Roof condensation problem!

Hi all, I am finishing up converting what was a detached, two-car garage into a one-room studio but I have come up against a nasty moisture condensation problem. First: Some background The room itself is about 19 x19 x 9 with a vaulted ceiling that goes up another 6 vertical feet. It comes to a bit under 1500 cu ft. There are lots of pictures of the room and the construction process here: http://www.flickr.com/photos/larrytheo For several reasons (including logistical, structural, financial, and temporal), I was not able to put in a ceiling. The roof is insulated with a couple of inches of mineral wool held in by Reflectix radiant barrier. There currently are no roof vents, but there is a 150 cfm exhaust fan in the gable. (There is also a ductless mini-split system; the fan is just for fresh air). The insulation and radiant barrier work great, in fact, a bit too well. Here's the problem: When the sun beats down on the roof in mid-day, the top 18 inches or so of the room heats up considerably, maybe 10-15 degrees F more than the rest of the room. The heat is highly localized to the very top of the room; move down another foot or two and the temperature is noticeably lower. During the summer things are very dry around here and I will probably have no problem, but it is winter now and between about noon and 6 PM each day I am getting severe condensation occurring on the radiant barrier, enough that it starts to drip! The problem is the reverse of the normal attic condensation problem where warm air from the house is making its way into the cooler attic. I've tried running the fan for hours, but it is placed maybe four feet from the apex of the roof, which seems to be too low to suck out the hot air. We are going to try raising it a couple of feet in height tomorrow, and we'll see if that helps. I also tried running the ductless mini-split in its dehumidifier mode overnight, but it is only about five feet off the ground, way below where the problem occurs. How can I solve this problem? Obviously, I could put in a roof vent, but that would compromise my sound isolation. It seems that any dehumidification would need to be located right there at the apex to do any good. That would be problematic because most traditional dehumidifiers are fairly sizable and collect water in buckets that would need to be emptied regularly. That would be a pain. Plus, prices seem to start north of $200. One thing I'm considering is mounting one or two of these Eva-Dry E500 passive dehumidifiers right up at the apex: http://evadry.com/products.html AC power can be made available relatively easily (I have outlets mounted at the 9-foot level). Does this seem workable? Any other suggestions? Thanks! Larry the O

"Obviously, I could put in a roof vent, but that would compromise my sound isolation." You know how to fix this you are just not ready to face the fact. Never mind the current isolation, your problem is wide spread and will contaminate the room, your equipment and potentially your health over a period of time. Not to mention the other people that you may enlist there. You have to do several things. One is to get a proper ceiling in place the other is to get proper ventilation installed for the roof. And that will require taking that NASA faced insulation off of the rafters and opening up the path from top of wall air access to top of ridge flow path. Your build thread http://www.flickr.com/photos/larrytheo/page11/ suggests that this is still an open environment. I guess, like you said, you can wait for equilibrium of weather or you can do what has to be done.

I am still a little confused as to the source of your condensation. For condensation to occur you need warm air and a cold surface, think cold glass of water in a warm room. If the roof is your heat source it would be equally as hot as the air next to it, thus no condensation. If you are going to use a sealed roof system, do some research on what are actual approved systems and follow one of them. It is incredibly easy to do it wrong. That being said, I am going to use a closed roof system in my build as well. The approach I am going to use is sprayed close cell foam applied thick enough to prevent condensation. this will also act as my air barrier. Good luck with your project Steve

Isn't this a textbook example Steve? I thought that the room having the heat and a potential NASA type barrier and the exterior being the colder side (with another barrier - roof felt) of the two would produce this effect. It might even be a dual barrier that is trapping the condensation above the NASA type facing and the condensation is overcome by gravity. But that is a WAG, if you know what I'm saying :)

