Replies

1. GBA Editor
   Martin Holladay | Jan 23, 2016 06:06am | #1

   Hal,
   You need to assemble a team. This team needs (among other professionals):

   1. An architect with commercial construction experience.

   2. An engineer with commercial construction experience.

   3. A G.C. with commercial construction experience.

   4. An excavation contractor with commercial construction experience.

   5. A wealthy client.

   Good luck.

2. 
   user-4243359 | Jan 23, 2016 04:09pm | #2

   Wow! This will be doable but very costly.
   First, I agree with all of the points that Martin detailed.
   In response to your question on a geo-technical evaluation, soil borings will likely be adequate, less disruptive and less costly. Your design engineer will likely be able to arrange this. Prior to committing to the expense of the borings, your engineer should consult with bedrock maps and well-drilling logs to predict the elevation of bedrock and groundwater to assess the feasibility of you plan. I don't have knowledge of your area but in most locations 20' is likely to intercept bedrock. The expense of bedrock removal will add woefully to an already very costly plan. The hassles of lowering groundwater would be a non-starter in my opinion.
   Most importantly, you should be aware that a 20' deep subterranean structure will be incredibly costly. Add the desire to park vehicles on top (pre-cast spancrete ceiling/floor) and waterproof the entire structure and you will likely be facing far more expense than I suspect you are imagining.
   I assure you that the thickness of cast-in-place walls and the necessary reinforcing will astound you. Martin is right too that this will be a commercial job. Residential contractors will not have the forms or expertise to build these walls or set the spancrete floor.
   Is there another location on which you can build a conventional frame structure above or mostly above grade for the court? If so, you will save tens of thousands.
   Don't misunderstand, your proposal is feasible just very, very costly and in no way comparable to a garage over a conventional basement. If you should move ahead with the project your engineer may wish to explore using precast, prestressed concrete panels for the wall system. I have used this type of system for wall heights of 12'. I don't know if they are available for the heights you need but if they are, they might be less costly and quicker to install.
   Good luck and ponder this carefully.
   Ed

3. 
   dankolbert | Jan 23, 2016 04:28pm | #3

   An easier question to answer would be "What complexities don't exist in building a racquetball court under the garage?"

4. 
   user-5706305 | Jan 23, 2016 05:42pm | #4

   Bedrock Map

   http://www.maine.gov/dacf/mgs/pubs/online/bedrock/bedrock11x17.pdf

5. Expert Member
   MALCOLM TAYLOR | Jan 23, 2016 07:15pm | #5

   Hal,
   As a designer my first question would be: is there nowhere for this at grade on your site? Over the years I have had several clients requesting squash courts and my experience is that these uses are usually not maintained over time. A room which could be repurposed makes a lot more sense than a submerged space for which another use is unlikely.

6. 
   Chaubenee | Jan 23, 2016 09:28pm | #6

   Instead of getting too technical, I will explain why it is hard to build such tall concrete walls. For every foot you add in height to a concrete wall, you dramatically increase the pressure from the soil that is pushing against the wall. Even the difference in height going from 8' high to 9' high is a huge jump that usually necessitates going from an 8 inch thick wall to 10 inch thick wall (depending on soil conditions.) so as you increase height you need more thickness, more steel, more footing, more pilasters, beams that span across to provide tension, etc etc. My mason can build you the walls to that height because he has forms that can be stacked in varying heights atop one another, but he would certainly decline because as you build this tall a wall, there is then the issue of bracing it so that it does not topple. And it is a risky proposition. After he poured my foundation at eight feet, he went anf poured a 13' tall one in Albany, NY. Anything is possible from the standpoint of engineering and work, we all know that. But it is going to be VERY VERY VERY expensive and finding a contractor outside of a major metro area to do it will be a challenge. If you are able to pay the price to engineer it, getting a capable contractor to do it without raping you will be an immense challenge. Good luck.

7. 
   rocket190 | Jan 24, 2016 12:09am | #7

   I just worked on a commercial project where a 48' x 52' structure was built and the basement walls were 20' deep. The walls itself were 16" thick. The groundwater level at this site was about 11' lower than grade, so sheet shoring was required to help hold back water. We also had eight dewatering wells running constantly. Because of the groundwater. The bottom foundation was poured as a mat. It was 30" thick with double rows of rebar. The foundation walls also had a tremendous amount of rebar. On such a deep "bathtub", determining groundwater depths is critical. The buoyancy can easily exceed 1,000,000 pounds of uplift. If your walls and structure aren't heavier than the buoyancy you might need to add concrete to avoid the court flavoring out of the ground.

   On the flip side, in good clay soils pouring a 20' wall would be expensive but not particularly difficult.

8. 
   STEPHEN SHEEHY | Jan 24, 2016 02:20pm | #8

   Joe- you said:

   "But it is going to be VERY VERY VERY expensive..."

   I think we need even more "VERYS." But anyone contemplating an indoor racketball court can probably afford a VERY, VERY, VERY, VERY, VERY, VERY expensive project.
   Maybe add one more VERY for contingencies.