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Window installation with full-thickness masonry: planning for eventual replacement?

Andy CD Zone 5 - NW Ohio | Posted in Energy Efficiency and Durability on

Basic question: what is the best way to design a window installation behind a masonry full-thickness veneer wall such that eventual window replacement is possible while maintaining the integrity of the drainage plane?

I’m building a new house with full-thickness (5″) natural stone veneer walls, and am trying to design for durability. Windows will have to be replaced eventually, that is a given. The drainage plane behind masonry is critical to the durability of the wall system. Replacing windows typically involves tearing open the WRB/drainage plane to get at the nailing fins. Yet masonry, typically installed after the window is flashed in, often covers up the nailing fins. How is window replacement even possible, let alone restoration of the drainage plane?

It would seem prudent to back off the perimeter of the masonry and install a brickmold, which would cover the nailing fins and provide access to them in the future. Even this is a very narrow space (about 2 inches) in which to work. Plus, wouldn’t the job be complicated by the tapes or mastics used to seal the original installation? Plus, the brickmold would be attached by screws or nails which would punch the drainage plane full of holes!

Any advice would be appreciated!

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Replies

  1. Andy CD Zone 5 - NW Ohio | | #1

    Followup question: are there proprietary drainage plane systems, designed for use in a typical masonry ventilation cavity, that include provisions for drainage around windows? The window would not be secured with nailing fins, but with a strap on the inside or screws through the jambs. Is such a thing possible, or even advisable? This way, the window can be withdrawn without affecting the drainage plane.

  2. User avatar
    James Morgan | | #2

    Windows will have to be replaced eventually, that is a given.

    Wrong premise, hence wrong question.
    "How can I install good quality windows so that they will last the life of the building?"

  3. Andy CD Zone 5 - NW Ohio | | #3

    James, it's good to clarify assumptions.

    I am building a house in northwest Ohio (mixed humid or northern, depending on who you consult), and God help me, I am designing for a life of 250 years. I am choosing to go with an extremely tight building envelope. This leads me to specify modern, efficient, tight windows. Further, with durability in mind, I am leaning towards an all-fiberglass window, since the alternatives (wood, wood-clad, and PVC) are generally assumed to be less durable.

    I think it's unreasonable to assume that ANY modern window made of modern materials will last 250 years. The high-end manufacturers' warranties top out at 30 years. Deterioration comes not from water, but UV and acid rain and baseballs and uneven settling of walls and who knows what else. And, I don't want to assume that the manufacturer will be around in a few decades to help me with replacement parts.

    I have repaired 150-year-old wood windows and reinstalled them in 150-year-old jambs. But that is NOT an efficient window, and the building had no drainage plane, nor insulation for that matter. Perhaps I should be building like that. (Someone is--have you seen HopeForArchitecture.com?) But I have conceded to comfort, and thus use modern materials with all the thermal and vapor control.

    One Canadian fiberglass manufacturer told me, off the record, that he feels his product is a hundred year window. "So," he said, "you shouldn't have to worry about it for 20-30 years." Apparently, that's considered a long time in window world. Andersen warranties stop at 10 years. Marvin is 20.

    Am I paranoid to assume my windows will need to be replaced in, say, a hundred years at best, or am I unreasonable to design the structure for a 250-year life?

    I guess I might rephrase the original question: how do you replace a window if the WRB is nearly inaccessible behind masonry?

  4. Daniel Ernst | | #4

    Andy,

    Several aluminum clad wood window manufacturers offer a window with an integral aluminum brickmold (no nailing flange). These are often used in solid masonry walls. To install, you first secure 2x pressure treated lumber in the rough masonry opening. You then set the window into the PT window buck, and attach it with nails or screws - through the jamb and into the pressure treated lumber. The brickmold hides the PT material.

    You could use a similar technique for a wood framed wall faced with masonry veneer. That way, you could replace the window without disturbing the WRB.

    It's also common for fiberglass window manufacturers to use an aluminum molding on the window exterior. You'll just have to find one that offers a brickmold option, and then make sure that they install strapping on the interior side of the frame, so you can fasten the window into the rough opening.

    The Brick Industry Association has some good information on how to properly flash veneer brick walls (I have yet to see it done to this level of detail). If you are building for durability, that means heavy grade galvanized lintels, a durable separating layer (to avoid galvanic reaction), heavy copper or lead coated copper flashings, flashing end dams, weep holes, etc.

    Like Martin keeps repeated here, flash the rough opening, air seal the window.

    Here are some graphics I pulled off of the web that show the level of detailing required:

  5. User avatar
    James Morgan | | #5

    Interesting project, Andy. I'm curious why you settled on 250 years as a target and what the rest of your assembly looks like.

  6. User avatar
    James Morgan | | #6

    The task of designing such a building brings to mind the Deacon's wonderful one hoss shay:
    http://rpo.library.utoronto.ca/poems/deacons-masterpiece-or-wonderful-one-hoss-shay-logical-story

  7. Andy CD Zone 5 - NW Ohio | | #7

    James, I'd love to discuss the project, but here ain't the place. Step outside with me: [email protected].

  8. User avatar
    James Morgan | | #8

    I'll check out your site Andy, but before I do a couple more quick comments here: first, don't confuse a warranty with longevity. No business will warranty a product for longer than the expected life of the business itself but a decent modern window will be around for a very long time indeed if properly installed, protected and maintained, with occasional replacement of IG units and possibly hardware. Personally I'd choose wood with alu. cladding over FG for longevity but that's just me. Second, if I were concerned about future maintenance access to the WRB - a smart decision considering the brief period of time these materials have been around - I'd be worried about more than just the window flashings so I'd probably choose another siding material than a stone veneer. Cedar over a rainscreen is removable, renewable and extremely durable.

  9. Hein Bloed | | #9

    " I guess I might rephrase the original question: how do you replace a window if the WRB is nearly inaccessible behind masonry? "

    We do it according to demand.

    Basic answer.

    Contact a professional window installer and ask for an aprenticeship.
    There are national and international standards to be adhered to, these change every couple of years.

    PS
    Usually the 'furnitures' (fixings, hinges, locks) fail a long time before the window (frame, pane) itself.

  10. User avatar GBA Editor
    Martin Holladay | | #10

    Andy,
    Windows installed in masonry buildings don't have fins or flanges. They are installed with masonry clips instead. Any good window manufacturer should be aware of this fact.

  11. Andy CD Zone 5 - NW Ohio | | #11

    Martin, it's not a masonry building. Masonry clad. For this scenario, most maufacturers' installation guides I've seen show a standard fin/flange installation behind the masonry. Cross sections show the masonry either fully or just partially overlapping the fins--in any case, as in my original question, I wonder how the heck one could ever replace these windows with the masonry in the way of the fins.

    Daniel above gives about as good an answer as I've heard. Either I have big wide brickmolds that can be removed to reveal the flanges, or the window is withdrawn to the inside by removing interior jamb extensions and casing to get at anchor straps.

    There's still the over-arching disconnect for me, though, as revealed in the exchange with James above. Even IF a window is good for a hundred years, I STILL want to have a strategy in mind to replace it if that becomes necessary. Indeed, such a strategy has to be included in the durability analysis required by my project's LEED certification.

    I know: this whole debate is moot with just about any other cladding system.

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