HELP - Insulation and vapor barrier issue

[ryan0402]

I'm in Vancouver, BC, so similar climate to Seattle. Mostly rain on fairly mild winters and not too hot summers.

I have finished a new garage recently. One level 24'x25' with hip roof. It got wrapped in Tyvec and then 3/8" rain screen strips applied all around to shim out the Hardieboard siding. Bug nets installed to prevent bugs to get behind siding. Also vented vinyl soffits installed. Then I insulted the walls with R14 and ceiling R28, also making sure rafter vents installed. 6mil vapor barrier installed and taped and top and bottom wall seams sealed with acoustic sealant. Drywall in a few months....

There are windows on south face and sun exposure is on south wall and west wall.

I've heated the garage to about 10-14'C.

Now after one recent sunny day I came into the garage and noticed condensation on inside of vapor barrier on about upper third of south and west wall ( the ones with most sun exposure). I promptly cut into vapor barrier near top of wall to vent this moisture out. Never had an issue on any other day? What gives and what should is check or do?? Framing and sheathing was totally dry during construction and roof has no leaks.

 

[ksj9393]

Clarify... was the condensate on the insulation side or living space side of vapor barrier? Condensation occurs when moisture laden air is cooled to its dew point. It is necessary to know the side with the condensate to define your moisture drive direction.

 

[Angelfire]

This document can help: http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design


Page 12 specifically addresses a climate like Seattle. Says for that local, you should have minimal moisture retardation (ie. paint or worst case, Kraft faced insulation). Too many believe a 6mil plastic sheet cuts it everywhere but really it's about matching your interior retarder with the climate and exterior construction. I live in NM where we can get away with pretty much anything due to our dryness but I elected to use a variable retarder.

 

[ForceFed70]

To meet code, he needs the 6mil.

My best guess is that the moisture was there before you sealed up the walls. A lot of moisture can be absorbed by the lumber, etc during the building proccess. Especially in your climate. Until the moisture leaves the wall cavity (through the tyvec, etc) you will get condensation from time to time due to temp changes, etc.

 

[ryan0402]

Clarify... was the condensate on the insulation side or living space side of vapor barrier? Condensation occurs when moisture laden air is cooled to its dew point. It is necessary to know the side with the condensate to define your moisture drive direction.

Moisture was between vapor barrier and insulation on living space side.

 

[ryan0402]

To meet code, he needs the 6mil.

My best guess is that the moisture was there before you sealed up the walls. A lot of moisture can be absorbed by the lumber, etc during the building proccess. Especially in your climate. Until the moisture leaves the wall cavity (through the tyvec, etc) you will get condensation from time to time due to temp changes, etc.

6mil is mandatory here. I was hoping same thing about lumber being wet but it isn't likely. I was thinking maybe it was some special case since we have cold rain for a few days and then a warm sunny day. Could the moist air between the siding and sheathing where my air gap is heated enough so that it went to the interior direction thru tyvec and insulation (colder side relatively speaking) and then condensed on vapor barrier. Typically the air in this gap should just rise and vent up into soffits and the into attic and out thru roof vents.

 

[CADPoint]

Moisture was between vapor barrier and insulation on living space side.

You could use a dehumidifier. These spaces if not continuously heated or cooled you will have this problem till it dries out more. Heat goes to cold just like the high point of your dew.