1.Define the assembly
Uncheck to reproduce legacy spreadsheet numbers, which omitted film resistances.
Set a code or design target to check the total against.
Adds the solid-framing thermal-bridge path (studs / joists / rafters) and reports the whole-wall R alongside the center-of-cavity R.
2.Build the layer stack
Listed exterior → interior. Pick a material (its conductivity fills in automatically) or choose a custom entry to type your own k or R.
| Order | Material | Layer label | Thickness (in) | k (Btu/hr·ft·°F) | Layer R |
|---|
3.Assembly performance
Wall section — exterior to interior
Each band's width approximates its thickness · exterior at left, interior at right
Where the resistance lives
R contribution of each layer — the tall bars are doing the work
4.Export to EnergyPlus
Generates an IDF snippet with full Material objects (thickness, conductivity,
density, specific heat, roughness) for the conductive layers, Material:NoMass /
Material:AirGap for set-resistance layers, and a Construction ordered
outside → inside. Surface films are intentionally omitted — EnergyPlus computes them at
runtime. Density and specific heat make these valid mass materials for a dynamic (CTF) run, not just
steady-state U. Edit any value below, then copy or download the .idf.
| EnergyPlus object | Name | Roughness | Conductivity (W/m·K) |
Density (kg/m³) |
Specific heat (J/kg·K) |
|---|
5.Save & compare assemblies
| Assembly | Layers | Thickness | Total R | Total RSI | U-value |
|---|
Method. Each layer's thermal resistance is its thickness divided by its
conductivity:
Surface films. ASHRAE standard surface resistances depend on orientation and air movement: interior still air is roughly R-0.68 for walls (horizontal flow), R-0.61 for roofs (flow up), and R-0.92 for floors (flow down); the exterior film is about R-0.17 at 15 mph (winter) and R-0.25 at 7.5 mph (summer). Fixed-resistance items — glazing units, reflective air spaces, membranes — contribute a set R regardless of thickness, so their thickness field is used only for the drawing.
What this is — and isn't. This is a one-dimensional, center-of-cavity steady-state calculation. It does not weight parallel paths (the framing factor that lowers a stud wall's whole-wall R below its insulated-cavity value), nor does it model thermal bridging, moisture, or dynamic mass effects. Use it for schematic comparison of layer choices before detailed envelope simulation. Material conductivities follow ASHRAE Handbook—Fundamentals and Brown & DeKay typical values and should be confirmed against manufacturer data for design.
R = t / k. Resistances add in series, so the assembly total is the
sum of all layers plus the interior and exterior surface air films, and the overall heat-loss
coefficient is its reciprocal: U = 1 / Rtotal. Conductivities are stored
in SI (W/m·K) and converted for display; the R-value conversion is
1 m²·K/W = 5.678 ft²·°F·h/Btu.
Surface films. ASHRAE standard surface resistances depend on orientation and air movement: interior still air is roughly R-0.68 for walls (horizontal flow), R-0.61 for roofs (flow up), and R-0.92 for floors (flow down); the exterior film is about R-0.17 at 15 mph (winter) and R-0.25 at 7.5 mph (summer). Fixed-resistance items — glazing units, reflective air spaces, membranes — contribute a set R regardless of thickness, so their thickness field is used only for the drawing.
What this is — and isn't. This is a one-dimensional, center-of-cavity steady-state calculation. It does not weight parallel paths (the framing factor that lowers a stud wall's whole-wall R below its insulated-cavity value), nor does it model thermal bridging, moisture, or dynamic mass effects. Use it for schematic comparison of layer choices before detailed envelope simulation. Material conductivities follow ASHRAE Handbook—Fundamentals and Brown & DeKay typical values and should be confirmed against manufacturer data for design.