Construction - Screened Porch Floor

This post focuses on the next-to-last phase of the concrete work, viz., the screened porch in front of the house.  Remember that you can click on any photo to enlarge it for a closer inspection.

Footings and Foundation
I over-excavated the soil next to the house to the level of the foundation footing and then sloped it downhill in order that the insulation/watershed umbrella can installed on top of the footing and sloped downhill enough to drain well.  In the process, the soil under what will be the concrete floor for the 14' x 16' screened porch on the front of the house was also over-excavated.  In order to compensate for the over-excavation, the footing for the porch foundation was much taller than it was wide on the downhill side which complicated forming it up for the pour.

I mimicked the forms we used for the 8" tall footings under the house foundation by using

Forms for the footings

some of the same salvaged 1 x 8s and the same lightweight braces. As a result, we almost had a blowout because the bracing and the 1 x boards were too weak and barely able to hold the weight of so much concrete on the tall downhill side.  Consequently, the footing after the forms were removed looked pretty amateurish. 

Poured footing; notice the bulge just beyond
the corner due to a near blow-out

I thought I had learned my lesson and made sure the forms for the short foundation wall on top of the footing would be, if anything, over-engineered.  Wrong! Despite robust 2 x 4 framing for the plywood form walls, we almost had another blowout.  As soon as we started the pour, a wall started bulging due to weakness of the spreaders that tie the two sides of the form together across the top.  Instead of using 1 x 4s and two 6d nails on each side, I used 1 x 2s and one 16 ga 2" nails from a nail gun. We had to stop the pour while I  added several 1 x 4s in the most susceptible areas and re-nailed the existing 1 x 2s with 6d nails.   If I were to do it again, I would use 1 x 4s and regular nails for the spreaders throughout and 2 x 4 stakes for all of the braces because they can be driven with a sledge hammer to a greater depth than the 2 x 2 stakes that I drove with a heavy hand mallet.  Fortunately, the wall did turn out to show a little less amateurism than the footing.

Poured foundation 

Backfilling
Before the slab can be poured, the backfilling must be continued until the cavity inside the footing and foundation is filled

Backfilled with sand to the height of the footing prior to
installing insulation

to within 5" of the finished floor level in order to support a 5" thick slab.  Also the foundation wall must be insulated in order for it to function as a shallow frost-protected foundation. Then insulation must be used horizontally under the floor as part of the watershed/insulation umbrella. Accordingly, I used sand to fill the cavity to the top of the footings in lifts (layers).  The sand was not wet enough for proper condensation so I hosed it down before condensing it with a manual compactor.  A good overnight rain finished the compaction.  In retrospect, I should have borrowed a friend's plate compactor for better compaction with less effort.

Insulation As Part of the Insulation/Watershed Umbrella
Over the sand, I layered mostly EPS but some XPS foam board following the

Horizontal and vertical insulation starting at the level
 of the top of footing

recommendations of Hiat, i.e., 4" thick for the first 8' out from the house then 3" thick for the next 4' followed by 2" thick. This 4-3-2 pattern was also used for the garage floor as described in the next post. For the rest of the subgrade umbrella on all sides of the house, the pattern changes to 4-3-2-1 in order to reach out a full 20' from the house. 

In order to satisfy the requirements for a shallow frost-protected foundation, the porch foundation must be insulated on both sides.  Inside, I merely stood EPS against the wall. For the outside, I will eventually install expanded polystyrene insulation board 2 1/2" thick supported by metal drywall track and covered with

Form for cantilevering the slab outward
with rebar to support the edge

parged cement board.  (This process was previously discussed in the recent post on the first retaining wall.) For a finished look, the slab will will be cantilevered out over the concrete of the foundation by at least 3" in order to cover the insulation and parged cladding. To this end, I built a peripheral form that would allow the slab to overhang the wall by the width of a 2 x 4 and controlled for height of the slab by way of  2 x 8 sideboards.  In order for the floor to drain southward, the sideboards were installed at the same height as the house floor next to the house then angled slightly downward such that the floor will fall 
1 1/2" over a distance of 15'.

Final backfilling, ready for 6 mil plastic and concrete pour

Slab Floor
After the insulation was in place, I covered it with a thin layer of sand to isolate it from the wind and to buy some time while another rainy period passed.   When the weather permitted, more sand was added in lifts and each lift hand-compacted until nearly flush with the foundation wall, thus leaving space for a 5" thick slab.

Completed slab for screened porch with cantilevered edge

Six mil plastic sheeting was fitted over the sand on the day of the pour. Jamie Schulte, the contractor that had previously poured the wide footing for the tall concrete north and west walls, the walls themselves and the slab for the house, returned to pour the porch floor first then to pour the forms for raising the height of the east wall of the garage.   The next day he came back to pour the garage floor.  The garage pours are the subject of the next and last post on the concrete phase of construction.