Hi, new member here from Winnipeg, Canada. My wife and I are at our wit's end, so I searched out this forum, hoping for some advice. I'm sorry it's long.

We have lived in our 1924 bungalow for 17 years. We have painstakingly restored and repaired all the original wood windows and storms. They are one of the prime features on the house, so replacement isn't really an option. And they've never been a major problem -- until we gutted our basement and insulated with spray foam, right from the floor up into the joist cavities. Note: our floor joists are encased in the concrete foundation walls (perhaps some of you know where this is going).

The first winter after redoing the basement, our main floor was so cold around the perimeter we had frost on the baseboards in several places. We were finally told that because no heat is escaping through the foundation walls, and especially through those previously-leaky joist cavities, that the foundation was getting much colder and that cold was permeating up into the main floor, since the main-floor walls sit right on the concrete.

So I scraped out as much of the spray foam from those joist cavities as possible. Yeah, fun job. To get at the concrete where the joists run parallel to the walls, I even drilled holes through the last joist and reached through with tools to scrape out as much insulation as I could.

The next winter, we found it made virtually no difference.

Next idea: insulate the concrete foundation from the outside. Because our foundation is high out of the ground, we didn't want an ugly bump-out caused by insulation, so we removed the entire stucco exterior, built out our window brickmoulds for all 21 windows and added one inch of rigid pink insulation (R-5), starting from 6 inches below the ground and all the way up the walls of the house, to the attic line. Yeah, fun job.

This helped. The following winter there was no frost. But it remains far colder than it used to be around the perimeter of the main floor. AND, now on very cold days, the windows sweat far more than they ever did before.

Our theory: the basement remains very tight, leaving our windows (single pane inside, plus a single-pane storm) as the weak point, meaning much more warm air is being pushed (we have a gas, forced air furnace) to the cold glass, where it condenses. That's just a theory. Note: we are not using a humidifier. Humidity is as low as 28% on a cold morning.

Have we changed the dynamics of our house so drastically? And what can we do now to prevent those beautifully restored windows from rotting with all the moisture on them every day? We're moving fans around right now to try to keep the moisture off.

Again, I apologize for the length of this. I hope somebody out there has gone through something similar and has some ideas. I have tried to attach two photos of the house, just for interest, before and after stucco removal.

Thanks for reading.


Views: 545


Reply to This

Replies to This Discussion

Cold floor edges around the walls are not the result of stopping exfiltration.  Before you insulated the inside of the cellar wall it was a giant thermal battery accumulating heat and delivering it to the floor system above.  By insulating the inside you changed that, now your masonry basement walls are being chilled by ground contact. 

Winnepeg = cold, so you built a heat source into a cold source.

When you put the frost wall down the outside (pink foam board) you made a step toward solving the problem you created.  What you really need to do is look into what is called an Alaska frost wall. 

Frost begins on top of the ground and travels across, then down.  Your pink foam needs to go deeper, and an apron at the bottom will deliver maximum benefit. 

The humidity issue is a whole different set of questions. 

What is the cellar floor and how damp or wet is it?

Tightening the cellar up may well have turned your cellar into a water drawing mechanism similar to a sea still. 

You need to put humidity sensors on all level and see where the problem is coming from.  Fortunately they cost about 2 bucks each on ebay and are direct reading digital units. 

Until you determine humidity levels floor by floor, it's pointless to speculate on source or cure of that issue.

Another thing you can do to prevent condensation on windows is plastic inside storms. 

I have 1/10" lucite on all my windows, inside.  I was able to take advantage of the casing design and hold the lucite in place with ¼ round molding.

There is a 10°f difference between the inside glass pane and the inside of the lucite.

Right now it is 20°f outside, 70° inside, and 44% humidity in the house.  There is no condensation on the windows.  Inside temp of the lucite is 55°f.

In addition to the humidity sensors I recommend you buy a point & shoot infrared thermometer.  It will be very helpful over time.

Thanks for taking so much time to respond, Franz. A few things:

We didn't change the basement dynamics that dramatically. It was always a finished living space, insulated with fibreglass (the pink stuff) and finished with drywall. It was always a warm space in the cold winter. Warmer than the main floor on very cold days, likely due to all the windows on the main floor.

