Humidity. Moisture. Water vapor. Evaporation. Condensation. Mold. Rot.
These are all words that go together in people’s minds when the topic of humidity comes up. But what is it and why is it so important?
I’m going to try to explain this as simply as possible, so for the scientists and engineers reading – please cut me a little slack. I’m going for clarity over precision. However, if you catch the inevitable factual errors, please point them out so I can correct them.
A Sure Sign of Collapsed Glass
Collapsed Glass Syndrome
I was recently visiting my brother and he pointed out a strange condensation effect he was having on some double glazed windows. Condensation formed in an oval pattern in the middle of the windows. This is really strange because condensation forms on the coldest parts of windows first. Thermal windows usually insulate best at their centers so condensation starts forming at the edges. But these windows were showing exactly the opposite condensation pattern as shown in the photo above.
The inside of a wall filled with entrapped moisture
I just received a question that was too complex to answer quickly, and so interesting that it deserves an entire post. Unfortunately, it represents a situation that occurs far too often.
To summarize, the question came from a reader who opened a small hole in their wall and found condensation on the vapor barrier at the inner surface of the wall. The question is, what could cause this?
Here are some more clues:
- The moisture was observed during the winter
- The hole was cut in a south wall
- The home has 3″ foam board sealed to the exterior wall
- A 2×4 framed wall was built inside this wall and insulated with Roxul
- A 6-mil poly vapor barrier was then applied just behind the inner sheet rock
- They did not measure high moisture towards the outer wall
- The wall was built during a humid summer
Bathroom windows will almost always "sweat" in the winter
When cold weather sets in, I invariably get a slew of questions from people worried about their windows “sweating.” There’s a perception, propagated by window salespeople, that condensation is a sure sign that you need to buy new windows for your home. What’s the truth?
The photo above is of a north facing garden window in my master bathroom. In general, I keep the humidity quite moderate in my home but this window definitely shows more condensation than others. In this case, during a spell of temperatures in the low teens, a layer of ice even formed. Should I replace this window?
Fiberglass insulation against roof deck plus moisture = roof failure
In the first post, we looked at how adding insulation could lead to frozen pipes if the insulation was put in the wrong location. But, just like a sweater, if you put everything you want to be warm inside the insulation, you can keep your house and pipes happy and energy efficient.
This time, we’re looking at how to install insulation properly so that you don’t rot out your roof. Unfortunately, the photo above shows how not to insulate under your roof!