Hi all:

I have finished the frame for my riser and am trying to figure out the best way to do the top.

I (foolishly) made the frame (using 2x6s) exactly 6'x8', with joists every 12 inches on center. Having seen how others do it, I have decided I want a 2" lip around the edge but it seems that the plywood/TB OSG sheets are all 4x8, so to do the top it looks like I will need multiple sheets.

Three questions:

1. It seems people suggest using two layes of plywood/OSG to make the top, so I am planning to do so as well, using two layers of 3/4" wood. Some people suggest the use of roofing felt in between the layers - how come?

2. Should I nail the top(s) in to the joists or screw them, or does it not really matter? I plan on carpetting the top once I am done.

3. Because of my size issue, to get a 2" lip all around, and given the standard 4x8 size of the plywood/TB OSG, I was planning to make each layer as follows:

a) left piece of 38x76
b) middle piece of 24x76
c) right piece of 38x76

with the inner ends of the left and right pieces meeting the 24" piece on center at the respective joists.

Does this sound right?

Many thanks for all of your help - this site is a tremendous resource!

I won't comment on the spacing, whatever works. The felt is to stop possible squeaks, and I would use screws which are less likely to come loose with a lot of shaking or vibration such as the bass in the theater produces. Do be sure to stagger your seams when you put the second layer or alternate the direction of them. Hopefully you already know not to attach the riser to the walls or floor.

You can add the lip as and after thought. You just rip a 2x4 to what ever depth lip you want. Screw to the edges with 4 inch deck screws every 8 inches or so.

The 2x4 takes to routing a rounded edge a lot easier then the plywood.

Clarence showed me this technique on his build and it's plenty strong. Not going to crack off.

http://i23.photobucket.com/albums/b393/bigmouthindc/DSC00475.jpg

http://i23.photobucket.com/albums/b393/bigmouthindc/DSC00535.jpg