Waller is a free wall assembly calculator that builds a residential wall layer by layer and computes the three things that decide whether a wall performs and lasts: its effective R-value (thermal resistance, including the parallel heat path through the studs), its interstitial condensation and dew-point risk (a Glaser analysis that shows exactly which layer would get wet), and its net embodied carbon. It runs entirely in your browser, shows a source for every number, and lets you share a wall by link or print a PDF report.
R-value adds up predictably — but dew-point and vapor behavior do not. They depend on the order of the layers, the climate, and each material's vapor permeance. A general AI assistant will confidently give you a wrong condensation answer because it is estimating, not simulating. Waller runs the actual physics — EN ISO 10456 / ASHRAE design values for heat, the EN ISO 13788 Glaser method for moisture — and returns the same correct, reproducible result every time, with the at-risk interface highlighted.
Each row below is a vetted Waller template, validated condensation-free at its climate zone's winter design conditions. R-value is the effective whole-wall value; net embodied carbon is EN 15804 A1–A3 including biogenic storage, per square metre of wall. A negative value means the wall stores more carbon than its manufacture emitted.
| Wall assembly | Climate zones | Thickness | Effective R-value | Net embodied carbon | Condensation |
|---|---|---|---|---|---|
| Plastered straw bale | CZ3–4 | 19.7 in | R-47 | −54 kg CO₂e/m² | None |
| Perfect Wall (exterior insulation) | CZ4–8 | 11.5 in | R-36 | +17 kg CO₂e/m² | None |
| Double-stud cellulose superwall | CZ5–8 | 11.8 in | R-26 | −58 kg CO₂e/m² | None |
| Cold-climate 2×6 + exterior CI | CZ5–6 | 9.9 in | R-25 | −23 kg CO₂e/m² | None |
| ICF (insulated concrete forms) | CZ1–5 | 13.5 in | R-25 | +63 kg CO₂e/m² | None |
| CLT + thick mineral wool | CZ6–8 | 10.5 in | R-24 | −54 kg CO₂e/m² | None |
| Mixed-climate 2×6 (cellulose) | CZ3–4 | 10.0 in | R-22 | −35 kg CO₂e/m² | None |
| Hot-humid 2×4 (no vapor barrier) | CZ1–2 | 6.9 in | R-17 | +11 kg CO₂e/m² | None |
| Brick cavity wall, insulated | CZ3–6 | 17.7 in | R-17 | +111 kg CO₂e/m² | None |
Open any of these in the builder above to see the full layer stack, vapor profile, cost, and code check.
It depends on your climate zone. The 2021 IECC requires roughly R-13 in hot climates (zones 1–2) up to R-30 cavity or R-20+5 continuous in cold zones (4–8). Waller derives your zone from a map click and checks your wall against IECC, net-zero-ready, Passive House, and EnerPHit targets live.
Warm humid air diffusing toward a cold surface inside the assembly. When the vapor reaches a layer below its dew point, it condenses — typically at cold sheathing in winter, or behind interior vapor barriers in air-conditioned hot-humid climates. Waller runs a Glaser dew-point analysis on every change and shows exactly which interface is at risk.
Usually you need vapor control, not a vapor barrier. In very cold climates an interior retarder helps; in hot-humid climates an interior plastic sheet causes rot; in mixed climates smart (humidity-variable) membranes are the safe choice. Two vapor-tight layers with anything organic between them is the classic moisture trap.
Yes. Waller is free, runs entirely in your browser, and uses published design data (EN ISO 10456, ASHRAE Fundamentals) with sources shown for every number. You can share walls by link and print PDF reports.
Walls built from carbon-storing materials — straw bale, cellulose, wood fibre, hemp-lime — can store more carbon than their manufacture emits while meeting modern energy codes. Waller computes net embodied carbon (A1–A3 with biogenic storage) for every assembly and includes vetted natural-wall templates.
Method & limits: screening-grade 1-D steady-state analysis (EN ISO 13788, Glaser method) — the field of the wall, not junctions, air leakage, or whole-envelope code compliance. Thermal and vapor data are EN ISO 10456 / ASHRAE Fundamentals design values; embodied carbon is EN 15804 A1–A3 with biogenic storage. Waller is an education and early-design tool, not a compliance or liability authority — verify with transient (WUFI-class) and code (REScheck-class) tools before building.