Frost on Vapor Barrier

We are in the process of finishing parts of our basement. While preparing for construction, I noticed a small patch of frost on the warm side of the vapor barrier where it covers a stud. There is fiberglass insulation between the studs, then the poly barrier. The stud is very cold to the touch. This part of the basement wall is above ground approximately 1.5 feet.

I live in Minnesota and it has been below zero for several weeks. Is this simply a humidity issue inside the basement that I need to resolve? Is there something I should do to prevent further frost before I lay sheetrock here? Any help is appreciated. Thank you!


I live in Hudson, WI and have been seeing much more frost on interiors than usual due the extreme cold.

For example:

In my own home I had to turn the automatic humidifier way down to avoid heavy frost on my double pane insulated windows.

There may be cold air in the sill area or in the area of the stud with frost. Firstly find some info on air leakage control (US dept of Energy) and brush up on the phenomenon. Open up the barrier and see if its air leakage (a day with the wind blowing onto this wall) …seal the area.

Check your humidity level and try to maintain it in the 30%-50% range.

I took your advice and read up on the articles from the DOE. I then did a quick ‘feel’ for drafts along the sill. There is a definite slight draft there! I will do as suggested and pull off the barrier to locate the leak and seal. Looks like it should be an easy fix (if I can find the leak). Thank you so much for the quick response!

The house does have humidity controls, but as the temps dropped, I raised the humidity. Clearly, I need to get educated ;). I suppose a few shocks is better than a moisture problem! Looks like a combination of issues. I appreciate your responses on the humidity - your ideas have helped a lot - really!

As the temp drops outside you need to lower the humidity inside.

I always thought it was the other way around, but then again, I am in the humid summers DC area!

Humidifier Settings, Installation and Maintenance Tips

During extremely cold weather, your home loses humidity to the outdoors and may drop to as low as 10%. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommend that your home maintain a humidity level between 30-60%. As the exterior air temperature changes so do the optimal interior humidity levels of your home.

As the temperature drops outside so must the humidity levels in your home. If the weather man calls for a prolonged cold snap be sure to lower your humidistat.


Wow was I off! Learning everyday! Here are a couple of sites I came across…

These were great articles. Thanks! It was interesting to learn of all the potential sources of major humidity that I hadn’t really considered.

One more thing. I just wanted to thank everyone for the help out here. This probably isn’t meant to be a resource for the average home owner. After reading some of the boards however, it seemed like you would understand the problem and have some solutions. Again, many thanks.


Had a quick look at both these sites. Saw 2 glaring errors in the gas assoc sheet…these folks sell gas and are not building scientists nor technicians. The second site looks all right but is at the homeowner level.

Just wondering - what were the errors? I tried to look up on ASHRAE, but I think you have to be a card carrying member…

(1) The vapor barrier graphic: a vapour barrier does little to stop moisture movement into walls/attics until it is properly sealed to be airtight. 98-99% of moisture movement into these areas is air movement which the unsealed vapour barrier does not stop!!! If you have a choice of an air tight drywall installation without vapour barrier or loose drywall with an unsealed vapor barrier behind it…choose the airtight drywall without vapor barrier!!! It’ll give you way more protection against moisture moving into walls!!!

(2) “Generally, older homes have an average of one to two ACH. Tight, new homes or older homes which are sealed may replace air only once every two hours or more (or .5 ACH).”

A “tight” new home will not be tight if it changes air naturally at 0.5 ACH. As a matter of fact, in northern climes during cold weather snaps, the house will be overdried, there will be nosebleeds, people will be getting shocks from door handles and energy bills will be high!! A truly tight home will change air naturally about every 20-24 hours without door openings and mechanical ventilation.

These things I know from personal experience:
(1) The first time I tried to make a house airtight was 1977
(2) I was a “certified” (recognized by US gov) energy auditor in 1981. (actually took the course (7 days) at Bowdoin College , Brunswick, Maine where INACHI member Marcel Cyr has done a lot of construction work)
(3) Bought a blower door in 1981 to do air leakage control work
(4) was trouble-shooter, researcher, site advisor for Canada’s R2000 Low Energy house program for 8 years in the 1980’s-90’s. During this period 2 of my clients were named Canada’s R2000 “Builder of the Year”.

PS: I have addressed only the 2 items I noticed in my first 30-60 second glance at the document…there may be more!

Sweet, thanks for the info, definately gives me something to chew on!