Latest Discussions : Basement & Foundation


12:06PM | 10/18/09
Member Since: 03/03/05
273 lifetime posts
When it comes to humidity, you would be best to have the levels below 50% to avoid mold growth and structural rot.

Winter air is by nature not humid, so the problem must be condensation related.

What are the humidity levels in the living area?


01:57PM | 10/22/09
Member Since: 10/14/09
5 lifetime posts
Hi, in response to your question ... the levels in the house rise and fall but generally are in the 42 to 51 range. I've read that a good range for your home is 35 to 55.

So ... I don't know what else there is to do. Should I lift everything and add a vapour barrier ? Block off the Continuous Ridge Vent & add a fan instead ?

As I said: I'm stumped ....


11:01AM | 11/20/09
Member Since: 01/08/06
21 lifetime posts
I have been trying to deal with the same problem for years now


04:16AM | 11/21/09
Member Since: 03/03/05
273 lifetime posts
I have been corresponding with ketchen via email. He seems to think his issue may be due to attic ventilation. He is going to block the vents for the colder months and take a humidity reading in a few weeks.

I am hoping he replies to your statement, if not, I will post something when I hear back from him.


11:29PM | 12/19/09
Member Since: 10/14/09
5 lifetime posts
Hi Mr. Volcano ! Hope all's well.

Now, I did block off the intake vents for two weeks. Plus, I ran a de-humidifier in the attic for 2 weeks. It only made a bit of a difference. Then with the heat on overnight the humidity level would rise back to the high 70's.

With our recent dry, cold spell with sun throughout the day, the levels would drop to the 50's. But then one day I checked in the morning and there was frost on a few of the nail tips above the bathroom.

Unfortunately, I think I'm going to have to take it all up again and lay a poly vapour barrier before the roof decking is ruined. Or ... take it all up check again and re-seal the top plates of all the interior walls. I wasn't as vigilant toward those as I was with the plumbing stacks, chimney ... etc. I read a few more publications and they both recommended going over those top plates thoroughly.

But ... I have dropped ceilings - lowered from 9' to 8' - in the bathroom, the living room and the front hallway. I'm going to restore them to their original height and I think I'll repaint the ceiling with a vapour barrier type paint. I've got to do this anyways ...

Additionally, I rec'd a phone call from the manager of the manufacturer of the gable style attic fans I found - I expected an E-mail ! It never ceases to amaze me the customer service in the US ! He told me NOT to add a gable end attic fan. It could create a whole new host of problems. He went on to say some people had added a fan with other types of venting. But he had checked with his engineers - no, I'm not kidding ! - He re-checked the intake/outlet ventilation #'s I provided to him and he came to the same conclusion: Do NOT install a fan.

Needless to say .... I'm frustrated.

Let me know what you think ... Take care. Cheers for now.


06:27AM | 01/20/10
Member Since: 01/08/06
21 lifetime posts
just wondering if you proceded w the vapor bar and results?


09:10AM | 02/06/13
Same problem, same questions -- 100 year old house, replaced an old tar and gravel roof with an IBRoof membrane -- a "cool white roof" as summer heat has been a problem, we don't have air conditioning.

We immediately got water dripping off the screws that hold the roof membrane down on cold clear nights when the roof gets very cold -- water condenses on the outside and some on the underside. It was dry for 20 years before we improved things here. Been running a dehumidifier that costs about $100/month in electricity -- when it's not running the humidity in the attic drifts steadily toward 100 percent over a few weeks and stays there. White mold, cold, dank.


12:24PM | 12/09/15
Hello, anybody? Any new ideas?

Our dehumidifier mostly dried out the attic so now it costs far less than the original $100/month to operate. But we can't leave it a week without the dehumidifier running -- that's all it takes to get up to an average 70 percent humidity (and climbing). Outside air moves into the attic, leaves its moisture behind, amd moves on. Lather rinse repeat.

This is exactly how water accumulates in your gas tank, by the way, the scientist next door explained it. Warm air holds moisture; the gas tank cools off, sucks in outside air, the moisture condenses. The next day warms up and pushes air out of the tank leaving moisture behind. The next evening cools and sucks in more damp outside air. Over and over.

Same problem under the cool white roof.

Am I right that dry rot is active at average 70 percent humidity?

Seems the only longterm fix is going to be to put on several inches of insulation on top of the roof, then another roof membrane over that, with that whole package air and vapor sealed. The attic's far too old and cluttered with wood props and braces to successfully put vapor tight insulation underneath the roof membrane


05:34PM | 12/29/15
Recommend you invest in a monitor so you can compare outside humidity and humidity in the attic.


09:31AM | 08/14/17
Member Since: 08/14/17
3 lifetime posts
My daughter had an house built couple of years ago,had all the upgrades vapor barrier her ac duck system is always sweating before her one year warrenty from dream finders whet out ,they put an solar fan and an electric fan on her rooftop a year and a half later we noticed mold on her bathroom again and it soaking wet up there what can she do


01:03PM | 03/30/20
What happens to the humidity when the insulation is removed? I am having the same issues, insulated and humidity rose and mold grew, I added bigger gable vents and made sure my ridge vents were open and working still floating around 70% plus or minus. I am seriously considering removing half the insulation I just added to let more heat get back up there. The house is 130 years old and never had any moisture issues in the attic until now. I know most people would say that is a dumb move because you wasting energy but if it saves my structure I can handle that.


07:48PM | 08/04/20
Where is your house located? Are there trees close by the house? I have a 120 year old house with no attic vapor barrier but has some insulation - about 8” of blown fiberglass. Ridge vent, soffit vents and two smaller gable vent. No condensation problem. The home is in northwestern South Carolina.

Post a reply as Anonymous

Photo must be in JPG, GIF or PNG format and less than 5MB.

Reply choose button


Post new button or Login button