Second floor humid and smelly

4 years ago

Hi everyone. We had our second floor remodeled a couple of years ago with raising the roof a little, new insulation and new upstairs hvac. The second floor still needs a portable dehumidifier as there is still humidity in the summer. Also a chemical type smell when the a/c runs. Almost smells like mastic.

The insulation went from traditional to spray foam open cell. We had one room untouched and they left the old insulation in there which was a problem with the rest of the upstairs being foam. That has been fixed but still have issues. We have had the hvac company out so many times I’ve lost track and they’ve even replaced the air handler upstairs and downsized a little.

Anyone have ideas or suggestions? We are now at a loss but fear mold issues down the line. Thanks!

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Comments (4)

toxcrusadr
4 years ago
Smells like mastic? Like a solvent odor, or more like tar? There are issues with roofs smelling on hot days long after the job is done, but a solvent odor sounds like something else.

Without knowing how the separate HVAC is set up and where it's located, it's hard to figure what's happening. Do you keep AC on up there or is the temp allowed to get hotter when no one is up there? Is the HVAC unit bringing in fresh air?

Even though I'm in a hot humid climate (Missouri), I never hear of humidity problems on top floors, but mostly in basements.
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Charles Ross Homes
4 years ago
High relative humidity in basements is normally a consequence of water infiltration coupled with little or no demand for air conditioning (and thus no dehumidification.)

Humid air is less dense (more buoyant) than dry air. Higher indoor relative humidity on upper floors is consistent with that characteristic.
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toxcrusadr
4 years ago
That makes a certain amount of sense. I live in a walkout ranch so it's pretty cool in the basement, and the central air system doesn't have the right outlets down there, so the basement isn't well served by the AC. I run a dehumidifier down there.
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Charles Ross Homes
4 years ago
last modified: 4 years ago
Hi, Adam,

Well, I was hoping that Ray Austin of @Austin Air Companie (the A-team) would have weighed in on the smelly part of your post by now. Ray's forgotten more about stink than most people will ever know--with the possible exception of Mike Rowe, of course. BTW, Ray's YouTube videos suggest he has more of an on-screen presence than Mike does, so if he's not next in line for the host of Dirty Jobs, those guys at History Channel are asleep on theirs.

Now for the other smelly part...

A chemical odor could be the product of spray foam insulation that was not fully cured or micro growth on the air conditioning coil or micro growth inside ductwork or contaminated air pulled into the air handler due to a negative pressure or simply pulled through exterior walls, around windows and/or up from a basement or crawl space due to stack effect. The micro assumption can be assessed by visual inspection. The air flow through walls, etc. with a blower door and smoke pencil.

Open cell spray foam is air permeable, and you report a high relative humidity condition on the 2nd floor, so it's possible that moisture is migrating to the back side of the sheathing or drywall (not sure if your spray foam insulation is in the walls, on the top side of the 2nd floor ceiling or underside of the roof deck) and causing mold mildew to grow.