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How to Build an Attic Insulation Shield or Chase For Your Chimney Pipe

Jun 8th 2020

How to Build an Attic Insulation Shield or Chase For Your Chimney Pipe

When installing a Class A chimney system, building code dictates we have at least a 2" clearance to combustibles as well as an Attic Insulation Shield. If you do not have the 15'' of space it takes to install an insulation shield, like when your chimney runs up the exterior of your home penetrating near the eaves, you cannot install a shield because building code also says you cannot cut it. Fear not! The following instructions, coupled with the preceding video, will guide you step-by-step on how to make your own insulation shield to code!

What you will need

  • Tape Measure
  • Marker
  • Screws
  • Drill
  • Sawzall

Step 1:
Climb into your attic and locate where your chimney system will enter this space. After you know where the penetration point will be for both attic and roof, add 2'' to all sides. Measure the height of the furthest point of the installation. If this height exceeds 15", you are okay to install a Attic Insulation Shield. Otherwise continue on with the following steps.

Step 2:
Once you have figured out where your chimney system will pass through, you will build a simple framing box around it. Keep in mind this box and the walls built with it will be outside the minimum distance to combustibles so a non-combustible material isn't necessary (but always encouraged). Cut 2 X 4's into the minimum lengths needed to build the box and nail/screw into place.

Step 3:
After your 2 x 4 box has been fastened down, it is time to put up some walls! Particle board or OSB will be fine for this application.


  • Measure the distance from the floor outside of your box to the ceiling on the front and back sides, then cut. Make sure to cut for width as well (the width is likely to the width between your roof trusses).


  • Measure both sides from either:
  • floor to ceiling or
  • top of the box on the outside of the minimum clearance (see video above starting at 3m 50s for a visual demonstration).


  • With your back piece set in place (not fixed in place), take a small section of 2 x 2 and trace it where the side walls will meet up with the back (the corners of the box).
  • Take the back piece out and screw/nail the 2 x 2 nailer into place.
  • Set the back piece back into place. The nailers should be sitting on the top of the box and will allow you to screw/nail the side walls into place.
  • Nailers should now be fastened to the front corners so the front wall can be screwed/nailed into place.

Step 4:
Run your chimney system through! You're done! After you clean up, of course.

Quick and easy, wasn't it? Where there's a will, there's a way and you too can find they way here at the NorthlineExpress Learning Center!