I was fortunate enough to attend a two day “Experts Session on Building Science” taught by Dr Joe Lstiburek and Dr John Straub at the Building Science Corporation offices outside Boston. Since then I’ve had lots of conversations with my team about building the best house for our Hot/Humid Austin climate. I’ve also been re-reading my copy of The Builders Guide to Hot/Humid Climates by Dr Joe Lstiburek. (If you don’t own a copy and you are a builder reading my blog I would tell you to STOP reading this, and immediately order a copy from the buildingscience.com online bookstore.) One of the most important parts of the book is the intro sections on building science principles. Here’s an excerp from a similar article from Building Science Corporation regarding Design Recommendations for Hot/Humid climates that I thought I’d share:
To bolster your own professional judgment and building common sense, the following ten building science principles are offered. It should not be a surprise that all of these principles are at least indirectly related to moisture.
- Our efforts to save energy and reduce the flow of heat through building assemblies have reduced drying potentials and, therefore, increased the importance of controlling moisture flow through building assemblies.
- Ideally, building assemblies should be designed to dry to both the interior and exterior. In heating climates, the primary drying potential is to the exterior (but not necessarily exclusively so); in cooling climates, the primary drying potential is to the interior (but not necessarily exclusively so); and in climates with both heating and cooling, some drying potential in both directions is typically a good idea (but not necessarily exclusively so).
- Building materials last longer when their faces are exposed to similar or equal temperature and humidity. This is why the ventilation of claddings, particularly those that store moisture (reservoir claddings), can be important.
- Drainage planes, air barriers, and thermal barriers should be continuous to be truly effective. Being able to trace each of these on a full elevation drawing without lifting your finger (or pencil or pointer) from the elevation is a good test of continuity.
- In moisture control, the priority is liquid water first, particularly when it comes in the forms of rain and groundwater. In these forms it is referred to as “bulk” water. Following in importance are air- transported vapor and then diffusive vapor. It’s always a question of quantities and rates, of wetting and drying, and the tolerance of materials (individually and in combination) for each and all of the above.
- Three things destroy materials in general and wood in particular: water, heat, and ultraviolet radiation. Of these three, water is the most important by an order of magnitude.
- When the rate of wetting exceeds the rate of drying, accumulation occurs.
- When the quantity of accumulated moisture exceeds the storage capacity of the material or assembly, problems occur.
- The storage capacity of a material or assembly depends on time, temperature, and the material itself.
- The drying potential of a assembly decreases with the level of insulation and increases with the rate of air flow (except in the case of air flow in severe cold climates during cold periods where interior moisture levels are high).
Copyright © 2006 Building Science CorporationHere’s the link if you’d like to download the full white paper.http://www.buildingscience.com/documents/houseplans/hp-hot-humid-recommendations/view?searchterm=creole
Comfort issues at my house. Next Post:
Come see me speak next Thursday Feb 23rd at the AIA office.