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Waterproof Window Installation

One of the most important aspects of window installation is weatherproofing. I’ve seen too many jobs with window flashing installed improperly, allowing moisture to penetrate the jamb, leading to air and water leaks, rot, mold—the whole mess.

From the critical components of housewrap integration, to flashing, sealants, and flanges, this detailed video will help you perfect your window installation process.



Rick ArnoldRick Arnold has over thirty years of experience in hands-on, residential and light commercial contracting in New England. His experience includes remodeling, framing, Energy Star construction, and concrete work. Rick is a contributing editor for Fine Homebuilding. He has also authored numerous articles and books on home construction and remodeling.

Rick travels around the country, presenting seminars and workshops at trade shows and events such as JLC Live, the International Builders Show, Affordable Comfort, The Remodeler’s Show, and the Katz Roadshow.


31 Responses to “Waterproof Window Installation”

  1. BobboMax

    Rick mentions putting a piece of clapboard on the sill to create a sloped drainage plane. My habit is to just slope the rough sill, with an angle on the top of the cripple. One degree will give you ~~1/4″/ft. Tipping the rough sill does cause it to stick out a bit, less than a 32nd overall w/ a 1 degree tilt. My preference is to put that on the outside- drywallers are pickier than siders.

    • Rick Arnold

      Sloping the rough sill is a good way to achieve the same results, in fact many of the older houses I’ve remodeled did just that, except the angle is usually closer to 5 degrees.

    • tim hale

      My son worked his way thru college installing doors and windows and is now an engineer with a fire department and has a building-handyman business on the side. Clap board is not popular where he lives, he runs the bottom sticky membrane 3/4 long to the inside of doors and windows, folds a 3/4 inch edge under creating a dam so water won’t run inside.

  2. Tim Gilbride

    I appreciate how concise and informative this video was, and I hope someday someone like Rick Arnold will address how to properly flash a new window into an old house. On my own house, built in 1961, they just stapled courses of tar paper over the sheathing. Perhaps the logic and sequence of the flashing is no different…

    • Rick Arnold

      You’re absolutely correct Tim, the logic and sequence are the same. Start at the bottom with the sill pan and finish at the top, avoid any reverse lapping and always allow for intercepted water to be directed to the outside in as short a run as possible.

      To me the same installation principles apply whether I’m installing a window or a skylight.


    • Rick Arnold

      I should have specifically addressed this, I usually do.
      I don’t put flashing over the bottom flange for the same reason that I don’t use sealant along the inside of the bottom flange, I want to provide a path to the outside for any water that finds it’s way into the rough opening.
      If I tape or seal the bottom flange any intrusive water has only one way to go, and that’s to the inside.


      • J. Alvis

        Thanks for your explanation. My main concern was an air barrier and the fact that I have never seen a window in my area without tape flashing on the bottom. Makes more sense to leave the bottom open.

  3. harlan

    @ BobboMax:

    I think that the best argument for doing it Rick’s way is to let the framers fly, and do what they do best, fast. Even when I’m framing it myself, I try to wear a framer’s hat, and think and act like a framer.

    I’ve also got overlay extensions on the chopsaw table with zero clearance at the saw kerf, so that I can mark it for cripples.blocks, etc. I screw down a 1×6 with about 1/2″ overlapping the blade, chop it off, butt a 2nd one to it, and chop that one off.

    A 1º blade adjustment would wipe out that zero clearance, besides slowing me down, and possibly allowing me to cut a whole wall’s-worth of studs 1º out-of-square, because I forgot to adjust the saw back to zero.

  4. harlan

    @ J.Alvis:

    Watch the video again closely, (make sure the sound is on!) and you will hear Rick explaining that you want any water that DOES find its way in to have a way out.

    Rick’s last step, the “skip-taping” of the top housewrap down over the drip edge, is one example of this principle. And the word “weephole” is possibly the oldest example of this principle.

  5. Mike Guertin

    Many installers overlook a step Rick pointed out – Some window manufacturers’ instructions require the flashing tape be lapped about 1/4 in. onto the jamb projection to protect the joint between the jambs and applied flanges or fold-out style flanges.

