Excavation for the Tire Bale Home
by Leonard Jones, P.E.
Preparing for Excavation:
- Determine the location of the building on the ground and mark it with wooden stakes at the corners. Make sure you measure across the diagonals to make sure that the building will be square. Put in some "offset" stakes so you'll be able re-locate the corners after excavation. Also mark out the locations of the front, middle and rear E-W tire walls.
- Next, determine the above ground elevation of the front wall tire bales from the plans and set a stake with its top at that elevation.
- Then, rent or borrow a contractor's level and leveling rod and set a temporary bench mark far enough away from the construction area so it won't be disturbed. This elevation will arbitrarily be called 100.00 ft. All other elevations will be set as plus or minus from this elevation. (see sketch)
- Next, from the plans, determine the elevations of the rough floor for both levels.
- Now lay out a 10' grid on the ground with wooden stakes and - using the contractor's level, determine the elevation of the ground at each grid point. Subtracting the rough floor elevation or the front wall bottom tire bale elevation from the ground elevation will tell you how much soil must be removed at that point to get down to the elevation you need... Mark this amount on the respective stake for the machine operator's use. Be sure to extend the excavation 3-4 feet beyond the outside of the tire walls so that there will be room to install the vapor barriers and drain pipe.
- Finally, again using the contractor's level, determine the point in front of the building where the bottom front wall tire bale elevations intercepts ground elevation. This is the front limit of excavation.
Excavation:
- Start with the upper level and have the operator excavate down to rough floor elevation for that level. Extend this excavation out to where it intersects with ground level. He will probably have to cut a small access way in the side of the excavation to get his machine in and out of this level... After he gets this area cut down level, have him ditch around the sides and back to accomodate the drain pipe per the drawing. In the areas where the tirebales will sit, he should cut the earth down as close as possible to the elevation where they will sit.
- Now have him excavate the "shelf" at the rough floor elevation of the lower level. Same process as the upper level, except you don't need to accommodate a drainage pipe in back of the middle wall. Be sure to have him cut down to grade for the area where the tire bales will sit.
- Now have him excavate in the front wall area at the elevation of the bottom of the front wall tire bales. Extend this excavation out to daylight sloping slightly downward for drainage...
- He'll probably have to do some clean-up digging to get the sidewall tire bale areas right.
- Finally, there's other misc. digging to be done. Ditches for drain pipes, water, electrical, septic tank, etc. need to be dug at this point.
Final Site Layout:
- Using the offset stakes, re-locate and re-stake the building corners. Double-check the corner-to-corner dimensions to make sure they're OK... Also double-check across the diagonals (REALLY IMPORTANT!!!) to make sure that the final layout is square.
- Erect a batter board (see diagram) at each side of each tire wall - far enough out to not get disturbed while you're setting the tire bales... Pound in the vertical stakes, then level the horizontal piece front-to-back at the elevation where the top of the first course of tire bales is supposed to go. You'll probably need the contractor's level again!! Use clamps to hold the horizontal piece to the verticals to start with - then, when you have it set exactly - attach it with construction screws. When you have the batter boards set for the front wall, stretch a string line TIGHT across the top of the horizontal piece - making sure that it goes exactly over the top of the corner stakes... Clamp the string to the batter board, then use a plumb bob to check that it's over the top of the corner stake. When you have it located properly, drive small nails or construction screws into the top of the horizontal. piece to permanently locate each string line... (this will let you take the string down and put it back up in the same place whenever you need to during the job. Start with the front wall and work your way to the back. The front string line is the baseline for the entire building layout, so it has to be EXACTLY right... See any good carpentry book for detailed instructions on batter boards...!!
- Now erect batter boards for the east and west walls. This is the same as described above, except that the string lines attached to these batter boards will not be level front to back. These will be used primarily for alignment of the E and W walls and for final location of the building corners. Once you have this done, check EVERYTHING again - especially across the diagonals of the building.
- Once you have completed this, you should be able to locate everything in the building using offset distances from the string lines... ...And you should be ready to start placing tire bales...
Additional Considerations:
- Don't worry too much about the exact location of the drain pipe around the building. Just make sure that it is below the bottom of the bottom of the tire wall in back of the building, that it stays below the tire wall as it continues around the sides, and that it is ALWAYS sloping downhill to daylight - or to a "dry well" if the slope, etc. won't let you get out to daylight...
- Excavation is a very inexact art... A good backhoe operator can get to about +/- an inch of the desired grade under good conditions. If everything turns out exactly right, your project will qualify for a "then a Miracle happened" award. Most of the time you will be left with some additional hand excavation or hand backfilling to get things to the exact grade you need... (like where the tire walls will be located!!) Depending on the situation, one or the other may be easier... Decide which up front and shed no tears while you're pushing the shovel and/or wheelbarrow...
- If you decide to over-excavate a bit and backfill where necessary, it's usually easier to backfill with sand or small gravel. It's easier to level up than typical soil - it doesn't have large rocks in it, and it compacts easily... You'll need sand and/or gravel anyway - so just figure in a couple yards extra for misc. backfill when you order it...
- Give some thought - before your operator starts digging to where you want the extra dirt (spoil) located. You can save yourself a lot of time, effort, and cost by putting this stuff in the right place. Remember that you will need some of it (but not all!) for backfilling, leveling, etc. And maybe some more for berming around the outside of the house... Also remember (IMPORTANT) that it's a lot easier to push a wheelbarrow downhill than uphill.
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