Tip #5

How To Construct A Double Pane Studio Window

Anyone with trim carpentry experience can build their own studio window if they plan correctly, take their time, and follow these steps. You will need at least one helper when installing the glass. This example project assumes the window is set in 2'' x 6'' wall with multiple layers of drywall, Sheetblok, etc. on both sides. Procedure is the same for single wall of any thickness. When installing window in two separate walls, there will be separate inner blocks for each pane.

Tools needed; hand saw or circular saw, sanding block or orbital sander, drill, screwdriver, level, utility knife, plane, etc.

A note about parallel vs. angled glass; Although angled glass is common in professional studios, we generally suggest parallel panes for most applications. This is because the air gap between glass is more important to isolation than an angle is. Unless the panes are several inches apart, the angle would probably not be large enough to make any difference, and would lessen the air space. If you prefer to angle one or both of the panes, there are additional tips at the end of the directions.

These instructions assume you are installing two panes of glass, in parallel, with the largest feasible air gap in between. Use very high grade pine with no knots, or finish grade poplar, for best results. Do not substitute plastic or Plexiglas for real glass.

1. Window opening should be roughed in level and plumb, and all surface substrates (drywall, etc.) finished flush with framing.

2. Line the entire inside of the window frame with Sheetblock. Use an adhesive, not nails or staples.

3. Install first casing around entire window frame, on top of the Sheetblock. This should be 1'' x6'' or whatever ¾'' stock is needed to cover inside of frame all the way from one finished surface to the other. Trim so it lands exactly flush with wall surface on both sides. Attach with adhesive and large finishing or casing nails. Fill in all the cracks and voids with silicone caulk.

4. Add another layer of Sheetblok on top of the first casing. Now you are ready to fabricate the actual window mounting system, comprise of inner and outer ''blocks'' or ''rails''.

5. If the panes are to be parallel, you can now order your glass. Carefully measure the inside dimensions where the glass will go. Order your glass smaller than the opening; 3/8'' less on both the width and height. This will keep it from actually touching the casing on all edges except the bottom. The type and thickness of the two panes of glass are up to you. Use laminated panes (2 of them of course) if possible; regular plate glass will work, but not quite as effectively. Whatever glass you choose, make sure the two panes are different thicknesses (3/16'' and ¼'', ¼'' and 3/8'', etc.). Plan on installing the thicker glass closest to the loudest sound source. If you have a live room and a control room, the thicker glass goes toward the live room. If you are going for a very quiet booth for voice-over work, and want to minimize outside sound, then put the thicker glass on the outside of the booth. Pay the extra few bucks to have the edges dressed by the glass shop, to make handling easier and safer.

6. Each interior surface (top, bottom, left, right) will end up with 3 pieces of ''one-by'' stock; an inner block and two outer blocks. The inner block determines the size of the air gap, and should be as wide as possible, but leaving enough width on the outer blocks to attach securely to the framing. If your wall is on 2'' x6'' framing, the middle block can be made from 1'' x3'' stock. The outer blocks hold the glass firmly in place, and are removable, in case glass needs to be cleaned or replaced.

7. Attach the inner block all the way around. Make sure it is dead center in the wall, and perfectly plumb. Use wood glue, and finishing nails or screws. Drill a 1'' hole in the bottom block for silica gel. Lightly sand all the pieces before installing.

8. Make all of your outer block pieces the same way. The width of these pieces can be determined by measuring from the middle block to the edge of the casing, and subtracting the thickness of the glass and 2 layers of weatherstripping to be used (leave the rails a little large, to allow for compressing the weatherstripping). I suggest the black, self-adhesive, closed cell, 3/8'' thick type. The outer blocks can land beyond the first casing, but keep this to a minimum, because you are going to have to come back and plane them flush after they are installed. Cut all pieces and dry fit, leaving the appropriate gap where the glass and weatherstripping will be. This will give you an idea about how they line up with the first casing.

9. Pre-drill mounting holes in all outer blocks, just big enough for drywall screws. Countersink for screw heads if desired. If you don’t countersink, you can use dress washers, or plastic screw head caps. Each piece should have a screw 1 ½'' from each end, and one every foot or so in between. We are using screws instead of nails, so you will have the ability to remove/replace glass if necessary.

10. Sand and paint (or stain) all pieces, including the inner block already installed (or cover with a strip of Studiofoam to control standing waves. This will be your last chance to access the inner block. Drop the silica gel into the predrilled hole before covering). Assemble all the materials needed for the final installation of glass; screws (2'' coarse drywall), weatherstripping, glass cleaner, etc.

11. Clean both sides of both panes of glass thoroughly. Check for smudges from all angles.

12. Install the self-adhesive weatherstripping on face of the middle block, on the side that is getting the heavier glass. It should be just flush with the corner all the way around. It should go all the way into each corner. Press it on firmly, and don’t stretch it – or it might start coming off at the most inopportune time. Also prep the pair of the outer blocks that are cut to go corner to corner on the side you are working on). Add an additional strip of Sheetblok on the bottom casing, where the glass is going to set. It should be just wide enough to start at the inner block and extend beyond the inner weatherstrip by slightly more than the thickness of the glass. It cannot be wide enough to come in contact with the outer block when it is compressed to its final position.

13. With the help of your assistant, carefully and slowly set the bottom of the glass in and tilt it up into position. Center it so the gaps on the left and right edges are equal.

14. While your helper holds the glass in place, carefully set one of the outer blocks in place, slightly compressing the weatherstripping. DON’T OVERCOMPRESS. Just enough to make it snug the entire length. Install the screws. If using a power drill, protect the glass with a towel and BE CAREFUL. It may be necessary to set the screws in enough to hold, then go back and do a deeper pilot hole for each one, one at a time, so it isn’t so hard to get them in all the way.

15. Finish up the rest of the outer blocks on the first pane and repeat all steps for the second one. Before installing the second pane, clean both inside surfaces one last time.

16. Plane all of the outer blocks down to be flush with the first casing and the wall surface. Now you are ready for trim.

If you are installing the glass at an angle the procedure is the same, except all blocks will have the appropriate angles. Make sure you have plenty of room on all outside blocks to set the screws through the casing and into the studs. To maximize the air volume between panes, you may want to frame the window with wider stock than the rest of the wall. (for instance, adding a 2'' x 8'' frame in a 2' x 6'' wall, before starting the casing procedure). Another alternative is framing with two separate sets of blocks, reducing further the sound transmission between panes. When angling panes, you should wait until the inner blocks are set before measuring for the glass, as the angle will change the vertical dimensions slightly. We also suggest angling panes up, rather than down (so reflections are directed at the ceiling.

The photos show rail preparation for an angled-glass installation, with the wider gap at the top (client’s request) and a couple of shots of this type of window.

1. Window opening, roughed in
2. Inner and outer rails, dry fitted
3. and 4. Inner rail installed
5. and 6. Examples of final appearance

1) 2)
3) 4)
5) 6)