# Air sealing and insulating a tri-level attic



## Windows on Wash (Aug 30, 2011)

If you adequate intake and exhaust on both attics and it is balanced, you don't really need to block them off. 

If you want to seal it off, feel free to but I would just use a piece of wood. I don't like exposed foams where they can be avoided. 

Where is the home? We will need to know that for vapor retarder recommendations. 

If the XPS is in line with the kraft facing on the insulation, the odds are that it is okay. Make sure the XPS is sealed up tight and pull the insulation to seal the back side of the kneewall prior to re-installing it. Be sure to align it properly and then install the XPS. 

Cellulose will settle out nicely and doesn't slide that much when you put it down. We put it on pretty decent slopes without much issue.


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## jbindy (Sep 18, 2013)

I'm in Indianapolis- didn't realize I hadn't included that in my profile.

I'll have to count soffit vents and do the math to see if things are balanced or not. I don't have a continuous soffit vent, so if anything maybe I'll need to add a few vents.

Sorry if this is a dumb question, but what do you mean by XPS being in line with the kraft facing?


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## Windows on Wash (Aug 30, 2011)

That they are in line and next to each other.


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## Gary in WA (Mar 11, 2009)

Welcome to the forums!

Split level house with two attics joined may give problems... IMO, in winter, the cold soffit air from the upper attic would spill over the edge and mix with the lower attics air flow- a really cold lower attic floor; use some house wrap to separate the two attics rather than wood... due to the higher ridge line of the upper attic, I would think it would try to exhaust air from both attics in the summertime, limiting the lower ridge's effectiveness. You may get a mixing of attic air because of the higher stack height on the one *and diagonally* a lower soffit height on the other. *Best to keep them in line*, though I haven't read any studies on multiple side-by-side but stepped attics and air flow, just my opinion from my reading. Which would require separate attics.... you could try it and see if air flow problems arise (wet rafters, spots on sheathing, rusty protruding fasteners at roof deck) but then way more work to house wrap than before adding insulation. 

The knee wall foam board goes on the *attic side* (prevents wind washing) with your existing paper faced cavity fill next to drywall, same as an exterior wall. This will keep the cavity warmer/dryer and stop the wood studs from thermal bridging, cover it with required ignition/thermal barrier as per local codes. http://www.buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders

Gary


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## Gary in WA (Mar 11, 2009)

If you do add soffit venting, try to locate it close to the gutter rather than the house, for positive wind pressure= less rain/snow in attic. The best is double louvered rather than the round vents; pp. 616---- http://books.google.com/books?id=Z8...page&q=attic airflow with gable vents&f=false

Gary


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