Step 4: Assemble the frame

Once all the pieces are cut to the rough sizes, start with the bottom piece of OSB, 16" x 32" (B). Cut 4 pieces of lumber at 31-1/2" to make the corners. Then drive a screw into each piece of lumber from the OSB side to fasten the corners to the board, aligning them with the corners. Then you can notch out the corners of the piece of Dense Shield that will be placed on the bottom of the frame, on top of the OSB. The Dense Shield is glued to the OSB. You can also fasten the two 16" x 16" end pieces (D) to either end of the frame, as well as attach one of the 32" x 32" sides.

Then you can notch out the corners of the piece of asphalt board that will be placed on the bottom of the frame, on top of and glued to the Dense Shield. A screw was used in each corner of the layered pieces to help keep them together.

Then you can now take a 32" x 32" (A) piece of the Dense Shield and asphalt board and fit them to the interior-side of the frame by cutting off the material that is taken up by the corner pieces, roughly 5" in this case. Then you can trim the excess material off the top of the Dense Shield and asphalt board to make them even with the OSB. Liquid Nails was used to glue each layer together as well as a screw in each corner.

So far, you have something like this, where you have an OSB frame with layered Dense Shield and asphalt board on the bottom and one of the sides.