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Installation of windows without housewrap

user-1152479 | Posted in General Questions on

I live about 30 miles south of St. Louis and own a 2006 home that was built using construction techniques that are standard for our area, but far from using green building and building science principles. For example, our home was built without the use of exterior insulation or a housewrap, meaning we have our OSB/plywood followed by the vinyl siding.

I am upgrading 3 windows to higher-efficiency windows and am looking for a proper installation method, which would involve removing the siding. However, all reputable methods I can find involve incorporating the housewrap into the flashing details and so I am left with either removing all siding from the house in order to cover all areas with housewrap or figuring out a way to “cheat” my installation… which is never a method I use in my home.

Could anyone point me to a building science proven resource for an installation method that does not include the use of housewrap? Or, do I need to plan on postponing installation until I am able to remove all siding and appropriately install housewrap/exterior insulation?

Thanks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ken,
    Your house requires a water-resistive barrier (WRB). WRBs are required by all building codes and are recommended by all reputable building experts. But you know that.

    For more information on WRBs, see All About Water-Resistive Barriers.

    There are two ways to proceed. One way, which you mention, is to remove all of your siding and install a WRB (for example, housewrap). This would be an excellent way to proceed, but it would be expensive.

    Most homeowners would compromise -- or, as you put it, would "cheat." This type of compromise happens all the time when working on old buildings. Don't feel too bad if you decide to cheat.

    However, I don't advise cheating if there are any signs of moisture damage near your windows. When you open up your walls to replace your windows, carefully inspect the rough sill and sheathing condition at the lower two corners of the window rough openings. If these areas are damp or spongy, you should address these moisture entry issues by removing all of the siding from your house and addressing the issue properly.

    Assuming the rough openings are sound and dry, however, go ahead and "cheat." The small rectangles of housewrap that you install at each window opening will need to be sealed to the plywood or OSB wall sheathing above the head of the rough opening with a high-quality tape that seals to the plywood or OSB with a waterproof seal. I recommend Siga Wigluv tape for this purpose.

  2. Envirocon | | #2

    When I encounter these, which is pretty common, I remove the siding from the wall that the window is on. Label each piece on the back as you remove. The short roofing nails are not driven tight, so this is an easy removal. Wrap and flash just those walls. Re-installing siding is quick and easy.

  3. Bill_NC | | #3

    Ken,

    One compromise that you could consider under a new window is to route any water that is on the outside of the house wrap under the window out through the weep holes in the second full piece of siding below the window. Remove enough siding to replace the window and to flash the opening / window per standard best practice. Below the window install a piece of house wrap or alum flashing that laps over the top of the hem of the second full piece of siding. The bottom of this piece should be flush with the bottom of the hem. The top of this piece of flashing tucks under the sill flashing of the window. This routes most of the water that might get behind the siding at the window out through the weeps at the butt (bottom) of the second full piece of siding. I think that CertainTeed shows this in their installation manual for their vinyl siding.

    It would, of course, be best to fully install a house wrap, especially if you find any damage to the sheathing that is not immediately adjacent to the windows. If the only degradation is at the window, then this might be a reasonable compromise.

    Bill

  4. elicon200 | | #4

    Looking to resurrect this thread to seek advice. I have to replace a couple windows in my 1978 house built in Connecticut that is sheathed in a type of T1-11 panelling. There is no house wrap underneath the paneling. From the outside going in - it is the panel siding, then framing/insulation. The windows are the original Anderson casement that are block frame and were water resistant by using a brickmould that has a gasket against the siding and caulked at the perimeter. The top of the windows don't even have drip caps, they are only caulked.

    After much research, the ideal installation would be to remove the panel siding, but I cannot do this as in one location since the electrical service is mounted on top of the panel siding that would need to be removed. In the other location, it will lead to having to remove other panels due to the shiplap connections. This leaves me with trying to flash the window opening with z-channel (then cut channels in the brickmould to leave a gap between the channel and the moulding) or tapes (trying to press the tape behind panel siding) or strips of house wrap (also by pressing).
    But this is not ideal because any water getting to the flashing would drain behind the panel sheathing and into the insulation. I guess my only route is to seal from the moulding...

    I appreciate any advice as this has been keeping me up at night.

    1. Expert Member
      MALCOLM TAYLOR | | #5

      Eli,

      It's probably the trickiest situation you can run into. There are good options to seal windows to sheathing when there is no house-wrap (as is the case with Zip panels), but when the window is mounted to a combined sheathing/cladding like T1-11 you are basically stuck with having to rely on a system similar to what was there originally.

      One way to make that connection more robust would be to add much larger brick molds - say 1"x4" or 1"x6", or depending on the look you want 2"x4", or 2"x6". That way you can slope the pieces at the head and sill to deflect some water, and it provides a wide surface you can back-bed in caulking to keep the intersection watertight.

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