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DIY airtight window?

Trevor Smith | Posted in Green Building Techniques on

Hello,

I am building a small (140ft^2) meditation cabin. It will be used a couple times a day for meditation and every few weeks for overnight stays. I would like to keep it heated to some constant, above freezing temperature even though it is only used a few hours a day. Therefore I want to air-seal and insulate.

My question is with windows — I would like to have most of the sides be windows (two of the sides will each have two, 4’x8′ windows — for a total of 4 windows). To keep costs low I am experimenting with the idea of making my own windows using a single pane of glass. I think this would work for this use case, because, as it is not used often, we could have thick thermal curtains on the inside, and the outside will have shudders that could be insulated.

I understand the R-value of single pane glass is about 1. My main worry though is about air sealing. If I want the house to score around 0.6 ACH50, what kind of gaskets/techniques can I use to:

1) create the window frames (eg does standard glazing work?)
2) allow the windows to open. I don’t have a strong preference as to if they slide, cantilever open, etc. I want to know if I can make them in any way, to keep airtight.

Is this a pipe dream? Too crazy of an idea?

Thank you all for the great articles and questions, this is such a helpful resource!

Trevor

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Replies

  1. Expert Member
    Michael Maines | | #1

    Trevor, do building codes apply at your location? They usually require buildings that will be inhabited, even for short periods, to be built to code levels of building thermal envelope performance.

    If they do not, or if you can convince your code enforcement officer that you don't need full insulation, you can certainly build your own windows. You can buy thermal glazing in custom sizes from a glass shop; it will save energy and also be a lot more comfortable when it's cold out. The operation style is up to you. Just be aware that it takes longer and is trickier than you might think. Fine Homebuilding has had articles on building your own in the past.

    With such a small building it will be nearly impossible to reach 0.6 ACH50, and there is no way you will get there with homemade windows unless you really know what you're doing. But you can probably get to 1.0 or 2.0 ACH50, which is still pretty good.

  2. Trevor Smith | | #2

    Michael,

    Thank you for this helpful reply.

    This structure is small enough that it falls below code requirements here (<200ft^2).

    Gotcha on the "takes longer than you might think".:) It's a labor of love. I feel confident if we go slow that we can make the window high quality -- I just didn't know about the air-sealing. Now that you've answered that -- all systems go.

    One followup if you don't mind -- if we are shooting for 1.0-2.0 ACH50 what should I use for my WRB? I'm in climate zone 6a.
    I was originally thinking of doing exterior mineral wool insulation (thanks to the great info on GBA) with a rainscreen then cedar cladding. I was originally thinking of an exterior air-seal+WRB using a peel & stick membrane but if I'm shooting for 1.0-2.0 maybe taping (air-seal) + tyvek housewrap (WRB) is a cheaper option and will do the job just as well?

    Thanks!

    Trevor

    1. Expert Member
      Michael Maines | | #6

      Trevor, there are a lot of WRBs that can work well, depending on the situation. The usual choices for high performance homes are Pro Clima Mento (or now Adhero), Siga Majvest (or Majvest SA) or Henry Blueskin. But Tyvek, Typar or even tarpaper can also work; they're just a step down in quality. Avoid low-cost perforated WRBs. Zip sheathing is another budget-friendly option.

      If you go with exterior insulation, mineral wool performs well but I would consider wood fiber insulation such as Gutex; it's easier to work with and has a much smaller carbon footprint. I like using Zip sheathing when the exterior insulation R-value is high enough to prevent condensation on the interior--in zone 6A, thats at least 32% of the R-value on the exterior, but more is better.

    1. Expert Member
      Michael Maines | | #7

      Trevor, I didn't have a specific article in mind, I just recall them running articles occasionally. Window technology has come a long way and if you want operable windows you'll have a much easier time getting a good air seal with swinging windows, as opposed to sliding windows. Have you seen European-style tilt/turn windows? They have huge frames, triple gaskets and seal like a bank vault door. American casements and awnings may be fine, just not as high performance as tilt/turns.

  3. Expert Member
    Akos | | #4

    I've done some DIY fixed windows. It is not a lot of work but at the end of the day is not much cheaper than budget vinyl ones.

    As other have said, best starting point is get a dual pane IGU from a window shop (this makes a world of difference in comfort/energy) and some quality glazing tape. Any wood that you use on the exterior should be knot free. Air sealing is not hard, after the IGU is installed, just spray foam around the perimeter of it before installing the interior trim.

