Framing the basement walls.

As the title suggests, this post will cover construction of the stick-framed portion of the basement walls. I didn't take many pictures during this phase of the build - I was so eager to get started on the framing - so I'll use graphics to illustrate instead. The process was very similar to "Framing the main floor walls" but with a few added details. Over-all this is probably the most complicated part of framing this house because close attention to measurement must be kept in mind for several reasons I'll get into later.

A few important things to keep in mind while framing:

• Ensure proper application of air-stop tape and gaskets prior to lifting the wall.
• If the wall section will butt up against a concrete wall, ensure that you account for the compressed thickness of the gasket when laying out the wall (more on this below).
• To tie the stick framed walls into the mud sill assembly over the concrete walls, the basement walls require a double top plate. The second top plate must be in the same plane as the mud sill assembly over the concrete walls. Measure twice...

The basic procedure was as follows:

• Each wall section was nailed together squared and braced.
• The mud sills were pre-drilled for anchor bolts then nailed to the bottom plate of the wall section.
• The bottom plate was shimmed off the floor with scrap 2x4.
• Air-stop tape was applied to the mud sill.
• EPDM gasket (BG 63) was applied to the mud sill.
• The wall was lifted into position and braced.
• 1/2" plywood sheathing was applied to the interior side of the stud wall.
• The air-stop tape at the mud sill was "connected" to the plywood sheathing.

Frame a wall section.

Square and brace.

Lay out the pieces of the mud sill, measure off the bolt-hole locations and pre-drill before nailing the mud sill to the bottom plate. Now that the bolt-holes have been drilled, don't loose track of which piece of mud sill belongs where.

Apply the air-stop tape to the interior edge of the mud sill. Leave a 2" "flap" with its backing still on underneath.

Apply EPDM sill gasket. Since these are compression gaskets, the wall should bear on the gasket.

As with the main floor walls, the tape will tie to the sheathing once it is installed. I framed my wall in short (16') sections so tipping the walls up onto the anchor bolts wasn't difficult. The mud sills were ripped 10 1/2" x 8' from standard (ACQ) 3/4" pressure treated plywood. Using a circular saw, ripping all the mud sills in advance of framing didn't take very long. Working with such short pieces was a slight pain in that there were just more pieces to lay out. When laying out the mud sill for bolt-hole locations, know where each wall section will begin and end. Otherwise you may end up staggering the mud sills relative to the wall sections which will make setting up and detailing an adjacent wall section tricky.

Application of the air-stop tape was as per "Framing the main floor walls" except of course that the tape is applied to the interior edge of the mud sill. The EPDM gasket staples easily. Where a section of wall butts up to another section, I provided an extra 1/8" of both tape and gasket. Where a section of wall butts up against concrete, a piece of treated plywood was face-nailed to the outside of the end stud adjacent to the concrete. Instead of the sill gasket I used earlier, I used a "P" gasket (BG 36) which spans a wider gap than the sill gasket. It's important to account for the compressed thickness of the "P" gasket when laying out the wall. Not close enough to the concrete, no compression and no seal. Too close and on top of wrecking the gasket, the wall won't fit. Having too tight a fit is more of a concern when closing into a concrete wall than when starting out from one.

As I mentioned earlier, the second top plate for the (stick framed) basement walls must transition into the mud sill assembly over the concrete walls. This is an important thing to remember when cutting the studs for the basement walls. The basement walls were nailed together and lifted up with only a single top plate to start then the second top plate was added after all the wall sections had been plumbed and straightened. The top of the first top plate should be flush with the top of the 3/4" plywood mud sill on top of the concrete wall. Another way to put it is that since the stick framed walls and the mud sill assembly over concrete walls both have a sill gasket, a 3/4" plywood sill and a 2x4 plate in common, the height of the stud wall with a single bottom and top plate only should be equal to the height of the concrete wall. For example, the height of my concrete walls came in at 7' 11 3/4" (95 3/4"). Therefore, to find stud length, subtract 3" for the combined thickness of a single top and bottom plate, and the stud length is 92 3/4".

Basement wall. Notice the mud sill terminates flush with the edge of the wall section.

Close up of mud sill assembly. the "flap" of tape has been "connected" to the sheathing. As with the main floor walls, the sheathing was shimmed off the floor 1/2" to avoid pinching the backing on the tape.

Mud sill at concrete step. The mud sills over the concrete walls are the subject of another post but notice how the second top plate of the stick framed wall transitions to the mud sill assembly over the concrete. Notice how the first top plate is flush with the plywood mud sill over the concrete wall. 

Mud sill at an outside corner and concrete step. Notice how the plywood extends out from the pony wall at the corner.