The power of the reverse ledge

Last week we saw that the wood was delivered.  This week, our first floor deck gets installed.  In the pic above, you can see a 2x4 stud wall inside the foundation wall, and the open web trusses sitting on top of them.  This detail is called a reverse ledge (more on that later).

​Here's a look from another angle:

Getting to this point has been a long, long journey with many ups and downs.  I'm so encouraged that we're finally looking at the framing being installed.  It's a huge milestone, and generally means that things will start moving faster now.

Speaking of, this framing crew worked fast.  Like announcing-that-dessert-is-out-and-watching-my-kids-run fast.  I feel like I turned around for a couple of seconds and the trusses were done and the plywood subfloor was installed.  Here, see for yourself: 

Pretty cool, right?  The opening in the floor on the left is where the stairs will be.

Remember that reverse ledge detail I mentioned earlier?  Let's talk about what it means, why we did it, and how it helps us and the neighborhood.

Typically, the floor joists that hold up your first floor sit on top of your foundation wall.  Since the joists are made of wood, and wood has a complicated relationship with the outdoors, there are code restrictions as to how close the bottom of the joists can be to the adjacent exterior grade.  That dimension is typically around 6".  So from the dirt, there will be 6" to the start of the floor system, then the depth of the floor system itself (for us that size is 18"), then the finished floor.  So if we built our foundation and first floor system according to the norm, our first floor would be about 24" above grade, or about 4 steps up.    

I've written a few times about how our lot has a steep slope and is already near the top of a hill, which puts us above some of our neighbor's houses.  We wanted to do our best to push the house as far into the ground as possible.  The first way we did that was by planning for a 4' retaining wall along one side of our property.  The other way is with the reverse ledge.

Here's what the typical detail I described above looks like next to our detail:

(BIG thanks to my friend, John, for consulting me on the specific detail here)           .

With the reverse ledge, we essentially made our foundation wall 18" taller around the entire house.  But how does making the foundation wall taller lead to the house being pushed lower into the ground?  Excellent question, I'm glad you asked.  Our first floor framing doesn't sit on the foundation wall - it sits on the 2x4 stud wall we built inside of it.  Basically, our foundation wall is creating a barrier between the wood framing and the exterior grade.  So the 6" requirement from grade to wood on our house doesn't apply to the bottom of the floor system - it applies to the top if it.  Awesome!!!  You can see this in the sketches above.  Notice how grade doesn't change between the two details, but in the second one our first floor is much closer to it.  

Between the retaining wall and the reverse ledge, we were able to save nearly 6' of overall building height, and still build a house with 8' ceilings in the basement and 9' ceilings above.  That's what I call a win/win for us and the neighborhood.

Bye for now,
​TJ

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