Design
Introduction
One of the most important aspects of a properly constructed building or home is providing the occupants with a warm, dry, efficient, and long-lasting environment in which to conduct business or live. Unfortunately, there are numerous variables that come into play when taking this dream from thought to reality, many of which involve the building envelope. What ultimately determines the level of human comfort on the interior of the structure is the building envelope. If it’s poorly constructed, what should be a dream environment can quickly become a nightmare.
Moisture, whether interior or exterior, can be a catalyst for premature deterioration of building components, health problems due to mold, insect infestations, and more. Sight planning, although not physically included in the building envelope, is equally as important to the success of any project. Sight planning includes development of the property to ensure proper exterior water drainage so that individual components of the building envelope have the best chance to succeed, therefore making the project a long standing success.
Building Envelope
The building envelope includes but is not limited to:
1) Floor Slabs
2) Wall systems
3) Fenestrations
4) Roofing System
As you can see, each of these components must be properly designed to fit together in a way which ensures that the “skeleton” or envelope of the building is moisture tight. For the purposes of this web site, we will focus on the importance of proper slab construction and how to ensure that it will perform as expected.
Floor Slab
When looking at concrete slab design, whether on grade or below, the old saying that “the prep work will make or break a project” really stands true. The expectations of the slab, weight and volume of traffic on the floor, and desired finished floor product are just a few of the variables that come into play. Stability of the soil, proper rock sub-base layers and compaction, and water table levels are others.
Once all of these variables have been evaluated, the vapor barrier is installed under the slab, and the concrete is poured and finished. Then all is good, right? Not quite yet. The cement, combined with the water, begins the hydration process almost immediately, starting the process of curing and developing compressive strength. Unfortunately, the amount of water the cement needs to fully hydrate and the amount of water that is conducive for finishing and placing are very different. For example, a cubic yard of concrete with a water-cement ration of .5 will have approximately half, or 150 lbs, of water which will not be utilized in the hydration process. This is what we call “free water” or water of convenience, not necessity. This “free water” must be evaporated, to varying degrees, prior to a finished floor product being installed. This equates to many pounds of water per square foot that must be evaporated from the concrete. Any additional moisture added to the slab through wet curing, rain, or high ambient relative humidity conditions further complicates the process.
In order to start the “drying” process on the slab, we need to protect it from any additional moisture and contain it in an environment that will allow it to evaporate the necessary moisture. Getting the building envelope completed, air and water tight, as quickly as possible and maintaining the conditions in the building close to service conditions, give the best odds of having a slab that will meet moisture requirements for finished floor products without the necessity of an additional remediation process. Specifying the correct type of moisture testing, based on industry standards, is something that needs to be called out specifically and not assumed. Below are two links to the ONLY industry-wide accepted methods. You make the choice which is best.