When we gutted the basement and underpinned the house three years ago, pouring a new concrete floor to replace the uneven, sunken one at the same time, we simply improved the insulation by spray foaming: at least two inches of closed cell (R-12?). I remain shocked at the difference (in a bad way) that has made on the main level, although your explanation basically aligns with what we've been told: the concrete walls are now a source of cold.

As for humidity, there is absolutely no moisture source from the basement. We've installed two sets of weeping tile, one inside the house and one outside, all connected to a sump pit and pump to keep water from going under the basement floor and causing heaving. The basement is a warm, dry comfortable living space without that "basement smell." I work down here in my office every day.
Right now in Winnipeg, it's 19F outside, 70 inside on the main floor, (61 on one of the window sills where I've put a thermometer) with 34% humidity, according to our digital thermostat -- and our windows are perfectly clear. The sweating problem only arises when it gets colder. Probably beginning around 14F (-10C). When we reach below 0F, it gets really bad. The key point: it was never a major problem before we did all this basement work!

Adding a molding and plastic storms to our original casing is something we'd sure like to avoid. We've been thinking of attacking the problem from the outside, by having a new double-pane storm window made for one window, and see how that works before investing in 21 of them. Problem is, our window openings aren't perfectly square and having new storms made would be extremely labour-intensive and costly. Not to mention all the hours and dollars we've already invested over the years by restoring the original storms -- even adding antique glass where it was missing!

Your suggestion of humidity sensors and an infrared thermometer are good ones. I shall ponder while waiting for more feedback here.

Thanks again.


Couple things you need to look at.

Unless you've added more humans or GreatDanes to the occupancy of the house, or somebody has taken to living in the shower, your new basement insulation system has cut off a lot of air infiltration and exfiltration you never knew about.

The condensation on the windows as they get colder is just basic Physics.  Water condenses out of air on a cold plane, your window glass.  Unless you can keep the innermost pane above the dew point of the house environment, the windows will be dew condensers.  If you use fans to keep the air on the inside of the windows in constant motion, you can minimize condensation, but it is doubtful if you can prevent it completely. 

Inside storms give you far greater bang for the buck than outside storms ever will, and using Lucite or Lexan for the inside storm yields the additional benefit of plastic being far less thermally conductive than glass. 

As to appearance, mine aren't noticeable,  The plastic sits snugly in the frame, and is held in place by ¼" quarter round molding.  The molding itself is behind the curtains, so it isn't seen. 

Your only possible alternative will be an air replacement system that trades inside air with  outside air constantly or multiple dehumidifiers.  That will be expensive.

An air replacement system? Sounds like an HRV. We decided against that when we gutted the basement and installed a new furnace three years ago. We thought with our old windows and a drafty old fireplace, we likely didn't need it. If we knew that would solve the problem, we'd probably do it now. But would it solve the problem? Again, humidity levels aren't bad. Woke up this morning and it showed 32% inside. Around 0 degrees F outside.

Thanks again, and Merry Christmas!

If i was living in that house I'd be doing some experimenting. 

I see at least 2 roof vents.  I see a fireplace chimnet.

My first move would be making a plywood closure for the front of the fireplace with a computer fan to exhaust air through the chimney.  You should be able to take air in through the roof vents and attic/second floor, and blow it out through the chimney.

You do not need to move a great volume of air, and you can easily baffle the computer fan to adjust volume.

0° outside ambient air is going to be nearly ZERO, so the humidity inside the house will drop considerably with a couple changes of air.

You have to remember you MUST have makeup air coming in to exhaust water laden hot air, so have a clear path for air coming from the roof or an upstairs window.  Ideally you want the air intake to be at least 13 feet above ground to get the cleanest air available.

One of my favorite ripoff products of the last few years is The Wave.


When you look at the contraption it's nothing but a muffin fan, a humidistat, and some duct. 

Anyone with minimal talent and a roll of duct tape can assemble a similar unit for under $50-

Based on the continuing advertising for this contraption, sales are doing well.

A second concern I have based on how tightly you sealed up the basement and installed a new furnace is the possibility you are going negative pressure inside the house to provide combustion air to the furnace if no outside combustion air is piped to the burner.

You've given this a lot of thought, Franz. We have, too. And we've done some experimenting, all to no avail.

We had a similar idea about moving humid air out of the house. So we left exhaust fans on in the bathroom and kitchen for a full day. Our idea was also to create negative pressure inside, as opposed to the positive pressure our forced-air, natural gas furnace creates. Our feeling was maybe the negative pressure would lead to less warm air being forced through the glass of our windows.

