Chapter 4 Exercises: Insulation and the Building Envelope

These exercises are designed to be performed in your own home. You will need a tape measure, a flashlight, and in some cases a notepad for recording observations. A few exercises require minimal materials available at any hardware store.

Exercise 4-1: Identify Your Climate Zone

Before you can evaluate your home's insulation, you need to know your climate zone.

  1. Look up your zip code in the DOE's climate zone map (available at energycodes.gov or by searching "DOE climate zone map by zip code").
  2. Record your climate zone (1–7 for most of the US).
  3. Using the table in section 4.7, find the recommended total R-value for your attic.
  4. Compare to what your home actually has (you'll measure this in Exercise 4-3).

Record: Your climate zone, recommended attic R-value, and any notes about your local climate (humid, dry, mixed).

Exercise 4-2: The Candle/Incense Smoke Test for Air Leaks

On a cold, windy day (or with your HVAC fan running on the "fan only" setting), perform this informal air leak survey.

Materials: A stick of incense or a candle, a notepad.

Procedure: 1. Hold the smoke source close to (but not touching) each of the following locations and observe whether the smoke wavers or streams in a particular direction: - Around the perimeter of each exterior door (top, sides, and bottom) - Around window frames at the edges of the trim - Electrical outlet boxes and switch plates on exterior walls - The base of baseboards on exterior walls - Around the attic access hatch or pull-down stairs - Where pipes or wires enter through exterior walls (under sinks, behind appliances) 2. Mark any locations where you detect drafts on a sketch of your floor plan. 3. Rank the three worst drafts.

Follow-up: Research the appropriate fix for each leak you found (caulk, weatherstripping, foam, or rigid cover) and estimate the material cost to address each.

Exercise 4-3: Measure Your Attic Insulation

Materials: Tape measure, flashlight, old clothes you don't mind getting dirty, N95 respirator mask.

Safety first: Do not step off the joists — always step only on structural members or a piece of plywood laid across them. Insulation conceals the floor between joists; stepping there will put your foot through the ceiling.

Procedure: 1. Access your attic. 2. Find a clear area between joists and measure the depth of existing insulation in inches. 3. Identify the insulation type (fiberglass batts, loose-fill fiberglass, loose-fill cellulose, spray foam, or other). 4. Using the R-values-per-inch from section 4.2, calculate the approximate R-value you currently have. 5. Compare to your climate zone's recommended R-value from Exercise 4-1.

Record: Current insulation type, depth, estimated R-value, recommended R-value, and the gap between them.

Exercise 4-4: Calculate the R-Value of a Wall Assembly

Choose one exterior wall in your home and research its likely construction (you may be able to find this in old building permits, by removing an outlet cover and examining the cavity depth, or by asking about the home's age and construction type).

Construct a layer-by-layer table similar to the worked example in section 4.2. Include: - Exterior air film (R-0.17) - Exterior cladding (siding type and approximate R-value) - Any sheathing - Structural framing (note framing size — 2x4 or 2x6) - Cavity insulation (type and depth) - Any interior sheathing or drywall - Interior air film (R-0.68)

Sum the layers to find your estimated clear-field R-value. Then apply the framing fraction correction from section 4.6 to estimate effective R-value.

Compare to the recommended R-value for walls in your climate zone (typically R-20 to R-30 for Zone 5).

Exercise 4-5: Inspect Your Rim Joists

Access required: Basement or crawlspace.

  1. Find your basement rim joist — it's the vertical framing member that runs around the perimeter of the house at the top of the foundation wall, just below the first floor.
  2. Note whether it is: - Uninsulated (bare framing visible) - Insulated with fiberglass batts (common in older homes; check whether batts are sealed against the joist or just stuffed in loosely) - Insulated with spray foam or rigid foam (less common, but best practice)
  3. Look for signs of air infiltration: cobwebs, dust streaks, frost or staining in winter, or visible daylight through gaps.
  4. Measure the approximate lineal footage of rim joist in your basement.

Follow-up: Calculate the approximate materials cost to do a DIY rigid foam cut-and-cobble upgrade. Assume you'll need 2-inch XPS foam board (approximately $0.50–$0.70 per square foot) plus one can of low-expansion foam per 50 linear feet. Is this a project you could tackle?

Exercise 4-6: Assess Your Attic Hatch or Pull-Down Stairs

  1. Locate your attic access point (hatch or pull-down stairs).
  2. On a cold day, hold your hand near the perimeter of the hatch frame and note whether you feel cold air.
  3. Measure the hatch or stair opening dimensions.
  4. Observe: Is the hatch door itself insulated? Is there weatherstripping around the frame?
  5. Go up into the attic and observe whether there is an insulation cover over the hatch from above.

If the hatch is uninsulated or unsealed: Research the cost of a commercially available insulated attic stair cover (approximately $50–$150) or the DIY option of building one from rigid foam board. Estimate the payback period assuming your heating cost is $150/month and an uninsulated hatch loses approximately $50–$80 worth of heat annually in a cold climate.

