A Well Insulated Slab.
Prepping for the slab insulation was fairly simple. Our slab will be poured to a thickness of about 4" and the insulation is 10" of top II EPS foam. We snapped a chalk line on the interior insulation, 14" below the top of the foundation, to use as a guide for filling the foundation with 3/4 crushed stone. Slugging stone by hand is slow and heavy work. We hired Weir's Construction to take care of spreading most of the stone using a stone slinger. The slinger operator was able to distribute the stone fairly evenly. However levelling the stone base before adding the foam sheets still requires some work. Our reference chalk line for the 3/4 stone was visible on the interior foundation wall so it was easy to establish the stone height at the edge of the foundation. However, levelling the inside was a little more laborious. Assuming the top of the foundation was level (and it was because we checked it!), we strung a series of lines across the foundation from side to side. Using rakes, shovels, and a 1 m landscaping rake we levelled the stone under the line to match the height at the edge of the foundation i.e. 14". My plumber, Melvin Way, made short work of the plumbing runs. My dad and I had a few errands to run so I figured I would get pictures when I returned....but it was already done and covered!
Using a small plate compactor the stone was compacted (Photo 2-1, 2-2). As we worked we raked out high spots and added stone to low spots checking the depth as we go. After compacting it was on to foam. The slab has one load bearing wall which supports the second floor but not the roof. To keep things simple we added a thickened slab under that load bearing wall which will be reinforced with rebar. Under that "footing" is 6" of Type 3 EPS which has a higher compressive strength than the Type 2 EPS used on the foundation and under the remainder of the slab. In Photo 3-1 you can see a section of foam in the middle of the slab protruding above the 4" foam surrounding it. We snapped a chalk line across the ground to represent the centre of the thickened slab. We then laid the 6" foam (2'x8' sheets) centered on that chalk line. We first started laying 4" foam starting in either corner of the foundation, working towards the 6" foam "footing" (Photo 3-1 to 3-4). Cutting around the penetrations is the most time consuming task. I have found that the quickest way to cut these holes is to mark the position on the sheet and using a 1/2" spade bit drill a series of consecutive holes through the foam at regular intervals. Use you fist to punch out the centre! I figure its going to be filled with spray foam anyways so it doesn't have to be really neat. It just has to fit around the pipe and spray foam will do the rest. After the first 4" layer is complete, we moved on to laying the next 2" layer in the same manner. Once it came time to cut holes and fit pieces, one person did the cutting and another person moved on to laying more 4" foam. It was ended with such a beautiful day that we decided to keep working. At 8:45 pm we threw in the towels...well not really! We had no option since we had used all of our 2" EPS!
Laying the foam took about 7.5 hours and we expect another 3 tomorrow to finish laying the foam. We secured the foam for the night by laying 2'x4" lumber on top and rebar that I had on site. You never know when its going to get windy!