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moisture in attic


John Dirks Jr
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I inspected a 3 level town home that has a significant problem with heat loss causing condensation in the attic. There is lack of sufficient insulation overall and further heat loss issues because of an attic pull down stair.

There is fuzzy white bio stuff (hmmmm I wonder what that is) growing on the sheathing that is wet to the touch, yada yada...

The ventilation was perforated soffit and ridge vent so that part looked ok.

The client has asked me for contractor recommendations.

I know the insulation needs to be upgraded and the trap door issues addressed to solve the problem in general.

What about the order of things? Should the coldest of winter be waited out to allow the attic to naturally dry? Then, after the material is dry, the bio issues can be cleaned followed up by the upgrades to solve the problem.

Does this sound like a reasonable order of attack?

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I don't see anything wrong with your plan of attack.

As for your diagnosis, let me first assume that by 'lack of sufficient insulation overall', you were referring to a lack of sufficient ceiling level insulation and perhaps other insulation also. I also assume that by 'sheathing', you were referring to the underside of the roof deck.

I would suggest that a lack of sufficient insulation at the ceiling level would hinder the formation of condensation rather than aggravate it, since the extra heat would elevate the temperature of the attic air and help provide for a gap between the air temperature and the dew point. It's when that gap is lost that condensation begins. The dew point itself might be getting help from humidity that is migrating from conditioned spaces to the attic spaces. The attic access is certainly one pathway for that to happen but there are other penetrations in the ceiling for lights, ducts, etc that could be poorly sealed and are contributing to that migration of moisture.

Of course, you're probably familiar with all this. This just refreshes your memory.

Marc

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Agreed,

Your primary cause is humidity migrating into the attic. Air sealing the pull-down will get the biggest violator but you have to look for gaps around/through ceiling lights and fans and wall switches. Here are some ideas.

That said, I've seen a lot of leaky old houses with poor insulation that don't have any condensation issues because there was enough air moving into/through the attic by convection to keep the underside of the roof too dry to support fungi growth. Apparently, the house you looked at has a combination of air leakage and insufficient air moving up the underside of that roof to fully dry it out.

When you say "perforated soffit vent" are you referring to that aluminum soffit sheathing with the rows of holes in it that's interspersed among soffit cover material under the eaves or are you referring to a full-length metal strip vent installed under the eaves? I personally hate that perforated material they use with aluminum and vinyl siding. The stuff looks like it will provide a lot of air but if you take the time to calculate how much air can move through that stuff, you'll find that you pretty much have to have 100% of it perforated instead of the 3 to 4 pieces every 8 to 10 feet I usually see. If you had that material, combined with ridge vents, and there were open gable end vents, most of the air pulled by the ridge vent will come through the gable end vents. Just closing gabel end vents that aren't oriented in line with the prevailing winds might improve air movement form eaves to the ridge dramatically.

If there are soffit vents, is every rafter bay open to the soffit or are just a few open to the soffit? Around here, they'll sometimes have frieze vents in only every other or every third rafter bay and then they'll install a ridge vent or pot vents and fill right to the underside of the roof between the frieze vents. When that happens, the air moving from the eaves will move right up the underside of the roof and out through the vents at the crest but it doesn't flow up the underside of the roof between those rafter bays where the frieze vents are. Consequently, the roof gets wet at the areas where the insulation is in contact with the roof, because there is no air moving between the insulation and the underside of the deck. Moisture-laden air from the house diffuses through the ceiling plane, moves up through the insulation, hits the cold underside of the roof and condenses and then literally drips back to the ceiling and frieze where it feeds fungi that moves up the roof plane from the eaves.

They need to combine good air sealing practices with proper ventilation and convective air movement needs to be along the underside of 100% of the roof plane.

In theory, a perfectly air-sealed home with an unvented attic should stay dry and fungi free. However, a perfectly air-sealed ceiling/wall plane is a pretty tall order. I'm not saying it can't be done; but even a small air passage into a "perfectly sealed" roof plane could cause formation of fungal growth.

