Can You Design for Durability?

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Can you design for durability? Yes!  But the idea of durability is like the elephant in a phone booth for architects.

I think there is an assumption on the part of the design community that manufacturers are able to create products that easily become systems in the field and therefore will be successful. It is also assumed these are all based on building science and experience.  That’s a really big assumption especially when a manufacturer may only make one component of a wall for example – they only make the sheathing or the air barrier or the moisture barrier or they only make the rain screen or they only make the insulation.  So their thought or design process may only be about that layer.

On most days, manufacturers are simply making a part and “throwing it over the wall” for the designers to deal with. If it all goes well, you get the wonderful, beautiful, sustainable, durable building.  The reality is that many of the buildings we build are not durable, they don’t last, they suffer from premature service life and fail because of things like moisture intrusion and other discontinuities in the building envelop. It’s not really a failure of design; it’s a failure to design. Not only by the architect; but by everyone in the entire process.

Fill in the Blank

There is an old saying from out in the field of building buildings “it’s not what you spec, it’s what you inspect.” That’s the reality.

On a majority of construction drawings you can find a wide range of details which are referenced on section sheets but when you go to those detail drawings, they are blank. Not only is it a great invitation to unexpected costs, it is also opens the door to an unexpected future.

From a Building Science perspective your drying potential must always exceed your wetting potential. If you can’t dry faster than you wet you are doomed.

If these critical junctures are left to the tradespeople, they will build it based on their priorities which may not be holistic. The solution might not be based on a broader realization of how all these things work together. The trades are very specialized and in the field tradesmen focus on the individual level of what they are doing. They can’t necessarily be expected to expand beyond that focus to consider how the building envelop needs to work as a synergistic system.  For example, a worker is trying to seal an air barrier to a window frame – for him that is where it all starts and stops.  But that is just a small piece of a much, much bigger picture.

That’s why the discussion of designing in durability is so important.  If we can manage to keep a few specific science principles as gate keepers at key points along the design process, we’ll be pre-disposed to success.

Prioritizing Constraints

Draining and drying are first and foremost.  There most likely will be constraints put on you for energy usage, for light harvesting, for using sustainable materials, to create clean environments and other influences heaped on top of just building the building. As all these things are being piled up, there is a base that you could start with that would lead toward success and that base is drain and dry.  If you cannot drain and dry, you will not succeed, the building will not last, the building will fail prematurely. You can expect that many of these constraints will be presented as you move into the design and if you are not paying attention – they could (most likely will) be in conflict with the draining and drying goal.

We have this philosophy from a Building Science perspective that your drying potential must always exceed your wetting potential.  If you can’t dry faster than you wet you are doomed. You always have to make sure you have “spigots” in your bucket that you can open and close to let water out when it gets in. In upcoming blogs we’ll build on this concept so that you see examples of these principles in action. If you can, tune in to our webinar on September 27th.

Sign up now for our webinar The Science of Specifying Moisture and Mold Control in Framed Wall Assemblies Wednesday, September 27th at 2:00 ET

 

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Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

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