Building science is the study of how our buildings interact with the environment; both from the outside and from us living inside.
We may not be scientists in the lab researching the relationships between heat, water and air flow, but, as we are constructing our buildings, we are implementing building science on a daily basis.
And if we get it wrong, the results can be disastrous; water damage, rot, mold, poor indoor air quality, unnecessarily high energy bills…
So, we need to get it right.
As our energy codes demand a more airtight and energy efficient building, the building science doesn’t change, but the potential for risk does.
It’s common sense that a leaky, poorly-insulated building uses more energy than a tight, well-insulated building.
What’s less acknowledged is the drying potential of that extra energy.
With the inefficient building, the builder does not need to be as careful with the building science because there is ample “leftover Btus” to dry out any condensation issues that might occur.
But the efficient building needs a better built-in “immune system” to mitigate these potential issues.
For example, let’s look at the wall system that many of us have been building for years: wood framed, 2X6, 16 on center, filled with R21 fiberglass batts.
In the middle of winter in Rhode Island, the dew point in this assembly is typically somewhere in the middle of the wall. Which means that any water vapor that makes its way into the assembly and comes into contact with the cold sheathing will condense.
In a leaky house with an over-sized heating system, water vapor that gets into this wall assembly is either ushered out by exfiltration before it can condense or, if it does condense, is dried out by the copious amounts of heat energy that are following behind it on its way out of the house.
In a tight, well insulated home, the dew point is still in the center of the wall, but now the water vapor doesn’t have the same opportunity to exit before condensing or dry out after condensing.
Some potential solutions in this example would be: installing exterior insulation (make sure to use enough!) or installing a smart vapor retarder behind your sheet rock (be sure it is well air-sealed particularly in high risk interior environments like bathrooms and kitchens!).
We could also choose to use CDX plywood over OSB for our sheathing. CDX has a higher safe storage capacity for water and can handle incremental amounts of condensation better than OSB.
As the codes require new constraints on our buildings, we can’t rely on our heating systems and leaky assemblies to dry out our buildings.
We will need to adapt our practices to mitigate potential building science issues.
