Ok, I'll mention a few mishaps and missteps that occurred before the Erskine Group was on site for their part.
1. As this is going over a garage which is 24' deep, there was a fairly long span to consider. The architect originally called for glulam or steel (12" steel or 24" glulam). During the back and forth, I told him about the weight of the sand (Dennis told me to confirm the floor would support it, since we weren't on a slab). He took into account the weight of the sand and in the stage area and then reduced the spacing of the floor joists. So, you would think all would be golden.
Just before we ordered the steel beam, I reached out to the structural engineer that was signing off on steel the local fabricator was installing and asked if we could go to a shallower beam, because the one spec'd by the architect was going to force us to either furr down around the beam, or drop the entire garage ceiling about an inch to keep it flat. So, I wanted to make sure that the engineer new about the sand and started telling him about the room, and he put on the brakes and said he needed all the details.
So, I sent him the full build spec's -- double drywall, serenity mat, extra layer of 3/4" on the floor, riser with 2" of wood decking, sand, 300lb door, etc., etc. Bottom line, not only could we not go to a shallower beam, but he spec'd a beam 3 times as heavy (in total weight of steel) as the original beam and a price to match. He said the original beams (three of them), when you figure in the thousands of pounds more (I don't remember the exact amount, but I think including the sand, 7,000-10,000 lbs or so) than a normal room would have, plus 8+ bodies and there was a chance for far more deflection than is desirable. Enough that you could pop sheetrock screws in the garage ceiling or notice a bowing (I was never clear on whether it was an actual safety issue).
This is likely more my fault than the architect. I never actually forwarded the architect the home theater plans from Dennis, because at the stage the architect was working on the framing and room layout (blueprints), it was just an outer dimension for the home theater with a note that detailed plans would come from home theater designer. I went back to him about the sand, but should have forwarded him the full set of plans, so he could have taken into account DD, serenity mat, multiple layers of 3/4" flooring, etc. So, most of this is on me.
So, moral of that story, if you are working with an architect or putting all of that weight on a non-slab, get it checked out and be sure to give them ALL the details.
2. Anyone that has read many of Dennis' posts, he doesn't recommend foam in the walls of the home theaters. If you have foam, you need to keep 2 - 2.5" of the stud bay clear to make sure there is room for fiberglass bats behind the hat channel. As I wanted to make sure things were air tight, I worked with the insulator to spray closed cell foam in the home theater walls (I'm using open cell elsewhere, but open cell takes up more space for same R value and air permeability rating). I went through with him no less than four times, and three emails how crucial it was that we spray 3-3.5" of foam, leaving at minimum 2" of the stud bay clear. I was out of town when it was sprayed (and the owner of the insulation company didn't supervise the spraying) and when I checked it out a couple days after they foamed, it was a mess. In some places, it was nearly up to or past the face of the stud. In other places, it was a good 4 - 4.5" deep, leaving 1 - 1.5".
We talked to them about it and they said they would take care of it. As early as last Saturday, two days before Steve was due to arrive, I was on site with the owner and he said, "don't worry, we'll get it taken care of." I go by the house on Monday mid day, they had done nothing and I ask my contractors to see if they can figure out a way to cut out the excess and then I called the foam guy. He says the stuff is like rock once it sets up and virtually impossible to cut out. He tell me to furr out 2" and he will cover the cost. I tell him that isn't acceptable, because we were already VERY tight on space in the aisle between curved seat and column that even losing 2" wouldn't cut it. So, my guys spend the next four hours trying every tool they have or can buy (hand saws, reciprocal saws, planers, etc.).
Finally, they were about to go buy some grinding brushes and masks and try to grind it out and I finally caved and told them to furr it out. Poof, there went my curved seating. The reality, I was probably too tight for curved seating. I had already lost 2" of my walkway (inch on each side) when I decided to switch to 2x6 wall instead of the 2x4 the architect called for, but how it happened with the foam pissed me off. Long term, I think I will be happier with the straight seating, as I will have about 30". Even as spec'd (without foam mishap or change to 2x6 wall, we only had 2' at the narrowest, but I had checked that, and that was ok when just walking past the column (considering that's to the arm of the chair and the backrest is further away). However, when you are that tight, dropping down to 1' 10" or a little less just was too much.
Moral of the story. If you decide to use closed cell foam, be on site and supervise and do it early enough that you know you can have time to force the sub to fix it if they go too thick. Open cell? No problem, you can tear that out with your hand, as we did in the angled portion, where they didn't put as much closed cell as they were supposed to and instead went with 3.5-4" of closed and then filled the 7.25" joist space with open cell. Glad they didn't do what they were supposed to here, so we could easily fix it.
Here's the room the night before Steve from Erskine Group showed up.