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USG Mold Tough Blog - Paul Shipp (Sponsor Blog)

Dr. Paul H. Shipp
Paul H. Shipp, Ph.D., P.E., has been selected by USG to be their thought leader around issues and solutions surrounding moisture management. Dr. Shipp is a member of ASHRAE TC 1.12 Moisture Management in Buildings and ASHRAE SPC 160P Design Criteria for Moisture Analysis in Building Envelopes. Dr. Shipp is active on the Responsible Solutions to Mold Coalition and previously chaired the Gypsum Association Technical Committee from 1996 through 2000.
About Paul H. Shipp

Tuesday, November 13, 2007

USG Mold Tough - Who’s Responsible for Where the Water Drains?

Nov 13 2007 9:03AM | Permalink | Email this | Comments (9) |
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In my last blog I talked about the fundamentals of mold: what causes it, how it can be avoided and the common elements of a moisture/mold resistance strategy. To recap, mold can grow on any surface—steel, glass, fiberglass, even cement—if four elements are present: mold spores, water, a source of food and temperatures conducive to growth. Of these four, the presence of moisture is the one most easily controlled by the builder or homeowner. I also stressed that preventing mold isn’t rocket science but it does requires attention to some common-sense concepts to help ensure that moisture doesn’t intrude and become a mold problem.

Control Moisture. Control Mold.
Let me dig a little deeper into this problem as it relates to new construction or remodeling. In simplest terms, if you control moisture, you control mold. The greatest source of problem moisture in buildings comes from leaks in the exterior envelope and in wet areas such as bathrooms and kitchens. Other design factors such as air barriers that seal against uncontrolled air leakage and vapor barrier location are important and require attention. But I think the majority of moisture problems can be eliminated by just controlling water leaks from the exterior envelope, plumbing and bath fixtures. However, with today’s emphasis on a rapid pace on the construction job site, quite often the responsibility for keeping moisture out of the building overlaps between trades and the ultimate responsibility for who makes sure the details work remains unclear.

New Construction: Who’s Responsible for Keeping out Moisture?
For example, the trades responsible for cladding the exterior walls of a building and those involved in roofing must coordinate their efforts where their respective areas intersect. Gravity rules: Water always drains down. Where roof and wall planes intersect, the person responsible for installing the weather-resistive barrier for each element needs to consider how water draining from above will transfer to the drainage plane below. If the membrane or barrier laps over the top of the lower drainage barrier, as roof shingles do, then water will drain down these surfaces and remain outside the wall or roof assembly. On the other hand, if the upper layer laps underneath the lower membrane, called “reverse shingling,” then water can drain underneath the lower drainage barrier and directly into the wall or roof structure. The drainage path needs to be visualized and maintained at every intersection where a wall drains onto a roof surface or a roof surface intersects and drains onto (not into!) a wall. from the top of the building to the foundation.

Don’t Neglect the Vents!
Another problem is where the dryer vents are located on the outsides of homes. If the flange for the vent is placed outside of the weather-resistive barrier, you have a “reverse shingling” condition and as rain moves down the exterior wall (beneath the cladding) it can be diverted into the building at the flange. The drainage membrane needs to overlap the vent flange above the vent and pass underneath the vent flange below the vent to preserve the proper drainage characteristics.

Excellent discussions on how to keep water out of the exterior envelope can be found in documents such as “A California Builder’s Guide to Reducing Mold Risk,” published by the California Energy Commission and Bill Rose’s excellent book, “Water in Buildings: an architect’s guide to moisture and mold” (John Wiley & Sons, 2005).

Modern building materials are more robust than many would have us believe. My company, USG, makes highly effective SHEETROCK® brand MOLD TOUGH gypsum panels which are moisture- and mold-resistant and can be a valuable component of a successful mold-prevention strategy. However, mold-resistant products are not a solution for poor water management. If water is being trapped in the building structure, it will eventually cause costly mischief somewhere. Everyone in our industry should be committed to keeping moisture and mold out of the buildings they construct. A quality job results in reduced callbacks, less litigation and ultimately happier customers—who are more likely to return.

