Linkedin Group Discussion

Should there be a code requirement for furring strips or some adaptation of rain screen technology to be used behind all claddings?



Why do I need a drainage plane? “Explain it to me like I am 5 years old.” Remember this line from the movie “Philadelphia” with Tom Hanks and Denzel Washington? I think of that line when I am asked, “Why do I need a drainage plane?” Although it can sound complex, a drainage plane is a simple concept. Drainage planes are the weather barriers or house wraps used under siding products. If you think of a plane surface, you might picture a flat surface like a counter top, although a counter top lying flat would not drain well. If you were to position the counter top on its side with the flat surface running vertically, it would now become a surface that would drain water or liquids down and off the surface, creating a drainage plane (See Fig. 1).

If you want to block or dam the flow of the water, you would place something long and flat horizontally against the counter top surface. Comparatively the weather barrier is a drainage plane until you attach something long and flat horizontally against it, namely the siding. Thinking of it like a 5 year old, I will use the example of a child playing outside in water running down the curb basins. The child is having fun piling up sand and sediment in an attempt to dam up the flow of the water. As the child works, some of the water finds its way around the blockage, creating new paths in whatever direction it can. Some of the water finds paths of least resistance, while some of it becomes trapped.

Siding on a house creates a similar obstruction. It can back dam and block the flow of moisture and water, pushing it in to areas of the wall cavity where it becomes trapped, eventually causing damaging effects such as peeling paint, or in worse case scenarios, rot and mold.

This is where furring strips or spacing devices come into play. These are accessories, simple in nature, that enhance the performance of the weather barrier, or as I like to say, “Allow them to do their job.”

The International Residential Code and the International Building Code both address the need for a drainage plane or a continuous drainage plane, although they do not clearly define a best practice for creating proper drainage. The National Association of Homebuilders recently addressed the issue in their report, “Improving Drainage and Drying Features in Certain Conditions: Rain Screen for Absorptive Claddings”. The concept of rain screen technology in its various forms has existed for many years in the use of wood lath furring strips and most recently poly mesh products. This type of installation of cladding is code in several areas of the world, including most of Canada. To sum up, the use of furring devices creates an airspace between the cladding and the weather barrier that eliminates the blocking of moisture flow and allows for air movement to promote drying. The use of furring devices creates a rain screen, a system that is imperative to creating the perfect wall assembly.

For more information on drainage planes, water and moisture management as it relates to envelopes and wall assemblies, or drain plane products, or to invite me to speak to a group or individual, please contact me: Peter D. Slama G.P. Williams, Inc. Drain-Plane pslama@drain-plane.com www.drain-plane.com

The building code in my area does not even require housewrap behind vinyl siding over OSB. One prominent local builder instructs his sales people to say that housewraps cause houses to rot. His homes sell very well because they are less expensive that comparably sized buildings.

The local saying is that his homes are built to last until the first door is slammed after closing. Even that does not discourage buyers.

A member of the builder's family did not want to allow me in before closing when I had been hired as a licensed home inspector by the buyer. The buyer said "No inspection, no sale." His answer to my question as to whether the house was Energy Labeled was to point at the E* label on the thermostat.

A very few of the best builders here understand and use the rain screen method to allow their claddings to dry to both sides. They are few and far between.

Code changes appear only after a long and arduous period of review and discussion. Education of builders, home buyers, lending institutions, and insurance companies may be an alternative way to encourage the understanding of rain screen as a key component to building durability. Pardon my digressions; I could go on indefinitely about this subject.

Ed Voytovich Executive Director at BPCA/NYS - info@home-performance.org

The International Building Code and International Residential Code require a "water-resistive barrier" behind exterior cladding. Either your local code is deficient in comparison to the national standard, or someone isn't reading and enforcing.

Unfortunately, most home buyers are woefully unprepared to make sound choices in purchasing houses. They are the amateurs in the transaction. The professionals in the transaction: the builders, developers, realtors, appraisers, and banks who are in a position to educate them and establish minimum standards for closing property sales have decided it is not in their interest to do so.

Phil Kabza Partner, SpecGuy: Specifications and training consultants to the construction industry at www.SpecGuy.com

"Either your local code is deficient in comparison to the national standard, or someone isn't reading and enforcing. "

I'm afraid it's choice one.

Ed Voytovich Executive Director at BPCA/NYS - info@home-performance.org

In the British Columbia Building Code, the areas where there are more than a certain level of "wet days" (precipitation), there must be a drainage cavity of at least 10mm (3/8") behind the cladding. This cavity can be achieved using different methods and materials: wood strapping, "drainage membranes" (benjamin Obdyke stuff, delta dry, several other manufacturers exist), hat tracks, z-girts, etc. Certain methods work better for different types of claddings and for different types of construction.

