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I just moved into a house with a finished attic. The second floor of the house (below the attic) is regularly 10 degrees warmer than the first floor with the AC running nearly constantly. I decided to open a wall in the finished attic and noticed that the knee walls and the floor between the knee wall and the rafters are not insulated. There is some insulation in some of the joist bays, but it's mostly falling apart or completely missing. There's also a ceiling mounted to the collar ties between the joists, and sloped wall between the ceiling and the knee walls. I have to assume based on the state of the rest of the insulation that these areas aren't properly insulated. Here is a diagram of what the cross section of the attic looks like, the red areas are where I believe insulation SHOULD be:

attic cross-section

My question then: Is there a way to go about fixing this that wouldn't require fully gutting the attic, tearing down the drywall, installing new insulation, and reinstalling drywall? I can easily insulate the knee walls and the floor between the knee walls and rafters with minimal damage, but the sloped wall and ceiling seem like they'd be nearly impossible to do without just removing all of the drywall first.

Some additional info: The attic has gable vents, soffit vents, and a ridge vent.

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    You want free flowing air between the soffit vents and the ridge vents along the roof deck.
    – crip659
    Commented Aug 15 at 15:34
  • @crip659 Right. I assumed for that baffles between the joists along the roof deck would be enough. Or should that sloped wall be left uninsulated entirely?
    – Bryan Coxwell
    Commented Aug 15 at 16:05
  • Baffles are good for keeping the insulation from blocking the air flow. You usually want living to have a full blanket of insulation. If you have baffles in place, blown in insulation is a choice(small holes in the walls/drywall).
    – crip659
    Commented Aug 15 at 16:12
  • You could add chimney vents to the roof at the top of each uninsulated kneewall spaces.
    – DelphicOracle
    Commented Aug 15 at 16:20
  • Depends on the rafter situation. You might be able to insulate and leave some airflow at the diagonal area. If insulating will block the airflow, I would consider basically adding a layer of wall (ceiling?) to the diagonal areas that can be insulated, so you can leave the rafters for airflow. If the floor below is 10º warmer than the 1st floor, what's the temp in the attic like?
    – Huesmann
    Commented Aug 16 at 13:28

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Your issue is just that you need access to the attic - and probably in more than one place. You won't need to rip out the dry wall, but you will need to frame out a little door or hatch/panel here and there so that you can work in the attic.

The schematic you have drawn is exactly how my home is finished including insulation, and others in my region that were built in the 1920s in various craftsman and tudor styles in the United States. Indeed, insulating these spaces is very challenging mostly because the overall air space of the attic is reduced significantly, and the attic is no longer one contiguous space since the interior walls finish at the collar ties like you guessed. In my home, each attic access is discreetly hidden in a closet.

Once there, blown in insulation is great because you can blow it into the walls if your home is balloon framed. Insulating a wall with blown in insulation can be achieved by tieing off a grid of rope and lining with butcher paper.

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