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Unintended consequences of new windows


hoytt
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We have all seen older 1950's homes with uninsulated walls, line-wire stucco and the single-glazed aluminum or steel sash windows.

I recently inspected such a home that also had an old, marginal radiant heating system. They had also replaced all the windows with high-effeciency vinyl double-glazed units and then painted the home inside and out so that it would be more marketable and sell quickly.

As a result of the new efficient windows, the original cold plane of the windows that used to cause major condensate buildup has been removed. The new windows no longer attract the condensate and it now builds up on the next-coldest plane... the drywall of the exterior wood-framed walls exposed on the interior. This in turn resulted in major mold buildup.

How many of you have seen this type of unintended consequence, and do you warn your clients of the potential for excessive moisture buildup and resulting mold? What would your advice be for the homeowner that is now stuck with this condition?

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As a result of the new efficient windows, the original cold plane of the windows that used to cause major condensate buildup has been removed. The new windows no longer attract the condensate and it now builds up on the next-coldest plane... the drywall of the exterior wood-framed walls exposed on the interior.

I disagree with your theory of the mechanism that's at work here. Condensation is not increasing at the walls because the cold window surfaces have been removed. The water vapor in the air doesn't choose one cold surface over another upon which to condense; it condenses on any surface that's at or below the dew point.

I think what's more likely is that the new windows are tighter than the old ones and, as a result, the house is experiencing fewer air changes per hour. This results in higher indoor humidity and a corresponding higher dew point.

How many of you have seen this type of unintended consequence, and do you warn your clients of the potential for excessive moisture buildup and resulting mold? What would your advice be for the homeowner that is now stuck with this condition?

I haven't seen this. Up here, putting in newer, insulated, windows doesn't seem to cause an increase in mold growth on the walls.

I f I did see it, I'd probably recommend either insulating the walls or running a dehumidifier.

- Jim Katen, Oregon

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You can't find this entertainment anywhere else. Chad, you crack me up. Kurt had better watch himself.

Jim, I know what you are saying, but either theory could be at play here. It is possible that the cold windows did serve as the dehumidifier for the space. In either event, I'm with you on the solution. Keep the energy efficient windows and add a dehumidifier.

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It's why I hang around. It was a red herring; he starts in w/the "we've all seen....", but his description doesn't specify. That's what happens when one (me) skips over the general & goes to the specific too quickly.

I had this exact same condition on a cheap shoebox rancher out in Hoffman Estates; change out the windows, the place turns into a mold farm.

We fixed it by insulating the walls, and installing a Fantech 500 cfm exhaust in the bathroom.

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Hi,

Lots of old houses around the Seattle area without insulation in the exterior walls, new windows and no problems. We've got a temperate climate like northern California but with more rain.

I agree with Jim and Kurt, increase the amount of air changes taking place and it will no longer be an issue.

The Fantech solution is good, you could put some FAV80 through wall vents in for intakes and put the Fantech on a 24 hour timer and set it to change the air in the home every few hours. Better yet, take a belt and suspenders approach and install a humidistat along with the timer to kick the system on in the event humidity goes over about 46% between the times it's programmed to come on.

OT - OF!!!

M.

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Originally posted by ozofprev

Jim, I know what you are saying, but either theory could be at play here. It is possible that the cold windows did serve as the dehumidifier for the space. In either event,

Sorry I don't see how the new windows could act as a dehumidifier. I think Jim has hit the nail on the head, so to speak. The air exchanges have been reduced and the home has been made "tighter". The cold/warm air is now seeking any hole to escape or to be drawn in.

If this home has a crawl space, it is a very good chance that the walls are acting like a chimney and the stack effect could also be in play. Warmer air from the crawl space enters the walls and rises. It is stopped at the new windows and you then have condensation in the wall cavity. I have seen this several times on older homes that have had windows replaced or have added A/C without the proper insulation being added.

Kurt's, solution works and I have seen used several time.

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Oh boy...

Scott, read it again. I said it is possible that the windows did act as a dehumidifier - obviously the newer, warmer windows aren't going to do that.

I'm not one to jump on band-wagons. Jim may be right - or not. He has a perfectly reasonable alternate theory.

With the current facts, it cannot be known which variable is responsible for the condensation. Less infiltration or the removal of a "poor man's" dehumidifier are pretty even candidates. (Associates?) There are other possible, but less likely, candidates (new whirlpool tub, young couple moved into the room and are steaming things up...)

Mike, make sure physics is in that curriculum! This scenario reminds me of a layman who has been in a commercial airliner. The layman says something that sounds like common sense, "You can't take an airplane up to 20,000 feet if it isn't pressurized!" If the layman has no understanding of partial pressures, or worse - a misunderstanding of partial pressures - then he surely believes he is correct.

Since the proportions of elements in the atmosphere is fairly consistent at every altitude (21% O2, etc...), but the pressure goes down as we go up, there are two options. Increase the pressure like we know and love close to the ground, OR take that little bitty pressure available and apply it completely to oxygen. (i.e., oxygen masks). In a group, some will invariably jump up and say, "Yes, pressurization. He hit the nail on the head."

I can't believe I have to explain this.

Originally posted by Scottpat

Sorry I don't see how the new windows could act as a dehumidifier. I think Jim has hit the nail on the head, so to speak. The air exchanges have been reduced and the home has been made "tighter". The cold/warm air is now seeking any hole to escape or to be drawn in.