I thank you guys for your responses, though I find your tone rather harsh, xSpace, and I feel like you are not acknowledging the realities of my situation. The fact that I posted looking for help with the situation should have told you that I recognize the severity of the problem and am seeking solutions, so lecturing me about it is neither necessary nor particularly constructive. Putting in a proper ceiling is not a viable option. The rafter structure you can see in the pictures made it impractical (that is, beyond my resources of money, time, and skills) to build a room within a room in which I could support a ceiling on the inner walls. I simply could not do it. I had a structural engineer come out and he felt the current roof and rafter system was adequate but could not support the additional weight of a serious drywall ceiling. We also discussed options for replacing the rafter system with a simpler one that would allow installation of a ceiling on top of inner walls, and he determined that could easily be done with three to six months of construction and a few tens of thousands of dollars. I am stuck with the roof as it is, that's just the fact. The "NASA" insulation immediately proved itself to be the best thing I could possibly have done thermally: while the outside temperature can vary from 100 degrees in the summer to the mid-40s in the winter, inside now varies between the low 50s and mid-70s...in the main part of the room. And that's without using any AC or heat, which makes it an extremely energy-efficient room from that standpoint. The very, very top of the room, however, gets much hotter. It seems that the problem is not that the inside is hotter than the outside, it is that the top of the room is quite obviously hotter than either the outside or the lower part of the inside. It was 80 degrees or more at the top of that room yesterday, while the rest of the room (up to maybe four or five feet from the apex) and the outside never got above the low- to mid-60s all day. In the evening, when the sun stops beating down on the roof, the condensation slowly subsides until the next afternoon. Note that there is no evidence of condensation above the "NASA" insulation: both the mineral wool and the roof itself remain bone dry at all times. The condensation is exclusively on the inside surface of the Reflectix. It is true that I did not properly research a sealed ceiling and must do so now. I did almost two years of research because I know nothing of construction, and, in my ignorance, did not anticipate this problem. In fact, the insulation went in last summer and no problem manifested itself until about a month ago when the rains started in earnest. (I am certain there are no roof leaks: the roof is fairly new and there were no leaks in the couple of years it was a garage before I started the conversion.) The best solution to the problem would seem to be the obvious one: to vent the hot, humid air. That is why I am moving the exhaust fan higher, where it can be useful in doing that. The question is whether there is any option besides adding a vent and compromising isolation, which is already less than it needs to be. I did install chutes under the mineral wool and the insulation stops six inches from the roof ridge, so there is a path for air to travel up the roof and out the top. If moving the fan helps move more air out, does the Eva-Dry thing seem like it might be helpful? If there is no clever alternative to a roof vent, what method of venting might be best for preserving isolation? I understand there are some roof vents that can be automatically opened and closed, but they generally seem to use a thermostat; are there any that use a humidistat and does it make sense to try and go that route? Thanks!

larrytheo wrote:

I thank you guys for your responses, though I find your tone rather harsh, xSpace, and I feel like you are not acknowledging the realities of my situation. The fact that I posted looking for help with the situation should have told you that I recognize the severity of the problem and am seeking solutions, so lecturing me about it is neither necessary nor particularly constructive. Putting in a proper ceiling is not a viable option.

Lecturing? ME? It may seem like that to you but to me it is a person telling another that what they have will not work, has to be corrected and goes on to explain how to correct it. X said: "One is to get a proper ceiling in place the other is to get proper ventilation installed for the roof. And that will require taking that NASA faced insulation off of the rafters and opening up the path from top of wall air access to top of ridge flow path." I don't see the lecturing, but no deal to me, many people think that I am using some tone that I do not possess ability to use :) To tell me that putting in a proper ceiling is not viable explains that you have no idea of what it is you have there. It can done, should be done, and doesn't cost tens of thousands of dollars. There really are limited options. Open up more air flow space is one. It is in your direct interest to unblock the overhand eave vents IF they are blocked. It is also in your interest to install another gable end vent. I see one, but do not see one on the opposite end. But the insulation with the reflective face...I would take that down, it is holding heat and creating a higher level than if none were there. It is also holding moisture.. Here is lecturing: This is not acoustics we are discussing. This is typical building procedure for specific reasons and the reason is that if you do not provide the thermal break and adequate drainage plane and/or air flow/ coupling, this is the kind of thing that happens. The end result is rotted wood. Dry-rot as it is called. The wetting period and the drying cycle will alter the wood characteristics and make it shrink in all directions and eventually collapse[ long term-worst case due to complete lack of attention] or distort from long term mass loss in the structure[medium case due to complete lack of attention] or start to mold and create health issues[first and minimum case in your near future]. /lecture :)

