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 Building Flashing Types, Installation, Inspection, Repairs -
home
- FLASHING on BUILDINGS - Guide to building flashing: master list of building flashing types, locations, installation, inspection, troubleshooting & repair
- Ten fantasies about building flashing - who needs flashing anyhow?
- Questions & Answers about building flashing installation, inspection, leaks, troubleshooting, repairs
- References
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Building flashing home page: this article describes the use of flashing on buildings to prevent leaks, to seal between intersecting building sections or components. We explain the basic principles of building flashing: why flashing succeeds or fails, and we list the types of flashing materials used on buildings. By links to additional articles on specific building flashing procedures we provide detals about how best to install flashing at all building areas where it is used: foundation, walls, windows, doors, roofs, and roof penetrations such as chimneys & plumbing vents.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Guide to Flashing Used on Buildings
 The consequences of a flashing error or omission on a building can cause serious building damage and even injuries or health problems as water intrusion eventually means costly mold contamination, building rot, building insect damage, and in extreme cases collapse of portions of a structure. Bad deck flashing, for example, has been the cause of more than one deck collapse.
At left we show a plumbing vent stack flashing properly installed on an asphalt shingle roof.
Common Flashing Problem Areas or Mistakes
When we trace leaks on buildings to flashing errors it is often remarkable to see where & how the installer forgot a few basic concepts that explain the use and success or failure of using flashing materials to protect a building against leaks.
Flashing is supposed to redirect water: flashing refers to the use of a material (metal, rubber, plastic, for example) to mechanically intercept water and redirect it back out to the building interior instead of permitting the water to enter the building structure
Water flows down hill: mostly. So if flashing is improperly positioned, say with an opening facing "up-slope" into the direction from which water originates, it's going to leak.
Tthe articles listed in Related Topics above provide detailed flashing selection, installation, inspection, troubleshooting and repair procedures for all building areas.
Also see
Top Ten Flashing Fantasies We Love to Find on Buildings
Flashing Fantasy No. 1: the bigger the blob the better the job
Why we cannot rely on roof flashing cement as a durable repair is illustrated in our photo at left. "The bigger the blob the better the job" does not hold true in this case.
Consider that we have multiple materials all installed in the same spot: roof framing, perhaps 2x10 SPF rafters, plywood or OSB roof sheathing, roofing felt underlayment, roof shingles, perhaps metal valley flashing (not visible here), and then a smear of flashing cement that the repair person fantisized would keep the roof from leaksing.
The variatiion in thermal expansion properties alone could explain why the roof materials tear apart when exposed to cycling sun and temperature changes.
Add the effects of weather and drying out of the flexible components of the roofing mastic or cement and it becomes obvious that reliance on coatings to seal roof component intersections is not going to be reliable. That's why instead we rely on flashing products that, properly installed, handle thermal movements without tearing and leaking. Also see THERMAL EXPANSION of MATERIALS.
Liquid roof Flashing Installation Details
Technical note: there are indeed "liquid flashing products" such as Firestone's UltraFlash™ system used on modified bitumen & built-up roof installations. These commercial roof flashing approaches are not simply a liquid or mastic application however.
- The roof surface (e.g. around a plumbing vent) is cleaned and sprayed with a primer
- A liquid flashing (sealant) is applied to the roof surface and the surface of the plumbing vent stack pipe
- A fabric (typically fiberglass or polyester fiber mat is wrapped and custom-fitted around the plumbing vent pipe and extended appropriately onto the roof surface
- A second coating of liquid flashing is applied over the fabric
- A third coating of protective mineral granules is applied to the liquid flashing to match the surrounding roof surface.
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Flashing fantasy No. 2: Install and forget flashing
This photo illustrates a different sort of use of flashing at the building foundation: as a termite shield.
Termite shields don't guarantee that termites won't enter the building; rather the shield makes it a little more difficult for the termites to get into the wood structure and forces them to build mud tubes on the inside or outside of the foundation wall where, in theory, somone can notice their presence.
