Architectural Design Mold Free Guarantee?
During one of my many presentations on Building Enclosure Commissioning to architecture firms, I had a question from a concerned architect that I think echoes the concern in many professionals’ minds about mold. The architect in question was wondering if there is any way to guarantee “on paper” that mold will never occur in an assembly. Architectural design mold free guarantee? So let’s take a look at this very pertinent question and see what an architect can do to ensure a mold-free assembly “in theory” at least. There is off course, always the possibility of imperfect installations, unforeseen conditions and improvisations that can happen in the field during construction, that can cause the best laid plans to go awry. But how about detailing your assembly so that in theory, it will never develop mold?
Fundamentals of an Architectural Design Mold Free:
- First and most important, we need a “continuous air and water resistive barrier. Most professionals know what a water (aka weather) resistive barrier (WRB) is. Some examples are Tyvek, building paper, roofing felts, etc..Similarly, an air barrier is the layer in your roof and wall assembly that will resist the uncontrolled infiltration/ exfiltration of air through the building skin. It can be the same as the WRB or, for a variety of reasons, this role may be played by another material. When we say these barriers need to be continuous, it means ensuring continuity at fenestrations, change in planes, change in materials, etc. Much easier said than done, though!!
- Secondly, the sheathing layer has to remain above dew point. How do you ensure this? The best way is to put continuous rigid insulation on the exterior face of the sheathing to the thickness necessary to prevent the sheathing from reaching dew point. I often see architect’s details with all the insulation inside the wall cavity to simplify window installation. The air, as it travels through this thick layer of insulation, drops in temperature, causing the moisture in it to condense out at the first cold surface that it hits, for example the ply or OSB sheathing. This will cause the sheathing to get wet and if it does not dry out faster than it gets wet, it can lead to mold growth.
- Thirdly, you ensure that the wall/ roof assembly has the ability to dry out ideally in both directions, or otherwise at least one direction.
- Some assemblies depending on building/ space function (indoor swimming pool, spa, etc.) and climate zone (very cold climates like Alaska) necessitate a strategically placed vapor barrier to prevent moisture migration via vapor diffusion.
For projects that have the fee for a WUFI simulation, you can also identify potentially risky wall/ ceiling assemblies via a dynamic hygrothermal simulation with WUFI Pro. https://wufi.de/en/
I hope this helps to shed some light on Architectural Design Mold Free. For more information on the continuity of water and air barriers and how to achieve them in your design, please look at some of my previous blogs on the subject. Thank you!
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