{"id":853,"date":"2015-01-23T20:38:14","date_gmt":"2015-01-23T20:38:14","guid":{"rendered":"http:\/\/bathursthandyman.ca\/?p=853"},"modified":"2015-01-23T20:38:14","modified_gmt":"2015-01-23T20:38:14","slug":"window-sill-pan-flashing-the-best-of-both-worlds","status":"publish","type":"post","link":"https:\/\/buildingology.com\/?p=853","title":{"rendered":"Window sill pan flashing custom made: The best of both worlds"},"content":{"rendered":"
\"Window<\/a>
Window sill pan flashing has already been installed with a custom made back dam on site in this picture.<\/figcaption><\/figure>\n

There are many different methods and materials that can be used to flash a window.\u00a0 I will show you some of the advantages and disadvantages of each, and the the creative solution I developed, and why I think it is one of the better ways of flashing your window.\u00a0 This post will not cover fluid or trowel applied membranes<\/p>\n

There are generally two categories of of sill pan flashing:<\/p>\n

Plastic kit sill pans<\/h2>\n

This method uses a piece of formed plastic to fit on top of your house wrap weather resistant barrier (WRB).\u00a0 They are sold in kits by various manufactures.\u00a0\u00a0 It is important to order one that includes a back dam.\u00a0 A back dam ensures that any water that falls on top of your sill does not move towards the interior.<\/p>\n

\"sill<\/a>
Here you can see the lip of the back dam preventing any rain water from entering the interior<\/figcaption><\/figure>\n

 <\/p>\n

Kits usually come in two or three pieces.\u00a0 I believe the two piece kits are better because they don’t have a seam near the corner of the window which can be a problematic area for leaks.\u00a0 I’m not saying the three piece kits are bad,\u00a0 it is more like extra insurance.\u00a0 These plastic kits must be taped or sealed with compatible sealant (caulking).\u00a0 If you use any old off the shelf sealant, it most likely not bond or melt the plastic or WRB.\u00a0 I used Dow Corning’s 758. (It is now a favorite of mine as it has many uses).\u00a0 These dams still have to either be flashed or sealed to the substrate.<\/p>\n

This method was how I was originally planning on flashing my pan, but I learned the hard way that you have to order ahead of time to obtain your flashing…… many weeks ahead of time to have the pan arrive on your front door.\u00a0 In some areas of the country, your local independent building supply yard may supply these.\u00a0 I had a lot of trouble finding them in Toronto or even in the rest of the country for that manner.<\/p>\n

One major advantage these pans have in comparison to tapes or membranes is that there is less build up in the corners.<\/p>\n

One major disadvantages is that you must know the exact installed depth of your window because the back dam can interfere with interior finishes or not sit all the way behind the window.<\/p>\n

Membrane and\/or tape method<\/h2>\n

Self-adhered membrane<\/h3>\n

This is a very common method used.\u00a0 A bituthene membrane or Henry\/Bakor’s Blueskin membrane is another option which is about 0.9mm thick.\u00a0 Be sure not to use the below-grade version which looks almost identical and is almost 1.5mm thick.\u00a0 This brings us to a disadvantage of using these types of membranes, it’s thickness.\u00a0 The buildup can change the dimensions of your frame in the corners very quickly if you need to put 2 or 3 or even 4 layers of overlapping material to your frame.\u00a0 You need to account for this when measuring your window.<\/p>\n

Another disadvantage of using this membrane is that some substrates require priming for the bituthene membrane to bond to it. \u00a0The primer is a messy nasty process. \u00a0 When attached to your WRB, these membranes also have a tendency to peel under its own weight over the years, so you still have to flash seams at the top with flashing tape. \u00a0 Reading the technical data sheets before using it is a must.<\/p>\n

The biggest disadvantage is when using this method is that you need a sill angle in place\u00a0 or some other method to act as a substrate for the back dam so that the blueskin has something to adhere to. Without a back dam, this method is a deal breaker for me.\u00a0\u00a0\u00a0 A back dam is cheap insurance to a real potential issue.<\/p>\n

Why would someone use this?\u00a0 You can cut it to size on site, no worrying about ordering ahead of time and it is a very durable, effective material if used properly.<\/p>\n

Tape<\/h3>\n

When I hear the word tape, there is a negative connotation that goes with that word.\u00a0 Most likely due to previous experience of tape not adhering well to substrates in general.\u00a0 Flashing tapes are very thick in comparison due other tapes making them more durable There is also far more adhesive than any other tape most of us are familiar with.\u00a0 Their thickness however is nowhere near a bithuthene membrane.\u00a0 These tapes stick well and stay stuck.\u00a0 There are many flashing tapes on the market for this specific purpose.\u00a0 I choose the 3M flashing tape 8067\/3015 for this project due to availability and a few other properties, and what a great choice it was!\u00a0 The 3M flashing tape is thick and tough enough to be used as a sill pan material.\u00a0 I want to point out that I have no affiliation with 3m for using their product.\u00a0 I’m just a fan.<\/p>\n