    It can be hard to bond a narrow 1/4 in. strip without the rest of the flashing tape sticking to the wall. For more control I cut the release sheet 1/2 in. in from one edge and peel it off. This leaves most of the adhesive covered and offers lots of control to get an even 1/4 in. bond to the jamb projection.

    I couldn’t tell from the video whether Rick was using the Typar BA or Typar RA flashing tape for the side and head flashing. Several window manufacturers prohibit the use of RA (rubberized asphalt) flashing tapes on their window flanges. As I understand it, plasticizers used in the gaskets of applied flanges and hinges of folding flanges can react with RA tapes. The reaction results in a gooey mess that can leak.

    And don’t forget to run a bead of sealant on the back of the flange corners on those Andersen windows – right where the corner gasket meets the jamb.

  6. redwood

    Now if Rick would just cover those cases when the window is not square. If the window was plumb and level, but not square (is that possible), how do you correct it with a vinyl window.

  7. harlan

    Rick’s trick of opening the window a crack (top sash, too!) and checking for parallel is the best thing to do –– who knows, the sash itself might be out of square. And the most important thing here is that the sash fit well in its frame.

  8. Dixon

    Right off the bat…a good method is to cut the house wrap and have it come over the flange, but if, as mentioned, for some reason water gets behind the house wrap above the window you have problems anyway, and the likelihood is that that water will get behind the window in any event. Also, I used windows that come from the manufacturer with casings installed, so the method mentioned won’t work.

  9. Joely Pozole

    Excellent tutorial. It’s not TOO hard to be smarter than a drop of water ! [But I’ve seen folks that don’t seem to be able to…]

  10. Michael

    Great tips Rick! I really like and agree with having the flashing tape stick to all three surfaces.

    I’d like to share a tip for applying the flashing tape (sides and top).
    Say you are using 6″ flashing, make a few guide marks 5 1/2″ off the window. Then starting from those marks, stick the tape from the outside and work it in towards the window. The flashing tape will cover by a 1/2″ perfectly up the sides of the window to cover that joint where the flange connects to the frame.

  11. Emanuel

    Hi Rick, Great video and well done. It’s nice to see a window installation done properly with all the necesary steps. Everything you mentioned will make that window live up to its name. Most people don’t follow the instructions and blame the window itself for its failure.
    well done

  12. Sean Rice

    If I had a penny for each time I’ve seen a window installed improperly…

    This is a very good video, and I hope some people view it before they install windows or as they are watching the windows installed on their new houses. It will save a lot of time and frustration in the long run.

  13. Dan Fosterer

    Nice job, very well explained. One thing i noticed. Even if your sill is level, wouldn’t you want to shim it up to have room for spray foam along the bottom as well?

    • Rick Arnold

      It’s a good idea to shim it up, some manufacturers require it. And when I seal it with canned foam I run a bead only along the inside edge (inside of the house), leaving a void beneath most of the sill open to the outside to prevent water from getting trapped.

  14. Brendan

    Hi Rick,
    I’m working on an old house that has new stucco (with foam insulation behind it), a second layer of stucco (original stucco) over 1×8 sheathing, there might be some builder’s felt in there, but nothing I can rely on. I am planning on replacing an old window with a new vinyl window with a factory installed brick mould, but I wonder if this is a bad idea as I can only get self-adhesive flashing on the the rough opening framing not the window, so I would really only be depending on the sealant around the brick moulding to keep the water out. I could go with a flanged window as you demonstrate, but it is a very small opening (19 1/2″ wide) so I would lose a lot of light. Just wondering what you would recommend.

    I really enjoy all of your articles and videos.


  15. Randy

    I too am in the process of installing a new Vinyl window similar to Brendan’s scenario. I have an old stucco home built in the 60s.
    I had all my windows replaced a few years back with vinyl windows. The guy that did it basically ripped all the old aluminum windows out, frame and all, leaving just the rough opening. I don’t think he used any flashing at all. I believe he just used sealant around the outside trim. I had one aluminum window remaining and that is the one I am working on now. I took a grinder with a masonry wheel and cut all around the window. I used my sawzall to cut the rest out. Now I am left with a rough opening. The opening is a bit too large so I plan to add to the opening about 1/4 inch on all sides. I am thinking the only option I have is to use your flashing tape, seal the bottom first overlapping about 6 inches, then overlap and run up the sides overlapping about 6 inches on top, then finish by adding a piece on the top overlapping 6 inches on the sides. Is there anything else you would recommend? I will also apply the sealant around the top and sides as you demonstrated in your video and stick it up against my stucco wall.

