No Moisture Barriers

1parkpointer · 12-07-2008, 11:48 PM

When we moved into our home several years ago (1990), we were not aware of an ice dam issue that would plague us every winter since.
The house did not have access to the space above the top floor, some construction over-sight or due to a very shallow pitched roof (28-foot width and 5-12 pitch). I had to see why we were getting the ice dams, and soon cut an opening up through the 2nd floor ceiling (Fall 1992). I installed an attic ladder so that I could get up there anytime.
I was surprised to find that the 2nd floor ceiling did not have a moisture barrier anywhere above the 5 rooms or hallway. In fact, who ever installed the ceiling insulation simply laid the R-19 batts in between the trusses that make up the roof system; they are loose and not stapled to the bottoms of the trusses. Moisture barrier no where to be found, certainly the insulation barrier doesn't seem to be working.
I also found that the styra-foam proper vent was hastily installed as well. The roof seems to be a modified mansard style gambrel, and the proper vent was jammed into the pitch change passageway and appeared to be broken in between several of the truss-joints on both sides of the roof. In places the insulation that was attached to the exterior roof walls had fallen away and had closed off the venting all together, especially where the proper vent was broken.
I knew I had to do something to fix the bad venting (one of the causes for ice dams). A number of summers ago (Fall 1998 to Spring 2000), I bought plastic proper vent and stapled (4) 48" long sections together. After opening up the soffits, and with some help, was able to pull the sections up into each space between the trusses and up to the attic to the pitch change. Each section was then stapled to the roof and an additional section was then added to it, so that there was a continuous venting from the soffit up to the pitch change and then up another 4 feet. That fixed the venting to the continuous roof ridge vent.
The next problem was the attic insulation itself and lack of sufficient insulation. I was able to get additional insulation brought up into the attic (Late Fall 2008), but I haven't installed any, because I was wondering what I could do to add a moisture barrier if that can be done. The roof pitch is 5-12, 24-inch on center trusses, and it is a 28-feet wide. The attic is made up entirely of trusses, and at 200+ lbs. and 6-foot 3-inches, any movement around must be done very carefully. The R-19 batts as stated before are not fastened down, but simply laying on top of the sheetrock ceiling that was installed without strapping.
The thought of pulling down all of the sheetrock and starting over would be extremely expensive and messy. I've thought of adding gable end vents, but some forum members say it would add more moisture than it would dissipate and not alleviate heat that gets trapped in the attic when winter's snow builds up over the ridge vent. Does anyone out there have any suggestions for installing a moisture barrier and/or additional venting, if something can be done?

AaronB · 12-08-2008, 07:25 AM

Add the insulation. Ice damming is not caused from the lack of a vapor barrier.

Whover said that the snow is preventing the venting of your attic might be a jackass. Your roof is cold if it is covered in snow.

Most batts come with their own facer, which means that it has a built in vapor retarder (a vapor barrier allows zero water permeation)

1parkpointer · 12-09-2008, 12:52 AM

Thanks,
I might have to wait till spring now, as temps in the attic are quite cold. Need some warmth to spend any amount of time up there.

Slyfox · 12-11-2008, 07:09 AM

I agree with AronB,
if you all ready cleared a passage for free air flow from the over hangs on the steeper pitched roof too the crawl space under the flatter pitched roof, and you all ready have ridge vent, than your venting situation is fine.

The insulation being loosed laid is fine also, it's laid on a flat surface and has no exposure to the wind, etc., thus no need for it to be fastened like it is in the walls.

Make sure you have enough insulation, and inspect the exterior areas at the point where it goes from steeper to flatter, that area is prone to problems because the 5/12 section of roof will wear out faster than the mansard section.
Steeper holds up longer than the flatter.

1parkpointer · 12-11-2008, 07:44 PM

Thank You both!