One deep reading near the attic hatch can conceal thin eaves, a displaced service path, or a bare patch. A small location map gives a better account of what exists before you enter an effective existing R-value in a planning tool. Depth alone does not establish R-value when material type, condition, or coverage is uncertain.
Sample the pattern, not only the deepest spot
Draw the attic floor outline from a plan or safe access point. Divide the accessible, relevant area into a few named zones such as A1–C3. Keep the grid approximate; its job is to make repeated observations locatable. Mark eaves, hatch, ducts, walkways, and any visible disturbance. If a location cannot be reached or measured safely, write inaccessible, not an invented depth.
At each safe point, measure from the ceiling plane to the top of the insulation without compressing it, and record the material as identified, suspected, or unknown. Note wet, compressed, displaced, or mixed material separately. Do not step between secure walking surfaces, disturb wiring, or work near heat-producing equipment to complete a grid.
Attic insulation depth map · Site: __________ · Date: __________ · Material: __________
Scroll the diagram sideways to read its labels.
| Sample | Example depth | Your depth | Material / condition / access |
|---|---|---|---|
| A1 | 8 in | ________ | ________________ |
| A2 | 7 in | ________ | ________________ |
| A3 | 6 in | ________ | ________________ |
| B1 | 9 in | ________ | ________________ |
| B2 | 8 in | ________ | ________________ |
| B3 | 2 in, disturbed | ________ | ________________ |
| C1 | 8 in | ________ | ________________ |
| C2 | 7 in | ________ | ________________ |
| C3 | 5 in | ________ | ________________ |
The example's common readings cluster around 7–8 in, but B3 is only 2 in and C3 is 5 in. Write “typical observed depth: 7–8 in; low spots: B3 and C3” rather than averaging the nine readings into one reassuring number. A simple average also gives every sample equal weight even when the cells represent different floor areas or conditions. If low areas are substantial, map or measure them as separate zones for review.
Decide what can be credited
Keep a separate line for known material, uncertain material, low spots, damp or compressed areas, and unmeasured space. A product label or qualified inspection is needed to translate depth and installed condition into a credible existing R credit. When that credit cannot be established, the insulation planner should not be fed a confident value based on a single ruler reading. Resolve moisture, air leakage, ventilation, and safety conditions before covering the layer.
ENERGY STAR's DIY insulation checks and R-value guidance provide authoritative context for uneven coverage and retrofit planning. Material choice belongs in the batt versus blown-in Decision page; this worksheet only records the existing layer. It does not prescribe a climate-zone target, diagnose hazardous materials, or specify an insulation assembly.