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Four windows better than groups of twos?

WMzJQvhd8a | Posted in General Questions on

This may seem like a strange question… I have a 28′ south-facing wall. It will be 9 inches thick and filled with cellulose. It is a gable end and will require no headers. I’ve calculated that I need about 64.6 sq. ft. of glazing which came out to 4 41×57 Pella Proline double-hung, Natural Sun windows.

The question is, should I group them together as doubles or keep them spread evenly? And why? Better insulation when grouped? More solar gain when seperate?

The house is in northern New Hampshire.

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  1. GBA Editor
    Martin Holladay | | #1

    How you group the windows is an aesthetic decision as well as one dictated by where you want the natural light to fall in your home's interior. Ideally, your window placement will achieve a graceful looking exterior and will provide pleasing sight lines from the interior, as well as allowing light to fall where you want it.

    Either of the options you listed will achieve the same result from an energy-gain perspective. When it comes to energy loss, ganging the windows in pairs will probably result in slightly better performance, because the rough opening will require fewer jack studs (thereby lowering the wall's framing factor).

    However, there are several ways you could improve the energy performance of these windows:
    -- Change the double-hungs to casements to reduce air leakage.
    -- Change some of the double-hungs to fixed glass to reduce air leakage and increase solar gain (by reducing the width of sash frame elements).

  2. Riversong | | #2


    Add to exterior aesthetic and interior daylighting a third criterion: usable wall space (furniture placement, etc.)

    I will agree with Martin with one exception: while placement itself will not effect total solar gain (unless there are trees shading part of the wall), but it may effect total useable solar gain if you're relying on a thermal mass floor. The more dispersed areas of the floor are swept with sun the more solar heat it can absorb and store.

    And you gain nothing by clustering windows together, only by factory ganging them together so you can eliminate the intermediate framing.

    But you also need to recalculate your window requirements. 64.6 SF of window is not 64.6 SF of glass (a typical window is about 80% glass, so you need to increase window sizing by about 20%.

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