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Flanged or undersill mounted passive house windows?

I will be using Intus Eforte windows in my passive house build. I have the option to purchase flanged windows that are installed on the outer of my double walls, or an undersill application that mounts almost between my double wall assembly. What are the pros and cons to these two options? Thanks.

Asked by Matthew Michaud
Posted Jan 1, 2013 12:43 AM ET
Edited Jan 1, 2013 1:40 PM ET


9 Answers

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Answered by Martin Holladay
Posted Jan 1, 2013 7:34 AM ET


On a somewhat related note, just a word of caution. I ordered Intus windows for a Passivhaus I am building back at the beginning of June and, due to a issue at the factory, still have not received the full order almost six months later. I'm told the balance of the shipment will arrive later this month. I am waiting to see how Intus fully resolves the issue but at this point I would be hesitant to recommend them.

Answered by Robert Hawthorne
Posted Jan 1, 2013 5:34 PM ET


That is unfortunate. For my sake, I hope this is an isolated incident; their performance and affordability is unmatched. Curious..where is your home being built? Did you opt with a flange or flangeless window? Thanks.

Answered by Matthew Michaud
Posted Jan 1, 2013 9:23 PM ET


Matthew- Centering the window in the insulation assembly has a much better performance profile as it represent the longest distance the energy needs to travel in order to traverse out to in. Placing the window to the outside of a double stud creates a short cut adjacent to the frame.
If you think of the insulation temperature as incrementally transitioning from the interior temperature to the exterior temperature at equal increments as you move through the wall, you'll want to place your window near the median temp location (near the center). The window will have an r-6 to r-8 performance and the energy in the adjacent wall will have to traverse a bent path around the frame rather than straight when exterior face mounted.
Also, Zola windows in the upvc materials run the $20's per square foot and doors in the $30's with the same lead time as Intus (I mean 12 weeks, not 7 months).

Answered by Sam McAfee
Posted Jan 2, 2013 1:42 PM ET


Thanks Sam. Do you have personal experience with Zola windows?

Answered by Matthew Michaud
Posted Jan 2, 2013 2:50 PM ET


Matthew- I used Zola on a few projects as a consultant and then worked with them to develop a cost affective simulated double hung window for the NYC Landmarked Passive House market. I enjoyed interacting with them so much that I began to rep their product and am currently working to develop Zola product to "intercept" customers in multiple price brackets. Once we are done, no one should ever need to install a low performing window again, even at the cheapest price points. (full disclosure. Yes, personal experience:)

Answered by Sam McAfee
Posted Jan 2, 2013 6:34 PM ET


Sam-Thanks for the full disclosure! :) Is the cost savings of the uPVC worth the slight drop in performance as compared to their other PH models?

Answered by Matthew Michaud
Posted Jan 2, 2013 10:39 PM ET



Can you update us on if and how Intus resolved your delivery issues?


Answered by Stephen Carlton
Posted Mar 23, 2013 10:49 PM ET


My order with Intus was finally delivered in whole. I am satisfied with the product as well as Intus' resolution of the issue.

Answered by Robert Hawthorne
Posted Mar 29, 2013 8:11 PM ET

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