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How to Install a Flashing

Jun 8th 2020

Even though the flashing may not be the hardest past of installing a class A chimney, it is one of the most important parts of your chimney system because it prevents rain water from seeping into the ceiling. We have created this video and step by step guide to make sure that you are properly installing and sealing your flashing.

Not only can an improperly sealed flashing cause damage to your roof, ceiling, and drywall it can damage your wood stove as well. Think about it, your chimney system is a straight path to your stove. Water leaking in can cause damage and rust on your wood stove as well. We hope that you agree that a few extra steps to ensure a proper seal is cheaper and easier than redoing drywall and painting!


What You Will Need

  • Caulk Gun
  • Keyhole Saw
  • Hi Temp Silicone
  • 8 Penny Nails
  • Pry Bar
  • Hammer

Step 1:
If you are installing a class a chimney you should already have a hole cut into your roof. You will want to test fit the pipe into the hole that you have already to make sure that you have the 2" clearance to combustible materials all the way around the pipe. When you are testing this use the keyhole saw to make the hole larger in any areas that are not allowing the 2" clearance. Make sure that you are not making your hole too large so that your flashing will completely cover the hole.

Step 2:
The next thing that you will need to do is pop up the shingles in the area that the flashing is going to be installed. Use the Pry bar, or flat bar, to first remove the shingles from the tar line and then to pop any nails. We recommend popping the shingles up about half way down the sides of the flashing to ensure that your flashing is secure and that you are getting a good seal. Make sure if you are installing your flashing on a hot day that you are careful not to tear any of the shingles. You will want to test fit the flashing until you have the flashing in the correct spot to make sure that you have popped up all the necessary shingles.

Step 3:
Now you will want to test that you have the flashing centered over the hole in your roof. The best way to do this is to use one of your chimney pipe sections. With the flashing slid into place under the shingles put your chimney pipe length through the flashing and lock it into place.This is an important step to take, making any necessary adjustments to the placing of the flashing before you secure it into place. Ideally you want the bottom of the flashing to be parallel to the bottom shingle and as straight as you can get it.

Step 4:
The next step is to start securing your roof flashing to the roof. Before you grab your hammer and start nailing it down we recommend laying a good bead of hi-temp silicone underneath of the flashing's base. The key is to get up as high as you can under the shingles to get the silicone under the flashing. Once you have laid the bead of silicone underneath the base of the flashing, press firmly around the base to get that initial seal. This is just a "safety bead" of silicone we will apply a final bead around the outer edge in a later step. We always say better safe than sorry when it comes to sealing holes up in your roof!

Step 5:
The next step is to nail your flashing down. Now there is no need to go hog wild with the nails, one 8 or 10 penny nail about every 4 inches will do the trick. We recommend keeping your nails about 1/2'' or so in from the outer edge of the flashing.

Step 6:
Once you have all of your nails in, you will want to make sure that you are applying silicone on the head of each nail. Remember that each nail is essentially a hole in your roof so it is worth the extra effort to prevent any potential leaks now. Once you have finished applying silicone to the nails you will want to apply a generous bead of silicone around the base of the flashing. This is your final seal for the base of the flashing. Make sure that you are making extra effort to get a little bit of that silicone underneath each of the shingle ridges as you work your way around the base of the flashing. Keep your silicone nearby, you will need it one more time.

Step 7:
Now we are ready to install the storm collar. To do this you will need to install you first length of chimney pipe. The storm collar is simply going to wrap around the chimney pipe and lock in place, deflecting water from traveling down the pipe and into under the flashing. Duravent storm collars are universal, so depending on the diameter of your pipe you may need to trim down the storm collar to the appropriate length. Once you have the storm collar in place, slide the tab at one end into the slot on the other and fold the tab up to hold it into place.

Step 8:
The final step in installing your flashing is going to be to apply a generous bead of silicone around the top of the storm collar all the way around the pipe.

If you follow the steps that we have provide you should be able to install your roof flashing like a pro. Make sure that you check out our Chimney Pipe Learning Center to find even more how to videos and articles on class a chimney pipe.

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