Reader Comments


at 11/14/2007 11:22:14 AM, Art Struss said:
Good Article Paul

at 11/27/2007 5:15:17 PM, Sharon said:
I am trying to see if I can have a functional window that opens in my master bathroom shower (is at corner of house) that has two exterior walls. Do you recommend opening windows or just use plate glass (tempered) so I can look out. Or will this cause more mold problems. Thx. Sharon

at 11/30/2007 5:36:40 AM, SCOTT said:
Paul, I was hoping you could comment on what can be done to get rid of existing mold and mildew. Especially the remaining smell. The previous owner of my house allowed mold and mildew to form under the kitchen sink due to a leak. I've had it all checked out and have been told there is no existing mold, but the smell is still there. Does this mean that I still have something going on there? If not, any advise on how to get rid of the smell? Thanks, Scott

at 11/30/2007 7:12:36 AM, Terry R Dalsky said:
Paul, the responsibiliy for water drainage is ALL of our jobs as builders.. Attending seminars that are put on by Joe Nagan and Joe Lstiburek, and similar people will go a long way for builders to adjust some of they're exterior wrap systems and methods of sealing up the outside of the building envelope. No, Joe and Joe did not pay me to write this but I have attended they're sessions,thanks.

at 12/1/2007 10:08:39 AM, Robert Cox said:
With 25 years mold investigation experence, more comment: 1st: your aricle is excellent. 2nd: Mold is also caused by nationally. If you boil foods the starch laiden moisture collects on adjacent surfaces and when the temperature and humidity are just right, the mold wakes up and see's dessert and rapidly grows. 3rd: The building codes all have requirements for drainage away from the structure. I find many violations and wateer standing against the foundation even draining under the structure via the foundation vents. Slab on grade structures have problems when the foundation is placed seperatly from the slab. The poorly prepared foundation/slab joint allows water under the slab which resulting moisture comming up via cracks or slab penitrations. Last: The paper covering on gypsum drywall is also food for mold. You could comment on what changes your firm has done recently to address the age old problem with drywall. Robert Cox ACIA Hon, CSI Emeritus, AIA Ret.

at 12/6/2007 9:51:51 AM, little help said:
To the guy who wants to be rid of the mold smell... after all has been removed you need an Ozone Generator. Flood the interior of the UNOCCUPIED building with large concentrations of ozone for a few days and that will kill any residual smells.

at 1/28/2008 1:01:38 PM, James Deane said:
A key element that must be addressed beyond correct detailing is construction supervision. All trades impact the building envelope and the construction manager needs to ensure there is a trained individual who can monitor the intersection of systems and materials. How many times are the sealants relegated to the painter who may not be on the job when framer places a window? Preconstruction conferences and tool box talks are an excellent way to remind workers of the issues and to prompt them to assist in identifying potential problems as they build.

at 2/20/2008 3:00:48 PM, Cornstoves@gmail.com said:
One mold prevention treatment for bathroom tile is a single coating of "rejex". The product is also an wax for glass, auto's, Let it dry 15 mins and wipe off the gray film. The second and most prolific enemy to mold is a cornplace or cornstove home heater. Because the hot air flow never cycles off, the room or basement RH can be controlled at precisely 50%. Molds hate 50% RH. www.groups.yahoo.com/group/cornstoves for satisfied customers across America. A staged HVAC system with multiple PID controlled HVAC could also be used to control room RH at 50%. Sorry, but it is physically impossible to control room RH with humidifiers and dehumidifiers. The only reason some percieve differently is because the 20 minute time delay of a humidistat exceeds the cycle time of the HVAC.

at 3/29/2008 9:36:01 PM, millennium1000 said:
Control room relative humidity at 50% RH continuously to resolve moisture, mildew, & black mold. Set point cycles can not control RH. Only a steady continuous heater can control room relative humidity. Humidifiers and dehumidifiers are not adequate. Purchase a local home heater that continuously runs. A set point control will cycle the HVAC on and off. One type heater that never cycles off is the NESCO Amaizablaze corn stove or cornplace fireplace insert. www.groups.yahoo.com/group/cornstoves or www.groups.yahoo.com/group/cornplace Find a local cornstove cornplace dealer that services the local area. Also locate a local fuel supply or corn farm to make fuel purchases. Fuels of choice include corn, grain, trash pellets, wood pellets, cherry pitts, soybeans, wheat, rice, peas. Underground facilities and naturally damp locations can easily maintain 50% RH with a cornplace cornstove by following the instructions on the websites.

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