moisture barrier for detached garage?

[chrisgraff]

I'm building a control room/booth in my detached garage. What can you tell me about sealing it as far as moisture?

I'm in the Southeast...do I seal the inside of the concrete block? Vinyl backed gypsum or oil based paint?

The floor seems dry; taped plastic wrap on the concrete floor overnight (no condensation the next day).

Good thing I read this board, less I get ahead of myself!

[Sandersd]

Seal with http://www.ugl.com/DRYLOKFrame.html

[knightfly]

Southeast, generally more cooling days than heating days?? IF so, that drylok stuff should be your ONLY vapor barrier even if you build inner walls for a second leaf. BTW, if the blocks are hollow, you ALREADY have a 2-leaf system and adding another will will LOWER your isolation - especially at LOW frequencies... Steve

[Ro]

And don't forget to ventilate the building, thumbrule for anti moisture.

[chrisgraff]

Southeast, generally more cooling days than heating days?? IF so, that drylok stuff should be your ONLY vapor barrier even if you build inner walls for a second leaf. BTW, if the blocks are hollow, you ALREADY have a 2-leaf system and adding another will will LOWER your isolation - especially at LOW frequencies... Steve

In Nashville we do have more cooling days. So I apply Drylok to the interior side of the cinderblock, correct? The outside is painted, not sure if it's oil based. Assuming it IS painted with oil based paint, would this be considered a moisture barrier as well?

As far as the cinderblock as a two leaf wall...

There seems to be quite a few (small) holes that need to be patched in the walls. I'm not confident a repaired cinderblock wall would constitute a (good) two leaf system. Plus we're going up a good five feet above the top of the cinderblock. Not to mention the two windows that need to be covered.

looking from the control room to the booth (where the windows are).

[chrisgraff]

And don't forget to ventilate the building, thumbrule for anti moisture.

Yes, installed HVAC this week. Ventilation's covered.

[rod gervais]

I believe in your location the code requirement is that the exterior face of the wall receive the vapor barrier.

You should verify that with your building official.........

If you do it wrong you stand a very good chance of moisture problems you don't want.

As far as how air tight your wall is- and your reference to

I'm not confident a repaired cinderblock wall would constitute a (good) two leaf system

although it might not be a good 2 leaf system -0 it still is a 2 leaf system if the block is hollow, which means you would need a heck of a lot more mass inside to overcome the losses you experience with a 3 leaf system.

Sincerely,

Rod

[chrisgraff]

I'm confused.

I understand that a third leaf compromises the air space between two outer leafs. Are you telling me that building a complete two leaf system inside the building would be worse than the cinderblock alone??

I sincerly hope we're miscommunicating, otherwise I'm gonna hurt myself.

PS thanks for the info on where to put the barrier; that's just the answer I was looking for.

[rod gervais]

I'm confused.

I understand that a third leaf compromises the air space between two outer leafs. Are you telling me that building a complete two leaf system inside the building would be worse than the cinderblock alone??

Chris,

1st - hopefully you aren't talking about building a 2 leaf system inside the masonry - but rather a one leaf system.

By this I mean -

outer face of masonry = leaf one
inner face of masonry - leaf 2
stud framing with insulation - not a leaf - just air space
inner face of drywall = leaf 3

Now - is it possible that at some particular frequency (or series of frequencies seeing as when a problem exists it usually spans about an octave of the specific frequency = 1/2 above and 1/2 below) that your masonry with a 3rd leaf inside could be worse isolation than just the masonry alone.

Yup - sure enough it could be............ but more probzably it would be closer to as if you just left the masonry walll alone - a whole lot of money with really no isolation gain.

Have you ever seen the picture of the vaious wall assemblies - where the difference (using exactly the same materials) is 23 dB of isolation just by moving the materials from a 4 leaf system to a 2 leaf system?

Well it's very true -

My best reccomendation for anyone working with hollow masonry is for them to figure out a way to fill the cores solid with either sand or grout.

Seeing as you say your masonry has a lot of holes in it - sand would be a bad idea - which leaves grout.

Then the entire masonry wall becomes 1 leaf - and your work inside becomes 1 leaf - best of all possible worlds.

Sincerely,

Rod

[chrisgraff]

I forgot to mention that there are windows in the cinderblock (see last picture).

This is why I went with this plan:

cinderblock (hollow)
airspace (two or three inches)
outer face drywall
stud wall with insulation
airspace (3 or four inches)
stud wall with insulation
drywall

Although this is a four leaf system, I'll end up with roughly two feet from the exterior face of cinderblock to the interior face drywall.

Comments? I so appreciate the advice!

[David]

Chris,

sharward posted this link elsewhere on the forum. I think this may give you a very clear idea what you will need to do in order to not only keep moisture out, but do it in an according to code kinda way.

http://www.buildingscience.com/resource ... novate.pdf

other than that: great space!