The effect was minimal.

The only change was not a good one: the negative pressure drew even more cold outside air in through the fireplace chimney and the bricks of the chimney, creating a very cold living room. We even put an inflatable bag up the chimney, designed to stop down-drafts. No better.

As for your concern about fresh air for the furnace: it was professionally installed, with fresh air intake and exhaust. We even had the installer put in an additional fresh-air intake, so the furnace can draw more outside air if it needs to. When this condensation problem began, we closed the additional intake, again with the idea of reducing positive pressure inside. There was no improvement with that, either.

You can see how we've come to our wit's end.

And, again, humidity levels in the house seem to range from 28% to 32% when I get up in the morning.

FYI, there are another two roof vents on the back side of the house, plus a gable vent at all three gables: the two gable ends of the house, plus one at the back. There is no second floor. Those windows are into an attic. The attic has never shown signs of moisture and is well insulated. We haven't changed that dynamic.

The only thing we've changed is spray-foaming the basement! And I've scraped as much of that out between the joist cavities as possible. Recently I removed some ceiling tiles from the basement ceiling (we custom-made tiles from MDF: medium density fibreboard) to see if some more warm air up in that space will help warm up the concrete foundation. Our weather has been warm since, so I'm waiting for another cold snap to see if the heavy condensation returns. I presume it will.

And I shall continue to scratch my head, and search for answers.

Happy New Year :)

Last night I ran this situation past a group of young associates who assure me I tortured them at every opportunity rather than just give them the answer.  The only exception to the torture argument is one wife who reminds them how much money I spent teaching them to find answers.  Today, all my students carry coveted PE money printing stamps.

I had a hunch, from the grins, they had seen the problem and solved it, and that I was going to pay.  I quit counting how many times I was asked by Beverly "What was added and what was taken away?". 

They finally took pity on the old man, and walked me through it.

The new furnace (probably a 90+ pile of junk) was added, and it brings in combustion air from outside of the house.

What was taken away was the old furnace, which burned moisture rich air from inside the "Contained environment" (house). 

They even have programs on their pocket computers (damn phones) that can calculate within a cubic meter  how much air that old furnace swallowed from the house, burned and sent up the smoke pipe when provided the  volume of gas burned.  Based on the house we were sitting in, the furnace alone accounts for 8 complete air changes a day, based on 5 hours of burn time. 

Your "containment" is no longer experiencing those daily air changes, ergo, you are gaining moisture until you reach maximum load, when it will start raining in the living room.  You definitely also have increased latent moisture in all your stuffed furniture, which needs to be removed. 

Because they are engineers, naturally there were multiple possible fixes.  The simplest solution revolves around circulating outside air through the "containment" as the furnace burner is running only.  This can be done with one or two computer muffin fans, and will take time to remove excess water from the environment.

Consensus is that the foam insulated cellar walls are a secondary issue, not accounting for more than 15% of the humidity according to Tommy's phone. 

You also probably have another problem caused by kitchen exhaust fans taking the house negative pressure for want of makeup air to properly ventilate.

I fully believe the girls are more brutal when it comes to getting even with me, but I deserve it, and it was fun to see my Socratic methods bore fruit.  I also have 2 dinner invitations out of the deal.  I hope those girls can cook.

Sorry to disappoint the engineers, but the new furnace isn't much different from the old: both "high-efficiency" natural gas furnaces of their time, the old one (a Lennox "Pulse") put in by the previous homeowner in 1992, the new one a Bryant installed by us three years ago, using the same intake and exhaust pipes leading to the outside. So the amount of "air exchange" hasn't been altered dramatically.

One more time: indoor humidity seems stable at around 30%, give or take a few. I've read that is within the desired range during a Canadian winter. Any drier and our noses would be bleeding (which already happens sometimes).

Our kitchen exhaust fan is rarely used, other than to try to reduce the condensation after it's happened. It's certainly not in use all night, and the problem greets us in the morning when we get up.

The only other change to the house I haven't mentioned: four new fibreglass basement windows, and the addition of a fifth, done at the same time as the spray-foam insulation. Of course, they are more efficient than the original wooden basement windows.

If I were independently wealthy, I'd fly you and your engineer friends over here for a look-see, Franz. On the coldest day of the year, of course. Show you some real Winnipeg hospitality.

