Attic Moisture issue - Vapor Barrier / Mold ?


Old 01-25-05, 06:11 AM
Visiting Guest
Posts: n/a
Attic Moisture issue - Vapor Barrier / Mold ?

Hi All - I had posted this in the roofing area by mistake - sorry - I have copied below my original post and subsequent progress / action - any input is greatly appreciated. Thank you very much
Hi All,
I have read many threads at length. Thank you very much for your help.

We purchased a house 2.5 years ago, and after purchase found an extensive mold problem on the roof decking. Long story short, we had to eat $ 10,000 and rip off all the decking and re-did the roof. We have an 1500 sq ft attic we put in 16 soffit (8 double sections per side) vents and a continuous ridge vent

1 year goes by on the new roof, and the first winter, there's ice all over the interior decking. I call the roofer, he states that it was due to the extreme cold, and not to worry. No mildew / mold in the spring. So I blocked it out as bad deja vu.

This winter rolls around. I hadn't been up there since the Spring, but upon my first visit, Mold is all over the brand new decking.

I had insulated with unfaced r-25 - which I know is a little light on the r-value - i wanted it to breather freely though. Upon finding this new problem - I called the roofer. Thankfully he is fairly open to come over and check it out. I also phoned an insulation guy; as I had read online, that a vapor shield is necessary.

He stated it was not. He has said, even if a sauna was under there un-shielded, the roofer having just redone the ventialtion - his setup is not working as the r-25, although unfinished, should not let enough moisture up there to mold in 1.5 years.

I am going to lay poly plastic tonight under the r-25 - in hopes of doing all I can to stop this problem before it gets worse. I pre-cut all my strips at 16" to fit in the joist channels - is this ok ? Should there be overlap up onto the joists ? I have already painfully, financially and physically, re-laid the perimeter of the roof with new r-38, with a kraft faced barrier.

In the Spring, also I plan to bleach the mold. Or should it be done now, as it is frozen and not as "sporey"?

Thank you all for any thought and help !!!!!!


Hi Guys, Again let me thank you all for your input and advice. I wanted to give an update as to what I have done, as well as some more spec's on the environment.

The home is in Northern Ohio - it is gas heated - the area in questions in an unfinished attic served by a hatch entry in a hall - it has a continuous length ridge vent served by 8 dual panel sets of soffit vents down each side (so 16 panels down each side - the area is approx 1500 sq ft. - there are 2 shower vents - but both vent via flextube hosing to outside roof vents

Around the perimeter I removed the unfaced r25 and replaced it with faced r38 - this then covers approx 4' in from the sides - all soffit vents are completely unblocked and show plenty of light through them.

Under the existing unfaced r25 - I have cut 18" wide 6 mil Poly sheeting and taken up the r25 - laid the plastic sheeting - then relaid the r25 back in over top.

On the product box of the Poly it did clearly state vapor barrier as a use for it.....

All top plates / romex chase / light fixture have been both Poly and then insulation - I see I may want to spray them still with foam though - I have not done that as of yet.

This new poly sheeting then, I placed under the r38 faced overlap by about 4 inches at the ends - packed the r38 back down snug.

The r25 which was removed from those preimeter areas - is now laying perpendicularly over several of the bedroms as a 2nd layer to bring those areas up to an r50 value - as r48 is spec'd for our area.

The areas which appear to be the possible culprit of the moisture - are the bathrooms - it appears their drop down soffit areas - above the shower stalls, as well as lighting areas - were left wide open up to the attic. Lighting cans had been replaced with airtight ones last year. It does also appear that they may have used standard drywall and not green board when the old owners had remodeled Also, it appears after this remodelling they did not insulate the walls - so when that humidifier was turned up, it had a fairly unobstructed path up and into the attic....

Above those areas however I removed all insulation and stapled the plastic sheeting over the channels - on all sides and ends - then laid the faced r38 back over top - hopefully "doubling up" the vapor protection. Also in one of the soffits I laid some r13 w/ kraft face on the soffits painted wall - the other 2 sides of the soffit are vinyl wall paper'd (which was stated to be a vapor barrier).

I have also shut down the house furnace humidifier - this is noticeable as several first floor wiondows now show no condensation - they used to however with the humidifier on. I did also speak to another friend who had said their humidifier was causing huge moisture issues. In our scenrio, with those open drywall soffits - I can only assume, this heat and moisture was simply rocketing up into the attic. Also, the humidi may have been even set a little higher than it should've been too - thus again point a finger at it as being a contributor - I won't say which finger I'm pointing at it though

The attic is now cold, and within the 2 days from completion some of the mold in the less condensed areas, looks to be visibly drying and hopefully die-ing. I am hoping and assuming the others areas will follow - it's just less noticeable as they were more "developed" in their growth

I do plan to paint the bathrooms with an oil based vapor locking paint in the Spring - to further supplement the v/b protection - I can't now as there is an infant in the house.

The bathroom main walls are wall paper'd with a vinyl paper, so the walls I believe are OK, it's the ceilings which are of concern. This then would in essence give me nearly a "triple" barrier in some areas.

Again, thank you all very much for all your help and advice, any and all of it is greatly appreciated !!!!

If anyone can offer their opinion as to my courses of action so far, please do so. Thanks !!!!

Thank you again very much
Sponsored Links
Old 01-25-05, 06:08 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873
Attic By-Pass Phenomena

This is where heat by-passes your insulation into the attic and you are correct, the light fixture and drop ceiling is common culprit for the moisture problems you had in your attic (air leakage). It was probably the reason you had condensation on your windows too (air infiltration).

The volume of the air inside the house remains constant. What this means is air cannot leave the house without the same volume of air entering the house. So as air left the house through the drop ceiling in the shower stall, the same volume of air entered the house through your windows. This caused the cooler surfaces on the window for heat in the house to condense. If you want to know more about the behavior of moisture in air under different temperature conditions, search the web for "Phychrometrics".

So in my opinion, neither your attic ventilation, vapor barrier or humidifier had anything to do with the moisture problems in your attic or on your windows.
Old 01-25-05, 06:59 PM
Visiting Guest
Posts: n/a
I'll give a look into that phenomena. It sounds very interesting. At this point anything is possible up there

Also, the showers are not drop ceiling'd above them, simply a dropped down drywall soffit to lower the ceiling height, as well as also in a few lighting areas above sink areas. I don't know if this clarification helps or matters.

Thanks again very much !!!!

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes