have to run a dehumidifier all the time. I assume the moisture comes threw the cinder block)

ALSO......including in this half of the house will be the master bedroom ALONG with the master bedroom's bathroom. So I'm not sure if the bathroom may need vapor barrier inside and out???

(I lived in Michigan for most of my life...so now in Florida for 9yrs......still learning the climate)

(I have two beautiful girls and wife.....I want to make sure their living area is the healthiest it can be for them to live in )
 
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Old 09-10-14, 10:35 PM
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For condensation to form on a surface, the surface temperature must reach dew point temperature or below. Using the calculator and adjusting the numbers to your situation you can tell when condensation would become present on a surface. Example: to solve for DP in a room at 75 with a RH of 45 percent we would expect to see condensation on a surface beginning at about 52.

In that example, if you took a soda pop from the fridge that is 38 , condensation would jump on that little feller immediately if not sooner. Wipe it off with a paper towel and it jumps right back on there and will keep doing so until the can surface approaches 52 degrees. You can actually very accurately check room relative humidity in this manner.

The moisture that will cause problems won't be coming through the concrete blocks but atmospheric conditions within the house will need to be controlled to prevent condensation.

Dew Point Calculator
 
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Old 09-11-14, 08:15 AM
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Ok....well I understand a little better. I guess this is why some say to glue ridged foam board to the cinder block?

I appreciate the calculator but most of the was over my head...lol

So...I already have framing up. Can I glue foam board in between each 2x4 onto the cinder block then radiant barrier....then drywall?

Or do I need to take framing back down......glue full sheets of foam board onto cider block and then framing?
 
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Old 09-11-14, 07:30 PM
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Since I have already built the 2x4 wall that are up agaist the block wall....I'm thinking this;

Most of the studs have at least 1/4" gap.
But thinking of buying a spray foam kit and just spray the walls??

Anyone with any thoughts....please reply???!!!
 
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Old 09-12-14, 03:53 AM
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Don't feel alone by not fully understanding dew point temperatures and how it changes with relative humidity and air temperature. I'm finding the subject is misunderstood not only by the average home owner but also by contractors and builders in the trades.

Being you are in FL I doubt there will be much concern with condensation. The colder climates are where the serious problem are.
 
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Old 09-12-14, 04:01 AM
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I've lived in both central fla and the panhandle but it's been over 20 yrs ago. The standard building practice back then was to nail furring strips to the inside of the block, install fiberglass insulation between the furring strips and then staple plastic over the entire wall. The concrete block was always painted on the exterior which pretty much prevents moisture from migrating thru the block.

Things may have changed since I worked in fla. What does your local inspector say?
almost forgot welcome to the forums!
 
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Old 09-12-14, 04:18 AM
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Moisture migrating through concrete block is another portion of the misunderstanding. The moisture forming on the interior surface of the concrete block is caused by condensation on the interior surface not exterior moisture migration.

It might be said, how would that happen when I insulated the interior walls. The explanation is fairly simple. To keep the inner surface from ever reaching dew point temperature the outside of the walls needed the insulation. And to make matters worse, interior insulation keeps room air temperature from reaching the wall surface where the condensation forms.
 
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Old 09-12-14, 04:22 AM
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Fla gets a lot of rain with rain driven moisture being the biggest issue with block homes. The biggest condensation issues I remember was on windows from the AC being run.
 
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Old 09-12-14, 05:48 AM
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I just made some quick note as I read through. Apology if I duplicate any answers.
************
If you are using treated lumber you need special fasteners.

In a hot and humid climate the VB belongs on the outside. The objective is to keep warm humid air and moisture diffusion from reaching a cool (air conditioned) surface.

Vapor barriers are supposed to be continuous and in full contact with the air barrier and insulation. A vb and an air barrier are not always the same, ie drywall is a good air barrier but terrible vb.

"(We get a lot of moisture in the air because we have to run a dehumidifier all the time. I assume the moisture comes through the cinder block)" It can, but all buildings leak air at an astonishing rate, which as it turns out is necessary. A minimum air exchange of about 1/3 the volume of the house every hour. Homes with less require fans or other options to make up the difference.

"So I'm not sure if the bathroom may need vapor barrier inside and out???" Never two vbs it traps moisture, inside only in your climate and a good exhaust fan to get rid of most of that moisture from the start.

Bud
 
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Old 09-12-14, 07:51 AM
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I've been nervously reading for hours....still since posting this.

What I have learned is like mentioned. ...no VB on both sides because it will trap moisture.

Warm climates....VB needs to be on outside. BUT...from what I understand is the inside block should have hard foam board then furring strips....then insulation. ....drywall.
WELL if foam board is glued and taped.....doesn't this become a VB also??

(And yes....I've made sure proper fasteners have been used with the treated lumber...thanks )

(Another thing I've learned is stated below....this topic does confuse many from amatures to pro's)
Since everything changes from cinder block applications to climate to wood stick to above...below grade....etc...etc..
 
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Old 09-12-14, 09:57 AM
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Here's some more reading if you haven't already found these.

Forget Vapor Diffusion — Stop the Air Leaks! | GreenBuildingAdvisor.com

Vapor Retarders and Vapor Barriers | GreenBuildingAdvisor.com

Basically, one inch rigid insulation does allow some moisture vapor to pass through, thus some drying.

With PT studs, even your drywall nails/screws need to be special along with all of the framing fasteners.

Most of the confusion comes from trying to give one set of instructions for basements that have a wide variety of issues. Add to this that moisture issues are not just liquid water. Moisture vapor will pass right through a concrete wall, all be it slowly, and if it encounters a true vapor barrier it will allow the moisture on each side to slowly equalize with whatever the source is on those sides. But I will let you read.

Bud
 
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Old 09-15-14, 10:13 AM
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Thanks bud....
Have not seen those.
Also...you pretty much told me what I needed to know about the foam board.
Thanks
 
 

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