Attic Insulation question

With regards to traditional attic insulation, assuming an unconditioned attic above 2nd level, I know that it is highly recommended to properly air seal and insulate the attic floor and not between the roof rafters for several reasons. So in a 1.5 story house or cape, where there is an unfinished attic area behind the knee walls, why does many “experts” and building scientists stat that the ideal way to insulate these areas is to:

  1. insulate the knee wall and floor (which I agree and understand)

  2. and insulate between the roof rafters in the sloped ceiling (doesn’t this contradict the above? By insulating the knee wall and floor, you’ve in essence, have separated the conditioned living space with the unconditioned attic area behind the knee wall. I would’ve thought that you wouldn’t need to insulate between the roof rafters in these areas.

Any thoughts would be highly appreciated as half the homes in inspect with such areas have insulation between the roof rafters, and I wouldn’t want to call it out if that is the “preferred” method of insulating these areas.

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One or the other not both.

“1. insulate the knee wall and floor …
2. and insulate between the roof rafters in the sloped ceiling”

To me this means insulating the vertical short wall leaving the space behind open for ventilation, and insulating between the rafters of the sloped ceiling, which is actually an exterior wall on an angle.


Good article.

Thanks. That’s what I thought, As others have mentioned, either insulate knee wall and floor OR the entire sloped ceiling if you plan on bringing the small knee wall attic into the thermal envelope of the home, but NOT both. Thank you all.