How To Properly Install And Flash Tiny House Windows

Windows are a beautiful and necessary part of a home; however, many people make mistakes during the installation that cause them to fail over time. By installing your windows properly, you will get years of use and enjoyment out of them. I’ve outlined the steps below on how to flash and install a window and included a step-by-step photo montage to help you follow along.

1. Locate the window opening and cut an X through the middle of it.

1. Locate the window opening and cut an X through the middle of it.

2. Cut the top of the house wrap about 1/2" higher than the top of the rough opening. Use the framing as a guide.

2. Cut the top of the house wrap about 1/2″ higher than the top of the rough opening. Use the framing as a guide.

3. Cut an extension of the top cut in line with the top of the rough opening that extends about an inch beyond either side of the opening. This will allow you to slide the window up under the house wrap later on.

3. Cut an extension of the top cut in line with the top of the rough opening that extends about an inch beyond either side of the opening. This will allow you to slide the window up under the house wrap later on.

4. Fold the sides and the bottom of the house wrap into the rough opening and staple them in place about 1/2" in from the face of the frame.

4. Fold the sides and the bottom of the house wrap into the rough opening and staple them in place about 1/2″ in from the face of the frame.

5. Cut the sides and bottom just inside the staples to expose most of the rough frame. Alternatively, you can cut the bottom flush with the rough opening and avoid stapling it at all if you prefer. Either way, the next step will seal the bottom rough sill completely.

5. Cut the sides and bottom just inside the staples to expose most of the rough frame. Alternatively, you can cut the bottom flush with the rough opening and avoid stapling it at all if you prefer. Either way, the next step will seal the bottom rough sill completely.

6. Cut a six inch square of self adhesive window flashing for each lower corner of the rough opening and stick it flat to the face of the wall.

6. Cut a six inch square of self adhesive window flashing for each lower corner of the rough opening and stick it flat to the face of the wall.

7. Cut a diagonal slice from roughly 3/16" away from the rough frame corner to the upper edge of the flashing. Fold the cut edges into the window opening and stick them tightly to the frame. Complete both lower corners before going to the next step.

7. Cut a diagonal slice starting roughly 3/16″ away from the rough frame corner to the upper edge of the flashing. Fold the cut edges into the window opening and stick them tightly to the frame. Complete both lower corners before going to the next step.

8. Cut a piece of self adhesive flashing 8-12″ longer than the rough opening is wide. Attach the flashing to the top of the sill so that it hangs over the edge of the window opening by at least 3″ and extends up the sides of the interior opening at least 4″ on either side. Don’t remove the backing from the entire piece at once as it will stick to anything and everything it contacts, including your eyebrows and beard hair! Instead, pull the backing away a few inches at a time as you seal the flashing to the top of the rough sill.

8. Cut a piece of self adhesive flashing 8-12″ longer than the rough opening is wide. Attach the flashing to the top of the sill so that it hangs over the edge of the window opening by at least 3″ and extends up the sides of the interior opening at least 4″ on either side. Don’t remove the backing from the entire piece at once as it will stick to anything and everything it contacts, including your eyebrows and beard hair! Instead, pull the backing away a few inches at a time as you seal the flashing to the top of the rough sill.

9. Cut the corners of the flashing on the diagonal once again. Start roughly 3/16" away from the corner as before.

9. Cut the corners of the flashing on the diagonal once again. Start roughly 3/16″ away from the corner as before.

10. Fold the bottom piece away from the window opening and stick it firmly to the wall at the sides and bottom. This completes the “counter-flashing pan.”

10. Fold the bottom piece away from the window opening and stick it firmly to the wall at the sides and bottom. This completes the “counter-flashing pan.”

11. Place a large bead of caulk around the window opening, leaving the bottom of the window uncaulked. Be sure to place the caulk on the wood frame at the top of the window, not on top of the house wrap. Slide the window up under the house wrap and set it firmly in the rough opening. Be sure to press it tightly against the bead of caulk on all sides. By sliding the window under the house wrap at the top of the opening, you eliminate the risk of water that has found its way in behind the house wrap (a problem in and of itself that would need to addressed) from bypassing your entire flashing assembly. This is a crucial detail that many people miss.

11. Place a large bead of caulk around the window opening, leaving the bottom of the window uncaulked. Be sure to place the caulk on the wood frame at the top of the window, not on top of the house wrap. Slide the window up under the house wrap and set it firmly in the rough opening. Be sure to press it tightly against the bead of caulk on all sides. By sliding the window under the house wrap at the top of the opening, you eliminate the risk of water that has found its way in behind the house wrap (a problem in and of itself that would need to addressed) from bypassing your entire flashing assembly. This is a crucial detail that many people miss.

12. Space the window evenly in the rough opening. Assuming the rough opening was framed properly to begin with, this will mean 1/4" gap on all sides of the window. This not only ensures that the nailing fin will be properly spaced over the framing all the way around the window, but also that the gap can be evenly insulated with window and door expansion foam once installed.

12. Space the window evenly in the rough opening. Assuming the rough opening was framed properly to begin with, this will mean 1/4″ gap on all sides of the window. This not only ensures that the nailing fin will be properly spaced over the framing all the way around the window, but also that the gap can be fully insulated with window and door expansion foam once installed.

13. Use shims to adjust the window perfectly level and plumb and check it with a level. You can also check the diagonals of the window (to make sure it is square). This is especially important on larger windows. To do this, measure from the upper left to the lower right and from the upper right to the lower left. The numbers should be exactly the same.

13. Use shims to adjust the window perfectly level and plumb and check it with a level. You can also check the diagonals of the window (to make sure it is square). This is especially important on larger windows. To do this, measure from the upper left to the lower right and from the upper right to the lower left. The numbers should be exactly the same.

