The house was built with SIP walls on a slab with a truss roof insulated with FG batts. Radiant in-floor heat was installed, but there was no foam placed under the slab, so the system would not heat the home.
In addition to the heat problems, there was mold growing near the ceiling on the exterior wall. We found that the homeowners had disconnected the dryer vent and were running it directly inside. To make things worse, there are seven people living in the house that is about 1300 sq ft.
In November we installed a forced air heating system and a booster fan for the dryer hoping that most of the moisture problems inside the house would be eliminated. We also stressed that they MUST run the bath fans when showering.
I got a call this morning from the homeowner, who said that the mold is now growing at the base of the walls and on the carpet and in closets.
I really don’t know what else we can do and wanted to get some opinions. Two options that I have thought of are a HRV and timers for the bath fans. I am going to look at the house tomorrow morning, so some tips as to what to look at would be great.
Thanks for anyones help.
Mark
Replies
mark..sounds like two possibilities.. the RFH system was leaking.. or
there is too much moistrure penetrating the slab...
tape some poly down on the slab, cover it with a carpet , and see if you are getting moisture from there
i assume you have already disconnected the RFH system , ( thus the new hot air system, right )
anyways.. you have to determine if it is an old problem or a continuing one
also measure the RH in the house.. you can do this with a sling psychrometer (wet bulb / dry bulb )
i would also bet , that the moisture problem you have is going thru the trusses, and thru the fiberglass and condensing.. bet the bottom of the sheathing is soaked..
you have to control the moisture source.. and then dry the house out... dehumidifiers will do it once you've eliminated the source
what is the surounding land like ?.. soil type... ground water level ?
Mike-
Thanks for your reply. I am sure that the water table in that area is high. In fact, it was suggested that it was the reason the RFH system couldn't heat the house, ground water was stealing the heat. There was supposed to be poly and pea gravel under the slab, but I can't say for sure if it is there.
Apparently the mold is much worse than with the RFH system. If a high water table is the source of the moisture, this makes sense. Originally the water prevented the RFH from doing its job, but the RFH kept most of it out of the house. I will check the humidity and see if they will let me pull up some of the carpet to check moisture through the slab.
Originally, the bath exhaust lines had been run to the soffit, so in November I rerouted them up through the roof. At the time the sheathing in the attic was fine. Of course it was still unseasonably warm. I will check the attic again today.
piffin-
I appreciate your input. The roof is a fairly complicated hip with soffit vent all the way around and a ridge vent, that is probably not adequate, and several through the roof type vents.
I believe we must consider both monthly utility costs and total mortgage payments as part of affordable housing. We can build a cheaper house, but the energy cost would make the total monthly cost more than what we currently do. But I also realize that there is a point of diminishing returns.
Later today I might have time to run through what we currently do, and what we hope to do this coming year.
Everyone-
Again, I appreciate everyone's input. I really want to take care of this homeowner and wanted some direction and you have been very helpful.
Thanks again,
Mark
See if there is a utility space in the house that does not have any flooring on the slab.Or better yet go into one of the closets that has the mold and pull up the carpet.Then get some plastic and tape it down flat. Then comes back and cheeck in a day. If you have condensation under the plastic then you have moisture moving through the slab.There are some chemicals that are suppose to react with the concrete to seal it and there are coatings. Don't know how effective they are.Also you can get moisture meters to measure the moisture levels in concrete and drywall. They are similar to those used to measure the levels in wood.But they cost a few hundred bucks, but you might find a home inspector that can check this for you.But for G*d's sake get at least the $10 humidity meter. Otherwise you have no idea of how bad a moisture problem that you have and how much any fix you make has on it.Even better would be something like this.http://www.professionalequipment.com/xq/ASP/ProductID.1214/id.22/subid.322/qx/default.htmBTW, what is the climate and what is the heating and does it use outside combustion air.
I just got back from looking at the house. The mold is not as extensive as the homeowner made it out to be, but is still there. I took some digital pics, but can't get them off of the camera until tonight, so I will post them tomorrow.
I measured humidity in several areas of the house.
kitchen 81
closet with most growth 74
mechanical closet 49
bath 51
attic 55
outside corner br 90+
In the outside corner bedroom the carpet in the corner was damp on the surface, but clean and dry underneath.
I know that there is no place in the house that doesn't have flooring. Tomorrow I will put some plastic down to test the slab.
As Mike suggested, I looked very carefully in the attic. The underside of the sheathing is dry, but there is some condensation on sheathing clips and roofing nails that are sticking through. Only one spot on the eaves showed any sign of moisture or mold and that was were the bath fan exhaust was sitting before I ran it through the roof. It looks like there is foam between the drywall and trusses, so that probably keeps most of the moisture in the house and out of the attic.
Thanks again for everyone's advice.
Mark
I would say the general rule of thumb for conventional construction is that humidity should not be intentionally raised (eg by a humidifier) above 40%. And at outside temps below 20 or so the inside humidity needs to drop.In theory, a super-insulated system with good vapor barrier and triple pane windows, etc, could be held at a somewhat higher relative humidity, but really the weakest link is what you need to worry about, and it sounds like the house you describe is not uniformly insulated and sealed.My gut feel is that you should strive for no more than 45% anywhere, except perhaps in cold corners. (It's the cold corners and nooks and crannies that you need to worry about. If it's 45% in a warm place it can be 95% in a cold place, and even higher inside the wall in that cold place, and when the humidity reaches 100% near a cold surface that's when you get condensation.)
