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How to Create Windows in Earthbag Buildings
Questions answered by Kelly Hart

Q: This is a question regarding building an earthbag dome - is there a limit to how many windows you can include in the structure?

A: There are various ways to introduce windows for lighting into earthbag domes. Basically any circular or arched shape can usually be accommodated, including a triangle with one of the corners pointing upward. As long as the windows are well-constructed and integrated into the structure, there is no limit as to how many you have. One way to get a lot of light into a space is to use a glass door of some sort.

Q: I have some discarded rectangular double glazed windows I'd like to use in the structure. Any reason why I couldn't fit a wooden lintel resting on the bags over the top of the window or do window openings have to be arched or triangular?

A: If you can calculate that whatever lintel you use can support the weight of whatever is above it, this would probably work. Arches, circles, and pyramid shaped triangular openings are inherently more stable and more likely to last over time.

Q: Can you put a glass circular skylight to finish a dome structure?

A: I see no reason why a circular glass or plastic dome skylight couldn't be placed at the apex of an earthbag dome, especially if there is a rigid metal frame that can be integrated with the bag structure somehow.

Q: I have a question on how you installed the cart-wagonwheel as a window in your earthbag house. Did you use a form of some kind and after removed that and installed the wheel? Or did you build around the wheel? The reason I ask is because I have doubts if the wheel has enough width to support the bags that go over the wheel and that still have to harden after tamping.

A: I did not use a form for this, but I was fortunate enough to find some very wide-rimmed old wheels that were able to support the bags directly. With smaller width wheels it might be possible to place a wide steel plate that curved over the top of the wheel to support the upper bags (the sides and bottom are not really a problem for thinner rims).

Q: We see Khalili's method uses at times to cut into the surface of the bags to accommodate windows, ventilation pipes and or even doors. I wonder what your experience has been with this when working with "Scoria filled bags".

A: Khalili can get away with this mainly because he only uses hardened adobe in his bags. Loose material would not hold its shape if cut into, and all kinds of problems would likely happen. But even with the adobe, I think this is a poor alternative to carefully planning where openings should be in advance and forming the bag walls around these. He suggested this with his "emergency shelter" where careful planning may not happen.

Q: Can I use square windows? I wanted to use tires, but I would like to have bigger windows.

A: Yes, you can use square windows, but you will need to provide a very strong "lintel" over the top of it to support the weight from above. Probably the easiest way to do this would be with reinforced concrete, which is commonly done in Mexican construction. But there are other ways to make the windows using arches of earthbags, or larger circular-shaped forms rather than tires (which would not be my first choice for this anyway), or even using a triangular shape, with the point going up.

Q: I would like to utilize skylighting as much as possible for natural light. I also want to install an exhaust fan to remove heat naturally from the inside. Would you utilize a non motorized exhaust fan or a motorized one. Which would be more of a benefit ? I would hate to force cool air out of the space with a motorized unit.

A: It is a fairly easy matter to place circular skylights at the apex of a dome, and these can be openable to allow ventilation. The question of the best strategy for venting a structure is complex. I tend to like solutions that have no moving parts if possible. I have never built a wind chimney, but I understand that they work pretty well. There is one built into the dome complex here. On the other hand, to assure that the interior temperature is as consistent as possible, there is definitely more control when you have a powered vent that is thermostatically controlled. Then you would not be sucking out your cool or heat unless you wanted to.

Q: I am really wanting to have good windows in my house, since I want good passive solar. I know you have all those large panes on your house. Did you get them new or were they used? Are there any creative ways to get good windows without paying an arm and a leg, so to speak?

A: Most of the windows that I used in my earthbag house were seconds, rejects, or extra windows that I bought at local glass shops. Most such shops have a bunch of glass set aside because nobody picked it up, or they were the wrong dimension or something, and they will often sell them very cheaply. The way I set them into the exterior plaster, all they needed to do is cover the opening, so the exact size was not so important. I saved a lot of money this way.

Q: Did you just set the entire window setup on top of the bags and that secures them in place? The windows don't need anything else to hold them in place?

A: I placed an inclined window sill of a 2X10or12 on top of the bags to shed water and frame the windows above.

Q: I read that in a dome I should not use windows over 2' wide. True? My window forms are made in a lancet curve and are 3'x4'x 4' deep for the non dome areas. Should I adhere to the 2' rule as there will be 3 in the bedroom and one in the small computer room?

A: Windows do create weaknesses in any structure, so the smaller the better...but I have not heard of the 2' rule for domes. Your standard 3' windows may work fine. However, where you have windows placed right next to each other, as with the two in your bedroom, these might be smaller. With so many windows in your kitchen, you will need to be especially careful to reinforce the spaces between them with vertical rebar and good connections to the window frames.

Would I simply drive rebar into the columns between the windows?

Yes, connecting the columns of bags between the windows with vertical rebar will help stabilize them.

Q: Have you made a tire window before? I attempted to make a window using glass bottles, some grout and a tire. It turned out ok, but it's really heavy. What are some Eco friendly windows that you have done?

A: No, I've never used a tire as a form for making an earthbag window, but I know that others have done this. We used both old farm equipment spoke wheels as permanent forms (they had rather wide rims) and also standard culvert couplers to frame circular windows. You can see some pictures of this here.

Q: Is it OK to have a lot of windows and or sliding glass doors around the structure with just the bags or do I need to do a hybrid of some sort.

A: The placement of windows and doors needs to be carefully planned so that they are fully supported, either through buttresses, rigid framework, connection to bond beams, etc. You can find some information about all of this here.

Q: Will 10mm round bar work at openings instead of reinforcing rods (rebar). It's not riffled so will go in more easily and is cheaper than reinforcing rods (rebar).

A: Such round bars should also do the job.

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