Framing

The Role of Framing and Its Importance

The framing is the foundational skeleton of a building, and its members—such as studs, joists, and rafters—are engineered to carry specific loads. These loads include the weight of the building materials themselves, as well as live loads like people, furniture, and snow. For us in the IAQ business, it's crucial to understand that removing or damaging a framing member can have catastrophic consequences. An accidental cut or removal of a load-bearing beam, for instance, could cause a section of the floor or roof to collapse. We must always exercise extreme caution and, when in doubt, consult with a structural engineer before altering any part of the framing.

Thermal Bridging and Its Effects

A key problem with framing, particularly in cold climates, is a phenomenon called thermal bridging. While insulation is placed between the framing members to resist heat flow, the framing members themselves act as a direct path for heat to escape. This is because wood and steel are much better at conducting heat than the insulation around them. This creates a "thermal bridge" where heat bypasses the insulation.

This thermal bridging has a direct impact on moisture and can lead to mold growth. During cold weather, the surface of the drywall or plaster on the inside of the wall will be colder directly over the framing studs than it is in the spaces between them. This is because the heat is being drawn out by the stud. When warm, humid air from inside the house comes into contact with this colder surface, the moisture can condense into liquid water. This constant condensation creates a damp environment inside the wall cavity, providing the perfect conditions for mold growth, which often appears in a vertical pattern on the interior wall, directly corresponding to the location of the studs.

Wood Framing

Wood is a poor conductor of heat compared to metal, but it still has a much lower R-value than typical insulation.

• R-value per inch: The R-value of wood varies slightly depending on the type and density. Softwoods, like spruce, pine, and fir, have an R-value of about R-1.25 per inch. Hardwoods have a slightly lower R-value, closer to R-0.71 per inch.

• Thermal Bridging: A standard 2x4 wall has an R-value of about R-4.4, while a 2x6 wall is about R-6.9. These values are significantly lower than the R-13 to R-21 provided by the insulation placed between the studs because the studs themselves create a thermal bridge. The wood framing can account for 15-25% of a wall's surface area, making thermal bridging a major source of heat loss.

Steel Framing

Steel is a highly conductive material, making it a very poor insulator.

• R-value per inch: Steel has a very low R-value, often considered to be near R-0.1 per inch.

• Thermal Bridging: Because steel conducts heat so well, it creates a severe thermal bridge. For example, a wall with R-19 insulation in a 6-inch steel-framed cavity might only have an effective R-value of R-7.1. This is why building codes often require continuous exterior insulation to break the thermal bridge and achieve the required total R-value when using steel studs.

Concrete and Masonry

Concrete and masonry are used in framing and foundation construction and also have very low R-values.

• R-value per inch: The R-value of solid concrete is exceptionally low, typically ranging from R-0.08 to R-0.2 per inch. Concrete masonry units (CMUs or blocks) are slightly better due to their hollow cores, with an 8-inch block having an R-value of about R-1.11.

• Thermal Mass: While they have poor R-value, concrete and masonry possess a high thermal mass. This means they can absorb and store heat, releasing it slowly over time. This property can help moderate temperature swings and reduce energy consumption, but it's not the same as insulation's ability to resist heat flow. To meet modern energy codes, concrete and masonry walls require a significant amount of continuous insulation on the interior or exterior.