I live in south Florida and have some ongoing moisture issues
leslie_jupiter
| Posted in Green Building Techniques on
I live in south Florida and have some ongoing moisture issues which have caused condensation / mold at the top of my cathedral ceilings. I can see from reading multiple articles that it is easy to make the situation worse in an attempt to correct.
I’m looking to have someone help me achieve an airtight house and resolve my ceiling / roofing issue.
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Replies
Leslie,
A RESNET professional or other type of certified energy auditor would be a good starting point. (Check to see if your local utility offers any energy conservation programs). Once you have a plan, you can prioritize the work and judge which activities make economic sense.
Leslie,
We need a lot more information to help you. Among other things, we need to know whether the problem you describe is worse in the summer or the winter; whether you house has an air conditioner; and the indoor relative humidity (RH), if you know it.
Thank you Steve and Martin - I appreciate this so much. I was able to find a RESNET professional and will set up an audit. The problem is worse in the summer.and the indoor humidity would be around 85% if I wasn't running dehumidifiers in all of the bedrooms. I have 2 central AC units. Replacing the downstairs system this past summer reduced the humidity downstairs. The upstairs AC system is not that old and contracters have said it is running efficiently, but the upstairs is where my humitidy problems are. This house was built in 1982 and has cathedral ceilings. I have read on this site that builders just did not know how to handle cathedral ceilings correctly in that era. For a little more history, 3 years ago, we sealed off the existing ventilation ridge because water was coming through. However without the ventilation ridge, come summertime, the upstairs temp would get to almost 90 degrees with A/C running non stop trying to cool it down. So, we had roofing company install a new ventilation ridge that did not allow water inside. This brought the upstairs temps back down, and we have no leaks, but condensation now forms at the top of the cathedral ceilings, with accompanying mold issues. Oh, also, after having the new ventilation ridge put in, I replaced all of the water damaged ceilings and had batt insulation put in above the new ceiling drywall. So I'm thinking I should probably do blown insulation instead? Also I probably need to get rid of the ventilation ridge to reduce humidity but until I can get a more airtight structure, my upstairs temps will probably be unbearable still. Am I on the right track? What makes sense here vs. what doesn't?
High SEER efficiency usually comes with crummier latent-load handling, and it will be even worse if the AC is oversized for the 1% loads.
Are any of the ducts &/or air handler on the outdoors side of the insulation?
It sounds as if there perhaps isn't sufficient insulation in the cathedralized ceilings if it gets to 90F even with the AC running. How soon are you due for re-roofing?
Humidity is (roughly) caused by air leakage. So pay someone to test and seal the house (and ducts if outside). And check/balance room-to-room pressures.
Leslie,
There are too many issues here to resolve over the internet. You need a smart person to visit your house and inspect everything.
As Jon noted, step one is to have a good air barrier on your house to prevent exterior air from leaking indoors. To make sure your house has a good air barrier, you may need to hire a home performance contractor to do some blower-door-directed air sealing work.
In your climate, there really is no advantage to having a ventilation channel in your roof assembly. That means that the best way to insulate a cathedral ceiling in Florida is either (a) by installing closed-cell spray foam on the underside of the roof sheathing, or (b) by installing rigid foam above the roof sheathing. For more information on these approaches, see this article: How to Build an Insulated Cathedral Ceiling.
In one of your comments, you seem to misunderstand the purpose of a ridge vent. You wrote, "Without the ventilation ridge, come summertime, the upstairs temp would get to almost 90 degrees with A/C running non stop trying to cool it down. So, we had roofing company install a new ventilation ridge."
A ridge vent has nothing to do with controlling the indoor temperature or the indoor relative humidity. When properly installed, a ridge vent does not connect with the house air in any way. The purpose of a ridge vent is to help remove moisture that accumulates in the roof sheathing. This type of roof ventilation system only works in cold, dry climates. It doesn't work in Florida. The presence or absence of a ridge vent won't affect your indoor temperature unless something is seriously wrong with your ceiling air barrier.
Thank you for all of the information. This is super helpful and I have learned a great deal on this site and from everyone's comments. I truly wasn't trying to solve the problem over the internet, just get some direction. Per your last comment Martin, I think we must fall into the seriously wrong with our ceiling air barrier category. I have contacted a certified energy auditor and hope to come out of that with some very specific direction. I feel pretty certain we have multiple ways / places where the outside humid air is coming inside the house, including one air handler that is outside the insulation, to answer Dana's question.
"I feel pretty certain we have multiple ways / places where the outside humid air is coming inside the house, including one air handler that is outside the insulation..."
When the air handlers & ducts are outside the thermal and pressure boundary problems are often magnified:
The penetrations of the pressure boundary by ducts and register boots are more numerous and harder to seal properly, and any duct/air handler air leakage will drive outdoor air infiltration directly at much higher rates than the natural infiltration rates when ever the air handler is operating.
With any ducted system the duct design and implementation has to be well balanced with ample return paths so-as to not to induce large room-to-room pressure differences. The maximum allowable pressure difference between adjacent rooms with the doors closed for Energy Star homes is 3 pascals, or 0.012 water inches. A typical HVAC pro's hand held manometer only has a resolution of 0.01 water inches, so the pressure between rooms needs to read 0.00 or 0.01, and not 0.02 under all operating conditions (doors open, closed, etc.) whenever the air handler is running to come close.
Unfortunately typical duct designs are hacked-in by rule of thumb by contractors, not compliant with ACCA Manual-D, and even when the design is fine, the "as-installed" implementation often suffers egregious errors of commission or omission (especially when flex duct is used throughout), all leading to duct imbalance, which will also contribute to air handler driven infiltration, even if the ducts & air handler aren't very leaky.