Weather Barrier Breakthrough

Liquid-Applied Weather Barriers Gain Popularity
as Alternative to Traditional Papers & Wraps

By Christopher Matthews, VP/Senior Consultant, Glazing Consultants International, LLC


At their most basic level, today's buildings are designed to offer occupants shelter from the elements.  But we've all seen what can happen when weather manages to sneak through the cracks:  leaks, stains, damaged wall materials and even standing water.  While water infiltration is often caused by a combination of factors, when it flows to the interior of the building, it is evidence of a failure of the last line of defense – the weather resistant barrier.   Due to the complicated installation process of traditional paper and wrap barriers, the failure of  weather resistant barrier is often due to installation issues.  For this reason, liquid-applied barriers are gaining in popularity. 


Building assembly

·        Interior drywall - wood or metal studs with insulation – plywood/Oriented strand board (OSB)/exterior grade gypsum (paper of fiberglass faced)– weather-resistive barrier – exterior wall cladding (brick veneer, siding, including wood, vinyl, aluminum and fiber-cement, Portland cement stucco, Exterior insulation and finish system (EIFS), metal panels, stone veneer)

·        Buildings are designed with the understanding that some water will eventually penetrate to the interior of the exterior wall cladding material.  As required by codes and good building practice, the function of the weather resistive barrier and the associated flashings is to control this water, allowing it to flow to locations where it is drained harmlessly to the exterior.


Traditional weather barriers – typically a building wrap or paper-type system

·        Includes building felt, kraft paper, plasticized fiber wraps, etc.

·        Popular over past 10 -15 years

·        Installation –

o       applied to building in a shingle-lap fashion with all seams taped.  Everything has to be lapped over pieces below, including all flashing

o       In an estimated 20% of buildings, it isn't installed correctly

·        Challenges

o       Sequencing – because everything has to be lapped over pieces below, the sequence of installation is critical.  Installation must be carefully coordinated with all trades involved in job, include anyone installing flashing, pipes, vents or any other penetrations in the building's exterior.   Can also be very challenging to integrate with waterproofing materials at balconies, breezeways, etc.  Very easy to get a reverse lapping of materials, which would direct water behind paper-based material.

o       Penetrations – Assuming the paper is applied and installed perfectly, it is then time to apply exterior wall cladding.  For stucco, you first have to apply a metal stucco lath over the weather barrier.  Securing the lath to the wall results in thousands of penetrations in the weather barrier – each one a potential spot for water to get in behind the paper and rush down.  This applies to any type of cladding – stucco (lath), brick (brick ties), etc.  All types are attached with nails or screws which penetrate the paper in many locations.

o       Weather exposure – After being applied, the weather barrier is left exposed to the weather until the cladding is applied.  During this time, it is susceptible to wind, weather and construction-related damage. Paper products have proven to be more susceptible to lifting and damage due to wind. If damaged, paper has to be replaced and properly taped and re-shingled. [insert case study]

o       Moisture resistance – some paper wrap products seem susceptible to prolonged water exposure.  When water penetrates behind the exterior cladding and does not flow freely down to a drainage location, some wraps/papers have allowed water to be absorbed through to the sheathing.

·        Benefits

o       Material cost.  Paper-type wrap products tend to be less expensive than liquid-applied.

o       Different paper/wrap products have different degrees of vapor permeability.  Some are engineered to be highly vapor permeable – allowing water paper to pass through to the exterior – but resisting bulk water intrusion.   The degree of permeability required is dependent on project location and climate, and building use – permeability requirements must be assessed in addition to the requirements for resisting bulk water,  Example:  you could wrap an entire building with self-adhered membrane flashing (“peel and stick”) which is basically waterproof, but is also virtually impermeable to vapor transmission to the exterior, and depending upon project location, could result in severe condensation within the wall assembly.


Liquid-applied weather barrier

·        Originally developed for use with EIFS systems.  Because many buildings have multiple types of exterior cladding systems, people began using liquid-applied weather barriers under all types of cladding.

·        Applied as a liquid with brushes, rollers or spray

·        Benefits

o       No sequencing required.  Paper has to be sequenced.  Liquid can be applied in any order and may be applied in multiple coats.  If a penetration or flashing is added after barrier has been applied, simply add another coat in that area.  This is very important in the typical schedule-dominated construction process.  Even when problems or oversights are discovered, they are easily rectified.

o       Bonds to sheathing.  Brush, spray or roll liquid to piece of sheathing.  It dries within a few hours and is bonded to the sheathing.  If water gets behind paper barrier, it can run down the wall behind the paper and cause damage throughout the wall – there's no way for the water to escape once it gets behind the paper.  With liquid barrier, if the barrier is damaged, water can enter a single point, but it can't run and damage other places, as the barrier is bonded to the sheathing.  Damage is localized.

o       Less susceptible to weather damage;easy to repair – Because liquid bonds to sheathing, it does tend to lift or tear after application and before wall cladding is installed.  If damaged, it an be touched up by brushing additional liquid over damaged area.

o       Greater resistance to water intrusion.  The experience of this author, to date, indicates that liquid barriers tend to provide greater resistance to water infiltration than paper barriers.

·        Challenges

o       Cost.  There is a greater up-front material cost for liquid-applied coating products.  However, given the benefits, many owners want to pay the price for piece of mind.  Worth it to have a worry-free experience. 

o       Less vapor permeable.  Greater water resistance also makes the liquid less vapor permeable.  This may be an issue in northern climates.  Vapor permeability issues should be reviewed by a mechanical engineer.


Bottom line.  Remediating water infiltration is costly and intrusive.  Selecting the correct weather barrier for a project – and installing it correctly – can be the key to successfully avoiding future problems.

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