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April 5, 2012 | Show All
Proper installation of soffit dams for blown in insulation

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I work as a building inspector and am trying to determine the proper installation of soffit dams for blown in insulation for CMU construction. The only illiustrations I can find are for wood frame construction and require that insulation covers the top plate. Does the insulation also need to be installed onto the top of the block wall to ensure that there is proper insulation at the joint where the wall and ceiling meet?


Posted At : 12:15 PM. | Posted By : KRISTIN | Link | | Comments (5)


All, The same principals apply, whether you are framing with wood, steel, or CMU. The point of a soffitt dam is to keep the attic blown-in or batt insulation from spilling out into the soffitt where it does no good. The dam always should be installed to the exterior face of the exterior wall. The attic or ceiling insulation when installed will then cover over the exterior wall assembly maintaining a consistent thermal envelope from the wall assembly through the attic or ceiling insulation. If the wall is basically "un-capped" then you will have created a cold or hot spot all the way around the top of wall location. This can easily be seen with an IR Camera.

Posted By STEVE MALON / Posted At 4/5/12 12:50 PM

I must absolutely agree with Paul on this. The Accuvent is a great way to insure against wind washing and keep insulation from spilling into the soffit. Bob

Posted By BOB HELLER / Posted At 4/5/12 12:51 PM

The idea of insulating all the way to outside of the top wall plate is to make the building envelope a complete “blanket” around the interior conditioned space. So if the CMU wall (blocks) is not insulated then the thermal boundary would stop inside the wall as opposed to above the wall. Blocks can be filled with vermiculite or different types of liquid applied foam so they may be considered part of the thermal envelope. Keep in mind that baffles also prevent “wind washing” in addition to providing a channel for air entering the soffits to move unimpeded above the attic floor insulation. So to me its more important to prevent air from flowing under the baffles into insulation on the attic floor than insulating all the way out to the outside edge of the wall. Lots of installers wedge the baffle in and then foam underneath it to further prevent wind washing. I will attach a couple very good publications that DOE commissioned on air sealing and ventilation. Let me know if you have any other questions. Regards,


Manager, Technical Services CertainTeed Insulation Group

Posted By RANDY STRAIGHT / Posted At 4/5/12 12:52 PM

Yes, the insulation must cover the top of the wall creating a complete envelope in most parts of the country. A typical concrete block wall in Florida requires a wood ‘furring’ strip to run along the top part of the wall for drywall to attach to. My suggestion is to use the AccuVent, the upper part can be installed traditionally, and the lower “lip” that fits over the top of the wall, and wraps down the front of the wall, can be attached to the furring strip. Paul Colley North America Accounts Manager Blow In Blanket Systems® Certified BIBS® Trainer 800.525.8992 O 303.263.7143 C 303.733.0414 F

Posted By PAUL COLLEY / Posted At 4/5/12 12:53 PM

I don’t have time today for a long answer but, being a mason in my past life, the top course was always a bond beam filled with concrete. If they are not doing that then the next question would be is the CMU insulated with cavity fill, if so then it should be in the top course also. If not, there really is no reason to insulate the top course. Should they want to require that you insulate the top course then they would need to use core fill, cavity fill, or foam. Unless the CMU is sealed moisture will past through fiberglass or similar products should not be used. I did look as my EEBA book for Cold Climates I was surprised they do not show block in the wall details, wood and, SIPS, and ICF. How that makes sense.

Randy Wilkerson CSI, CGP, CAPS Construction Operations Manager TriState Habitat for Humanity 9900 Princeton- Glendale Road Ste. 216 Cincinnati, Ohio 45246 513 608 8265 Mobile 513 942 9211 ext 14 513 942 9311 FAX

Posted By RANDY WILKERSON / Posted At 4/5/12 12:56 PM