2 many chimney leaks are from cracks in the chimney crown.
Seal airspace along side of chimney in attic.
Access the attic through a crawl space in the ceiling using a stepladder or use or the attic stairs.
This is bad advice when sealing around chimneys and vents because they have the potential to get very hot.
Blocking the air from leaking through the attic door is one of the most important things you can do.
Sealing a chimney diy air tight removable seal duration.
As you note the chase on the attic floor is not as much of a problem because your basement and your attic are both inside of your thermal envelope.
Air sealing the attic door.
It s by far the largest hole in your ceiling and it s probably costing you a fortune.
Sealing an air leak around a chimney in the attic 1.
You can see that the very purpose of the chimney crown is to keep rain out.
Seal with silicone caulk.
So you should certainly seal the air leaks around the chimney at this location by installing metal flashing with sealed seams around the chimney on the underside of the rafters.
The bricks go up around the tile flue liners but at the top you need something to stop the rain and snow from just falling in around the tiles.
If your hatch rests directly on the moldings like ours did add 2 1 2 in wide stops around the.
This folded leg strengthens the unsupported edge and created a perfect little trough for firestop caulk.
Finally prepare for adding insulation foam or.
Set up a cordless drill with a.
Seal the gap between the flue and metal flashing with special high temperature caulk.
Even though most of the gaps spilling warm air into your attic are buried under insulation you might be able to find evidence of them.
It s often recommended to use spray foam insulation when sealing gaps in a building s envelope.
Then finish up by sealing the access hatch with self sticking foam weatherstrip photos 10 and 11.
I used pieces of various widths up to 6 in.
Look for areas where the insulation is darkened.
When you re done sealing your attic bypasses push the insulation back into place with an old broom handle or stick as you back out of the attic.
In places to seal the airspace between the ceiling joists and the chimney as shown in the drawing.
I installed it upside down with the drop leg pointing up.
Put on work gloves.
The ideal way to air seal in this situation is with a piece of sheet metal and high temperature silicone sealant.
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Do not use spray foam.
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Insulating and air sealing an attic with spray foam long version duration.
The chimney crown is the cement part on top of the chimney.
Your options for air sealing the attic door are.
Once the metal is in place seal the remaining gap between the metal s edge and the chimney with a thin bead of high temperature silicone caulk.