Site-built window pair, for high isolation.
Posted: Mon, 2019-Dec-30, 00:11
Site-built back-to-back studio window pair, for high isolation.
A quick photo-sequence on how to build your own isolation window for your studio, and still get good isolation.
These photos come from a client in Australia, who teaches drums in his studio. His neighbor's front door is also just a few meters away from this window, so he needed to get very good isolation. The window design I did for him is not complicated, and he also came up with some good ideas of how to implement it in practice. Theoretical isolation is 55 dB, and is good down to about 30 Hz. (MSM resonance at 15 Hz, predicted). In practice, it's darn good!
This is a companion article to the site built door for high isolation, and uses a simple but very effective design that I have developed for such windows.
This sequence of photos is actually from the same studio as the site-built door, so all the comments there on the level of isolation that we achieved for that, also apply to this window.
The build starts with the construction of the casing, or frame, for the window unit. For this build, there was a need for high isolation, thus thick heavy glass, so the wood has to be rather thick too. The casing is sized to fit within the rough opening in the wall, leaving only a small gap around the sides and top to allow for some maneuvering to get it in, as well as to shim it to get it straight, level, and plumb:
Similar to the way the door casing was done, here too a pair of frames are temporarily attached to each other with blocks, to keep them the correct distance apart. When placed into the rough opening, one of these frames will be in the inner-leaf wall and the other in the outer-leaf wall. Once they are firmly attached in place, the blocking is removed, and they become separate, but spaced. Note that black cloth has been wrapped around the frame, over the gap between them, and has also be glued and taped in place. This hides the small gap between the frames, so you can't see through the gap into the ugly interior of the wall, but still leaves the wall cavity insulation exposed to the window cavity, which is important for damping.
In the next image, the pair of frames has been presented into the rough opening, and is in the process of being shimmed, to get it level and plumb, and check that the corners remain perpendicular to each other (90° angles), to ensure a tight, clean fit for the glass and seals. Note that the two frames are still connected by the temporary bracing, until they are both shimmed together, to line up perfectly:
Next up: the frames have been fixed in place, and the temporary blocking removed. The backer blocks have also now been attached. Those are the thick wooden strips you can see in there, around the perimeter of the casing. The glass presses up against those, and they keep it in place. The white tape on the front face of the backer blocks is glazing tape. It's a double-sided adhesive foam tape that sticks to the blocks at the back, and the glass on the front, creating a good seal between the glass and the wood, and holding the glass in place. I sometimes also use rubber strips there, instead of glazing tape, to do the same job but without the adhesive.
Now the glass itself is ready to go in. You can see how thick it is! This is laminated glass, and for this project (a drum teaching studio), high isolation was a key issue, so thick laminated glass was needed. Here, a wooden beam has been set up to support the glass in place, just before it is raised, so it can be cleaned. You need a lot of hands to raise that glass, as it is heavy, fragile, and dangerous. However...you have to be careful here! Those "hands" need to be clean, and wearing cotton gloves for installing the glass... once it is in place, it is impossible to clean the side that faces the wall cavity... and you don't want fingerprints, smudges, or dirty marks stuck in there forever, messing up your view.... so you need to clean that glass perfectly just before it goes in, then handle it very cleanly as you put it in place. The side facing the room is fine: that can get smudged and dirty, as you can access it later for cleaning.. but the side that faces the cavity is "forever". So clean it carefully, and inspect it carefully, and use clean cotton gloves when you touch it to raise it.
You will also need some type of desiccant to put in the gap between the window panes, to adsorb any moisture in the trapped air. If you don't do that, then the glass can fog up on the inside surfaces under some climate conditions, and perhaps even have condensation droplets forming on the surface, then running down the glass... leaving permanent dirty marks! So it's important to get the desiccant in. Silica Gel is good, and there are other types too. You need to calculate how much to put in. It's not a lot, and it's not expensive, but you do need to get the amount roughly right: too much could potentially cause the wood to dry out excessively, and not enough means... well.. misted windows with condensate tracks! I don't have photos of the desiccant going in, unfortunately. We missed that here.
Here the glass has been raised into position, up against the glazing tape, and is being held in place with some more temporary bracing while the front blocking goes in, and the caulking is done.
This is a view from the other side, taken in the middle of the frames, showing how it looks after a bead of clear caulk has been placed around the rim where the glass meets the backer blocks. Applying that caulk is a very tricky job, as you do not want to get marks and smudges on the glass as you work, and you also want a clean, smooth, even bead, so it looks good. The reason for the caulk is to have an extra seal: for high isolation, never trust just one seal. Even though the glass is resting in glazing tape (one seal), pressed up against more glazing tape on the front face of the backer blocks (seal #2), and will have yet more glazing tape on the front trim blocks (seal #3), I also like to caulk the glass to wood joints hear (seal #4) and on the front as well (seal #5). Of course, you can't really caulk the back of the other pane when it goes in on the outer leaf, so that one can only get 4 seals, but the inner one has 5 seals. The caulk also has much more mass than the glazing tape, so it helps to keep the mass consistent across the entire leaf.
Now the second pane of glass goes into the other frame, on the outer leaf. Once again you can see the temporary bracing holding the glass in place while the front rim blocks are added, and you can also see that this pane is sealed in with rubber, not glazing tape. This is an external window (faces the wind and the rain), so it needs something more substantial than glazing tape to resist the elements better. It also can't be caulked on that inner face, so no extra mass from the caulk. But rubber has plenty of mass. So this side is a bit different: rubber, instead of glazing tape, for the seals. Apart from that, the same process was used to raise it into place, and hold it there until everything is finished.
A view of the final finished window from the outside, with the front blocking and trim in place.
Another view from the outside, showing the complete window. (The marks are on the outside of the glass, not the inside).
And finally, the finished window from the inside, with all the blocking and trim in place, and the wall also completed (the wall is built "inside out" in this case):
So, there you have it! A very simple method for building and installing a site-built high-isolation window. As I mentioned above and in the article on the doors, the total isolation for this studio is around 55 dB. The studio owner teaches drums, so he sometimes has two drum kits going at once in there! Hence, the need for good isolation. As you can see, it is possible to attain these high levels of isolation even when you build your own window, if you do it carefully and based on a good design. It's also a LOT cheaper than buying a commercially made studio isolation window!
- Stuart -
