Author Topic: Soffit vent in cantilevered floor  (Read 5352 times)

mikepm711

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Soffit vent in cantilevered floor
« on: August 14, 2015, 03:26:04 PM »
I live in a 3 story townhouse in northern Virginia. The top floor gets hot in the summer and cold in the winter, while the main floor is comfortable and the basement is cool year round. The top floor is cantilevered about 2-3 feet over the main floor in front.

I want to do something to make the top floor more comfortable. My first thought was to air seal the attic. I can see evidence of air leaks from the black dust in the insulation where the walls meet the ceiling in the storey below. But then I noticed there is a vent in the soffit under the cantilevered floor that seems to let outside air into the floor joists. Is this normal? All the other houses in my community that have cantilevered floors have the same thing. Would it be okay for me to replace the vents with solid plywood?

MDM

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Re: Soffit vent in cantilevered floor
« Reply #1 on: August 14, 2015, 03:50:39 PM »

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #2 on: August 14, 2015, 04:46:46 PM »
@MDM
Thanks for the link, but these vents are not in the attic. They are in the floor, where the top storey overhangs the main floor. I have attached a photo that might help.

MDM

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Re: Soffit vent in cantilevered floor
« Reply #3 on: August 14, 2015, 05:31:52 PM »
Maybe we're getting hung up on the definition of "attic".

Do you know for sure these vents admit outside air under the second story floor?

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #4 on: August 14, 2015, 10:36:49 PM »
No, I am not sure if it goes under the floor. I pried open one end of the vent and could see joists. I couldn't see very far in, but there was no obvious insulation.

MDM

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Re: Soffit vent in cantilevered floor
« Reply #5 on: August 14, 2015, 11:15:36 PM »
That's a good picture of the soffit underside - can you get one of the roof above it?

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #6 on: August 15, 2015, 08:03:19 AM »
I am out of town at the moment. I can take a picture of the roof soffit when I get back. What are you hoping to see?



Greg

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Re: Soffit vent in cantilevered floor
« Reply #7 on: August 15, 2015, 10:01:59 AM »
The vent in the overhang is meant to allow some airflow into the overhang area only, and shouldn't allow air in between the floors.  If it were my place I'd remove a small area of the vented soffit and verify that the overhang-floor joist area is blocked off from the between-floor joist area.  If it is then the vent detail is ok, if there's no blocking keeping the fresh air from the rest of the floor joist area, then it needs blocking and air sealing in line with the wall.

Regardless, the vent detail for such a small overhang is likely unnecessary.

MDM

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Re: Soffit vent in cantilevered floor
« Reply #8 on: August 15, 2015, 10:19:58 AM »
I am out of town at the moment. I can take a picture of the roof soffit when I get back. What are you hoping to see?
A ridge vent or similar.  Makes more sense if there is a place on top for the air to exit.

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #9 on: August 15, 2015, 11:35:52 AM »
@ MDM I am fairly certain there is no ridge vent. I think the only vents for the  roof are in the soffit under the eaves.

@ Greg Thank you for the advice. My next task will be to take a closer look inside and verify that the spaces between the joists are blocked off.

Is it possible the temperature difference on the top floor could be due to air leaks along the ceiling edges alone?

Greg

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Re: Soffit vent in cantilevered floor
« Reply #10 on: August 15, 2015, 04:08:14 PM »
Yes, but also likely due to poor attic/ceiling insulation and convection inside the home.

paddedhat

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Re: Soffit vent in cantilevered floor
« Reply #11 on: August 16, 2015, 10:58:07 PM »
Greg is, once again, 100% correct on this. I have torn this detail apart on at least two homes, and was blown away by how much evidence of air movement was evident. This included black streaked fiberglass ceiling insulation that looked like a filthy furnace filter, and mold growth on top side of the sheetrock, at the ceiling edge. The area needed to be properly insulated, and tightly sealed, for the building to perform well.

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #12 on: August 18, 2015, 05:57:05 AM »
@ MDM I was wrong there is a ridge vent. I had not noticed it before.

mikepm711

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Re: Soffit vent in cantilevered floor
« Reply #13 on: August 18, 2015, 06:03:50 AM »
Thanks everyone for your input.

I had gotten a book from the library (Insulate and weatherize : for energy efficiency at home / Bruce Harley) and was planning to air seal my attic. I ordered some Great Stuff and a dispensing gun. My attic is small, about 20 by 30 feet, and I am hoping to do this over a few weekends in the Fall, when it is cooler.

If you have any tips on air sealing, I would be happy to hear them.

Jack

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Re: Soffit vent in cantilevered floor
« Reply #14 on: August 18, 2015, 07:43:52 AM »
The vent in the overhang is meant to allow some airflow into the overhang area only, and shouldn't allow air in between the floors.  If it were my place I'd remove a small area of the vented soffit and verify that the overhang-floor joist area is blocked off from the between-floor joist area.  If it is then the vent detail is ok, if there's no blocking keeping the fresh air from the rest of the floor joist area, then it needs blocking and air sealing in line with the wall.

Regardless, the vent detail for such a small overhang is likely unnecessary.

I'd suggest removing the whole soffit, blocking and air-sealing as Greg wrote above, spray-foaming the overhang area with closed-cell foam, and then reinstalling the soffit without a vent.

Fishindude

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Re: Soffit vent in cantilevered floor
« Reply #15 on: August 27, 2015, 01:55:50 PM »
If the upper floor is hot, I'd guess the attic is poorly insulated, and also likely poorly ventilated.

Floor of attic (right above your upper floor ceiling) should be heavily insulated, at least R-30 so you don't feel the hot air from attic in summer and cold air in attic in winter.   Should have soffit vents in the roof overhang, as well as ridge vents on the peak of the roof and / or gable end vents to let heat out of the attic.