New to basement excavating, starting one this week. I understand overdig and floor height using benchmark, but how do u figure where to set the elevation for the footings for the garage rectangle? Is it a certain height off the basement floor?
the blueprints/plans should tell you all of that.
It depends on a couple of things. In this part of the world, there aren't that many totally flat lots to build on. So, sometimes the garage might be even with the first floor, sometimes it might be at the same level as the basement floor, and sometimes it might be a few steps higher or lower than one of those floors. Regardless of where it is in relation to the rest of the house, at least across the door, you've got to consider frost depth. What's considered to be frost depth in your area? You always want your footers to be below the depth where frost may occur, because it can heave the footers up and crack the foundation. Here, we always go at least 36" below finish grade. That's the main thing. On a related note, if you have a "walk out" basement, meaning that the yard on one side of the house is at basement level, you also have to keep the footer at that location below frost depth. I've seen some pretty crappy prints. It's best to know for yourself whether they make sense in the real world.
i've discovered that should things end up in a courtroom, it's better to have archi/egineer's stamp than my guesstimate. i can always question them before i dig.
Are you doing the concrete work ? If not then the concrete contractor should have the responsibility to establish the elevations for that particular job.
Thanks for replys. Prints are few and far between on residential excavating here. Engineers set benchmark and write on stakes the dig dept of basements. I have backfilled 100's of basements but never paid attention to garage footer placement. I want to kick myself for not looking. I want to say always seemed about half of the basement walls. I hate learning as I go, but always have had to. I at least want to have an educated question when I ask so I don't sound too much like an idiot
I would have the general contractor set your elevations, and give you something in writing that specifies the benchmark elevation relative to the various footing elevations if you do not have plans to go off of. It might pay to become familiar with Storm Water Pollution Prevention Plans (SWPPP) as well, and hopefully the general will have the SWPPP in his name if one is necessary.
Around here the frost line is 48" deep, so we go to the top of the finished foundation height, measure down 56" and cut at that level for garage height, enough space for a 8" footing and a 48" wall. if the lot has a slope or something steep on the garage side they might use 8' walls all the way around the garage, just gotta see how the grade lays out. Also, not sure how its done in your area, but around here we strip the topsoil off the garage area, then dig about 4' wide trench where the walls go, that way you don't have a bunch to backfill with sand for the garage slab.
We have done 100's of these and the way digger described it is spot on. Anywhere that doesn't have 3ft of cover after final grade gets a frost footer. Also the lay of the land can effect what you bulkhead height will be.