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  1. #1
    Join Date
    Oct 2013
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    Default Adding insulation in attic with ridge vent

    My house is 17 years old, has a ridge and soffit vents along the whole length of the house. Attic has 24 inches of blown in insulation. I am considering following three options - which one would be most efficient performance and cost wise?

    1. Expanding foam insulation between the rafters underside of the roof
    2. Or rigid foam insulation held back with some sort of strapping
    3. or just adding more blown in insulation

  2. #2
    Join Date
    Dec 2007
    Location
    Tennessee
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    1,713

    Default Re: Adding insulation in attic with ridge vent

    None of those are cost effective. If the attic insulation is even and not bunched up in places, then you will never even come close to recouping the cost of adding more insulation. certainly option 1 and 2 will have zero savings.

    Look for excessive infiltration around your doors and windows. Then after upgrading any weather stripping, the next step would be to find a service that uses an infrared camera to locate any heat losses. At least then you won't be blindly throwing money at the problem with no results.

  3. #3
    Join Date
    Jan 2008
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    1,987

    Default Re: Adding insulation in attic with ridge vent

    24 inches of attic insulation should be all you need for cost-effective purposes up there. anything on the rafters and sheathing above that will be wasted and possibly detrimental Spend elsewhere where it will be more worth the money spent. Most insulation companies will now do an IR scan to tell them what;s going on. You'll have to pay for that but it's usually worth it in newer homes with good attic insulation like yours.

    Phil

  4. #4
    Join Date
    Oct 2013
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    2

    Default Re: Adding insulation in attic with ridge vent

    Keith and Phil thanks for your kind reply. I was hoping to reduce the attic temperature specially just above ceiling by trapping and redirecting the very hot air right under the roof to the ridge vents. The ceiling temps feels at least 10-15 degrees hotter than the room. Is there another solution? Unfortunately, there are no returns (high or low) in each room in this house that I had in my previous older houses.

  5. #5
    Join Date
    Dec 2007
    Location
    Tennessee
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    Default Re: Adding insulation in attic with ridge vent

    One problem with blown in insulation is that it is often blown up against the roof sheathing near the edges of the attic and blocking air flow from the soffits to the ridge. You need to get this inspected. It is often hard to inspect because the depth of your insulation covers your ceiling joists.

    It might have to be done by removing your soffits themselves. That is a bit of labor and might need a bit of repaint afterwards.

    If this turns out to be the case, it will be just another example that no amount of insulation will help if it is not properly installed.

  6. #6
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,948

    Default Re: Adding insulation in attic with ridge vent

    I'd head up to the attic with a rake and fix what you have first. Unblock the eave vents and see how much of a difference there is.

  7. #7
    Join Date
    Jan 2008
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    1,987

    Default Re: Adding insulation in attic with ridge vent

    Insulation is to help the conditioned areas- ie the living space under the ceilings- and it does that pretty well. Insulating under the rafters will only trap heat there, causing the attic temps to be even higher.

    Heat rises, so as long as it can escape at the top ridge vent that's what it will try to do. But in order to do that well, there must be cooler air admitted at the bottom- ie soffit ventilation- and this must not be blocked which is what I bet you'll find happening in your attic. The heat inside your house will rise to the ceiling so it will naturally be warmer than the walls and floors all the time. If this is a big problem then having HVAC return air from there will help mitigate this but it will also add to the AC load since it now has to cool warmer air than before. We live on the floors so don't worry so much about what's going on at the ceilings. Just be sure the insulation in the attic is adequate and that the airflow from soffits to ridge vents is not inhibited and all will be fine.

    Phil

  8. #8
    Join Date
    Nov 2013
    Posts
    4

    Default Re: Adding insulation in attic with ridge vent

    If you look at the edge of the insulation (where it meets the roof deck) you should be able to see air channel baffles fastened to the roof deck and protruding above the top of the insulation. If you can't see them, you need to install them (not a difficult task - just rake back the insulation from the roof deck, slide the baffle all the way down, and staple it with a staple gun). Depending on the pitch of your roof, you may neeed more than one baffle to get the air flow above the top of the insulation.

    As others have said, 24" is plenty of insulation if installed properly.

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