Reuben's Home Inspection Blog


Photos Of Attic Bypasses, The Least Understood Attic Problem

Yesterday I talked about what needs to be done before adding insulation to your attic - seal bypasses!  Today I have several photos of bypasses that I find in attics every day.  These bypasses cause serious problems with attics, but a lot of people just don't understand this.  Bypasses cause frost and ice dams, and they need to be corrected before adding insulation to attics.

This photo shows a bypass to the attic space around a furnace flue.  The square piece of metal is not sealed to the drywall, and there is a fair amount of air leaking into the attic space from this gap.  I brushed the insulation away to show the gap for the photo.  The insulation has turned black because of the air leakage - as the warm air passes through the insulation, the fiberglass acts like a filter and collects the dust / dirt particles in the air.  Any time you see darkened insulation, you can bet there is air leakage occuring.  The black insulation is often confused with mold because it looks similar.
Attic bypass at a furnace flue

In this photo the gap around the plumbing vent is allowing air in to the attic.  Notice the dark insulation?  An easy fix would be to fill the gap with expanding foam. 
Attic bypass at a plumbing vent

This photo shows several holes that wires pass through to get to the attic.  These holes could easily be sealed up with expanding foam.  I didn't move any insulation to find these holes - this is exactly how the insulation looked when I climbed in to the attic, so there is obviously missing insulation here too.   The recommended insulation depth for loose fill fiberglass is 18", but the silver areas have no insulation at all. 
Attic Bypasses Around Wires

There is a major attic bypass around this furnace flue, and this is one of the most common bypasses that I find.  You can clearly see the walls on the floor below, and you can even see the basement ceiling from this opening!  To correct this bypass, the owner will need to install a large piece of wood, metal, drywall, or any other material that air won't pass through, and caulk all of the joints to make it airtight.  This wasn't obvious just by looking, but I always make a point of pulling the insulation away from furnace flues to look for bypasses.  The fiberglass batt on the right side of the photo was sitting on top of this opening.
Huge Attic Bypass Next to Furnace Flue

Hopefully these photos have helped to illustrate exactly what attic bypasses are and how to correct some of the issues.

Reuben Saltzman, Structure Tech Home Inspections - Email - Minneapolis Home Inspections


Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 4 commentsReuben Saltzman • February 19 2009 06:34AM


Reuben - wonderful pictures and captions.  Looks like the sheetrock cutout that fell into the open chase in the last photo has combustible paper that is now in direct contact with a gas vent.

House would be a good candidate for an energy audit.  Penetrations through top plates for wires and cables should have been "fire-stopped"

Posted by Hank Spinnler, Atlanta Home Inspector (Harmony Home Inspection Services of GA) over 11 years ago

Thanks Hank - good catch with the drywall!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago


Nice pictures!

There is one note you left out; when passing thru an insulated assembly, a shield is required around the B vent.

This is what I say in my reports:

As per the mechanical code (G2426.4), a shield "shall be installed to provide clearance between the vent and the insulation material..." I strongly recommend installing such a shield for safety.

PS- I hope the code police don't come and arrest me for inserting a code section in my reports!

Posted by Darren Miller (About The House) over 11 years ago

Darren - thanks!

Hey, I think you can quote as much code as you want to.  Just because you're not required to quote code doesn't mean you shouldn't.  I've never heard a good reason for not quoting code, but I've heard a lot of home inspectors give ridiculous reasons why not to quote code.  I'm sure you have too. 

I sometimes put that comment about the insulation lacking a 1" clearance to the vent in my reports, but not always.  When I do, I include this diagram.  What is your reason for strongly recommending this?

A diagram of insulation up against a vent

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 11 years ago