  16. Rick Arnold

    Brendan, Randy,

    Flashing replacement windows is always a little tricky and I can honestly say that I have no experience with stucco siding but I know that Gary has so let’s see if we can get him to weigh in here.

    Regardless of the siding, the strategy remains the same;

    Intercept water at the top, prevent water from entering along the sides, and provide a path out at the bottom for any water that finds it’s way in.

    Here are some pointers:
    1. Install some sort of drip cap over the top of the window even if you have to fabricate something by using aluminum coil stock, galvanized metal, flashing tape, or a combination of material. It should be worked all the way beneath all layers of siding and build paper, and up as high as possible, and terminate to daylight on top of the window.
    2. Install a sill pan like the one in the video and make sure it’s either pitched toward the outside or create a dam along the inside edge of the sill with sealant, foam or backer rod to prevent water from traveling to the inside. Ideally you want the outside section of the flashing tape to go on top of the siding (maybe hide it with a piece of trim). Don’t slip it down behind the siding without addressing a way to prevent the water from following it.
    3. Since you will be relying a lot more on the sealant make sure that you get a good quality exterior window and door sealant. Don’t just grab any off-the-shelf caulking or generic type silicone that says windows and doors (I like OSI’s TeQ::SEAL sealant). And use plenty of it during the install.
    4. If you’re removing the interior trim then also seal the window from the inside after it has been installed by spraying foam sealant deep into the gap between the framing and the unit so that the foam is in contact with the back side of the flange or brickmold. You must used a closed cell foam because it’s waterproof and it must also be low expanding and low pressure. I don’t bother filling the entire cavity with foam, OSI has a very long and narrow extension for their foam gun that gets the foam to the right area. Seal the side and top in this manner but not along the sill of the window, you must leave a path for the water to exit.

    I hope this helps, if anyone out there has more to add please jump in.

    Rick A.

  17. John Gowrie

    Hello Rick,

    I saw you demonstrate this last year at a local lumber yard during a Katz Road Show. Good stuff that many may think is overkill but it’s worth the time when you think about what is at stake!

    Up at the beginning of the comments a poster suggested, or wished, that such a video could be done to show what might happen with an older home where you are installing a new window through a new rough opening. Makes sense that most of this applies as shown. What about a situation where you have two layers of siding on the house? Would the best practice be to take off both layers of siding to get at the sheathing layer of the house or is just getting behind that first layer of siding effective enough?

    My situation is aluminum siding over the original clapboard siding. My plan is to pull off the aluminum above and down to just below the new rough opening. Then cutting through the clapboard a 3-1/2″ boarder than I will apply strips of plywood to so there is a flat surface to apply flashing to and some trim boards after. Don’t know what I will find for house wrap under that clapboard but the house was built in the late 40’s and is located in NY. From inside the gutted upstairs we have what looks like fiberboard as the house sheathing so I would assume I’ll probably find tar paper as the wrap

    Any tips or hints on this type of situation and adapting the flashing methods shown?

  18. Tim


    Great video! But what would be the proper install to replace new construction windows on a 15 year old vinyl sided house? Cut the flange and insert and caulk, cut back the siding and put another new construction window in with proper flashing and trim around, or tear the siding back and do it like it is a new construction project again? When the house was built, I know the windows were not flashed but there is house wrap on. Most window companies just want to cut the flange off, put a replacement window in and caulk. When I tell them I want a proper install with tape most don’t even know what I’m talking about. Any advice would be greatly appreciated.

  19. Mike

    Hi Rick,

    The best video by far.

    I want to install a wall louver (for range hood) which has a rectangle size of 8″ x 8.5″. Does it need any flashing at all?

    I couldn’t find any video on it. I thought it would be roughly the same idea.

    Appreciate your advice.

  20. Dave


    Excellent detail.

    I have been trying to find the proper flashing for use as the sill pan. You demonstrated in the video working the corners of the flashing on the sill w/o cuts. What flashing are you using?

    Also, your other flashing tape – would you identify?

  21. Paul B


    Thanks for this great video.

    When installing doors, would you use the exact same principles?


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