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Attic venting, air sealing, and insulation

Loya1ty | Posted in Energy Efficiency and Durability on

I’ve read on here various recommendations on attic insulating, conditioning, venting, etc. Please correct me, but my interpretation of the results is that if you have ridge vents, then gable vents should be sealed due to airflow patterns. Also, an attic fan is proven to more costly than beneficial (climate zone dependent?).
The roof was replaced a few years ago on the house I recently purchased, and although I don’t know for sure it looks as though they added the ridge vents at that time. The gable vents are still open, and poorly sealed I might add. I was going to do some repairs and fix them up, but upon research it appears sealing them is proper (and easier tbh).

This then leads me to the attic fan. It’s relatively new (probably when the roof was done) and I’ve set the temperature fairly high on it. Obviously if I seal up the gable vents, it’s a no brainer to remove. However the fan also has a humistat setting in which I set at 35-40ish% (I think). I’ve heard it running a few times since then, so my main concern with sealing the gable vents is that humidity will build. But perhaps those vents are the reason!

If it helps for best course of action, I will explain my plans for the future improvements in the attic:
– install vent baffles for the first few feet of roof decking from the soffits
– complete the rest of the roof under the trusses with foil barrier up to the ridge vent
– reinforce insulation R-value. current blow in is old and settled. will need to remove some. plan to relocate blow in stuff from the middle of truss over to the sides towards the soffits to make thicker, then lay osb flooring along the middle and lay thick batt insulation on top so I can remove more easily when accessing the attic in the future.
– while doing the insulation, air seal fixtures on the top side of ceiling
– and hopefully remove all of the ducting from the attic in order to run a ductless mini split throughout the 2nd floor to improve hvac efficiency. running duct through walls will be too difficult. Worst case I’ll build casing around the existing ducts to insulate better.

The goal isn’t to necessarily fully condition the space, but more so to manage climate extremes. HVAC inefficiencies are super noticeably at the moment.

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Loya1ty.

    Though you didn't say where the house was located, it many climate zones, if you have a well air sealed and insulated attic floor, including air sealing at the top plates and other thermal bypasses, along with soffit to ridge venting, you shouldn't have any humidity concerns and don't need an attic fan. You can also close off the gable vents.

    However, you said you were hopefully going to remove ductwork from the attic. You should probably figure out if that is happening before starting all of this work on your attic. If the ductwork remains, you may want to consider a conditioned attic instead. In other words, insulating the roof line. Here are some articles I'd recommend:

    Fans in the Attic: Do They Help or Do They Hurt?
    All About Attic Venting
    Air Sealing an Attic
    How to Insulate an attic floor
    Creating a Conditioned Attic

    1. Loya1ty | | #2

      Thanks, Brian. Climate Zone 4. As I update and/or renovate each upstairs room, I plan to go up to the attic and air seal things. The ductwork is older and would definitely need some tightening up, sealing, and insulating. If I'm going to be crawling around the attic to do work, the ducts are simply coming out and I'll be putting in a cleaner ductless mini split system with heads in each room for greater control (the landing is pretty large too, so I'll have that analyzed if I could do a larger single head to supply all rooms, although close 1 door and it's not ideal). Removing the supply and return duct will also gain me a lot of room in one of the walk in closets as well as the dining room on the 1st floor.

      This is also a big concern area for me to remove that return duct, since lately I suspect cooler air from outside (attic) makes its way in, and as it passes the furnace flue in the same wall channel, it condensates. I get a strong mildew and mold smell from the return vent, especially so on the 1st floor. The cheapest way would to just get a 2nd zone unit and direct it into the existing supply duct for the 2nd story, but I'm all about efficiency, climate control/comfort, and clean installation even in areas not seen such as the attic. I don't plan to store anything up there so I feel content not going through fully conditioning it and closing it off. Providing baffles and foil along the rafters and tightening up air flow will be sufficient. I'm also noticing all the dirt and dust that has been free to roam the house as I remove the outlet covers lol. I have my work cut out for me. But the resources you've provided and other posts on here will certainly help me turn my home into an energy efficient smart home.

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