I favor a belt-and-suspenders approach. If I had what I thought was a perfectly air-sealed ceiling/roof plane, I'd still want to ensure that fungi couldn't grow up there and I'd hedge my bets by recommending that they apply BoraCare to 100% of all exposed wood in the attic to kill all existing spore and to make that wood Chernobyl for fungi.

ONE TEAM - ONE FIGHT!!!

Mike

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What about the order of things? Should the coldest of winter be waited out to allow the attic to naturally dry? Then, after the material is dry, the bio issues can be cleaned followed up by the upgrades to solve the problem.

I don't know of any contractors around my parts that have a clue when it comes to solving wet or black attic problems. However, there's a number reputable drainage contractors with years of experience solving wet crawlspace and basements problems.

In theory, air sealing the ceiling would work, but William B. Rose has always advised controlling humidity in the building over that and attic ventilation. With 3 stories, you might have a stack effect that's agravating the problem. The roof decking is probably so soaked, that even with fans it will take near summer to dry the attic out. The lack of insulation in the attic I think would help rather than hurt. The insulation will not block the vapor and it will lower the temperature and impede ventilation in the attic and allow more condensation to occur.

Questions:

Is the home occupied?

What's the foundation - crawlspace, slab or basement?

Is the home partially built over the garage?

How's the home situated on the lot, sheltered by other buildings, trees, is it on flat or sloped lot?

What's the square footage of each floor ~?

What are the floor and wall coverings, and whats their moisture content looking like?

What kind of windows?

On what floors are the bathrooms,kitchen and laundry located?

How are the kitchen and bathroom exhaust systems ducted out?

Where's the attic access - hallway, room, near stairs?

Is there a fireplace?

What kind of heating system?

What's the homes orientation into the prevailing winds?

Is the attic wet through out or concentrated in some areas rather than others?

Chris, Oregon

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The many question that you have asked are helping me contemplate all the possibilities. Thanks for asking them. Let's see if I can answer them.

There is a humidifier installed on the air handler in the basement.

The soffit venting is pretty much full along the length of the front and back except for a small portion where the chimney chase passes the eave. I turned the lights out in the attic to check for daylight shining through the eaves to verify this.

Is the home occupied?

yes

What's the foundation - crawlspace, slab or basement?

basement

Is the home partially built over the garage?

no

How's the home situated on the lot, sheltered by other buildings, trees, is it on flat or sloped lot?

end unit town home, pretty much flat lot

What's the square footage of each floor ~?

roughly 500sq ft

What are the floor and wall coverings, and whats their moisture content looking like?

carpet and tile in basement-wood and tile on main-carpet upstairs, no moisture issues noted on floor coverings

What kind of windows?

vinyl framed double paned - relatively new

On what floors are the bathrooms,kitchen and laundry located?

laundry and half bath in basement-half bath on main level-two full baths on top floor

How are the kitchen and bathroom exhaust systems ducted out?

upstairs bathrooms terminating in the attic

Where's the attic access - hallway, room, near stairs?

bedroom

Is there a fireplace?

yes-in basement

What kind of heating system?

forced air with central returns-heat pump

What's the homes orientation into the prevailing winds?

the main entry is on the side and faces the prevailing winds

Is the attic wet through out or concentrated in some areas rather than others?

more moisture on the side where the hatch is located

Here are some photos. You can see the moisture pattern is formed around exterior details that I assume are making a temperature difference in the patterned locations seen in the photos.

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just to throw a few things out:

Does anyone have any ideas why the gable vent (which is not a vent) is dry on the sheathing and where there is siding the sheathing is moist? I would assume it has to do with permiance. The water not being able to get out through the siding but it is allowed out through the louvers of the vent.

The other item is the vent pipes that I see leaning against the wall are connected to nothing I presume? It just seems the roof sheathing is darkest near the top of the pipes.

This would make me look for the things Mike and others have allready mentioned, I would also trace the dryer vent and see if it daylights somewhere on the building.

I know you have a moisture encounter meter, what were your readings on the sheathing?

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As Marc & Mike already said, heat loss into the attic doesn't cause condensation. It might even help to avoid it. Moist air leaking into the attic will certainly make condensation more likely.