Look, xSpace, I came here for help and I feel that is what you are trying to offer. I am not trying to put out attitude, I'm not looking to argue or be contentious, and I don't claim to be knowledgeable in the area of construction. Because I know that I don't know, I have done some research, consulted some who are knowledgeable and am asking for help here. But just blithely telling me I must tear out everything I've put in and do something else is not an acceptable or achievable solution; there is neither time nor money for it. Nor do all of your certain statements about my space seem to jibe with the facts. If that means you can offer no help and I've gotten myself into something I'll have to figure my own way out of, then I will handle that and I am confident I will find a solution one way or the other. I think there may be other options and I want to explore them. I did not say it would cost tens of thousands of dollars to put in a ceiling, a structural engineer estimated it would cost about that to replace the existing rafter system because of the complexity of supporting the roof while the old support system is removed, and so forth. However, putting in a ceiling is neither as cheap nor as simple a task in my circumstances as you seem to think. You don't have to accept that, but I'm sure you recognize that advice offered on the basis of information that is limited to some photos and a little bit of description cannot always be entirely appropriate to the situation. You clearly don't believe my judgment either that putting in a ceiling is impractical in my circumstances or that there are great benefits to the Reflectix. So be it. I understand your viewpoint and you do not seem to understand mine, which is unfortunate for me. I may not be knowledgeable, but I'm not an idiot and I'm not in denial. I am simply relating the facts of my situation as I see them. I'm still going to try and get some help, if you can possibly bear with me. I don't understand the point of removing the Reflectix or how it will facilitate greater ventilation of the roof. Perhaps I did not clearly enough state that there are ventilation chutes under the mineral wool running all the way from wall top to roof ridge. They are not doing the job they normally would, since there are not vents at the bottom or the top because of concerns about isolation, so there is not outside air flowing up. As I've indicated, if there are no options besides cutting vents and losing what isolation I have, then that is the option I must pursue, but I am looking for other options first. As for your contention that the Reflectix is holding in heat that would not otherwise be there, I can assure you that before the Reflectix was installed the entire roof area had the same level of heat that now exists only at the ridge, which made what was then a garage a much hotter place than it is now. I was up on a ladder quite a few times sanding the rafters as well as installing the Reflectix, so I can say with certainty that the heat level is not higher than it was without the insulation. What is different now is that the rest of the room and roof HAVE changed from what they were before, and the ridge has NOT. Thinking about it more I wonder if perhaps the vapor barrier characteristic of the Reflectix is playing a role in the problem. You seem to be implying (but have not said) that you do not think a repositioned exhaust fan and passive dehumidification will work. Do you (or anyone) have any experience with the Eva-Dry stuff? Again, thanks.

The issue I have, overall with the insulation at the rafters, is two fold. The first is that the heat is not being removed as it >should< be. You say there is not that much heat, but I ask this. Get on the top of that roof when it is the heat of day. The heat you fill on your naked feet from standing directly on the shingles is just as hot on the underside. You may not feel it with the insulation underneath, but it is there, and those air chutes are not extracting it fast enough :) Like I mentioned earlier...the overhang soffit vents are >required to have air flow from convection. The problem in structures like this is that the air flow is not channeled [even with the chutes that are designed for a typical ceiling/rafter roof] properly due to the removed ceiling barrier/panels and basically the air flow path is broken. Sure, you need to make some holes in this thing, ridge vents, soffit vents, eave vents and maybe even a power vent. What good is that room after that? I still see the 5/8 inch sheetrock ceiling with a proper ventilated roof system as a productive way of establishing a long term relation with both the elements and your desires. Frankly I don't know why you hate me :)

