Yet another vapor barrier question.

[Hapis]

Here’s my question. I am insulating my garage with R-13 insulation in the walls but there is no vapor barrier in the garage. In all of the threads I seem (to me) to get conflicting answers. If the outside was not wrapped in Tyvek or some sort of barrier can one be put on after the insulation (do I need it?) goes in and before the drywall goes on? Of course the mold question I think should go in here as well. I am willing to spend the extra to get mold resistant drywall. Seems to me to be like putting on a raincoat then putting on a down coat. Hope my analogy made sense. As I had never planned on really finishing my walls until I came across you guys. I defer to the experts for some answers. Thanks in advance.

 

[wadd1]

Im old school... whether you have Tyvec or not
i always go with poly vapor barrier on outside walls
my 0.002 cents

 

[redsky49]

A vapor barrier/retarder should always be utilized whenever an occupied space is conditioned to a temperature, or relative humidity condition, other than ambient outdoor conditions. Period.

This applies to 99% of all structures, with a few exceptions (none of which apply in your case).

The location of the vapor barrier depends on the climate. A heating predominant climate has different requirements than a humid cooling predominant climate. In mixed climates such as the mid-Atlantic area, the placement of the barrier is a little more challenging. The brief answer is that prolonged dew point conditions are far less frequent during summer than during winter. That being the case, you protect against the more prevalent and more damaging conditions - in this case winter heating.

In your location (and I spent twenty years practicing in the DC metro area, including Annapolis, St. Mary's, etc.), the wall construction should be as follows, from the inside out:

Gypsum board (5/8" for garage construction)
Vapor barrier, 4-6 mil poly, continuous and sealed at all penetrations
Fiberglass batt insulation, R-19 if new construction
Fiberboard or other exterior wall sheathing
Building paper or air retarder (Tyvek)
Siding (or air space and brick veneer)

The intent of the vapor barrier is to reduce the movement of moisture into the wall cavity where it can cause damage. The permeable barrier (Tyvek) at the exterior will (in theory) allow moisture to pass through the wall assembly. You don't apply a vapor barrier to both sides unless you are constructing a "Thermos" bottle.

I am unsure how the use of vapor barriers has become so contentious. This is certainly not the result of the engineering or construction industry. Are there other ways to accomplish vapor control? Of course there are. But there is a reason that builders and Architects specify vapor barriers and that is because they have a track record of success, with little capital cost.

As always, offered only as opinion

 

[Hapis]

Thanks for the insight.

redsky49-Sonds like you know the area well. I can swith what I have remaning to R-19 for the rest of the garage walls. There is no barrier between the siding and the sheathing. I don't know why. I'll have to check. But with that said....still ok to put up a barrier on the inside? I am not trying to get this place real cold or real warm. It would be nice to even it out a little. Also in the spring I cat a few days of condensation on everything. I open the doors let it air out and problem solved. I am going to do the doors with the aftermarket kits that I read about in antoher thread. I have a 1-ton Move-N-Cool unit that I can run as a dehumidifier in the summer to help. I can stand most of the cold but the heats is.....well you know. How about the ceiling? do you run a barrier there as well. The rafters were designed to be a storage area. I have a ridge vent and gable fan to keep the air moveing up there. Needless to say it runs all summer.

wadd1-thanks as well. I didn't forget ya'

Let me know your thought if you have a minute.

 

[redsky49]

If you are going to insulate above the ceiling you should provide a vapor barrier. The non-conditioned space above the ceiling insulation should be ventilated. Sounds like you have it covered with the gable end fan.

If the lower level is open to the attic, you will have a difficult time achieving your desired results. Consult a local Architect if you need further help.

as always, offered only as opinion

 

[AmickRacing]

A couple years ago, back when I was doing HVAC in new houses I asked several builders about vapor barriers.

99% of them did the tyvek on the outside, and also the viscreen on the inside. I often wondered why they never did anything on the roof.
I was told by some builders that almost makes the house too tight and causes a "sick house" with out proper procedures like HRVs or ERV's to help keep the air exchanging.

My dream garage is years down the road, but I will admit my dream garage (dreams have no pocket books) would have that sprayed on foam that eliminates all air seepage and does a great job of insulating.

 

[bmwpower]

All the insulation I've seen has the vapor barrier built in - ie, no need for an additional installation of poly.