vapor barrier in Phoenix AZ

[sluggo85024]

I am creating a storage area under my stairs. It was originally closed up. Now I would like to dry wall it but am not sure if I need a vapor barrier and if so - does it need to face the interior or exterior. It will have a door on the storage area and is not air conditioned.

[oldslowchevy]

contact your building code enforcement office, they will tell you what you need for your area, that is something that chages from area to area.

[sluggo85024]

yep was going to do that- they are closed til Wed though.

[oldslowchevy]

ahhhh that sucks.

[BHD]

More than likely if it is in the "interior" of the house NO, If it is an exterior wall than I would think yes, normally the vapor barrier is on the inside of the wall next or under the dry wall,
there are a few exceptions to every rule. (in the north is on the inside of the wall) as the moisture will condense on or in the cool exterior walls in the winter, now in your area were the "cool" is provided by AC and it is inside I have not a clue to where they prefer it, but my guess is the moisture is normally created from baths and other living actives, and I would still think the inside of the wall, your air is normally very dry, I would still guess inside, but I would probly wait and check what is suggested,

The purpose of a vapor barrier is to block moisture from passing through into the wall, and condensing in the wall or insulation, (thus mold formation can occur, and moisture usually reduces the effectiveness of insulation).

http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11810

[Keyser Soze]

A vapor barrier in Phoenix???

Never.

Except where mandated by CODE the only places in N. America (the contiguous 48) where a vapor barrier is a generally good idea is in Minneapolis-type climates.

In AZ this would be a galactically BAD idea.

Keep in mind that a wall system (and for that matter the whole house) needs a drying mechanism. In the cooling season (~10 months in Phoenix) the dehumidification is accomplisthed by your HVAC system. However in those months where the AC isn't running 20 hours a day you have a challenge dehumidifying... certainly spot ventilation is great (bath and kitchen fans) but these alone won't solve all of the moisture issues (e.g. cooking, breathing, etc.) that can accumulate over time. The wall system needs to be able to move moisture (diffused not bulk) into or out of the building.

In AZ it is a VERY good idea to have a wall system that can either dry to the outside or the inside.

Some cardinal rules to follow (they are actually LAWS....):

1. Heat rises.
2. Cold falls (puddles).
3. Heat follows/goes to cold
4. Wet goes to dry.
5. High goes to low (as in pressure).
6. More goes to less (air, heat and water)
7. One cubic foot out = one cubic foot in (for every cubic foot of air that is exhausted from your house - another one replaces it).

[Slight Topic Hijack]

If anyone is interested I will write-up a little Building Science Primer for you all... this will hopefully shed some light and common sense approaches to how a building acts; how air and moisture effect the building and how to build in 'tolerance' into your structure.

[/Slight Topic Hijack]