Construction - Concrete Work - Narrow Footing Under Stick-Built Walls

This is the third post on the concrete phase of construction.  The first post covered the excavations for all of the footings.  The second post covered the wide footing under the concrete walls.  This post deals with the footing under the stick-built walls. (Reminder:  Click on any photo to enlarge it.)

Pouring the Concrete Walls
Here's where I had to stand aside and watch.  Jamie Schulte and his crew of +/-8

Forms in place; ready for the pour.

strongbacks (sorry for the pun -- "strongbacks" are integral to the bracing of concrete forms) took two days to set up the forms, a half-day to do the pour and another day to dismantle the forms and pack them off.  The wall took 36 yards of concrete, including one yard to prime the pump on the truck.

Once the concrete guys were gone, I dismantled the forms for the footings and turned my attention to the footings under the stick-built walls.  

Pouring the wall from a pump truck

Narrow Footing for the Stick-Built Walls
Unlike the wide footing under the concrete walls that was poured largely without forms, the narrow footing was poured in wood forms entirely.  The choice of wood forms was based upon the low tolerances specified for the insulated concrete forms  that will be used on top of the footing for the foundation walls.  The specs for level call for no more than 1/4" variance.  However, we were later to find out that our best efforts at forming up and pouring a level footing still yielded a variance of 7/8" over the span of 164 linear feet of footing.

For an 8" thick concrete wall, the code minimum for the footing is 8" thick and 16" wide. The forms were set for 8" thick and slightly more than 16" wide using salvaged 1 x 8s lubricated with diesel oil.  For the +/-20' section over the conduits for the solar collector, the thickness was increased to 16". The design of the forms was taken from Chapter 7 in the book, "Carpentry & Building Construction; A Do-It-Yourself Guide" by William P Spence.  It took several days to get the forms ready for the pour.  My step-son and a friend, a journeyman carpenter, contributed 2 1/2 man-days towards building the forms.  Surprisingly, it took me as much time to wire in the rebar as three of us took to build the forms.

Rebar Configuration
As with the wide footing, bolsters with plastic sheeting under them were used to support

the horizontal rebars at a height of 4" and at intervals of 4'. The horizontal rebars were wired to the bolsters 8" apart. The latter dimension was easily attained from the 8" distance between two of the vertical elements of the bolsters.

In earlier times, a rhomboidal-shaped two-by-four was typically nestled into the top of the fresh footing concrete to create a "keyway" depression into which the base of the concrete wall locked.  That practice seems to have been abandoned in more recent times in favor of "L"-shaped rebars projecting upward from the footing to be incorporated in the wall.  In our case, the plans called for vertical rebar on 2' centers (which matched the situation in the wide footing for the concrete walls as described in the 

Since the 20' section of the footing over the conduits for
 the AGS system is essentially a beam, the forms provided
for twice as much concrete and twice as much rebar as
 the rest of narrow footing.  Notice the rebar (painted 
orange) protruding from piers

second post).  All rebar was #4, i.e., 4/8" = 1/2" in diameter.

The vertical "L-bars" could not be plunged into the fresh concrete randomly but had to be

The poured wall and the forms for the narrow footing
ready to pour; notice the deadmen behind the wall.

positioned accurately in order not to interfere with the webs in the insulated concrete forms (specs called for them to be situated on multiples of 6"). So-called "spreaders" were used on top of the form boards on 2' centers but not to brace the forms as typically done -- the forms were rigid enough without them.  Instead, the L-bars were wired to them for support in a vertical direction while being wired to the horizontal rebar for support in the other direction.  As soon as the concrete was poured, the spreaders were
removed so they did not interfere with screeding off of the fore and aft form boards as Pat is doing in the photo below. As the concrete gained stiffness, the L-bars were straightened as much as possible with the intention of making them perfectly vertical by bending them later if necessary.  Later, when the forms were set up, a few rebars had to be redirected but none had to be cut off and repositioned.

Pouring the narrow footing was definitely within the grasp of the DIYer. Five of us amateurs were able to off-load the concrete and get it screeded before it began to set -- but

Friend, Pat, and family volunteer, Archie, screed;
off-loading concrete utilizing the extra 14' of chute

barely.  And, unlike the pours for the wide footing and the wall, the forms could be reached by the ready-mix truck with a conventional chute plus, in one area, a 14' chute extension.

The bottom photo is included to show the relationship of the narrow and wide footings.  The insulation was cut away and shallow holes were made in the wide footing into which the horizontal rebar in the narrow footing fitted.  The concrete in the narrow footing cold-jointed with that of the wide footing.  

Fortunately, for the first time this year, rainfall has been, for over a month, less than normal providing the perfect weather for the concrete work.  We were able to get the narrow footings poured while the dry weather persisted.  My hope is that we can get the foundation walls up while it is still dry.

Parenthetically, the Building Director who inspected the forms before the pour, was very complimentary, saying something like "this is the way it is supposed to be done and rarely is".

