This is not very easy in most of the older houses we work on because the hatches and attics are too small to get rigid foam board through.
Insulate attic knee walls.
The best materials for the attic and thus the knee wall are spray foam fiberglass and cellulose.
This method can be made to work but the necessary air sealing details are demanding and fussy.
There are two ways to insulate triangular attics behind kneewalls.
If you re insulating an attic the knee walls are important.
The traditional approach is to insulate the kneewall and the attic floor behind the kneewall.
A better approach is to insulate the roof slope above the attic.
Knee walls are found in many older houses where the ceiling on the top floor is an attic or.
If you plan to insulate the roof deck of your attic then you would use spray foam or fiberglass batts.
One of the best methods is rigid foam board with sealed joints over insulation in the knee wall.
Insulating only the attic roof rafters and the walls at the end of the attic is one method some use to insulate the knee wall area underneath but carson dunlop author of principles of home.
They are short walls usually no more than 3 feet high used to support the rafters in roof construction with attic space behind them.