The need for a drainage cavity is best evaluated based on exposure conditions, as demonstrated in the nomograph presented in the "Best Practice Guide for Wood Frame Building in the Coastal Climate of British Columbia." The worst building I've looked at in the last 6 years in terms of mis-lapped or missing building paper had no damage whatsoever - the plywood sheathing was in pristine condition. The building is two stories with a 4 foot overhang. Does it need a rainscreen? No. Are there good reasons to have a rainscreen anyway? Yes, namely to allow interior generated moisture vapor to easily diffuse through the wall assembly, assuming vapor permeable materials. Interior moisture could be handled with the mechanical exhaust, but we don't seem to be willing to require that our mechanical systems actually work.

I would be in favor of a code requirements that requires the exposure conditions to be analyzed and the design professional take responsibility for choosing the most appropriate assembly for the exposure conditions.

Since we're advertising here, if anyone is interested in the building science behind why rainscreen wall assemblies work and how you can screw them up, or the relationship between building science, sustainable building, and global warming, please feel free to contact me or invite me to speak as well. :-)

Michael Aoki-Kramer

www.rdhbe.com – maoki-kramer@rdhbe.com

I would just like to clarify the use of the term "rainscreen" and drain plain. A rainscreen is used to help reduce the external pressure exerted on face of a building by varying wind pressures. The furring strips help to create compartments along the facade to reduce the secondary wind pressure that is exerted on the interior cavity wall. This cavity does act as a drainage plain for moisture but this is usually not it's primary purpose. Back to your original comment I don't believe that rainscreen furring should be a code item. Most of the time the lateral pressure exerted on these members is nominal.

Derek Wilfong -Project Manager at SOLARC Architecture & Engineering Inc.

This is a very interesting conversation.

It has been my understanding that a drainage plane is needed to prevent bulk water (i.e., water in liquid form) from coming into contact with inadequately protected wood fiber materials (i.e. OSB, plywood, and so on) and creating a micro environment where wood-destroying fungi and insects can damage the cellulose-based material to the detriment of the structure.

Rainscreen installation of claddings, meanwhile, is intended to minimize the movement of bulk water from the outermost wall component (whether sheathing, building wrap, foam insulation, or whatever) to the back of the cladding material (see: http://www.buildingscience.com/documents/digests/bsd-105-understanding-drainage-planes?full_view=1 ). Since the maximum distance water can travel by this mechanism is 1/8", a rainscreen of 3/16" allows water on the back of the cladding to drain more freely and therefore to dry to both sides. www.sikesdesign.com Joe Lstiburek has mentioned in several trainings that back-drained claddings outperform undrained claddings in every case (vinyl siding is pretty much its own rain screen).

Ed Voytovich Executive Director at BPCA/NYS - info@home-performance.org

Ed you are correct that a drainage plane with air movement on both sides of the exterior cladding allows water to drain more freely. When I think of the term rainscreen I should clarify that I am referring more to a Pressure Equalized system. The purpose of these systems is to neutralize the exterior pressure by introducing pockets of air within the cavity wall. This system aids in preventing the capillary movement of water through you external cladding system by exerting a equal or sometimes slightly less than equal pressure back on the internal face of the system.

Joe Lstiburek has some good resource documentation on the effects of wind pressure on exterior cladding systems. www.sikesdesign.com Back to the original question; I'm still trying to think of a system that you would not want some type of furring or cavity behind the exterior cladding. Not only does this help in the mitigation of water intrusion in you wall system but it also helps create a thermal break in the exterior system.

Derek Wilfong -Project Manager at SOLARC Architecture & Engineering Inc.

Many of the siding manufacturers’ require that their products be installed at 16" on center with 1" embedment into the structure. These requirements at times put a halt to furring strips and rain screen assemblies especially if you are trying to go with an OVE strategy or even a continuous rigid foam strategy on the exterior of your framed walls.

Anthony Grisolia - IBACOS Services Manager

Where a rainscreen assembly is required due to exposure conditions, the tail can't be allowed to wag the dog, Siding attachment requirements can always be accommodated in a rainscreen assembly and there is always going to be some amount of thermal bridging at attachment points, except in the case of adhered rainscreen EIFS, where there are no fasteners that penetrate through the exterior insulation. The amount of thermal bridging is a function of the choice of attachment method. There are a couple of good intermittent attachment systems (similar to masonry veneer anchors), as well as rainscreen furring alternatives other than plywood. It's ultimately a design and engineering issue that has relatively straightforward and simple solutions.

Michael Aoki-Kramer

www.rdhbe.com – maoki-kramer@rdhbe.com

Could you expand on that a bit, Anthony? Exactly which claddings do you have in mind?

Let's look at HardiePlank, a popular, durable, yet somewhat brittle cladding.

I've spoken with technical guys from James Hardie three different times about HardiePlank when architects, builders, and contractors didn't want to do exterior foam with 1X3 furring on top of it to create the rain screen.

