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  1. #1
    Join Date
    Nov 2011
    Posts
    1

    Question New home, conditioned attic/crawl space

    A builder from CA, TX & AZ is developing its first community in Raleigh, NC. They are using open cell spray foam insulation in the crawl space, attic, and exterior walls. In addition, they are running a duct line to the the crawl and attic spaces and advertising them as positive pressure "condition spaces". The crawl space foundation block and walls are insulated, but the underside of the house floor is not (the earth floor is lined with 10 mil plastic, sealed to the foundation block). Also, there are no vents for air circulation. The attic is insulated completely with no vents as well. The builder states that this is the latest building practice. Is anyone familiar with this technique? I am concerned about whether the high humidity in the Southeast would eventually cause mold without the air circulation.

    An HVAC technique they are using is to install a 3x3 solar panel grid on the roof in a way that allows air to flow under the panels, and enter the return line of the air handling unit. The top row of panels is actually only used to preheat the air before it enters the duct (via an intake fan to a "heat transfer" module built into the duct line). This preheated air is used to maintain the water temperature of the hot water tank and to supplement the heating of the forced air heat pump system. My concern here also is the growth of mold due to the higher humidity levels in the Southeast. Is there a comparison that can be made of this method between the southwest and southeast?

  2. #2
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,737

    Default Re: New home, conditioned attic/crawl space

    The conditioned crawl space is growing in popularity in the southeast. It actually lowers the humidity and inhibits mold growth. Its expensive though, especially for a retrofit. Maybe not so bad on new construction.

    The conditioned attic is a new one on me. I see the logic in the conditioned crawl space, not so much for the attic. In both cases, I'm not sure that an open cell foam is the right choice either. I think I would rather have a closed cell foam, especially in the attic.

    Open cell foam in the crawl space might be OK if there is a moisture barrier between the blocks and the insulation.

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: New home, conditioned attic/crawl space

    Quote Originally Posted by PaulLo View Post
    A builder from CA, TX & AZ is developing its first community in Raleigh, NC. They are using open cell spray foam insulation in the crawl space, attic, and exterior walls. In addition, they are running a duct line to the the crawl and attic spaces and advertising them as positive pressure "condition spaces". The crawl space foundation block and walls are insulated, but the underside of the house floor is not (the earth floor is lined with 10 mil plastic, sealed to the foundation block). Also, there are no vents for air circulation. The attic is insulated completely with no vents as well. The builder states that this is the latest building practice. Is anyone familiar with this technique? I am concerned about whether the high humidity in the Southeast would eventually cause mold without the air circulation.
    Yep -- this is the modern thinking in the building science communit -- although I'm surprised they aren't pouring a concrete slab for the crawl space ( likely saving a few dollars )
    . Including both the crawl space and the attic to the conditioned space greatly improves the heating/cooling of the home. Especially for you folks in the States that have the HVAC located in the attic , insulating the entire attic maintains a more even temperature within that space and lessens the load on the HVAC.

    You mentioned there will be vents in both the crawl space and the attic -- so -- there will be air circulation.
    As long as there is no water infiltration and the foam is properly apllied, you shouldn't have any issues with mold.

    An HVAC technique they are using is to install a 3x3 solar panel grid on the roof in a way that allows air to flow under the panels, and enter the return line of the air handling unit. The top row of panels is actually only used to preheat the air before it enters the duct (via an intake fan to a "heat transfer" module built into the duct line). This preheated air is used to maintain the water temperature of the hot water tank and to supplement the heating of the forced air heat pump system. My concern here also is the growth of mold due to the higher humidity levels in the Southeast. Is there a comparison that can be made of this method between the southwest and southeast?
    This sounds very strange to me.
    Unless , an ERV ( Energy Recovery Ventilator ) is being used ---
    The HVAC system is a closed system and shouldn't have any outside unconditioned air directly introduced to the conditioning air system.
    In the summer months this would introduce hot humid air from outside into the air conditioning air stream --- in the winter this would introduce colder outside air into the heated air stream --- greatly reducing the performance and creating condensation within the ducting and air handler.

    Being in your location open cell foam will likely be fine , otherwise if you were in a colder region I would definately recommend closed cell foam.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #4
    Join Date
    Nov 2011
    Location
    Charlotte, NC
    Posts
    12

    Default Re: New home, conditioned attic/crawl space

    Yep, sealed crawl space. While I'm not a fan of spray foam, and I question 'sealing' the attic (stacking effect pushes air out the top of the home... why seal that?) sealed crawl spaces are amazing at controlling the humidity in the SouthEast.
    A sealed crawl is completely allowed by state code, and while one option is a concrete floor, it's completely unnecessary unless you have a very tall crawl that would allow storage or usable space.
    Sorry, can't comment on the HVAC portion - sounds odd, but never heard that.
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