Maybe this is going to sound really harsh, almost insulting perhaps, after Brien's responses, but it always amazes me how some people manage to paint themselves into a corner with their builds, in one sense or another, then come here asking for help, only to be told what that what they have to do in order to fix things is take something apart and re-do it the correct way, so then they end up raging against the world because they don't like what they are hearing, and go off in a huff, figuring that there just has to be a magical solution that will solve all there problems, real cheap and in minimal time. Brien (as an expert in construction issues) has explained what you need to do if you want to fix the problem that you created by not doing it right the first time. The fact that you don't LIKE what he says, just because it implies time, money and ripping out stuff that was done incorrectly, is not Brien's fault. Yeah, I reckon I'd be pretty frustrated if I did something dumb like that in my build, but I reckon I'd also be smart enough to not take out my anger on the only guy who is trying to HELP me! Ans I'd also (hopefully) be smart enough to realize that magical materials and methods doesn't exist in construction, and there is a reason why things are built they way they are. It seems to me that Brien is being your friend here, not your enemy! You asked what has to be done to fix your problem, he told you, and now you are complaining that you cannot do it because it will cost time and money that you don't have. Once again, that isn't his fault: He's just giving you the correct solution, that's all. Don't shoot the messenger, just because you don't like the message! - Stuart -

larrytheo wrote:

"if you can possibly bear with me."

As long as you need it, I'll be around :) Hopefully, I'll be helpful...I know I can get trying at times...hey, but I am raising an Apso lhasa puppy...doesn't that count for anything?

Maybe I was too subtle. The issue is not what you think it is. The condensation is the end result of the construction issues and as Brien pointed out the condensation is only one of many problems that you have with the way this is currently constructed. Now as to a solution.... I'm going to offer a couple of suggestions, but I don't think your going to like either of them. 1. If you really want to maintain your ceiling height and keep your isolation start by pulling all of your roof insulation, foil insulation, any styro vents.... then phone a few foam insulation contractors and get a couple of quotes. Now at this point you can start thinking about air movement.... 2. Follow Brien's suggestions..... rip all the insulation out, vent the roof properly, soffit and peak, and install a conventional ceiling. 3.Put in soffit and peak venting and leave the rest as is. At least your building will breathe, but you loose isolation. But before you do anything, spend a couple of weeks reading about this stuff, Talk to an HVAC engineer about their ideas. Good luck, Steve

As a quick and dirty experiment, I lashed a small household fan to a rafter right up near the ceiling and the condensation disappeared entirely less than five minutes after I turned it on, and no condensation reappeared at any time through the afternoon. It seems that air movement is indeed the key and it takes very little to make the difference. This indicates that a very simple and inexpensive solution is at hand; further testing in the next few days should confirm that. Since I have an exhaust fan that is being repositioned for greater effectiveness, in the rainy season I will normally be using a heat pump that also dehumidifies (which is currently out of action while I paint), and the summer is very dry here (and I have air conditioning that dehumidifies), I believe I will opt for the easier solution. Cheers, Larry

My suggestions would be to install a circulating vent system - inlet high in the room - outlet low in the room - with an inline fan. I would not recommend a dissicant style dehumidifier - they are a pain in the arse to maintain - however I would recommend a non-vented dehumidifier tied into the line of the circulating vent - higher the better - and you can use a small pump with a 3/8" flexible plastic hose to dump your condensate from the pan. it would be well worth your money to invest in this for a whole variety of reasons. I am (though) a bit at a loss to understand exactly why this is happening - where (exactly) is all this humidity coming from? Is your outside air adding that much humidity into the space due to your fresh air supply? Rod

Thanks, Rod. It seems I situated my venting backwards. Inlets are currently low from the outside, while the outlet is through the exhaust fan up in the gable. (We made ducts of about five feet for the inlets to give some changes of direction so that air actually enters the room at about a six-foot height.) This suggests that at some future time I need to redo the inlet/outlet/fan setup. For the time being, I'll have to find a kludge like putting a fan up at the top, because I am out of money and have to get the facility online ASAP so that it generates money instead of sucking it down. As for where the moisture is coming from, that is a question I would really like the answer to, as well. I have to guess that it is purely from fresh air intake during a particularly rainy season because there is no other apparent source and the problem did not manifest itself until it started raining constantly. Once I paint (the phase I am in now), I will be adding the ability to seal the fresh air inlets, which I will do when I am not in the room or when I have critical recording to do (in which case they can only stay sealed for a limited time, of course). That will facilitate dehumidifying the room, though as soon as I unseal the fresh air inlets so I can breathe all bets will be off. As one friend of mine said, "You can't dehumidify the world." If I am right about the source of the moisture, I can use a short-term kludge to get through this rainy season and have a better solution in place by the time the rains come next season. This problem is unfortunate because I did try to do research ahead of time and did not find the appropriate information. I had an electrical and HVAC contractor who ended up being a flake and had to be dismissed, by which point the urgency of getting the facility online forced me to commit myself to a plan which he seemed to feel was fine, but in which I did not have full confidence. I knew the risk of it being all wrong but was had no choice. A classic case of "live and learn," but that did not come as a surprise. Thanks for the help. Larry