Paul, I would venture Winnipeg has little Rochester NY lacks, in terms of winter. 

we've played bouncy between 20 and 50 so far this winter, and my inside humidity in the house is 45%, a bit higher than I like.  Since this thread started I've been watching for window condensation. 

NOT happening here, other than on the inside of the outermost 1950 wood storm window with single weight glass.  That is accounted for by humidity coming in with air around the storm window.  The middle pane of doubleweight glass has shown no condensation on any day, be it 20° or higher.  The innermost pane of Lucite shows only cat nose prints, which I am powerless to stop.  Distance between panes averages 2.5" between the outers and 2" between inner panes. 

The nearest I have come to a comparable with your situation has been condensation on the outside of a basement oil tank when 200 gallons of 25° oil was pumped in.  Ambient around the oil tank is 65° with 45% RH. 

The inside surface of my Lucite panes is running a consistent 58° when outside ambient drops below 30°. 

I am not a believer in so called high efficiency glazing that is fashionable these days.  My system has outperformed every high efficiency I've compared it to for 20+ years be they vacuum or argon filled. 

As simple as it gets, your window glass is dropping below dew point for ambient conditions inside the house.  Either you raise the surface temperature of the inner pane above dew point, or you lower the RH inside the house. 

Since your furnace replacement was more or less like for like, we take that possibility out of the game.  I just glanced at Winnipeg average temps for October through February, and your outside temperatures make it near impossible for a winter humidity average to run 20%.

If the house is maintaining around 40% through that time period water has to be getting into the interior atmosphere.  If the roof isn't leaking, next likely candidate is the cellar floor. 

Have you laid sheets of toilet paper or paper toweling on the floor with plastic over them to see if the floor is delivering water?

Is the foam open cell or closed cell?

I'll relay your invitation to the kids, if you have ski facilities and snow at least 3 of them may be at your front door.  I must warn you, the girls can eat large volumes of food and do not gain weight.

It is closed-cell spray foam. A full 2 inches thick, more in places. Supposed to provide a vapour barrier as well.

There's no bare floor anywhere in the basement. All covered in flooring. When we gutted the basement and removed the old uneven concrete floor, we went all out to keep moisture out and prevent future heaving in what is a clay-soil area: installed all kinds of weeping tile, a sump pit and back-filled with pea gravel. In the previous years we'd already waterproofed the exterior of the foundation walls, professionally, using a rubber membrane. No sign of moisture in the basement since.

I just took two photos and have attached them: one of our living room window bank, facing northeast. The other a closeup of the condensation on one window, right at this hour: 1 pm Central time, sunny day, -15F outside (plus a bitter windchill of even worse) with 74% relative humidity outside (according to our TV weather channel) and 28% humidity in our house (according to my digital thermostat readout).

You should be able to see the moisture pooling in that second photo.

Again, this, and the cold perimeter on the main level (baseboards and floor) has only become a major problem AFTER spray-foaming the basement walls. Before spray-foaming, there was always some condensation on the windows on cold days, but it was manageable.

Franz, if you don't mind, post a photo or two of your "indoor storm" setup. I'm curious.

Thanks again for taking the time to correspond.


Sorry, did NOT attach the two photos in my previous post. Here they are. Hopefully. The second one shows the condensation pooling at the bottom of the window. The previous post outlines the conditions outside and inside. This is typical on cold days, sometimes even worse, on all 21 of our old windows.

For those who may just be tuning in, the problem is much worse, and the main level much colder along the perimeter, since we insulated the basement with spray foam.


Lets see if the pictures work for me.

Inside temp 68f, 38% rh with gusty winds to 15mph from the west.

This window is on the west side of the house.

Note, there is no condensation occurring on the window pane or lucite.  Temperature of the lucite is 54°f according to the infrared temp gun.  That is well above dew point.

From what I can see in your pictures showing frame detail, you have a similar trim structure and should be able to encapsulate the cavity where you have blinds currently.

I initially intended to include blinds between my window and lucite inside pane, but gave up on that idea and went to a mylar window shade to stop solar gain in summer.

Disclaimer: I accept no responsibility for pictures displaying in proper orientation.



Get Connected:

Follow Us on Twitter We're on Facebook!



© 2018   Created by Community Host.   Powered by

Old Houses | Restoration Products  |  Report an Issue  |  Terms of Service