Your friend is building a new house in Half Moon Bay and called you for advice...

 

Transcribed Image Text:

Your friend is building a new house in Half Moon Bay and called you for advice on designing the wall given you're taking CEE176A. Half Moon Bay is generally cooler and wetter than Stanford so they want to make sure to prevent any water vapor that may get into the wall from condensing and leading to rotting of their wood frame and mold in their cavity insulation. Your friend chose a 2"x6" at 24" on-center (o.c.) wall construction based on your advice, with a framing factor of 15%. Your friend happens to work for a recycling center and wants to use the recycled paper for cavity insulation, after making a deal with a company that would turn the scrap paper into insulation and give your friend free samples for their home. The company says the final cavity insulation product should provide an R-value of 2 per inch. Otherwise, your friend is planning a standard wall with specifications below (Remember, a 2"x6" stud is actually 1.5x5.5") Ta 1/2" plywood R-0.6 Revo 0.17 W Siding R-0.2 2x6 Fir, k=0.8 Btu-in/hr-ft²-*F Rcvi 0.68 Cavity R-2/in Housewrap R-0.1 T₁ = 70°F 1/2" drywall R-0.5 Figure 1: Original Wall Construction Design for Half Moon Bay Home. a. What is the average R-value of the total wall construction detailed above? Assume Revo = 0.17, and Revi 0.68 ft2 °F-hr/Btu). b. You want to ensure that the exterior surface temperature of the housewrap never gets colder than the dew point temperature to ensure the wooden wall construction never sees condensation. Based on your thermostat setpoint of 70°F in the winter and the typical humidity, the dew point temperature is 56°F. How cold would it have to get outside to cause condensation inside the wall? If the typical low temperature at night in the winter in Half Moon Bay is in the lower 40's Fahrenheit, should you be concerned about condensation? c. You recall hearing of others using 2 inches of polyisocyanurate external (between housewrap and siding) insulation (R-7/in) in Northern California. If your friend took this advice and added the external insulation, how cold would it have to get outside to cause condensation in the wall now? Would this amount of insulation be sufficient in general? Your friend is building a new house in Half Moon Bay and called you for advice on designing the wall given you're taking CEE176A. Half Moon Bay is generally cooler and wetter than Stanford so they want to make sure to prevent any water vapor that may get into the wall from condensing and leading to rotting of their wood frame and mold in their cavity insulation. Your friend chose a 2"x6" at 24" on-center (o.c.) wall construction based on your advice, with a framing factor of 15%. Your friend happens to work for a recycling center and wants to use the recycled paper for cavity insulation, after making a deal with a company that would turn the scrap paper into insulation and give your friend free samples for their home. The company says the final cavity insulation product should provide an R-value of 2 per inch. Otherwise, your friend is planning a standard wall with specifications below (Remember, a 2"x6" stud is actually 1.5x5.5") Ta 1/2" plywood R-0.6 Revo 0.17 W Siding R-0.2 2x6 Fir, k=0.8 Btu-in/hr-ft²-*F Rcvi 0.68 Cavity R-2/in Housewrap R-0.1 T₁ = 70°F 1/2" drywall R-0.5 Figure 1: Original Wall Construction Design for Half Moon Bay Home. a. What is the average R-value of the total wall construction detailed above? Assume Revo = 0.17, and Revi 0.68 ft2 °F-hr/Btu). b. You want to ensure that the exterior surface temperature of the housewrap never gets colder than the dew point temperature to ensure the wooden wall construction never sees condensation. Based on your thermostat setpoint of 70°F in the winter and the typical humidity, the dew point temperature is 56°F. How cold would it have to get outside to cause condensation inside the wall? If the typical low temperature at night in the winter in Half Moon Bay is in the lower 40's Fahrenheit, should you be concerned about condensation? c. You recall hearing of others using 2 inches of polyisocyanurate external (between housewrap and siding) insulation (R-7/in) in Northern California. If your friend took this advice and added the external insulation, how cold would it have to get outside to cause condensation in the wall now? Would this amount of insulation be sufficient in general?