Resistance to this has two sources: the language in the manufacturer's instruction manual and, as always, the ominous scrutiny of the lawyers. Let's take them one at a time.

The Hardie manual says that the siding cannot be nailed through more than one inch of foam. Siding contractors often interpret this as the eleventh commandment. www.sikesdesign.com Their reluctance can be attributed partly to a natural anxiety about change, and partly to a primordial fear of liability.

In my climate zone, one inch of foam is what we use for coffee cups. Two inches puts the dew point well outside the wood structure at the design temperature of -2F, and condensation is a non-issue. Plus the cladding still needs to be allowed to dry to both sides.

The good folks at Hardie have told me on three different occasions that the furring strips screwed to the framing become the nailing surface, and the siding is not being nailed through any foam at all. The people who have spoken to me are like White House " sources" who cannot be identified "because they are not authorized to speak publicly." This is how the government gets information to us unofficially without taking on liability, and it is how manufacturers give us info in the same manner. Go ahead and call them.

Once again, Joe Lstiburek is a determined advocate for rain screen installation even though it costs him money in the end. After all, Building Science Corp may very well get the call when there is a colossal failure.

As for installing this material over OVE framing, google "HardiePlank siding 24." And, finally, there is the matter of lawyers and liability. At the same time that builders across the country are installing EIFS over OSB, many of them fail to understanding that this cladding can work well only if it is perfectly installed. Perfect is a difficult condition to achieve. Don't miss this: http://www.stuccolaw.com/reclad/frame.html .

Meanwhile, roofers argue that an unvented or inadequately vented roofing installation voids the manufacturer's warranty. By the time you factor in the prorating of the shingles over time, the fact that the warranty does not cover labor, the research by ASHRAE that the color of the shingles is a greater determinator of material durability than the temperature of the roof deck, and the fact that condensation in unconditioned spaces can only be controlled by air sealing and not by ventilation, the warranty on durability is worth as much as a concert pianist playing quarterback for the Packers without a helmet.

If we consider those two matters carefully, we may well come to the realize that manufacturers' instructions with regard to installation may not always be followed by contractors in the field and that warranties are written to protect the manufacturer, not the contractor. Finally, people can be and are sued despite following instructions, and being right doesn't always help you. Litigation is not about what's right or wrong, it's about winning. Even worse: even if you win you lose in time wasted, money put up in front for expert witnesses, sleepless nights, and recurring paranoia.

Our goals are 1) health and safety, 2) occupant comfort, 3) durability, 4) energy efficiency, and 5) environmental quality. Rain screen installation and OVE framing are both consistent with advancing those goals.

What other kinds of siding are you thinking of that cannot be installed using rain screen over 24" centers?

Ed Voytovich Executive Director at BPCA/NYS - info@home-performance.org

Well put Ed - thanks! As a lawyer, and building scientist, I can unequivocally state that the best defense is a potent offense: rainscreen assemblies are the offense the building industry needs to combat lawsuits, manage risk and liability, and let's not forget provide clients with the product they thought they bought in the first place.

Michael Aoki-Kramer www.rdhbe.com – maoki-kramer@rdhbe.com

Jack, it is great to hear that Jay is recommending and promoting the practice.

Although we do have proof that ********* siding can be subject to the damaging effects of moisture, this is not directly the point we are trying to make. The practice of creating a drain and dry space behind the cladding is based on the fact that ALL claddings will allow bulk water penetration at some point, and ALL claddings can potentially trap moisture in unfavorable areas behind the façade. This in turn creates the hazard of substructure damage as has been reported in thousands of cases here in the Midwest and extensively more nationally. So, while ********* siding along with other claddings has had its issues, the debate is really about enhancing the wall assembly system in an attempt to create the “Perfect Wall” that drains the bulk of the moisture and dries the rest, protecting the structure from collateral damage such as mold and rot.

There are also a half dozen other benefits from this “Best Practice” application that are recognized throughout the industry. ********** would stand to set itself apart in the industry by recognizing the value and added benefits of this application. You can use the analogy that it is like what the addition of the airbag to the seatbelt brought to the vehicle safety industry – the weather barrier, like the seat belt, is the primary line of defense. Drain-Plane, like the airbag, enhances the protection and makes the system work better.

Let’s keep the dialog open. Please continue to share your questions and suggestions. Best regards,

Peter D. Slama G.P. Williams, Corp. 5866 Blackshire Path Inver Grove Heights, MN 55076 Main - (651) 457-2011 Toll Free - (877) 457-2011 Cell - (651) 274-9196 Fax - (651) 994-1388 www.drain-plane.com

pslama@drain-plane.com

All comments were taken from my Linkedin group the building science community. We have over 200 members and have some of the best scientists of buildings discussing these issues every day. Please visit or become a member if you have an affiliation with the building science industry. contact me for more info at www.sikesdesign.com