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Eric01
frost in ceiling

I built my house about 5 years ago.cathederal ceiling,ridge pole down the center with 2x8's for rafters. I ran air chutes between each stringer and used the plastic wrapped insulation.I get frost and ice build up between my insulation and chutes.Every spring,or winter,when it gets above freezing,i get moisture running down my exterior walls. Any suggestions.Thanks

canuk
Re: frost in ceiling

The rafter bays should be completely full of insulation ---- exception would be the air space between the air chutes and underside of roof.

Doesn't sound like there is a continious and sealed vapour barrier on the back side of the drywall.

Eric01
Re: frost in ceiling

doesn't the plastic wrapped insulation act as a barier, or is there anything i could do for that beings i already have it sheetrocked and finished off.may be a dumb question, but is there anything paint wise that would help.or any other suggestions on what I could do.

canuk
Re: frost in ceiling
Eric01 wrote:

doesn't the plastic wrapped insulation act as a barier, or is there anything i could do for that beings i already have it sheetrocked and finished off.may be a dumb question, but is there anything paint wise that would help.or any other suggestions on what I could do.

No --- these are not vapour barriers.

The plastic wrapped is more for convienence for DIY's to ease the discomfort from the itch and fibers in the air during installation .
The best the plastic offers is a vapor retarder not a barrier. A retarder still allows vapour to pass.

Besides there are likely gaps and other irregularites in the way the batts were installed allowing air movement and vapour to circulate.

A continious 6 mil poly sheet completely sealed should have been in place before the drywall went up , preventing any vapour from the living space to pass through into the cold rafter cavities above.

There are special vapour retarder paints available that may help or at least 2 coats of oil paint will also act as a retarder. These might help in that they will be a continious layer on the ceiling surface --- keeping in mind these paints aren't a barrier but retarders.

Another method that would help would be to apply 3/4 - 1 inch rigid foam to the existing ceiling taped and sealed then cover with drywall.

However, if there are electrical boxes or recessed lights that aren't completely sealed air tight these would be a major avenue for moisture to enter the cold zone regardless of how much vapour barrier or retarders are in place.

Also consider if there are other sources of moisture from outside --- bath , kitchen or dryer exhaust vents in the soffits for example. These would have moist air being blown back into the attic space and creating all sorts of moisture issues.

Eric01
Re: frost in ceiling

thanks for the reply, i really appreciate it.I have something to start with now.

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