I am replacing the front deck on my house, and I was hoping to get advice on two things relating to the foundation.
First, I am replacing the old stairs (consisting of on-grade P.T. 6×6 treads with stone-dust fill) with standard 2x P.T. stringers with treads and risers. After clearing away the old stairs, the frame supporting the new stairs and landing will be founded directly on bare limestone bedrock, which has a bit of a slope to it. How do I connect the frame to the rock?
Second, I need to place new piers, which will all sit on bedrock under sand backfill (placed against the house when it was built about 50 years ago). The house is on a sloping lot, so the sand is about 5 feet deep near the house, and is about 2 feet deep at the edge of the deck. The piers will be at the edge (with 2 feet of sand cover) and mid-span (about 4 feet of sand cover). Frost depth is 4 feet. Should I expect to clear away most of the sand (wheelbarrow brigade), or do you think oversized post-holes will hold up long enough to get the piers in.
Q 1 is the one I’m most interested in. Q 2 is really just to get an idea of the fun I have in store.
Any insights welcome
Umberto Eco, The Island of the Day Before
Replies
For anchoring the frame to the rock, there are several options, and others will have their solutions as well.
Assuming you are using risers, cut a 2x spacer to fit between the stringers (it would prevent the stringers from rolling, and keep them spaced apart) and anchor it to the rock using sleeve or wedge anchors, epoxy set all-thread, or even a Ramset. Drill the holes in the rock using a rotary hammer as opposed to a hammer drill; it will go a lot more smoothly and quicker. I usually use this method over Ramsetting depending on the concrete condition and location.
You could also anchor down a 4x4 standoff and set the stringer in the standoff, and fill the left over void with a 2" cut off from a 4x4. You could also Ramset an angle bracket to the rock and nail off the bracket to the stringer.
Lots of different options, some might be more practical than others, depending on your situation.
For Q.2, I recently tore down a covered porch and built a free-standing replacement, and the soil was sandy. Three of the eleven holes had to be hand dug, and the tops were funnel shaped and close to 3 foot in diameter due to the sandy soil gravitating to the bottoms of my holes. It might be best to just clear away the sand to begin with, rather than fighting to up to the time to backfill.
Good luck.
"I am the master of my fate, I am the captain of my soul." Invictus, by Henley.