I'd tell them to disable the freakin' dehumidifier. If dry indoor air becomes a problem for them later, they can deal with it separately. For now, remove the humidifier from the equation.

I'd tell them to have those bathroom exhaust ducts vented to the outdoors through tight vent caps -- caps that have sleeves on the underside to accept the ducts. Right now, air might be entering or exiting via the ridge vent. I know that the conventional model is that warm attic air rises and exits via the ridge and fresh air enters via the soffit. But that model doesn't always work. I've been in plenty of houses where the attic air flow was complex and not nearly so neat as that model. In fact, I'm beginning to suspect that the attic air in most houses behaves in a much more chaotic fashion then we previously imagined. It's best to remove exhaust fan discharge from the equation.

Next, I'd tell them to seal all of the holes in the ceiling plane. Any gap that air can move through should be sealed up tightly.

After those issues are addressed, I'd re-evaluate after a few weeks. In my experience, those three tasks will almost certainly cure the problem.

If there's still a problem, I'd start measuring indoor humidity levels. If they're high, I'd recommend lifestyle changes and perm-rated ceiling paint.

Now, if there's still a problem after that, I'd take a different tack and start to recommend *closing* attic vents. In a few attics in my area, I'm convinced that the ventilation is the source of the attic moisture problem. And that's another discussion. . .

- Jim Katen, Oregon

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Yep,

Wish you'd mentioned in the initial post that the bath fans were emptying into the attic. That's probably about 90% of the moisture right there.

Very bad ju-ju. Get a dedicated rain cap with a male extension installed for each, connect them and insulate the danged things.

ONE TEAM - ONE FIGHT!!!

Mike

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I've seen these bath vents done like this in this area. I know it's wrong and could only make matters worse. However, this is the first time I've actually discovered the obvious, active condensation on this level in an attic. It's gotta be more than just the bath fans.

The humidifier on the air handler and the poor hatch stair seal are high on my list now.

There were also some water intrusion issues with siding and window flashing details. Could water getting in under the siding and around windows contribute to moisture migrating into the attic?

Jim, in your post you said, "disable the freakin' dehumidifier".

You actually mean "humidifier", without the de, correct?

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The problem with most folks is that they over humidify their house - if a little is good a lot is better. 99% of the time when I see mold in the attic I also see a humidifier on the furnace. This applies to the climate where I live - your mileage may vary.

I don't think it is necessary to disable the humidifier but folks need to be taught how to properly operate them. First off the humidistat was out of calibration one week after it was manufactured - they're junk. Also most of them have that goofy "when it is 20 deg f turn to 30%, when it is 0 deg f turn to 20% etc." 2nd, when it get's really cold out, and the furnace is running all the time, so is the humidifier - this really cold weather is when the problem(s) crop up. I did an inspection in the summer for a client who called me back in the winter saying there was water dripping from the attic ceiling. In that instance I told them to shut the humidifier off and call me in two weeks. The called back and said that the attic was fine and drying out.

I tell the buyer to get a real humidistat, the type that comes with a barometer in most cases. In cold weather, 0-20 deg f. do not keep the home above 10% RH or so. I also tell them that if they start to see water condensing on the windows they're putting to much humidity into the home.

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I've seen these bath vents done like this in this area. I know it's wrong and could only make matters worse. However, this is the first time I've actually discovered the obvious, active condensation on this level in an attic. It's gotta be more than just the bath fans.

No it doesn't. You're making the mistake of thinking that all houses behave the same. Every house is different. Discharging bath vents into the attic in this particular house might, indeed, be causing the condensation.

. . . There were also some water intrusion issues with siding and window flashing details. Could water getting in under the siding and around windows contribute to moisture migrating into the attic?

I think that's unlikely unless the moisture is entering the interior and contributing to higher humidity indoors.

Jim, in your post you said, "disable the freakin' dehumidifier

You actually mean "humidifier", without the de, correct?

Yes, I was so enthusiastic I committed a typo.

- Jim Katen, Oregon

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It's gotta be more than just the bath fans.

