Glazing Options to Meet Code Requirements
We’re building a new home in Portland OR, with most windows south facing. There will be generous overhangs over the windows, so we expect full shading in the summer, and partial shading in the fall/spring.
The code requirement for Oregon is U < 0.27. Our window supplier is proposing using Marvin Essential with Low E3/ERS glass. Looking at the specs, that gives us a window SHGC of 0.19 and VLT of 0.43.
These VLT numbers seem a little low; I’m afraid we’ll always feel “in the dark”, especially in the PNW climate. But the window dealer says that there are really no other options other than E3/ERS.
I’d really appreciate any suggestions on how to meet code without the windows being too dark.
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VT (or VLT) of 0.40 or higher is indistinguishable from clear glass, at least from the interior; there can still be a reflective hue on the exterior, depending on the coatings, but it's pretty subtle.
That's a very low SHGC but I see that Marvin has few options. https://search.nfrc.org/search/cpd/cpd_search_detail.aspx?cpdnum=MAR-N-377
I would push your dealer for performance values using LoE-180 with i89 and LoE-272 with i89 rather than 366.
Keep in mind that VT is based on whole window and not glass alone, so the sash and frame are used in the calculation for window VT.
Window VT will always be lower than glass VT. VT for 180 is 80%, for 272 is 72%, for 366 is 66% - definitely a pattern.
Oberon, you aren't concerned about the increased condensation risk of using i89 on the interior? (And is i89 89% clear?)
Michael, if the home was in zones 6 or 7 I would be very hesitant to use the surface 4 coating and would recommend looking at triple pane for that climate, but I wouldn't be concerned at all in Portland.
Although surface 4 coatings do lower glass temperature, particularly at the edge, the surface temperature is still warmer than clear glass would be and the number of hours of potential risk for increased condensation really is minimal in any but the more severe cold weather zones.
Yep, i89 is 89% clear compared with clear glass that is usually in the 91-92% clear range.
Since the windows face south under "generous" overhangs, and VT is the primary concern, I suggested 180 because there is only a U.02 drop from 366 with much better VT. Again in Portland or comparable that .02 difference wouldn't concern me at all.
Thank you so much for the inputs, it really helps me understand. So since the whole window VLT numbers are weighted with the frame, it seems that I should only be looking at the glass VLT numbers, since I care about light coming through the glass, not through the frame? Does that make sense? And if the glass VLT is 66% with 366, then that's not as bad as the 43% I was seeing in the dealer's estimate. Still, obviously 80% would be better, especially for Portland.
Greg, I did ask my dealer about 272, and he specifically told me they are not available in Essential. I don't know how to check that, Marvin does not seem to have a phone number for consumers to call. He sent me the four options that he got quoted from Marvin (attached), but I do see that he included ERS (i89) only on the E3 option, not on E1 or E2.
Is there a way for me to get in touch with Marvin directly to get these options? Or try a different dealer (unfortunately my builder only wants to work with this dealer, but I suppose I can try to get information from a different one).
Even if you do talk to a customer service rep at Marvin they are almost certainly going to direct you back to the dealer. And I would not expect a customer service rep to know much of anything about the glass packages that they offer at any rate, that isn't really an area where I would expect to find an expert.
Yes, I am quickly finding this out. So doing my own research through the NFRC database seems like the best option, though tedious.
This seems like an opportunity to mention that Oberon, Josh Salinger (a design/build contractor in Portland, Oregon) and I will be participating in a Fine Homebuilding webinar on selecting/designing windows, two weeks from today on May 24. I'm sure they will be announcing it via email sometime soon.
What a small world - I am hoping to use Josh's consulting services for our build, so I can't wait to hear the webinar with all three of you!