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Humidity Issues in Converted Space

I've been having humidity issues for the past few years in the near building:

The unit was originally built as a garage, and some time before I purchased the property it was converted to living space. The unit is built on a concrete slab. The ground is (I think) pretty wet. There are no soffets and no ridge vent.

The interior is divided into two spaces. Here is the "front" living area:

This is behind the windows in the first photo. There is a wall running the length of the room. Behind the wall is a utility room. (Accessed from the door off the patio in the first picture.).

As you see, the living space has a cathedral ceiling. The utility room behind the wall has an attic space -- the vent to the left of the room in the first photo opens into the attic above the utility room. There is a whole house fan venting out of the attic.

A few years back, I had an insulator come in to look at space because the insulation in the attic was falling apart.

He recommended closing off the vent from the living space to the attic to keep the hot air from escaping during the winter, which we did with a piece of rigid foam insulation.

The problem is that the next summer I started experience bad humidity problems in the room. The dry wall tape is cracking up in the corner of the cathedral ceiling. There is mildew forming above those beams. And there is what appear to be mildew stains forming around the arch window (as if humid air is coming out from little gaps where the molding meets the drywall):

You can see from the bottom picture, that those beams are just the ceiling joists sticking through the sheet rock of the ceiling. That gap is open to (I assume) the space between the sheet rock and the underside of roof (plywood, I'm guessing).

There is a green plastic vapor barrier under the laminate flooring in the living space. (again, I assume it's a vapor barrier, what it really is, I don't know.) The floor of the utility room just has vinyl tile over concrete -- no barrier. Behind the walls of the living space is another plastic sheet (clear, but with rips) and fiberglass insulation -- although with lots of gaps.

Thanks for reading this far.

I think what was supposed to happen is that the hot, humid air building up at the top of the cathedral ceiling was going up into the roof where the joists went through, and from there, flowing to the left, into the attic space and out through the whole house fan. I think that when the insulator blocked off the vent, he also added insulation to close off the space at the top of the attic leading under the roof. You can kind of see that up at the top of this picture (above the netting):

I think this is preventing the humid air from venting out of the living space. It travels up and tries to get out where the joists are, but gets trapped there.

So, what do I do?

I've opened up that vent during the summer, which seems to have helped a bit.

I could remove the batting from in the attic where it's blocking the gaps to the space over the cathedral ceiling. But for all I know, they should be there.

I thought about "plugging" those holes where the joists go through the ceiling. But I don't see what good that will do.

I'm not sure what I can do about humidity escaping from behind the arch window -- except caulking the gap. But it may be worse to trap the humidity in the wall.

Other than putting down a vapor barrier in the utility room, I'm not sure what I can do to prevent humidity from getting into the room.

Sooooo. Any suggestions?

Thanks. I'd appreciate any help. Maybe someone can confirm/explain how this room was supposed to have been vented/insulated.

I thought I might be able to get a skylight with a vent, but apparently those don't exist.

Re: Humidity Issues in Converted Space

Can you add soffit vents and ridge vents? If not, dormer vents? turbine vents? attic fan?

You need to get the air moving up there.

Re: Humidity Issues in Converted Space

Don't know about adding soffets and a ridge vent, or whether that would be good. If I had a ridge vent, in the winter, I assume all of the warm air in the room would go up and out through the "joist holes" in the ceiling.

Here's something I don't understand. Isn't the living space supposed to be "sealed"? The soffets/ridge vent are to create air flow in attics and the space under the roof?

What's the standard way to get hot humid air out of a room? I guess an air conditioner or dehumidifier?

Re: Humidity Issues in Converted Space

I would assume that the garage is converted without a permit, was not inspected or approved. A lot of folks convert garages without permits, but at least they do it to meet code.

- You need an attic, then you can make sure it's ventilated. Or have all rafter cavities ventilated.

- You just want to get the humidity out of this place? a wall a/c will do.

- A living space is not built to be 100% sealed. Look at your car. When you drive it, you feel outside air, a small draft, even when the windows are up. The reason: to get rid of CO2.

Re: Humidity Issues in Converted Space

The vent to the attic from the living space shouldn't be required. It's a heated/cooled air looser. If you don't cool in the summer it would provide ventilation from the whole house fan. I would close it if you run A/C or close it in the winter.
The gaps to the space above the cathedral ceiling should be left open. If scissor trusses there should be room above insulation to allow for ventilation.
The gaps at the beams should be closed off.
Is the attic vented? How does the whole house fan exhaust air? Directly to the outside or into the attic first, then out through louvers or vents?
The stains at the half round window almost look like dirt stains where air is being drawn or blown in. Possibly the whole house fan is forcing hot humid air through the wall. Is the whole house fan being run when the windows are all closed?
Caulking shouldn't hurt. Hopefully the window was installed correctly with flashing, caulking or foam.
How much insulation is above cathedral ceiling? 10 or 12 inches at least would be best if you have the room, but likely you're stuck with what's there.
Plastic on the wall insulation in the attic above the vent shouldn't be there. In general nothing impermeable should be against that side. It is trapping moisture. In a heating mostly climate a vapor barrier should be toward the inside.
Ridge and soffit venting would work best, but it doesn't look like you have soffit overhangs. Next time you need a new roof I would still have ridge vents installed. Additional attic venting may be needed. I can't see any on the house.
Use fiberglass tape when you have the drywall repaired. Don't let anyone try to remud the old tape. Replace any that is loose or suspect. The drywall seams cracking may be from movement as well as high humidity.
I suspect poor roof ventilation may be at the root of your problem.
That's my two cents from here.

Re: Humidity Issues in Converted Space

(Sorry, double post.)

Re: Humidity Issues in Converted Space

Thanks for the responses. This is very helpful.

It seems that what I need to do is add an A/C unit in the room. (There is no A/C in the house. The main part was built in 1888, this part was build around 1970.) I'm surprised that my humidity issues started soon after I did the insulation work -- although the recent summers have been "wetter" than usual.

I can seal the gaps where the beams enter the ceiling. Should that be with pieces of drywall? I have no idea what insulation is under the roof.

I can open the gaps in the attic that lead to the space between the ceiling and roof. Although if I close the gaps where the beams enter, I don't think there will be any airflow. ??

I'll caulk around the window. The whole house was probably run with all of the windows closed. I hadn't known until recently that this was a concern. I have no idea whether the window was installed correctly -- I assume it was not (nothing in this room was done right).

The whole house fan vents directly outside, through louvers. It was meant to pull air out of the living space through the vent. (It did an ok job to create a slight breeze throughout the entire house, but not great.)

This is what the fan looks like in the attic (in case it matters):

When I get the A/C installed, I'll close off the vent to the attic again. Of course, when I do that, the whole house fan no longer serves a purpose.

I'll be replacing the drywall tape this summer. Do you think fiberglass tape is better than paper for the corners? (I don't know much about taping, but I thought I've read that paper is better for corners. Perhaps it's just a matter of individual preference.)

While I'm here -- You can see that the two far roofs each have ridge vents. The lower roof had a vent when I bought the house. There are no soffets, but the siding has these soffiet vents. I have no idea if they're doing anything.

On the upper portion, the insulator guy convinced me to add a ridge vent. I later realized that there are no soffets. Without soffets, does the ridge vent do anything? Or did I get fleeced?

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