No it doesn't. It's sending humidity directly into the attic.

Venting exhaust fans into an attic is wrong regardless of circumstances or lack of evidence of negative consequences. No amount of arguing about how, "I've seen it done dozens, hundreds or thousands of times without a problem," will every convince me otherwise.

You could have a house with a poorly sealed hatch and ceiling plane and absolutely no fungal growth because the existing ventilation in the attic might be able to can handle the bypasses fine; however, introducing moisture-laden air into the attic via exhaust fans is just looking for trouble and that should be the first thing addressed by the homeowner or prospective owner.

ONE TEAM - ONE FIGHT!!!

Mike

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The problem with most folks is that they over humidify their house - if a little is good a lot is better. 99% of the time when I see mold in the attic I also see a humidifier on the furnace. This applies to the climate where I live - your mileage may vary.

I don't think it is necessary to disable the humidifier but folks need to be taught how to properly operate them. First off the humidistat was out of calibration one week after it was manufactured - they're junk. Also most of them have that goofy "when it is 20 deg f turn to 30%, when it is 0 deg f turn to 20% etc." 2nd, when it get's really cold out, and the furnace is running all the time, so is the humidifier - this really cold weather is when the problem(s) crop up. I did an inspection in the summer for a client who called me back in the winter saying there was water dripping from the attic ceiling. In that instance I told them to shut the humidifier off and call me in two weeks. The called back and said that the attic was fine and drying out.

I tell the buyer to get a real humidistat, the type that comes with a barometer in most cases. In cold weather, 0-20 deg f. do not keep the home above 10% RH or so. I also tell them that if they start to see water condensing on the windows they're putting to much humidity into the home.

You are, as usual, correct. But why do the manufacturers put that nonsense on the humidistat?

The photos are from my own house. The RH reading on the hygrometer--which probably isn't the most accurate instrument on the planet--was the same in the living space as it was in the basement. Is +/- 25% too high, you think?

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Interesting looking hum. Would you have more info on it, brand name etc?

Is it a bypass model?

I like the double check valve idea and I'm guessing you're pre-filtering the supply.

Another question if I may, is the unit on the supply plenum?

Is +/- 25% too high, you think?

I get that question from first time buyers and I tell them it's like marriage, a matter of keeping everybody happy.

It's a game of keeping the ratio nose to window in equilibrium.

Too dry - the nose is unhappy (window happy)

Too wet - the window unhappy (nose happy)

Balanced - the window and nose are happy.

As far as those meaningless numbers.....I ignore them.

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But why do the manufacturers put that nonsense on the humidistat?

My guess is they want user to turn down the humidistat, when it starts getting cold outside, so that you don't do exactly what we're discussing. It's still goofy though. When I talk to people about this most of them get a glazed over look and want to move on. It is important though. I always put wording in my report regarding the ramifications about too much humidity in the winter.

The photos are from my own house. The RH reading on the hygrometer--which probably isn't the most accurate instrument on the planet--was the same in the living space as it was in the basement. Is +/- 25% too high, you think?

25% may be OK depending on the outdoor air temp. Knowing what the warning signs are helps you judge. We were at 10F this morning and 25% would have been way too high. At that RH there would have been water on my windows (and in my attic). Don't forget that humidity can travel through drywall so as it goes into an attic it also goes through walls.

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Original quote by Terence:

I tell the buyer to get a real humidistat, the type that comes with a barometer in most cases. In cold weather, 0-20 deg f. do not keep the home above 10% RH or so. I also tell them that if they start to see water condensing on the windows they're putting to much humidity into the home.

I don't quite follow. I always though that an RH value of between 40% and 60% is healthiest for humans. My daughter got nosebleeds in the winter until I installed a portable room sized humidifyer in the largest room of the house which is set to maintain 60% humidity (duty cycle hits 100% for a few days during cold spells as the RH varies from 40 to 60%).

Water condensing on the windows is a sign of heat loss. Of course, I'm from the Gulf Coastal area where the winters seldom get below 32 degrees.

