So I live in Canada, where winters are cold, and where there's not much soil above the bedrock. I would like to build a sturdy structure for an existing "shed" (in fact a 100-year old former stable or something) that's about 4m by 5m (12'x 15') and that's kind of collapsing. Currently, there's no real structure to speak of: it's only 2-inch thick boards piled up and nailed together, with small posts (like 2x4s) in the corners, resting on slabs of cement or something, each one about half as big as a basketball.

There's only about 60 cm of soil above the (granit) bedrock, and I was considering pouring concrete "posts" to rest directly on the bedrock, then using them as a basis for my structure (placing a metal plate on top that I can put a wood post on). My neighbour says that in the spring the meltwater will accumulate over the bedrock and may damage the concrete posts. Also, I would guess the ground probably freezes down to the bedrock in winter.

Any thoughts about this? alternative solutions? Note that I don't want to take the shed apart because it's 100-year-old wood and I think I would inflict substantial damage to it.


Question: Can I wire 2 ceiling fans, 5 ceiling spot lights, and 3 closet lights on a singe 15 amp circuit?
Answer: There should be no problem putting it all on a single 15 ampere circuit. Likely in the worst case scenario, each fixture would consume ~100 watts. That would be using large 52" fans, and 100 watt bulbs in each fixture. With the 10 fixtures, that would be 1000 watts (10 * 100 = 1000). A 15 ampere 120 volt circuit can provide 1800 watts of power (15A * 120V). 

More realistically, you're going to be using lower wattage fixtures, especially nowadays with CFL and LED bulbs becoming more common. Here's some calculations based on various wattage devices. 


10 devices @ 75 watts each = 750 watts.
10 devices @ 60 watts each = 600 watts.
2 fans @ 100 watts, and 8 lights @ 60 watts = 680 watts.
2 fans @ 75 watts with 3 60 watt blub light kits, and 8 lights @ 100 watts = 1310 watts.
2 fans @ 100 watts with 3 100 watt bulb light kits, and 8 lights @ 100 watts = 1600 watts.


Since it's a 15 ampere circuit, you'll only need 14 AWG conductors. Unless there's a specific reason you're using 12 AWG instead, which is also fine.