How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes

How do I minimize roof penetrations?

Saturday, March 12, 2022

More roof leaks start at roof penetrations—like skylights, plumbing vents, gas appliance flues, and dryer vents—than anywhere else on a roof. Each thing that pokes through the roof surface increases the likelihood of a leak. And penetrations on the street-facing sides of the roof also detract from the home’s curb appeal. But you can reduce the number of roof penetrations when planning a new home, and then you get a second chance to eliminate some of them when reroofing. Here’s how:

•• Plumbing vents - A minimum of one plumbing vent through the roof is required by the building code, and you can reduce or eliminate the number of additional plumbing vent pipes through the roof by using air admittance valves (AAVs) and consolidating multiple vent stacks into one below the roof where possible. See What is an auto vent, air admittance valve, or check vent? and What are the code requirements for plumbing vent terminations? for more on this.

•• Bathroom and kitchen exhaust fans - can be routed to terminate through walls or soffit instead of the roof. 

•• High-efficiency gas appliances - can be vented through a sidewall.

•• Dryer vents - can be terminated at exterior wall or the duct run underground to exterior. This may require locating the laundry room closer to an exterior wall. Rooftop dryer vent terminations are also problematic for another reason. They are often out of sight and difficult to reach, so roof vents don’t get cleaned regularly and become clogged with lint, which is a fire hazard.

•• Choosing electric appliances - for HVAC and water heater eliminates the flues required for natural or LP-gas units. 

•• Switch to a tankless gas water heater - when it’s time to replace your old gas water heater. It can be mounted on an exterior wall or vent through an exterior wall.

•• Choose underground electrical service - when planning your home, to eliminate a rooftop service mast.

•• Install only best quality skylights - Yes, we know that a skylight is an asset that brightens the interior any home. If you choose to have one installed, make sure it has a high curb with correct flashing, and installed by a professional roofer. A cheap skylight sits almost flush to the roof and is guaranteed to leak after a few years, no matter how much caulking is slathered around it—like the one below.

    While some of these penetrations can be eliminated when reroofing your home, it’s also a good idea to check in the attic for any unintentional removal of penetrations after the roof is complete. A couple of times each year we come across a dryer or water heater vent termination that was removed while installing new roofing and not replaced—with the opening shingled over—or the vent termination was replaced, but not reconnected to the flue below it in the attic. Either way, the appliance ends up venting into the attic just below the sheathing

• • • • • • • • • • • • • • • • • • • • • • • • • • • •  

  To learn more about roofs and attics, see these other blog posts:

• What things can void a shingle roof warranty?

Why is my roof sheathing sagging between the trusses?

Why is granule loss a problem for an asphalt shingle roof? 

What causes roof shingles to curl up at corners?  

What causes shingles to buckle along a line on the roof? 

• Why is my roof leaking?

What causes leaks at a fake roof dormer? 

What causes a sagging roof ridge line?

What causes bubble-like blisters in a built-up and gravel roof?   

How can I inspect my roof for hurricane damage?

How can I tell if a roof has more than one layer of shingles? 

What's the average lifespan of a roof?

Why is it a mistake to replace a roof and not replace its flashings? 

How can I make my roof last longer?  

How can I find out the age of a roof? 

Should I buy a house that needs a new roof?

     Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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