If this home has a crawl space, it is a very good chance that the walls are acting like a chimney and the stack effect could also be in play. Warmer air from the crawl space enters the walls and rises. It is stopped at the new windows and you then have condensation in the wall cavity. I have seen this several times on older homes that have had windows replaced or have added A/C without the proper insulation being added.

Kurt's, solution works and I have seen used several time.

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If you install a big CFM fan wouldn't you have to consider its affect on depressurizing the house and back drafting appliances?

Wouldn't an air to air ventilator be better or heat recovery unit?

Does anyone recommend these or even see them installed in the homes they are inspecting?

I have yet to see such a system around here.

Chris, Oregon

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Maybe, but in an uninsulated shoebox w/POS windows originally, I doubt the envelope is tight enough to matter. The 500 cfm fan gets cut down to about 350 cf w/static; that's not much for a loose little box.

Wouldn't be hard to test & figure out, though.

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Hi Gary,

I simply said I did not see the windows acting as a dehumidifier. I have seen a stack effect on older homes. I have also seen new windows and doors with similar issues as in the original post.

Have you ever found this condition on a house? If so what was the cause and solution.

You said;

Since the proportions of elements in the atmosphere is fairly consistent at every altitude (21% O2, etc...), but the pressure goes down as we go up, there are two options. Increase the pressure like we know and love close to the ground, OR take that little bitty pressure available and apply it completely to oxygen. (i.e., oxygen masks). In a group, some will invariably jump up and say, "Yes, pressurization. He hit the nail on the head."

I can't believe I have to explain this.

I don't recall anyone asking you to explain this, but thank you anyway. Yes, you have more education than myself, many others on this board and in our profession. Use it to help others, not to be condescending.

Whatever issues you have with me, why don't we leave it to personal emails or over at the ASHI board.

Maybe you and I just got off on the wrong foot with each other. Why don't we start over.

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Originally posted by kurt

Maybe, but in an uninsulated shoebox w/POS windows originally, I doubt the envelope is tight enough to matter. The 500 cfm fan gets cut down to about 350 cf w/static; that's not much for a loose little box.

I ran into a 70's ranch where they had resided it using a WRB and put new windows and doors in and thus tightened up the exterior envelope. The result I believe was the wet insulation I was now looking at in the attic.

I don't know yet how to address such problems. It seems to me that an empirical approach is needed perhaps using les's fog machine to come up with something that works.

I like the idea of the fantech on a 24 hour timer in parallel with a humidistat and a 20,30,60 short timer in the bathrooms.

But what I am worried about is depressurizing the home and sucking in rank crawlspace air or garage odors.

Chris, Oregon

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Careful...

No condescension intended. Look, I said the old windows could be acting... you said you didn't see how the new windows could be acting... I said I didn't say the new windows. I'm frustrated, but it's not a big deal.

The last post says there are two solutions:

1. Insulate the walls.

2. Install a dehumidifier.

Our job isn't to tell people what to do, it is to tell them their options.

Both will work. That's all.

Quote:Originally posted by Scottpat

Hi Gary,

I simply said I did not see the windows acting as a dehumidifier. I have seen a stack effect on older homes. I have also seen new windows and doors with similar issues as in the original post.

Have you ever found this condition on a house? If so what was the cause and solution.

You said;

Quote:Since the proportions of elements in the atmosphere is fairly consistent at every altitude (21% O2, etc...), but the pressure goes down as we go up, there are two options. Increase the pressure like we know and love close to the ground, OR take that little bitty pressure available and apply it completely to oxygen. (i.e., oxygen masks). In a group, some will invariably jump up and say, "Yes, pressurization. He hit the nail on the head."

I can't believe I have to explain this.

I don't recall anyone asking you to explain this, but thank you anyway. Yes, you have more education than myself, many others on this board and in our profession. Use it to help others, not to be condescending.

Whatever issues you have with me, why don't we leave it to personal emails or over at the ASHI board.

Maybe you and I just got off on the wrong foot with each other. Why don't we start over.

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Hmmm,

Some of you guys should drift on over to my building science forum at JLC once in a while and do battle with some of the crotchety contractors over there. Warning: There's also a bunch of guys over there that know their building science better than the average home inspector, so expect that, if you don't have your stuff in order, to be soundly thrashed.

Either way, it would liven things up over there. Come to think of it, I oughta invite them over here! Man, wouldn't that make for some dicey discussions - a bunch of contractors drifting in over here. That's be like a bunch of Hell's Angels stopping in to lunch at a bar where the local frat boys hang out. Hmm. [:-devil]

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by hausdok

. . . Either way, it would liven things up over there. Come to think of it, I oughta invite them over here! Man, wouldn't that make for some dicey discussions - a bunch of contractors drifting in over here. That's be like a bunch of Hell's Angels stopping in to lunch at a bar where the local frat boys hang out. Hmm. [:-devil]

ONE TEAM - ONE FIGHT!!!

Mike

Sure, ask them. We could use a couple of wuss-girlie contractors here.

-Jim Katen, Oregon

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Originally posted by Chris Bernhardt

I ran into a 70's ranch where they had resided it using a WRB and put new windows and doors in and thus tightened up the exterior envelope. The result I believe was the wet insulation I was now looking at in the attic.

I don't know yet how to address such problems. It seems to me that an empirical approach is needed perhaps using les's fog machine to come up with something that works.

I like the idea of the fantech on a 24 hour timer in parallel with a humidistat and a 20,30,60 short timer in the bathrooms.

But what I am worried about is depressurizing the home and sucking in rank crawlspace air or garage odors.

Chris, Oregon

Can't disagree w/the empirical approach. I'm a complete believer in doing what works.

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