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Site-built windows / direct glazing recomendations

blamus20 | Posted in General Questions on

Hi,

I’m in the process of building a new construction residential home in climate zone 5 at 6000ft – Boulder, CO. With conditioned floor area at about 3500sqft, I need to install 20 or so fixed picture windows approx 4’x6′ on the south side of the house (mainly greatroom/dining room).

Design wind load is 131mph and over all air infiltration rates of <3ACH50 need to be achieved. The building department does NOT allow 100% vinyl windows – they need to be fiberglass/wood/aluminum/fibrex with U factor <0.30. Site built windows are allowed but this is where it gets complicated. I’m looking for different ways to achieve this glazing. From my research I have found that it has been a popular practice to achieve this by framing patio door insulated glazing units directly to the walls. The IGUs in question should be superior to normal window glass – these are 1/4″ tempered glass on each side with 1/2″ argon gap in between. LowE 366 coating from Cardinal. I’m aware that this was done in the 70s for passive solar homes (and I’ve read on GBA how passive solar is more trouble than its worth – but this is more for aesthetics and views) I have read through the very few posts on here concerning this type of glazing, but I have a few specific questions: 1. Are site built windows durable from your experience? Have you seen many site built windows fail over time? Or does this method actually work well? 2. I notice that even though the thought is to frame the raw frameless glass directly to the walls, you are actually building the frames out of wood, in the form of stops, which also require weep channels. Should I expect maintenance issues down the road as compared to say manufactured windows made of fibrex? Should I be concerned the wood rotting and failing in years to come? 3. attached is the framing details I sourced from the glass supplier. Is that the way to do it? Any further recommendations/corrections? 4. From speaking with the building department concerning site built windows, they said I can do it, but will need to work with a HERS rater – instead of going the prescribed path, because site built window (frames) are not factory rated, even though the IGUs are. They did not mention the need to have the framing details approved by an engineer for designed wind loads. BUT, from your experience, do you think my site built windows can achieve such wind loads (131mph)? 5. Are site built windows more difficult to air seal effectively compared to manufactured windows? Do you think I will have a problem achieving <3ACH50 because of these windows? 6. Will it make a difference in installation difficulty which wall assembly I choose? (SIP or double wall or 2×6+ex.foam) These IGUs are a tiny fraction of the cost of other windows that I’m allowed to use – aluminum is out of the question (cant meet U factor requirement), Fiberglass is way too expensive. I want to avoid wood for maintenance reasons (but site built frames are of wood anyway?). The only thing that comes close are anderson 100 fibrex. With the thinnest glass, not tempered, I can get anderson 100 at twice the cost of these Cardinal tempered IGUs. I assume I should expect site build windows installation cost to be higher – but not significantly? My priorities are – Durability, maintenance, satisfies code(ACH and windload), Budget, energy. Would you recommend site built windows at half the cost with better glass? Or am I going down the wrong path completely?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Bernard,
    I built many of these in the 1970s. I would never build them as shown in the pdf document you shared.

    Each fixed window needs a frame. I built mine with pine jambs and a pine head, but a white cedar sill. When you assemble the frame, you cut dadoes in the jambs for the sill. The dadoes are sloped for drainage -- about 5 or 10 degrees. The sill extends out to form a drip, and there is a kerf on the underside of the sill so that water doesn't curl around back into the wall assembly. The sill should have exterior ears at least as wide as the jambs.

    Assemble the frame with waterproof glue and stainless-steel screws.

    You can install stops on the interior and exterior of the jambs and head. The sill gets an interior stop, but on the exterior you use a short (about 2 or 3 inches long) piece of angle aluminum as a stop. It goes in the middle of the fixed window, held in place with one stainless steel screw into the sill.

    You use butyl glazing tape between the stops and the fixed glass.

    The interior stool is installed later. It should be level, not sloped.

    Most of my 1970s era fixed windows are just fine. A few developed failed seals, so I had to replace the glass. The frames are still good.

  2. GBA Editor
    Martin Holladay | | #2

    Bernard,
    Making your own windows isn't rocket science; it's woodworking. Doing it right takes time.

    People buy windows instead of making their own for a reason: to save time. If you value your labor, site-built windows may be more expensive than purchased windows.

    I was hired in the early 1980s to build wood-framed storm windows for a homeowner who liked the old-timey look of the storm windows of his youth. I did it. They took a lot of time, and they were heavy. If you're patient, you can build anything. I wouldn't want to build storm windows like that again.

  3. blamus20 | | #3

    Thank you martin,

    I will be contracting out the windows installation (hopefully to someone who knows what they are doing!). I'd assume there would be an extra cost to constructing and installing the frames of these site built windows - but I don't know how much. If its like e.g. extra $150 per window, I'd just spend that extra money on manufactured windows.

    The IGU supplier assured me that this is not rocket science (and so did you). But I'll still need to find someone who has experience doing this. Not all framers/window installers are comfortable doing this. If only you were up for hire :-p

    I'm also interested in people's general experience and opinions about them. My architect isn't very comfortable with the idea, and the general contractors I know also advice against it (speed + simplicity = money)

    And the fact that its discussed so little on the internet (and most discussions are pre the 90's), makes me wonder if its a good idea in 2017.

    best regards

    Bern

  4. [email protected] | | #4

    Bernard,

    I would also add that you need to make sure that the sealed IGU's are appropriate for your elevation.