Exercise 4-7: Survey Recessed Lights in Ceilings Below the Attic

  1. Walk through your home and count every recessed light fixture in any ceiling that has an unconditioned attic above it.
  2. For each fixture, go into the attic (if accessible) and observe whether the fixture: - Has no cover or seal around it (most common in pre-2000 homes) - Has a fire-rated, air-tight cover installed over it from the attic side - Is an IC-ICAT (insulation contact, air-tight) rated fixture
  3. Calculate: if each unsealed can light loses approximately 8–15 CFM of air at average pressure conditions, and you have 12 such fixtures, estimate your air leakage contribution from can lights alone.

Follow-up: Identify the cost to replace old can lights with new IC-ICAT LED fixtures (typically $30–$60 per fixture plus labor) or to add airtight covers from the attic side (approximately $15–$25 per fixture, DIY-friendly).

Exercise 4-8: The Hand Test for Thermal Performance

On a cold day (outdoor temperature below 35°F), after the house has been heated for at least an hour:

  1. Hold the back of your hand close to (not touching) the surface of an exterior wall in the middle of a room — not near windows or doors.
  2. Compare that surface temperature sensation to an interior partition wall.
  3. Hold your hand near the ceiling in the top floor rooms.
  4. Hold your hand near the floor in basement or first-floor rooms.

The wall temperature differential you feel is a rough proxy for how well the assembly is insulated. An exterior wall that feels significantly colder than an interior wall indicates high conductive loss. A ceiling that feels cold indicates inadequate attic insulation.

Record your observations: Note which surfaces feel coldest and hypothesize which improvement (more insulation, air sealing, or both) would address each one.

Exercise 4-9: Evaluate the Cost-Benefit of an Attic Insulation Upgrade

Using your results from Exercises 4-1 and 4-3, perform a simplified cost-benefit calculation.

Data you need: - Current attic R-value (from Exercise 4-3) - Target R-value (from Exercise 4-1) - Your home's approximate conditioned area (square footage) - Your annual heating/cooling cost (from utility bills)

Simplified calculation: 1. Percentage improvement in thermal resistance: (Target R − Current R) / Target R × 100 2. Estimated annual savings: Your annual heating cost × percentage improvement × 0.10 (the attic represents roughly 10–25% of total heat loss — use 15% as a default) 3. Estimated upgrade cost: Get one quote from a local insulation contractor, or estimate using approximately $1.00–$1.50/sq ft for blown-in insulation (including some air sealing) 4. Simple payback period: Upgrade cost / annual savings

Is the payback period under 10 years? (Most energy efficiency upgrades with a payback under 7–10 years are considered financially attractive.)

Exercise 4-10: Research Utility Rebates and Tax Credits

Energy efficiency improvements may qualify for financial incentives that dramatically improve their economics.

  1. Visit your utility company's website and search for "rebates" or "energy efficiency programs." Note any rebates available for insulation, air sealing, or weatherization.
  2. Visit energystar.gov/rebate-finder or irs.gov and search for the current federal tax credit for home energy improvements (under the Inflation Reduction Act, energy efficiency home improvement credits were extended and expanded — verify current amounts).
  3. Check whether your state offers additional tax credits or low-interest loan programs for weatherization.
  4. Recalculate your payback period from Exercise 4-9 after applying available incentives.

Many homeowners are surprised to find that federal and state incentives can reduce the net cost of insulation and air sealing by 30–50%, dramatically improving the financial case.

Exercise 4-11: Identify Your Home's Vapor Retarder Strategy (Advanced)

This exercise requires removing an electrical outlet cover plate on an exterior wall.

Safety: Turn off the circuit breaker for that outlet before removing the cover.

  1. Remove the cover plate and look into the gap around the electrical box.
  2. Can you see any plastic sheeting (polyethylene vapor barrier) behind the drywall?
  3. If you have access to an unfinished basement wall, observe whether there is poly on the interior face of the framing before any drywall.
  4. Research your climate zone's current vapor retarder requirements (IRC Table R702.7.1).
  5. Compare what you found to what is currently recommended for your climate zone.

Reflection: Is your home's vapor management strategy appropriate for your climate? If you are in a mixed or hot-humid climate and found poly on interior walls, note this as a potential moisture risk to discuss with a building scientist before doing any wall re-insulation work.

Exercise 4-12: Create a Whole-Home Air Sealing Priority List

Synthesize the findings from Exercises 4-2, 4-5, 4-6, and 4-7 into a prioritized action list.

For each air leakage location you identified, create a row in a table with: - Location - Estimated leakage severity (small, medium, large) - Appropriate fix - Materials cost estimate - Time to fix (DIY hours) - Priority rank

Rank items by cost-effectiveness (largest leak fixed for least money and time first). Use this list as your actual home maintenance roadmap. This is the kind of analysis that a professional energy auditor would charge $200–$500 to produce — you've now done it yourself.