14. Secure the window in an upper corner and then the opposite lower corner. I prefer to use screws so that I can adjust things as necessary if they don’t seat properly the first time. Be sure that whatever fasteners you use are corrosion resistant and lay as flat as possible once fully installed.

14. Secure the window in an upper corner and then the opposite lower corner. I prefer to use screws so that I can adjust things as necessary if they don’t seat properly the first time. Be sure that whatever fasteners you use are corrosion resistant and lay as flat as possible once fully installed.

15. Recheck that the window is still plumb and level and then check the window’s operation to make sure it functions properly. If both of those criteria are met, then secure the rest of the window per the manufacturer’s specifications. Be careful here as some manufacturers will void your warranty if you don’t follow their exact installation instructions. Read the instructions before you begin to make sure you are on board with their procedures.

15. Recheck that the window is still plumb and level and then check the window’s operation to make sure it functions properly. If both of those criteria are met, then secure the rest of the window per the manufacturer’s specifications. Be careful here as some manufacturers will void your warranty if you don’t follow their exact installation instructions. Read the instructions before you begin to make sure you are on board with their procedures.

16. Use self adhesive flashing on both sides of the window over the top of the nailing fin. Be sure to keep it tight to the window and as flat as possible. Bubbles make for weak spots in the flashing and may cause leaks down the road. Extend the top of the side pieces at least an inch above the window so that the top piece will cover it completely.

16. Use self adhesive flashing on both sides of the window over the top of the nailing fin. Be sure to keep it tight to the window and as flat as possible. Bubbles make for weak spots in the flashing and may cause leaks down the road. Extend the top of the side pieces at least an inch above the window so that the top piece will cover it completely.

17. Install a piece of self adhesive flashing to the top, again tight to the window and flat. Make sure that it is long enough to cover the window fully and also extend beyond the side pieces by at least an inch to ensure a proper seal.

17. Install a piece of self adhesive flashing to the top, again tight to the window and flat. Make sure that it is long enough to cover the window fully and also extend beyond the side pieces by at least an inch to ensure a proper seal.

18. If you live in a very wet location, you can add a piece of metal flashing over the top of the window. If you do that, use minimal nails and apply another piece of self adhesive flashing over the metal flashing to complete the installation.

18. If you live in a very wet location, you can add a piece of metal flashing over the top of the window. If you do that, use minimal nails and apply another piece of self adhesive flashing over the metal flashing to complete the installation.

You’re done!

Pay attention to the details here and take your time. Windows and doors are the weakest point of the construction process as they are literally holes in your wall system. Take the time to install and protect them properly.

Additionally, I highly recommend that your windows be tempered glass if you’re building on a trailer. Keep in mind that as part of a moving vehicle, there is a lot of potential for broken windows. It’s not unheard of for rocks flung up by other vehicles and/or road vibration to break windows. Tempered glass is safer in these locations and may even be required in your area. If you are not building on a trailer, there are still requirements about when a window needs to be tempered. For example, if closer than 18″ to a floor, bathtub and/or shower as well as other restrictions. Be sure you know what those are so you can build safely and with the highest quality possible.

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8 Responses to How To Properly Install And Flash Tiny House Windows

  1. Ryan Mitchell November 6, 2013 at 10:41 am #

    Great how to! Grace makes a product called Grace Vycor Plus Flexible Flashing which is pretty neat, you can see someone using it on a tiny house here:

    http://youtu.be/wZsr0Tly8Dc

  2. Andrew Morrison November 8, 2013 at 8:17 pm #

    Hi Ryan. Great to see you here and thanks for your comment. I love Vycor too and use it on almost all of my projects. It figures that the one time I film, I can’t find it at the store!!!

  3. Mike February 27, 2015 at 6:12 pm #

    I love your windows. I’ve been having a hard time finding windows that are black or dark gray both outside and in. Are these aluminum or fiberglass?

    Milgard doesn’t seem to be an option in the Northeast. I’m afraid I may have to buy Marvin Integrity fiberglass and paint the inside myself.

    • Andrew March 5, 2015 at 7:45 pm #

      Ours are aluminum. As much as we love them, they do get cold in the winter as aluminum are not nearly as energy efficient as fiberglass. If you want to spend even more, you can get wood interiors with aluminum clad exteriors. They are beautiful. Good luck.

      • Mike March 10, 2015 at 4:22 pm #

        Thanks Andrew. I’m thinking I’ll either do fiberglass with wood interior or all fiberglass and paint the inside to match the outside. We’ll see.

  4. jason June 27, 2015 at 9:41 pm #

    Hi Andrew,

    What type of caulking did you use for the windows on your mobile tiny house? With RV construction, often butyl/ putty tape is installed where the window frame sits against the exterior wall and fasteners are located. The window flashing is great to see around the windows.

    Due to previous owners not properly repairing the seal around my windows and the seams of my vintage trailer, i have lots of rotted framing members around the windows. This is especially the case in my floor, sill, and skirt board. With an aluminum under belly, the water doesn’t drain and has a great time at rotting all of those main structural areas around the floor.

    Thank you for sharing!

    • Andrew June 30, 2015 at 11:51 am #

      I have to admit that I cannot remember what I used. I know it was pretty nasty stuff! I got the best stuff my local lumber yard (not big box, but locally owned) recommended.

  5. Andrew December 12, 2016 at 11:10 am #

    Yup. I agree. I usually leave the bottom uncaulked. Honestly, not sure why I did it this way in the blog post. Thanks for pointing that out. I’ll see if I can update the post to make it more accurate.

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