    Make sure the bottom exterior glass stop and sill is sloped and you are not creating any areas where water can pool.

    Air tight+operable+DIY, not impossible, would be a big stretch though.

  4. Expert Member
    Deleted | | #5

    Deleted

  5. Expert Member
    Malcolm Taylor | | #8

    User ...323,

    Two other considerations.

    - Except for a few specialty products, manufacturers don't offer operable windows anywhere near 4'x8'. it's just too hard to build a frame stiff enough or supply strong enough hardware. You might think about making them fixed, and having some smaller ones that can open

    - Building codes typically require that glazing that is close to the floor be made of tempered or laminated glass for safety. I know codes don't apply, but it's something to consider anyway.

  6. Jamie B | | #9

    I agrees with akos, I'd stay away from trying to make them operable. I've once wanted to site build windows, so I've done some thought on it before. but the opening part is really where the complexity comes in.

    Also, from a carpentry standpoint. It's not about going slow, it's about redoing it many times until you get it right, because as the phrase goes, "you don't know what you don't know". just my spitball initial thoughts of a 4x8' window/door, I'd be concerned about the weight of it. You'd have to think about it like building a door. So thicker hardwood frame, actual door hinges that are rated for the weight, then a silicone gasket around a door stop with an interior cam latch to press it tight against the seal.

    But I think the final product could turn out better if they were fixed. you can build your frames and it's simply using glazing silicone for the glass to wood connection and it will certainly be airtight. Depends on your carpentry experience and what to what level is acceptable to you.

    Sounds like fun to me though.

  7. Expert Member
    Zephyr7 | | #10

    You could try building the window with acrylic or polycarbonate. It’s easier to work with plastic than glass if you’re building your own stuff. You could also solvent weld either of those plastic materials to build up your own multi pane IGU with good seals. Polycarbonate is the easier of the two materials to work with, since it’s less prone to chipping when you cut it.

    I’d price this out against some of the less expensive commercial window options (Anderson 100 series for example) before you get too far along in your project. You may find it’s actually cheaper to just purchase commercial windows.

    Bill

  8. Trevor Smith | | #11

    @Michael - yes the tilt/turn windows are very cool. I have not worked with them. It does look like replacement hardware is easy to come by. I will look into that. I will also look into the wood fiber insulation. From a glance it looks to be a good deal more expensive than rockwool but I like that it is made of wood.

    @Malcolm, @Akos, @Jamie B - I will consider making them fixed. As you all suggest this would be substantially easier to do. I could then purchase smaller crank windows that were less expensive due to their smaller size.

    @Jamie B - good points about thinking of it like a door build. Agreed that doing things again and again, and again :) is the way to get there.

    @Zephry7 I will look into that as well thank you for the suggestions!

    Thanks all!

    1. Expert Member
      Malcolm Taylor | | #12

      Trevor,

      As Jamie B said: Sounds like a fun project. Good luck with it!

  9. Walter Ahlgrim | | #13

    I have no Idea of your woodworking skills, but building operable windows that keep water out, are air tight, thermally efficient and will not rot away, very well may be among the most ambitious home project imaginable. This project puts you in the club with the guys that build own airplanes or ocean going sailboats.

    I think your best bet is source a few used patio doors and build like this shed made from old doors.

    If you are someplace where it gets below 0° and thinking you will capturing enough solar energy to keep the room above freezing, I think you are dreaming.

    Walt

  10. James Howison | | #14

    I recently used windows from these guys on a similar build: https://shedwindowsandmore.com/

    Their operable ones are small, but they have some really cool 12"x72" (and longer) that look great turned vertically. They fit inside a stud bay and could provide both visual interest and useful light.

    https://shop.shedwindowsandmore.com/12-x-72-transom-double-pane-vinyl/

    1. Expert Member
      Malcolm Taylor | | #16

      James,

      Are you sure it can be turned? It is advertised as transom window, and most vinyl windows are designed with vents on the bottom.

  11. Keith Gustafson | | #15

    Non insulated glass in that large a size in that small a building is a huge mistake. You will never be comfortable. The thermostat might say 65 degrees, but the glass will be sucking the heat out of your body.

    I would use less glass and use insulated glass. Shop around for the best deal.

    Consider using the panels from a sliding glass door. Find one used or at a discount/building salvage place

    If you end up with single pane glass, trust me, you will never use this space in cold weather

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