    It isn't uncommon for IGU's at 6000ft to use capillary or breather tubes to equalize pressure between the airspace and the outside.

    Although tempered lites aren't likely to break due to pressure differential at 6000 ft, you could be putting a strain on the IGU seal and it could fail within a few years, if it wasn't manufactured to be used (while sealed) at your elevation.

    Also, and emphasizing, keep the edge of the IGU away from the wood in the frame, especially at the bottom of the window. You need to use narrow and thin (preferably plastic) spacers between the glass edge and the wood of at least 1/16" to avoid water from affecting the IGU seal.

    Letting the IGU rest on a couple of 1/8" thick spacers on the bottom edge wouldn't be overkill.

  5. blamus20 | | #5

    Yep, the IGU have tubes, so the argon is just for show.....

    I'll discuss all these extra installation details with the installer when it comes to that. But I'm still on the fence whether I should do it or not......I just don't have a way to judge the "extra risk" vs cost savings.

  6. Jon_Lawrence | | #6

    Bernard,

    What do you think your cost will be to make the windows yourself?

    As a data point, I have priced out large (50 - 80 sf), fixed, aluminum clad, triple pane, R-7 windows from many of the European manufacturers and they are coming in around mid-$40's/psf. That is before tax and delivery.

    I have not priced out Alpen, but they are in your backyard, might be worth checking out.

  7. brp_nh | | #7

    A couple thoughts...

    Sounds like you'll be contracting out the site built windows (if you go that route) and are working on a budget, that might not work out well. Unless you can find and afford to hire a really top notch contractor, standard windows might be a safer option.

    We used Alpen fiberglass windows for our house, even their lower line 525 or 525s series would be a great fit for your climate and goals.

    Saw your drawings in the other thread about walls. Have you considered potential over heating issues with that much east, south, and west glazing? The roof may provide some shading in the summer for the upper windows, but you're going to get a lot of sun, possibly too much, even in winter. You should look into this and consider reducing the amount of windows or provide better shading.

  8. blamus20 | | #8

    That is pretty much my conclusion at this point - originally the IGU supplier told me that its pretty simple and most carpenters can do it. But having seen the amount of details to get perfectly right, it might not make sense. I chewed on martin's descriptions for a while and then found this video:

    https://www.youtube.com/watch?v=z50BGPuPPl4

    They did a good job showing me whats involved, and at 7 minutes they show the results and I love it. I bet you those are the exact IGU's I have been referring to that came from surplus patio doors.

    I could get these IGUs for $150 each but once I factored in the extra installation details, and then imagine having to do all that 12' up in the air on scaffolding, I imagine I won't be saving money at all.

    I still think the "frameless look" is better than the anderson 100 fibrex I'll have to use, and the andersons won't be 1/4" lites nor tempered. But I think it will be a safer bet to just go with a simpler approach, which often means a less costly approach.

    The over heating concern from the windows is on my mind. But the windows are there for aesthetic and view reasons. My architect has convinced me that using other means like blinds to mitigate the over heating is worth it. I won't lie, I built many different models with less glazing and it just doesn't look as good. I know at GBA looks isn't a particularly high priority, but it is important and kind of personal. If its all about energy I'd not have any double height space at all and have half the windows (and I did request that at an early design stage - it made the space look like an apartment from the inside).

    One option I'm considering is using a heatpump hot water heater which will help cool the house. Don't know if thats a good idea in the cold winters though.

  9. GBA Editor
    Martin Holladay | | #9

    Bernard,
    The details shown by Matt Risinger's woodworker are slightly different from mine, but they are high-quality details. What the guy calls a "nose-piece" is a little bit like a sill -- he says that the nose-piece is "sacrificial."

    I prefer the sloped sill to be under the IGU, not butted up to the IGU, because I think like a roofer. But the details are good, and the sacrificial piece can be replaced in the future if necessary.

    1. Expert Member
      NICK KEENAN | | #11

      I know this is a long-dead thread, but I'll try to revive it. I think it's curious that Risinger puts the removable stops on the outside, most windows have them on the inside. Thoughts?

      When putting the sill under the IGU, do you have any stop on the outside? A stop with weep holes? It seems like if you don't have an exterior stop the window is at risk of blowing out, with a stop it's going to be hard to make sure that any water that gets between the glass and the stop drains to the exterior.

      Also, Matt looks so young in that video!

  10. sribe | | #10

    Would you mind posting an update on what you wound up doing? In particular, who were you planning on buying the IGUs from? (I'd like to know that even if you wound up going the Andersen 100 route instead.)

    I have an old house with window walls built in this manner, and am looking at upgrading from the current (probable) U0.3 windows to something more efficient. I don't like how much glass I'll lose by putting in any windows that I've found. (Tall & narrow, 32" width, so 2.5" frame loses >15% of glass, and I'm afraid gives kind of a "porthole" effect.) So now I'm considering going to the same thing as current: bare IGUs framed in place, but triple-pane.

    Well, actually, I'm considering re-framing to go wider and get less interruptions in the view, and getting rid of the somewhat dated style of interior trim. But that's another story.

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