The tapes have a release paper for easy installation that is discarded.\u00a0 The 6″ version which is the best width for window flashing in my opinion, has two release tape strips which come in handy during the install.\u00a0 The tape can also be used over the nailing flange of your window.<\/p>\n

Of course the one downside of using this product is it also has no back dam.\u00a0\u00a0 I can show you how to solve that problem and create your own back dam instead of using a sill angle material, which is easy to create.<\/p>\n

Use flashing tape and create your own custom back dam<\/h2>\n

The trick to having a back dam while using tape is the flashing tape needs to stick to something, but minimizing the profile of other materials is desired because it should not interfere with the installation of interior finishes or brick mold.\u00a0 The best material I could think of was using a self-adhered closed-cell foam gasket.\u00a0 1\/8″ high is high enough for a back dam.\u00a0 I got the smallest width possible which was 1\/4″.\u00a0 After measuring the window frame, the gasket was self adhered to wood, coming up about 2″ on either side.<\/p>\n

\"IMG_3603\"<\/a>
Here is the foam gasket being fully adhered to the plywood substrate.\u00a0 It is 1\/8″ high and 1\/4″ thick. Note that the end is extended up the jamb<\/figcaption><\/figure>\n

Here is the key to making this work:\u00a0 Only remove one side of the release paper, leaving the other one still on.\u00a0 This will allow you to adhere it to your WRB if it is not already installed in place.\u00a0\u00a0 Take the edge of the tape and place it on top of the foam gasket.\u00a0 The tape is best adhered to the wood using a J-roller, but other methods can be used to press the tape in place to fully adhere it.<\/p>\n

\"\"<\/a>
Here the back dam is now created with the foam gasket and only one side of the release paper has been removed from the tape. You can see that the tape is opaque on the side with the release paper still attached. It will be removed later. At the jamb\/sill intersection, the paper can now be cut along the red line in preparation for the next step.<\/figcaption><\/figure>\n

 <\/p>\n

The recommended installation video provided by 3M<\/a> is not wrong as there are many ways to flash a window, but the sill detail could be slightly better.\u00a0 The method to seal the sill is okay, but the sill connection to the jamb needs a slight adjustment in the way it drains.\u00a0 It is important to practice the 4D’s of moisture management in a building enclosure as best as possible.<\/p>\n

\"NEW<\/a>
In this window frame, 3M’s recommended method on the left for installing tape on the sill does not allow the WRB (blue dashed line) to overlap on top of the tape (red). This presents a possible method of entry for rainwater as it is not the best drainage strategy. The new method presented on the right allows for drainage from the WRB on top of the sill without potential for water to leak behind.<\/figcaption><\/figure>\n

Here is another advantage of this taped sill: The connection to the jamb includes good overlapping drainage.\u00a0 To solve this, a scrap piece of tape is cut measuring about 6-8″ long. \u00a0Cut notches in the centre so that the piece of tape resembles a bow tie. \u00a0 The double release paper comes in handy again as it is best to only remove and adhere one side at a time to prevent misaligned accidental taping.\u00a0 Only adhere one side into the corner as show below, and leave the other piece of relief paper on.\u00a0\u00a0 Using a bow tie method has been used for a long time by many others and works great.\u00a0 The tape can be stretched if need be if there is a misplacement.\u00a0 It is very forgiving that way.<\/p>\n

\"IMG_3828\"<\/a>
This is how the bow tie piece is placed in the corner.\u00a0 Leave the release paper on any parts that are not adhered at this stage.<\/figcaption><\/figure>\n

The next step involves installing the WRB on top of the rough opening and cutting out the centre.\u00a0 This technique allows the excess to be used to wrap around the jamb and on top of this new piece of bow tie tape we installed.\u00a0 Fine homebuilding<\/a> has a good succinct video on how to do this.\u00a0 Be sure to temperately tape back any release paper inside the opening so that the WRB can be installed correctly.<\/p>\n

Now that the WRB has been installed with staples, it is time to fully adhere the bottom half of the tape on the WRB.\u00a0 The bow tie can also be adhered to the WRB afterwards.\u00a0 The sill pan stage is now finished.\u00a0 Notice how every layer is properly overlapped to ensure proper drainage.<\/p>\n

\"IMG_3613\"<\/a>
The second half of the release paper on top of the WRB. can now be fully removed and adhered to the WRB. \u00a0 Notice how the wrap that is inside the jam overlaps the inner side of the bow tie.<\/figcaption><\/figure>\n
\"IMG_3619a\"<\/a>
The red dotted line shows the drainage path of water using\u00a0 overlapping layers.<\/figcaption><\/figure>\n

I really like how the flashing installation and final product worked out.\u00a0 I would use this method again in a heartbeat and recommend it to anyone.\u00a0 This is the best of both worlds in comparison to bituthene membranes and preformed pans.\u00a0 They easy to install, fully adhered, and includes a back dam.<\/p>\n

\"Buildingology<\/a><\/p>\n