Larry...what about the slab? Is this concrete old enough to possible not have had a moisture barrier installed underneath it and it[the slab] is sweating?

I can't be certain, but I don't think so. I have not noticed moisture coming from the slab and I cleaned and sealed it before starting construction (and will do so again when I finish painting). The garage was originally at the end of the driveway, but the previous owner moved it to the side to make room for an RV, at which time a new slab about 11 inches thick was poured. It is clear it is a newer slab than the driveway, but not clear how much newer. I'm guessing the slab is at least 10 years old, but I don't really know. However, I can find out because the previous residents (who lived here for 13 years) live next door, so I'll ask them.

If you can get your hands on some visqueen clear plastic you can place a 24" X 24" piece on the slab in an area that isn't going to get in your way. It depends on the moisture, but if, after you place this plastic down and at least a day or two has gone day, if the slab does not have a proper moisture barrier, then the slab moisture will cling to the side of the plastic that contacts the concrete. This may not be the issue, but at least it would rule it out.

Great suggestion! I'll do that. Where do I get visqueen plastic? Is that a common thing I can get at Home Depot or a hardware store or do I need to go to a construction supply or plastics place?

It is a common plastic used for a barrier underneath the slab. Big box stores and even local hardware stores will have it. Unfortunately it is sold in large expensive rolls...so you may have to get some from a friend of a friend...if at all possible.

I'm going to put an idea forward here that it may be your roof that is giving you both your issues. If the sun is heating only one side of your roof and the other side is cool... what direction does your roof face? Steve

Okay, One last comment and I will stop bugging you. Please verify your roof system. I think it is shingles, paper, sheathing,plastic vent channel , roxul, foil radiant barrier. The reason this is important is because you did not put in venting at the soffits or the peak. This system is designed around convective airflow going in the bottom and exiting the top. This convection keeps the inside of the sheathing at the same temperature as outside. This prevents condensation. Now if you seal up the venting so air cannot flow freely through the channel, you've now also created a moisture collector, this is bad. If left as is this roof will fail. Steve

Well, now, that certainly would seem to bear some investigation. My roof construction is exactly as you surmised. I put the chutes in with the thought that I might end up needing to add soffit and ridge vents if it couldn't be avoided. It did not occur to me it could promote a problem to put them there and not have the vents. If you don't have chutes will the inside and outside be the same temperature? The roof faces east-west, but there is plenty of clear southern exposure, so it definitely gets sun on the roof. I can wait until afternoon when the sun has been pounding down on the roof for a while and then try swabbing out a chute or two about halfway down. That ought to tell me if there's moisture collecting in them. Thanks for the heads-up on that. Larry

xSpace wrote:

"Obviously, I could put in a roof vent, but that would compromise my sound isolation." You know how to fix this you are just not ready to face the fact. Never mind the current isolation, your problem is wide spread and will contaminate the room, your equipment and potentially your health over a period of time. Not to mention the other people that you may enlist there. You have to do several things. One is to get a proper ceiling in place the other is to get proper ventilation installed for the roof. And that will require taking that NASA faced insulation off of the rafters and opening up the path from top of wall air access to top of ridge flow path. I guess, like you said, you can wait for equilibrium of weather or you can do what has to be done.

I sure thought we covered this already :)

Yes Brien, you had, But it seemed to be being ignored, So I brought it back into the forefront. I am also aware of where the advice came from when I asked a similar question. :D Steve