Foundation French Drain
If I am not mistaken the code that Collinsville is using, requires a footing/foundation French drain -- as well it should.  In

Junction between wide and narrow footings.  Notice he
loose end of the French drain and the fact that it is
bedded in sand instead of rock.

our situation however, it is probably overkill. With the final grade behind the concrete earth contact wall severely sloped northward, an insulation/watershed umbrella under grade extending 20' from the wall plus seven French drains 10' below the floor level, it is highly unlikely that water will ever reach the level of the footing once the house is completed.  If I thought otherwise, I would not have compromised on its installation.

The one thing we did that was not a compromise was to trench for the drain next to the footing so as to keep it below floor level and slope it gradually to daylight.  (Apparently, it is not uncommon for the drain to be laid on top of the footing against the wall.)  But, that said, there were a couple of compromises.  I used corrugated and perforated drain pipe with a sock on it from the local big box home center knowing full well that the sock will not filter out our wind-blown loess soil forever, that it will eventually allow the drain to clog with silt. Moreover, instead of bedding it in clean stone, I used sand, which will work as well and almost as long as stone before clogging with silt.  

Since I plan to backfill in 5' layers and let nature do the compaction, as opposed to shallow lifts and mechanical compaction, the umbrella and final grade will be months away. Therefore, an atypical rationale for the drain was advocated by the concrete contractor. Even if it functions only temporarily, it will serve to keep the backfill drier and reduce the pressures against the wall as the backfill compacts over time.  In this context, the compromises become acceptable.

Construction - Concrete Work - Wide Footing for Concrete Walls

As described in the first post on concrete work, there are two kinds of footings -- one for the stick-built walls and another for the concrete walls.  This post visits the wide footing for the latter.

Wide Footings
The footing under the earth contact concrete north wall required a hefty footing, plus five deadmen, because (a) it is very long, (b) it will have only one "T-wall" bracing it, (c) most of it is two stories high and (d) it will be backfilled to the top. Therefore, it is a retaining wall on steroids rather than a typical "basement" wall.  The footing for it is 4' wide and 2' deep and poured directly against the earthen walls of the excavation except for the top few inches that were formed up with lumber.

Wood Forms
Salvaged 2 x 4s were used for the forms but they could not be installed in such a way as to seal off completely the gap between the forms and the adjacent grade. Also I wanted to keep the lumber as clean as possible so it could be used later in construction.  So, in order to kill two birds with one stone, I stapled 30# felt (Craigslist-bought for pennies on the dollar) over the tops of the boards and let it hang down along the walls of the trench.  In this way, the boards did not come into contact with the concrete and the gap between the forms and the grade was sealed off.  (Jamie Schulte, the concrete contractor, said the heavy felt was overkill, that 6 mil plastic would have worked as well).

Horizontal Rebar
The rebar for the footings presented two learning opportunities.  First, the "L-bars" that are tied to the horizontal rebars and protrude upwards to tie the footing to the wall should not be DIYed.  The local supplier, who cut the rebar to size and bent it, charged only the per-foot price for the rebar without adding a surcharge for cutting and bending.  The second learning opportunity was my naive choice of plastic high chairs to support the horizontal rebar in the trench -- they were a joke.  Their selection was based upon trying to avoid steel in contact with the soil to avoid the potential of its rusting, expanding and cracking the concrete. 


Bolsters
After trying to stabilize the rebar on individual plastic high chairs (talk about the domino effect -- a nudge to the rebar at the east end caused the entire rebar assembly to fall off of the chairs clear to

Good view to show the wood forms covered with felt paper
and the configuration of the rebar. Notice the outcroppings
 in the form for the deadmen.  (Click on the photo to 
enlarge it for detail.)

the west end of the trench  over 90' away). When I mentioned to Jamie ahead of time that we were using the plastic high chairs, he was not critical but did say that he used what is known in the trade as "bolsters" but what is called "continuous high uppers" on the supplier's website. They come 5' long and have to be cut to length. Professionals use gas-operated portable abrasive cutters; I gang-cut them with a metal cutting blade in a reciprocal saw.  Then, in order to obviate the potential for steel contacting the soil, I cut rectangles of 6 mil plastic sheeting to slip under each bolster.

Rebar Configuration
For the 4' wide footing three courses of horizontal rebar were necessary.  First the two outer courses were tied to the bolsters then short pieces of rebar were tied at right angles to the tops of the outer courses.  Then the third, i.e., middle course, of horizontal rebar, was tied on top of the short bars.  The bolsters were the tallest available (6") in order to raise the horizontal rebar as high as possible in the exceptionally thick footing. 

Pouring the footing with the help of a conveyor truck
and rotary laser.  The view is from the NE corner.

The vertical "L-bars" were tied to the horizontal bars on 2' centers.  The short end of each "L' rested on one of the outermost horizontal bars, passed under the middle horizontal bar with the vertical portion butting against the middle bar, thus centering it in the wall. Once wired to place, they were secure at the lower ends but were tipsy at the tops. So, another course of horizontal rebar was used to tie the tops of the "L-bars" together and keep them upright. The fact that the rebar turned the corner at the west and east ends helped to keep the entire assembly stable.

