Question

For a water resistant barrier on an exterior wall, felt shall be applied horizontally with the upper layer lapped over the lower layer not less than ____ inches.

1) 4
2) 6
3) 8
4) 10

Answer 1

The question involves calculating the rate of heat flow through a wall with multiple insulating layers, requiring knowledge of thermal resistance and the ability to average the effects of different materials in the wall.

Step-by-step explanation:

The question pertains to heat flow through a wall and requires an application of the physics concept of thermal resistance.

Part (a) computes the rate of heat flow through a wall with multiple layers. Given the dimensions and the R-factors for each layer (drywall with R=0.56, fiberglass batts, and siding with R=2.6), along with the inside and outside temperatures, one can calculate the steady-state heat flow by using the formula Q=ΔT/(R1+R2+R3), where ΔT is the temperature difference, and R1, R2, and R3 are the R-factors of the different wall layers.

For part (b), the studs reduce the overall R-factor of the wall due to their lower insulating properties compared to the fiberglass. To find the heat current in this realistic situation, one has to adjust the R-value calculation to account for the presence of the studs. As the studs and the insulation have different R values, this requires averaging their effects on the total heat flow based on their respective areas.