Roofs and Water-Where Leaks Occur

I recently began writing blog posts for several manufacturers.  This specific post was written for Sashco, a sealants manufacturer (Big Stretch and Lexel are two of their product lines).  They also produce a line of log home stain and finishing systems.  I recently visited their facility near Denver, Colorado and was blown away by their values and company culture.  Learn more about Sashco at

There are four control layers to every home, water, air, vapor and thermal, but none are more important than water.  If we can’t keep water out of our building assemblies, none of the other control layers matter.  Water management starts on the roof.

Design has a lot to do with how a roof will shed water.  Simple roof designs with steeper pitches and large overhangs are much more effective at protecting the rest of the structure than minimally pitched (flat) roofs with no overhangs.  Down, out and away rules the day.  Dormers and skylights will add natural light to the home but will also add a layer of complexity to how we approach water management.  Chimneys, plumbing vents and electrical masts, exhaust fans and roof ventilation products may need some sort of hole through the roof.  All these require well thought out flashing and sealing strategies.

This log home with its steep pitch and large overhangs is good at managing the water from rain and snow events. The roof intersects, different planes, dormer and chimney all add a layer of complexity.

The exposed roofing material is the first line of defense.  Asphalt shingles, metal panels, slate, wood and clay tiles are all common roofing materials, some of which have been used with success for centuries.  A modern roof will have some sort of back-up product directly beneath the main roofing material.  For years we’ve used asphalt impregnated paper (tar paper), more recently synthetic papers have gained popularity.  Peal and stick membranes (ice and water shield) are code required in some instances.  The last line of defense is roof sheeting.  The days of using board sheeting are gone, codes now require plywood or OSB sheets, and when the seams of these sheets are taped, a back-up to the back-up is created.

This kick-out flashing installed where the roof meets a wall prevents water moving down the roof from getting behind the cladding.

The primary water management strategies for roofs, which include the main roofing material along with the products used underneath, are the easy part of any roof.  The harder parts are changes in direction of the roof that results in hips or valleys, roof lines that end along exterior walls, and any required penetrations and holes we need to make through the roof.  If a roof is going to have a leak, often this is where leaks are located.  We have many products designed to simplify the process to make these planned penetrations water-tight, including roof jacks or boots, flashings and sealants.

One common roof penetration that requires both proper planning and good execution is a simple plumbing vent, a hole in the roof to accommodate a 1 ½” to 4” pipe.  It’s best to place these vents higher in the roof and away from skylights and other roof penetrations and also located the vent away from hips and valleys.  Keeping the hole through the roof sheathing as tight as possible to the pipe will prevent the pipe from moving, which may damage the seals designed to keep water out. (I’ve also seen a vent pipe tear a metal roof from the force of the snow sliding off the roof.)  I prefer to first make a water-tight connection between the pipe and roofing underlayment using either a gasket, tape, or sealant (like Sashco’s Through the Roof!).  This back-up detail will prevent any water that ends up under the roofing material from finding a pathway into the home.  The next step is to install the main line of defense, a roof jack or boot that is designed for the purpose, in our case, a product specifically designed for pipes.  The boot is installed shingle style in the roofing material so that the bottom of the boot lands on top of the finished roofing material.  (Metal roofing materials and flat roof designs use different methods.)  Generous beads of sealant while installing the boot will prevent water from moving in areas we want to keep dry.

Another roof penetration that needs careful detailing are chimneys.  This roof chimney chase has two metal flashing details to keep water out, the first is a traditional bent flashing at the upper and lower portions of where the chimney meets the roof and a step flashing at the sides.  These are covered with a counter flashing that wraps the first flashing.  This allows the roof on this log home to move independently from the chimney chase and still remain watertight.  An important detail when new log structures are expected to shrink several inches in height over the course of a couple years from when they are first built.

There are many other roof penetrations to worry about, far too many to discuss in this blog post.  I’m hoping to cover more roof topics in future articles.

Ice dams can also be hard on roofs.  The weight of a large ice dam can create structural problems for roof eaves and damage gutter systems.  The big ice dams can become ground coupled.  Ice accumulation primarily forms on older homes that have lowers roof insulation values and poor air sealing at the ceiling level.  The heat moving through the roof will melt the roof snow.  As the liquid water moves down the roof, it is cooled when it reaches the eave or overhang of the roof.  The water will freeze and build up along the roof eave and back up the roof.  If the ice dam becomes large enough, the dam can cause a water back-up that penetrates the roofing material and eventually cause damage to the interior finishes.  Ice and water shield extended up the roof for a distance helps to reduce the risk of water penetration.  Improving the insulation levels and air sealing is the best fix for the ice dam problem.  Removal of the snow before it can melt can also be effective, but care must be taken not to damage the roofing materials.  Ice melting cables are also common in older neighborhoods with ice dam issues, but they can greatly increase a home’s operating cost.

A good plan and proper execution will keep water damage from a roof leak from happening, but what about storm damage or emergency roof leaks?  There are a few products on the market that have been designed for just such an event.   We used to use tar-based products for these “temporary” fixes, but most professionals have now moved to co-polymer rubber elastomeric sealants, a fancy name for synthetic rubber.  Products such as Sashco’s Through the Roof! can be installed on wet surfaces and even in the rain.  It sticks to almost any product that would be found on a roof, remains flexible, is UV resistant and is paintable.  It’s sold in both small (10.5oz) or large (28oz) caulk tubes and in 1-gallon buckets.  Through the Roof! is available in black, white, and clear.  I’ve used it for years as a preventative protection for high-risk areas (designed penetrations) in new roofs and for both temporary repairs and permanent fixes on existing roofs.

The best roof you can build is the one without anything sticking out of it, no penetrations from inside to out.  I have yet to build one.  To best protect a home from the potential of water damage from all the needed holes we plan on having in the roof, I’d recommend finding a good synthetic rubber sealant designed for the purpose, I’ve had great luck with Sashco’s Through the Roof!.

2 Replies to “Roofs and Water-Where Leaks Occur”

  1. A good coverage for water management regarding roofs but what are you going to do with the water once it exists the roof ?
    As you know site drainage is very important. Thanks for your article.

    Maurice Pickett

    1. Hi Maurice,

      You are absolutely correct. Down, out, and away applies to not only the roof but also the walls and site.

      Thanks for the comment.

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