The Pour
The pour might have been within DIYer capability but I am glad that I delegated it. The

Finishing up the pour; notice the outcroppings for the
deadmen.

access to the forms was limited to the extent that a conveyor truck was necessary and, instead of screeding off of the form boards, it was poured level without screeding using a rotating laser. Altogether, 37 yards of concrete went into the footing which is slightly more than the wall itself took.

Insulation
Click on either of the bottom two photos to enlarge it and notice the pink insulation lining a small section of the outside wall of the trench and serving also as the form between the wide footing and what will be the narrow footing for the stick-built walls. The vertical insulation is critical for the shallow frost-protected foundation (post on foundation design) that is being used here and for the rest of the house.  And it should go without saying that the same configuration for the insulation was used at the south end of the footing for the west wall.

Construction -- Concrete Work - Footing Excavations

This is the first of at least a couple of posts on the construction of the footings, concrete walls and slab floor.  (Click on any photo to enlarge it.)

Earth Contact Walls
Previous  posts chronicled the amount of earth sheltering and specifically the north wall. In the end, the earth contact walls were poured in concrete which turns out to be a good decision but way beyond anything an inexperienced DIYer ought to tackle.  

Since the north wall will be supported internally by only one "T"-wall and most of it backfilled to a depth of 12', it had to be treated as a free-standing retaining wall.  The footing had to be 4' wide and 2' deep and the wall had to be 10" thick.  In addition, it had three deadmen extending northward 5' that were 10' thick and 8' high.  By turning the corner and extending the wall for 20' on the west side and 5' on the east side, the extensions also served as two more "deadmen". The final design was not that of the highly-paid structural engineer that stamped our plans but that of the experienced concrete contractor that we hired.

The engineer's design called for a 12" thick wall with an 8' footing and a fortune in #5 and 6 rebar mixed with the more common #4 rebar.  By using the deadmen and by overlapping the footing with the slab floor, as advocated by Jamie Schulte, the contractor, the wall is far more stable at much lower cost.  Our Building Director, the local permitting person, agreed.

Footing Excavations

Trenching for the north wall footing 2' deep and 4' wide

In terms of width and thickness, a different footing would be necessary for the concrete wall versus the other stick-built walls.  The footing for the concrete walls, as mentioned above, needed to be 4' wide and 2' thick.  The footing under the stick-built walls needed only to be 16" wide and 8" thick.  Due to the 2' thickness of the wider footing, the depth below floor level for the two kinds of footings was the same so all the trenching could be done at the same depth with a 4' wide backhoe bucket.  The wider footings under the concrete walls could then be poured directly against the earthen walls of the trench with minimal wood forming at the top.  For the narrower footing under the stick-built walls, the wide trench provided the room we needed to set and brace the wood forms.

Batter Boards
I used the house plans to set up batter boards, first, to guide Brian Hayes, our excavation

Mason lines and corner posts delineating stick-built walls

contractor, as he did the final grading and excavating for the solar collector then to guide the placement of the piers under the front wall of the house.  But their real value came when laying out the footings. Contrary to most of the references I studied, the batter boards had to be positioned abnormally far away from the action in order to be out of the way of the backhoe and concrete trucks, which was no big deal except for creating longer mason lines that could only be used accurately in the absence of any wind. (As an amateur, I did lose sight of the fact that the north batter boards would eventually be rendered moot by the concrete wall in front of them and would have to be relocated in front of the wall before the foundation walls could be properly sited.)

Identical trenches for wide and narrow footings; Brian uses
track loader to backfill pit between house and solar collector

I used taut mason lines running between boards and the equivalent of a plumb-bob to find the outside corners of intersecting walls and drove stakes under the plumb-bob and then a nail on top of the stakes to mark the intersections precisely.   I ran another line at the bottom of the trenches 5" inside the prospective 10" concrete walls and 4" inside the prospective 8" foundation walls under the stick-built walls to delineate the middle of the footings.  I then used marking paint alongside of the string to transfer the middle of the footings to the bottom of the trenches.

Leveling the Narrow Footings
The tolerance in footing height for the insulated concrete forms (ICFs) that we are using for the foundation walls under the stick-built walls is tighter than for concrete foundation walls poured in conventional forms -- actually a variance of only 1/4". Then, when the ICFs are set dead level on the footings and filled with concrete, the concrete could be finished flush with the smooth tops of the forms to give a perfectly level foundation throughout the house.

The reason for opting for footings poured in wood forms, as opposed to pouring directly into the trenches as is commonly done and was done for our wide footing, was for more precise leveling.  In order to accomplish it, I used the rotary laser as a guide for fastening a short piece of 1 x 4 to each corner post to delineate the exact height of the form boards -- therefore the final height of the footing itself.  Using straight boards and setting all of them exactly level with one another was extremely important in assuring a level foundation wall and, since the concrete floor would be screed level with the top of the foundation wall, assuring a level floor as well.

Parenthetically, l should add a caveat.  The decision was made later to increase the depth of the concrete slab from four inches to five to give it more strength.  The extra inch could be gained by either reducing the amount of gravel base under the slab from four to three inches or by increasing the height of the foundation wall by raising the footing by one inch. I elected the latter for reasons yet to be discussed in a subsequent post.