Marc

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It's a Honeywell TrueSTEAM, Rob, and it's a direct injection, so there's no membrane in the ductwork and much less water is used than traditional humidifiers. The water supply is filtered as you supposed, and the system is on the supply-side trunk duct. You can Google the unit and learn a lot more than I can tell you about it.

You and I are fairly close to each other, Terry, and the low was in the upper single digits last night. There was the slightest bit of moisture on a couple of windows--single pane with storms--directly above registers, but the others were clear. I'll crank down the RH per your advice and see what happens.

I know what moisture does to buildings, but the humidifer is a recent addition and it's incredible how much more comfortable it makes my house. Skin, nose . . . virtually everything is happier in a house that has a little humidity.

Also, if you look to the left of the humidifier, you'll see an RGF Guardian air purifier. It's the total nuts (Does anyone here play poker?). Cooking odors, big-ass wet German Shepherd odors . . . they're all just a memory now.

Here's a brochure for the purifier. Scroll down to the second page to get the lowdown on how it works.

Download Attachment: icon_adobe.gif rgf guardian.pdf

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(Umm, and I promise I'm not one of those spammers in disguise that show up every once in a while to hawk a product.)

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Original quote by Terence:

I tell the buyer to get a real humidistat, the type that comes with a barometer in most cases. In cold weather, 0-20 deg f. do not keep the home above 10% RH or so. I also tell them that if they start to see water condensing on the windows they're putting to much humidity into the home.

I don't quite follow. I always though that an RH value of between 40% and 60% is healthiest for humans. My daughter got nosebleeds in the winter until I installed a portable room sized humidifyer in the largest room of the house which is set to maintain 60% humidity (duty cycle hits 100% for a few days during cold spells as the RH varies from 40 to 60%).

Water condensing on the windows is a sign of heat loss. Of course, I'm from the Gulf Coastal area where the winters seldom get below 32 degrees.

Marc

The key is your regional area - this is why I said this applies to the climate where I live in one of my previous posts. If I tried to stick an RH of 60% in my home when it's 10F outside I'd be mopping up condensation for sure. Over humidifying a home in this area is a real problem.

I try to keep my home where we stop shocking each other (most of the time) but don't see any problems with condensation.

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John,

If I'm reading that right, you've plugged an ozone generator into your HVAC system. Everything I've ever read about those things - except the stuff printed by the folks that make them - said that ozone kills living organisms and that, though it's really effective at eliminating the bacteria and stuff that leaves odors in the air, it literally kills lung tissue. Is this gizmo somehow different than the typical ozone generator?

ONE TEAM - ONE FIGHT!!!

Mike

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Terry, it's wired into the fan. The humidifier and blower will energize whether there's a heat demand or not.

Mike, I'd never heard of that, but a quick Google explains what you're talking about. I don't know what to say other than, "Holy Mackerel." I will definitely probe further and get back to you.

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John,

If I'm reading that right, you've plugged an ozone generator into your HVAC system. Everything I've ever read about those things - except the stuff printed by the folks that make them - said that ozone kills living organisms and that, though it's really effective at eliminating the bacteria and stuff that leaves odors in the air, it literally kills lung tissue. Is this gizmo somehow different than the typical ozone generator?

ONE TEAM - ONE FIGHT!!!

Mike

The humidifier

That would be my concern too.

Do we have anybody here that could shed some light on this subject?

They make it sound like the ozone lives inside the plenum and somehow magically transforms itself into a 'friendly' after it leaves the system.

The idea of it being approved by the Chinese govt is questionable at best.

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I purchased a Fluke 971 a few months back in anticipation of this winter, and it's been quite interesting.

First, whatever the dial says on any humidistat is fluff; I've yet to find any humidistat that provided the RH printed on the dial; it's always off at least 20% from what they say, both over and under.

Second, I've now been educated on how wildly different every attic is. It's amazing how some attics can have everything set up completely wrong, and be just fine, and how some attics are set up "perfectly", but the RH is excessive.

Point being, Katen and Mike are right when they say all houses are different. One can't point at anything as a culprit until one has gone over the entire "machine" and figured it out.

Does anyone else have a 971, and if so, how are they using it?

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