How High Can You Build an Attic Stem Wall For Stick Built Rafters
In an unvented attic you can order high heel trusses in order to get enough insulation depth over the tops of the exterior walls but what is the best way to build a “high heel” stick framed attic roof?
Now, I plan on building a second storey “floor” on top of the main floor walls (with sheathing on top of the joists to act as the air barrier) so if I want about 20″ of insulation over the tops of the exterior walls is it best to build a 20″ tall stem wall on top of the attic floor at the eaves or is there a better way of elevating the roof rafters?
The one thing I worry about is the “hinge point” that would exist between the bottom plate of the stem wall and the sheathing on top of the second floor deck. Could outward force from the roof rafters cause this little wall to push out at the top and if so how could I brace it?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
rockies63,
The height of the wall doesn't matter at all. It's the same at 10" as a full storey wall.
The only stick-framed roofs that don't need to deal with the lateral loads from the rafters are those framed directly on (and attached to) the attic floor. For all others you need to either:
- Use rafter ties in the bottom third of the span.
- Use a load-bearing ridge beam.
There are two other options as well.
You can build taller main story wall that includes the height of raised heel and balloon frame the ceiling lower down from where the rafters would rest. This avoid the hinge point as the studs are now continuous. Air barrier continuity is harder though.
The other option is to extend your ceiling joists past the wall to your facia board. Instead of setting your rafters onto the top of the wall, set it onto the end of the ceiling joist. You can then use a piece of 2x on edge ripped to height right above the wall to carry the vertical load from the roof down. This is how commonly older homes here are framed and you can get a lot of insulation into the space if you have reasonable overhangs.
Akos,
Good points. I should have said "the two most common solutions".