New Construction Condensation??!!


I am new to this forum and I must say it is very informative. I am a home/ condo builder and I am having a problem with condensation in a new attic. The home is a condex(side by side) with a firewall running up the middle. About a week after I turned the heat on in the 2 units I was getting water stains through the loft cieling in one of the units. After cutting a hole in the cieling I looked in the attic to find it “raining” in there. It is what I guess you could call a finished attic (loft) above the master bedroom with a knee wall, sloped cieling and then a flat cieling above. After removing the whole sloped cieling and all the “wet” insulation I found only one bay to be dry. This rafter bay happened to land on the knee wall directly above the heat supplies feeding the loft. It seemed as if there was heat loss from these supplies rising up the bay like a chimney into the attic thus causing my problem. I discontinued 2 of the 3 three supplies (overkill I suppose), blanketed the kneewall with insulation and put the unit back together with new insulation and drywall. After cranking the heat for 4 days I went back in the attic this morning to find that my problem appears to have been solved by 90%. I am still getting some frost build up on some of the roofing nails for about 2 feet from where the sloped cieling meets the flat. I also cut the ridge open an additional 2 inches to allow more air flow. Now my question. Is it possible the minimal frost is normal? or could it be from the replastering I just did on the cieling? Or do I still have a heat loss problem that needs to be investigated further? Any help would be appreciated as I do not want to sell this unit until I am sure I and the future owners won’t have a problem.

If this is a condex/new construction and you are the builder/seller I would suggest 1st contacting the architect and the hvac company to review the problem and if that doesnt work hire an inspector that can do thermal imaging for you.

The key is insulation and ventilation. Sounds like you pretty much solved the problem.

Dan, I agree with Linus, that your area of insulation and ventilation are the points of interest and you seem to be on top of it by your own mistakes.
Any help would be appreciated as I do not want to sell this unit until I am sure I and the future owners won’t have a problem.
The ethics you have shown here by posting what you did is second to none.
It is proven, that proper insulation and ventilation will prevent such occurrences.

Marcel :slight_smile: :slight_smile:


Thank you for your responses. I wanted to add that as of this morning the attic space is completely dry. The remnants of frost must have been remaining moisture from the first time around or the plaster. It appears the cause was the heat supplies in the knee wall. My HVAC contracter is going to be getting a nice long talk about the dangers of heat loss.