One of my rules of thumb is that humans are comfortable and healthy at 40% but houses are happy at 20%. Reported levels are way too high for either.
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You should have seen my eys bug out and eyebrows hit the cieling when i saw those figures! No wonder you have a problem! That is close to sauna moisture levels.If it turns out that there is no moisture migrating from under the slab, then the occcupants are causing the problem, intentionally or ignorantly or as an unintended consequence of living there. Gotta find that source!The foam under the trusses is probably acting as a VB pretty well to trap the moisture in the house. A thermograph could tell you where the leaks are too
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Is cold air infiltrating at the base of the wall because of a lack of a sill sealer, condensing at the base of the sheetrock inside?
What about a delay-off timer for the bath fans so they can't "forget" to use the fan?
http://www.nutonesales.com/vent-broanswitch.html
Billy
Edited 1/4/2005 8:31 pm ET by Billy
Even better is a humidistat that will will control the fan automatically. The first thing that you need is a psychrometer. wWhile the sliing psycchometer is more accurate a $10 digital unit is much easier to use. And with that you can call them up from time to time and get the reading.Or if needed you can get a recordign system or phone dail up. But those will start at a few $100, which you porbably don'thave.
Bill, do you find that the cheap humidistats work O.K.? I had one in my attic that I disconnected -- what I really needed was a differential humidistat that compares the attic humitiy with the outside humidity but those are $$$. No soffits and no eaves on the house, and drip edge vents were impractical so I had to go with gable vents and fan.
Billy
Hook the bath lights to the fan. If the lights come on, the fan comes on...
I don't know how you could then put the fan on a timer so it stayed on for like 5 minutes after the lights go off, but there might be a way.
Put a dehumidifier in the air system for the forced air heat. Have it running all the time, even when the furnace is not going.
The person you offend today, may have been your best friend tomorrow
The switch that I posted turns on the fan with the lights, and the fan stays on for "x" minutes (programmable) after they turn off the lights.
Billy
Cool !
The person you offend today, may have been your best friend tomorrow
I feel for ya!
Is the attic vented?
and how?
Is the dryer vent still hooked up right?
Do the timer on the fans and wire it to the lights so they can't jhave light without fan, or use a humistat.
I'm suspecting much of what Mike said, but also that the sill is leaking ( infiltration) air into the house at the base of the walls from no sealer. You have added a combustion heater that uses air and the makeup air might be coming in at those baseboards. The fart fans are also adding to that draw.
Looking to the future, I hope you are doing your best to be sure that housing is built well. I have seen too many of these lower income projects ruibn themselves due to shortcuts based on income and budget, along with the semi-skilled labor. I tried to volunteer to help on one but they weren't interested in being told how to do it right, even for free. "Just shut up and put it up" was the message.
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Humidistats for the bathroom fans.
SIPs=Tupperware. The house is too tight. You need to install an air-exchanger. (Or punch lots of little holes in the walls to let it breathe....)
We frequently have this problem in our climate where people go nuts about locking out every molecule of cold air they possibly can. All new construction here now requires air-exchangers; for renovations it's not required but ought to be in many cases where a complete re-insul job is done.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
With FG Batts in the attic , I tend to doubt that the house is too tight. Just the walls. I found it really curious that the walls and not the top were SIPS. Maybe donations ...
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I don't remember whether or not he specified a poly VB on the ceiling; most people here do that so I just assumed that was the set up he was dealing with there.
Your climate is similar to ours. Does Maine have a requirement for air-exchangers now in new construction?
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
None that I know of. The island here is thirty years behiond everyone else though, with exception of self educated HOs and contractors.IMO, any SIPs house should have climate control
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When I re-built this place 10 years ago, I deliberately used the old foil-backed kraft instead of poly to avoid this very problem. So far that decision has been justified; the house is 'healthy' in spite of 10-15 degree (Celsius) daily temperature swings due to being empty during the day and wood-stove heating. I don't notice the extra heating costs (maybe half a cord of wood per winter?) and the insulation is good enough that during the hot part of summer I just leave all the windows closed tight during the day and am able to maintain the house a solid 10-degree C cooler inside than outside until sundown...when I open everything up and draw cool air up through the basement to the upper floors.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Dinosaur & piffin-
I don't know where the SIPs came from. I do know that the home was intended to be an energy efficient home. When I saw the house, my first thought was 'why didn't they use SIPs for the roof, too?' I know that the house is not as tight as it should be. A blower door test was done after the home was built and the energy rater was suprise at the tightness of the house. He expected it to be much tighter.
The home was built in conjunction with a major construction research organization. I can't say for certain how much involvement they had, but I do know that they designed the house. They have basically washed their hands of the house now though and won't really provide any help.
Mark
Just out of curiosity...Let's pretend for a moment that the problem is simply too much vapor coming up through the slab.What would be the fix???I suppose the first thing would be to address the exterior water handling...downspout runoff diverted, grade away from building, etc.Would a sump pit be helpful??Is there a way the slab can be sealed from the top??Rich BeckmanAnother day, another tool.
That makes it sound like they were doing tests with somebody's home and life, donating so they were free of liability.But maybe I'm too cynical.
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You got problems :1 You have to solve the venting issues , bathrooms , dryers , attic .2 I think you should remove a piece of drywall and see how bad the mold is . If it is bad sorry to say you have to gut the area and replace .