We started construction. There's been about 2.5 months in prep, but just three weeks with crews on site -
Starting Tuesday Jan 10th:
Moving out, finalizing drawings (ongoing!), disconnecting electricity, gas, water, phone, etc. Salvaging all we could form the old bungalow, sourcing specialty materials, building window and door bucks for the forming, and getting the detached garage ready to act as an onsite workshop and office. The house was standing until Jan 10, 2012, when the following took place:
- Week 1: demolition and excavation - Details: removal of soil: $600 per load (including excavation). For haulage only, the soil removal is $275/load - one load is one full size dump truck), 35 truck-loads to remove - building foot print was increased only about 500 SF, but we also went about 12" deeper into the earth. Garbage - everything other than masonry/concrete. The excavator crushes the building into the basement until everything is in small pieces - then scoops it out into the garbage bins. The 40-Yd bins are $125 delivery/p/u plus $75/ton dumping. Concrete/masonry recycling is $275 flat fee for 14-yd bins. Excavator on site for 3 days.
This phase was pretty standard. Expensive to remove soil!
Terraprobe performed a soil verification just an hour after the final excavation with the entire pit open (3-page report - $450 plus tax). They found our soil strong enough to hold 200kPa at SLS and 300 kPa at ULS. It is Glacial Till.
Straw was spread in the pit Thursday evening. - It is lovely and easy to work with at this point.
Surveyors came on Friday to drive in these 3/8" pins marking the corners of the building. They used standard practice, marking the exact corner of the building, without any offset. Normally, the pins end up inside the footings, and the footing forms are placed outside these pin locations. In our case, this caused a problem because our footings were to be exactly in line with the outside edge of the building - so the pins were in the way. Note also the surveyors don;t really provide any height reference - they expect the footings to be placed on the bottom of the excavation, and levelled using bubble levels. As we would be making very precise footings, we didn't like this idea. We used a laser site-level instead.
- Week 2: Footings - Form and Pour - Cold weather this week - we worked in minus 5C to minus 10C weather - one day it was minus 17 C wind-chill. The 30 bales of straw kept the earth in the pit from freezing. We added another 8 bales later. Footing forms took extra time - we did it ourselves due to the careful design of the wall-to-footing intersection. As the basement walls would be in-line with the edge of the footings, the forms had to be executed precisely along their outer edges. The forms for the outside edges of the footing would stay in place after the footing pour. They were anchored to the footing using the Zamac T-35 female anchors at 8' OC. Wall forms could then rest on the footing form, which was 2x12 material, so only 1.5" wide. These had to be precisely in the right place, and also very firm. We felt this was necessary because we wanted to form a key at the outer edge in the footing to hold the walls against earth pressures, and also to improve water sealing (dowels would have been enough to hold the wall, I think). There is no concrete floor slab to hold them, as in most regular basement foundation structures.
The floor slab was to be placed between the footings rather than on top of them. This, and the thick footings (11.25") will allow us to place insulation under the basement sub floor, while the basement floor joists rest upon the footings. We seemed to have done a good job forming the footings, because there were absolutely no issues in placing the 10' wall forms later on. This seems an ideal way also to form lot-line footings. We used higher-strength (25MPa) concrete all around to improve water-tightness. I also feel drainage of water down along the basement wall is improved by having the footing and wall edges in line. The seem between wall and footing is easily bypassed and the water can flow right down to the weeping tile. Weeping tile will be placed on both sides of the exterior footings, draining to a deep sump pit in the bottom of the elevator shaft. Drainage of the basement is of utmost importance since the airtightness requirements will mean a permanent subfloor will be needed in the basement, as far as we can figure out for now. - And we don't want any water under this floor.
|Footing Forms made using 2x12's. Ext footings are 26" wide to accommodate the double basement wall system. Ext surface of basement walls will be inline with the outside edge of the footings.|
|Female concrete anchors to hold outer footing forms after the pour. Note also the continuous 2x4 key at footing edge. 2x12 forms.|
|Exterior Edge of completed footing. 15M Rebar Dowels at 2' OC placed against the 'key'. The 2x4's that formed the key have been removed.|
Week 3: Concrete Basement Walls - Form, Pour, Strip, Spray, and Apply Weeping tile, membrane, etc. It took a crew of 8 the full day to place all the 10' forms, place the ties, the rebar and window bucks, and straighten and brace the forms, and place the scaffold. Next morning they oil-sprayed, did some final straightening and bracing and poured all the concrete (4.5 trucks - 36 Cubic meters) in 3 hours. We cast electrical outlets into the walls - I looked long for plastic boxes designed for casting in place. I did find them (Kwik-on is one), but they needed ordering, and weren't cheap. The normal stuff to use is what contractors call 'slab-boxes', which are just metal boxes without holes - all knock-outs instead. Cheap, but not good, IMO. I came up with my own instead.