Chapter 4 Quiz: Insulation and the Building Envelope

Multiple Choice

1. Which of the following best describes what R-value measures?

a) The rate at which a material transfers heat b) A material's resistance to conductive heat flow c) The amount of moisture a material can absorb d) The reflectivity of a surface to radiant heat

2. In an older home with significant air leakage, which improvement typically delivers the best return on investment?

a) Replacing all windows with triple-pane units b) Adding R-15 wall insulation throughout c) Air sealing at attic penetrations, rim joists, and other bypass locations d) Installing a radiant barrier in the attic

3. A homeowner in a cold climate installs 6-mil polyethylene sheeting on the interior side of their basement wall to "keep moisture out." What is the most likely problem with this approach?

a) Polyethylene is not fire-rated and violates building code b) It creates a double barrier that traps moisture with no drying pathway c) Polyethylene degrades rapidly in basement humidity levels d) The sheeting will reduce the effectiveness of any insulation added later

4. A 2x4 framed wall with R-15 fiberglass cavity insulation and 25% framing fraction has an effective R-value of approximately:

a) R-15.0 b) R-13.2 c) R-9.4 d) R-6.0

5. Which type of insulation provides the highest R-value per inch?

a) Fiberglass batt b) Loose-fill cellulose c) Closed-cell spray foam d) Expanded polystyrene (EPS) rigid board

6. The stack effect in a home refers to:

a) Heat stratifying with warm air at ceiling level and cool air at floor level b) The tendency of warm air to rise and exit through high openings, drawing cold air in at low openings c) The building up of insulation layers to achieve higher R-values d) Moisture vapor stacking up at the cold surface inside a wall assembly

7. Dense-pack cellulose in existing wall cavities (drilled retrofit) is preferred over fiberglass batts for which reason?

a) Cellulose has a significantly higher R-value per inch than fiberglass b) Cellulose does not require a vapor retarder while fiberglass always does c) Dense-pack cellulose provides significantly better air resistance and fills irregular cavities d) Fiberglass batts cannot be used in exterior wall cavities by current building code

8. Polyisocyanurate (polyiso) rigid foam board is rated at R-6.5 per inch at room temperature. Why might you choose XPS foam instead for an exterior application in a cold climate?

a) XPS is less expensive in all applications b) Polyiso's R-value degrades significantly at cold temperatures c) Polyiso cannot be used on vertical surfaces d) XPS provides better vapor barrier properties in humid conditions

9. A blower door test result of 15 ACH50 for an older farmhouse indicates:

a) The home meets current energy code requirements for new construction b) The home has five times more air leakage than a Passive House-certified building c) The home's air leakage rate is significantly above average and represents a major energy loss d) Both b and c

10. Which of the following is a correct statement about thermal bridging through wall framing?

a) Thermal bridging only occurs in steel-framed buildings, not wood-framed ones b) Adding continuous exterior insulation reduces thermal bridging because it covers all framing members simultaneously c) The thermal bridging problem can be fully solved by using higher-R-value cavity insulation d) Thermal bridges increase effective R-value by conducting heat into the wall cavity

Short Answer

11. Explain in your own words why air sealing is often recommended before adding insulation in an older home. What happens to the insulation's effectiveness if air sealing is skipped?

12. A homeowner in Atlanta, Georgia (a hot-humid climate, Climate Zone 2) is finishing their basement and wants to install a vapor barrier. They've heard they should put poly sheeting on the interior face of the walls before drywalling. Is this correct? Explain what the appropriate vapor management strategy would be and why.

13. You are helping a friend evaluate two insulation upgrade options for their 1970s home in Minnesota (Climate Zone 6): - Option A: Blow cellulose into all wall cavities via exterior drilling, adding R-13 to currently uninsulated walls. Cost: $8,000. - Option B: Add 2" of continuous XPS rigid foam to the exterior of the walls when re-siding (which they plan to do in 18 months anyway). R-10 of exterior insulation. Cost of foam and modified trim: $3,500 incremental to the siding project.

Which option would you recommend and why? Consider both the thermal performance outcome and the cost-effectiveness of each approach.

Answer Key

Multiple Choice: 1-b, 2-c, 3-b, 4-c, 5-c, 6-b, 7-c, 8-b, 9-d, 10-b

Short Answer Guidance:

11. A complete answer should explain that air leaks allow warm air to bypass insulation entirely through convective loops — moving around or through the insulation without being stopped. Adding insulation without first sealing air leaks means the insulation's rated R-value is not achieved in practice. The insulation resists conduction but cannot stop the convective flow of warm air through unsealed penetrations.

12. Poly sheeting on the interior of basement walls in Atlanta is incorrect. Atlanta's hot-humid climate creates summer vapor drive from outside in (moist outdoor air is driven inward). An interior poly barrier would trap this inward-driven moisture in the wall assembly, creating conditions for mold and rot. The correct strategy is either: (a) closed-cell spray foam on the exterior face of the wall (acting as the vapor control on the exterior side), or (b) an assembly that allows drying to the interior, with no interior vapor barrier.

13. A complete answer should recommend Option B (exterior rigid foam during re-siding) for these reasons: (1) It addresses thermal bridging through studs, which Option A does not — Option A adds R-13 cavity insulation that is still bridged by studs, yielding perhaps R-8 to R-9 effective; Option B adds R-10 continuous insulation that fully covers studs, with potentially better effective performance at lower cost. (2) Option B's incremental cost is $3,500 vs. $8,000 for Option A — significantly cheaper. (3) Since re-siding is planned anyway, the marginal cost of adding foam is much lower than a standalone project. (4) Option B also provides an opportunity to address window flashing and improve the water management details of the wall, which is a co-benefit.