Latest Discussions : Basement & Foundation


08:53AM | 10/15/09
Member Since: 10/14/09
5 lifetime posts
Hi. Hope all's well.

Now, I'd really appreciate your help ... I'm stumped. Greg V. of Bob Vila's site suggested I post this. Questions:

Do humidity levels rise and fall in the winter months ? e.g. up to 60 to 70 % then down ...

What is the proper level ?

Is it a mistake Not to have a vapour barrier ? It's an old house. Attic square footage is approx. 1000 sq ft.

Bear with me. Forgive me if I repeat items. Here's what I've done ...

Background: my house was built in the 1920's. I had insulation blown in after the attic was supposedly sealed to an approx. R35. The

installer suggested not to add a vapour barrier given the age of the house. He added 2" round, button type vents between the eave blocks

as there were no intake vents.

And I know humidity readings in the attic will rise and fall obviously without a vapour barrier in place. But what's normal ? Will they go

up to the 70's for a few winter days then drop ? Trouble is I have to

wait for winter to test ...

The first winter after the insulation job I noticed water dripping from the nail tips. Reason given: not enough intake venting. Add more vents 4 x 14 (3 X 12 actual opening). No difference. Humidity level 80 to 100 +

Problem @ the Ridge Vent. Reason given: poor ridge vent product & blockage. Replace entire roof for the 2nd time and install new continuous ridge vent manufactured by Lomanco. Better. But the humidity level still too high for my liking - 70ish.

So you know .... I did have a blower test performed and it did expose a # voids into the attic. Fed up with excuses by insulation installer. I removed the entire blown in insulation. I found 12 + knob & tube holes that weren't sealed. There was a 2 " gap in places around the chimney. None of the plumbing vent stacks were gasketed or sealed ... The smoke test really showed where the leaks were.

I read that sealing was more important than a vapour barrier given the age of the house ... I read this over and over ... so I sealed all the voids I could see with spray foam.

I made certain the intake vents were open and positioned the shoots so that they're right down to the edge of attic for good airflow. I laid R12 batts between the joists. Re-spread all the loose fibreglass insulation on top of R12's. Approx. 16 inches of insulation R-40ish rating.

I've replaced all the 2" button type vents on both sides of the house with 4x16 grilles.

*** Here's what I found and measured for the intake/eave vents:

32 Grill Type Vents with a 3 3/4" X 16" size with actual intake

opening/venting @ 3" X 16". They're placed as 1 unit - 1 hole cut-out @ the eaves.


I think I've got a intake/outlet venting ratio of 150 to 1 as the 1 to 300 ratio didn't seem to cut it.

There's also 36 foot length of Continuous Ridge Vent Outlet over the living

space. New Lomanco Product. Attic square footage is approx. 1000 sq ft.

Now, here are what I think may be my options:

- As there's No Vapour Barrier, Add more batt insulation on top of existing insulation in cross hatch pattern ? I was thinking to add

R20 or R35 batts to slow the heat rise ... takes it to a R50ish + range. Waste of money ? Or ... is a layer of blown cellulose a better option ?

- Add Gable vents to create a cross flow ? I've read NOT to mix vent systems.

- Do Vapour Barrier type paints in the ceilings work ?

... I'm at a loss as to what else to do. I just don't want to have to lift everything again & add a 6 mil poly vapour barrier ...

I think I've done all I can and I really tried to seal all the possible air holes that I could find. All my fans - kitchen & bathroom - are directly vented to the outside and we use them.

The only other thing I can come up with for the humidity issue, is a humid basement. I've placed a de-humidifier in the basement and that lowers the hygrometer readings significantly. I know we contribute to the humidity - breathing, showers, cooking ... etc. But " the moisture source " ... the extra humidity from the basement could be it. The only thing to cure that is to re-do the perimeter drainage and spray a sealant on the concrete basement floor.

So ... that's where I'm at. I guess I'll have to wait for winter. I know humidity levels go up and down. I measured the attic this morning it was 71.

Thanks ... if you can give me your angle I'd appreciate it. Take care. Cheers for now.

P.S. For the time & money I've spent maybe I just should have had the attic spray foamed ....

J. K. (D.A.S., D.CDN.S., B.A., M.A.)


12:06PM | 10/18/09
Member Since: 03/03/05
271 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
271 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.

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