In this installation, where visual access was inconvenient, the termites simply built mud tubes around the termite shield and entered the buidling unobserved - because nobody troubled to look for them in this awkward area.
Flashing at the building foundation top or between the masonry foundation wall top and the wood sill placed atop the wall is is installed also as a damp-proofing course to stop rising damp in some climates. |
Flashing fantasy No. 3: half a (flashing) loaf is as good as a whole
This photo illustrates a common fantasy about step flashing: that we can just tack the flashing upper end to the building side wall and imagine that it will never rain, or that wind-blown rain will never strike the wall and run down behind the upper edge of the flashing.
Counter flashing let into the side of the building wall is what's required. Why was it omitted here? Probably because of the technical difficulty of cutting counter flashing into the surface of an undulating log wall.
But just tacking flashing against the wall is about as unreliable as pasting a bead of caulk or sealing behind the upper edge of the step flashing -this is not a leak-proof, durable installation. |
Flashing fantasy No. 4: longer flashing is better
Flashing in a roof valley with nice looking copper or aluminum is so satisfying - wouldn't it be best to make one giant long piece - after all that elimninates joints. Leaks happen at the joints, right?
Well sort-of. But a too-long copper or aluminum valley flashing segment cycles between hot and cold temperatures, flexes, and eventually cracks as these photographs make plain.
Flashing fantasy No. 5: improvised wall flashing materials are fun and profitable
This photo shows asphalt roof shingles caulked to the building side wall in the role of counterflashing. Will this work? Well yes. Our written warranty would be:
This roof is guaranteed not to leak before our truck leaves the end of your driveway. |
Flashing fantasy No. 6: we can just leave the old roof -wall flashing in place when re-roofing
The old roof-wall flashing didn't leak so why not just use it again? Well that's a great idea, sort-of.
First off the length of flashing extending out from the sidewall in this photo is about one-inch: a tiny fraction of what's required.
Second off, the old roof flashing is bent-upwards so if the roof slopes even a teeny bit towards the building wall, or if wind blows rain in that direction, water will run underneath the flashing.
Third off: the new asphalt roof shingles rarely line up exactly with the stepped flashing of the prior roof.
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Flashing fantasy No. 7: if flashing sticks up, we can just nail the buggers down!
The temptation to nail down recalcitrant roof flashing or counter-flashing is overwhelming. And it looks so neat when you're done.
But every nail puncture through the on-roof flashing is a leak spot, especially in climates where wet snow may end up sitting on the roof surface.
If you are going to go ahead and nail your flashing anyhow, a blob of roof sealant or silicone underneath the flashing at the nail point and atop the nail head on the flashing will at least keep the nailed-flashing from leaking before your truck leaves the end of the driveway.[ I confess I've done this.] |
Flashing fantasy No. 8: roof flashing is optional - who needs it anyhow? I mean, isn't the roof supposed to keep the water out?
Well yeah! Our friend Herschel was told by his roofer, the low bidder on the job, that flashing was extra. So Herschel said "optional? I don't pay for optional. Leave it off". Grinning, the roofer had Herschel sign the contract.
When it rained the roof leaked around the roof chimneys, plumbing vents, valleys, and roof-sidewall abutments. Everywere. The attic was a soak-pit. Hell, nobody goes into the attic anyhow. Who cares? |
Flashing fantasy No. 9: Vinyl siding is waterproof, right?
Why should we need flashing around windows and doors? I mean, vinyl is obviouslyh waterproof, right?
No. |
Flashing fantasy No. 10: heck no water goes there anyway, right?
I don't see why we need flashing at the deck ledger board. I mean after all, it's all outdoors anyhow. Water just runs off the deck, right?
No. The deck will rot and collapse as will the wall and ceiling of your finished room below it. |
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
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- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com 11/06
- Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.
- Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
- Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
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