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Hi Folks. Found this in a home in which the home owner had been complaining about mildew smells, humidity and tiny insect infestation. What are the possible consequences of insulating an attic floor and I think sealing the soffit vents in this manner? 

Hi Larry, this would be a great addition to BPI's monthly newsletter segment, Stump the Chump. May we include it in an upcoming edition? Shoot me a message and we can iron out the details!

Hi Quinn. I'm first trying to find out if this is considered a bad insulation installation. And if so, how bad. I can send you the image, just let me know how.

I'll send you a message on here for more details. Keep an eye on your inbox!

Larry, are they trying to assign blame? If so, it's a bit like blaming the foot for Colin cancer. If this was a prescriptive job and not a home performance job, you can't blame the insulation guy for the homeowners improper operation of their home.

If it was a home performance job, the contractor should have recommended basement work, and continued RH awareness and management.

The insulation job is quite simply a freaking eyesore & mess - with that it shouldn't be the issue where they are smelling mildew, getting bugs in, etc... (assuming you are talking about inside the house) - put your sleuthing hat on, find the source of moisture

As for humidity - oh yeah that can be an issue - they have to use the exhaust fans properly (that vent outside) & maybe even buy a dehumidifier

Soffit vents blocked affect the attic & roof, not the house - as for how bad...

can insulation be sprayed directly on the ceiling & then covered (if not deep enough already) with cellulose, etc... yes & I have seen some great results

Hi Larry, what a mess.  Give us your climate zone so we know outside temp and humidity.

Did you do a blower door test to see how tight the building is,  I'm wondering where else he might have used that foam?

What is in the basement, dirt floor, crawlspace, air sealed, or insulated.

Are they using air conditioning, I see the one duct?

I suspect the home owner did the foam job and I also suspect he did his own wiring.  To be honest, I don't even try when I see something this bad, I make up an excuse and walk away.  You can't fix stupid.


Hi Bud. This home is in the North East (NYC Suburbs). We are a mechanical contractor and were called in to do some work unrelated to building performance. The homeowner did complain that since the attic insulation they have been experiencing moisture problems. I don't know if it coincidental or a result of the foam on the floor which was done by a contractor. I was just wondering, in general, what are the possible consequences by spray foaming the attic floor instead of the roof line or even just cellulose or fiberglass on the floor? I have been in many homes and have not seen spray foam on the floor, only on roof lines.

The contractor that did that should have his toys taken away.

To answer your general question, applying rigid or spray foam to an attic floor would follow the normal rules of ensuring any surface that can come in contact with humid air must always be above the dew point.  With foam insulation that is often easy as the foam is not air permeable.  BUT, with that sloppy job who knows where there may be gaps where a cool ceiling below can result in condensation from the attic air above.  An inspection with an infrared camera might locate some problem areas.

Do you know what is under that foam?  Did they apply it over old insulation and all of the dead bugs, rodent droppings, and whatever is common in an old attic?

Adding the foam would have also reduced the air exchange in the house and that could have intensified the musty smell from an already existing problem.  That is why I asked about a blower door test, which you typically wouldn't do, but it would tell us how tight the resulting home is.  Too tight and alternate ventilation is required.

Lots of other steps an energy auditor would take and perhaps that should be his next step.


I don't know what is under the foam, but probably just the floor deck. I would have to think they removed the existing insulation but you never know. I suspect that the moisture problems are emanating from a damp basement or crawlspace and are now trapped in the home. It is a large home, about 5000 sqft. We may go in there to do a blower door test to see how tight the home actually is. Maybe add some fresh air to the home and have them address the basement moisture problems. 

You have a BD, that's good.  IR would add another star.

@Larry "I would have to think they removed the existing insulation but you never know"

Looking at their foam job I wouldn't expect they did a lot of cleaning up.

I agree with the basement as a possible source, especially if there were major bypasses from basement to attic that got sealed by the foam.  Is there a known moisture problem in the basement?

Side note, not sure about attics, Sean would know, but foam often requires it be covered by a thermal barrier.  Plus, sealing holes requires a fire rates material.  Plus, it doesn't look like the amount of foam meets code requirements.


Long time no hear Bud & good points

As for codes - yes it requires a barrier unless the foam meets certain requirements which isn't that big of an issue doing the attic floor as the drywall underneath counts & then you apply blown in cellulose on top

Air sealing doesn't require fire rated (until you hit commercial) materials but it is a good idea - nice thing for those that like Great Stuff is the large "red" cans that require a gun are fire rated. For the homeowner "straw" cans the red isn't but the orange ones are

Foam meeting the R-Value requirements - not a chance, in most cases that it is used on the attic floor it is just to form an air-barrier with the rest made up of blown in materials. Of course with that job I doubt it even suffices as an air-barrier


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