Stack the layers of a wall, roof or floor from your wall section, mark the one the studs interrupt, and watch MEEB Example 9.2's parallel-path arithmetic written out with your numbers in it — plus the temperature at every interface, so you can see where the wall gets cold enough to condense.
| # | Layer | in. | R | Bridged |
|---|
Your wall is nothing like the examples? Start from scratch: it keeps only the two air films. Add your layers from outside to inside — each new one goes in just inside the last, ahead of the inside film — then tick Bridged on the layer the studs interrupt.
R in h·ft²·°F/Btu. Thickness only matters for per-inch materials. Pick Custom to name a layer, type its R from your product data, choose how it is drawn, and give its source — the name and source go into the assumptions-log line. Values marked typical are MEEB Tables E.1, E.3 and E.4 — check the table for your exact product.
Softwood at R 1.24 per inch (MEEB Ex. 9.2). ASHRAE 90.1 Appendix A assumes about 25% framing for 16 in. o.c. and 22% for 24 in. o.c., counting plates, sills and headers. MEEB's example uses 12%, which is studs alone.
Outside defaults to Detroit Metro's 99.6% heating design dry-bulb, 3.2 °F (TMYx, 2025 ASHRAE). Detroit is climate zone 5A, the same zone as MEEB's Indianapolis example.
| # | Layer · outside to inside | R | °F out → in |
|---|
Four things the layer table makes obvious that the formula alone does not.
Through the framing, 1 ÷ 10.25 = 0.098; weighted at 12%, the wall comes out at 0.051 — and MEEB's SI solution, 0.291 W/m²·K ÷ 5.678, gives the same. The framing costs about 14% over the 0.045 you get by ignoring it. This is the Verifier's whole job in one line: a number you can check beats a number you were given.
Heat takes both paths at once, so the paths add as conductances: U = 0.75·Uins + 0.25·Uframe. Averaging the resistances instead (0.75·Rins + 0.25·Rframe) always flatters the wall, because it lets the insulation vote on the stud's share. LV 1's tolerance is set so that the R-averaged answer falls outside it.
MEEB §9.3(e): a 2×4 wood wall with R-13 is U 0.094; the same wall on steel studs is 0.134, "equivalent to an R-3 decrease in insulation." Continuous insulation outboard of the studs is the fix, and the reason Zone 5 code walls on steel need it to reach 0.064. And the batt still matters: the effective R is the batt's value after the steel has taken its share, so leaving the cavity empty costs you that too.
MEEB §9.4(b): in a cold climate the retarder goes as close to the warm side as possible, because the indoor air is the source. The gradient here assumes the indoor vapor reaches every layer; the drawing is telling you why it must not. Move the insulation outboard (Orenco preset) and the sheathing warms up — that is the other cure.
Each layer contributes R = thickness × R-per-inch, or a fixed R for films, air spaces and batts. Through the insulation, ΣRins is the sum of every layer; Uins = 1 ÷ ΣRins. Through the framing, the bridged layer's R is replaced by the stud's R (softwood at 1.24 per inch) and Uframe = 1 ÷ ΣRframe. The area-weighted U = (1 − f)·Uins + f·Uframe, MEEB Example 9.2. For steel studs the bridged layer (the cavity insulation) and the studs around it count together as one effective R from ASHRAE 90.1 Appendix A, and there is one path. The effective R exists because the cavity is insulated; it is not what the steel leaves when the insulation is removed. The gradient (Example 9.5) puts the temperature at each interface at Tin − Δt × (R accumulated from inside ÷ ΣRins). Dew point from the indoor dry-bulb and RH by the Magnus approximation. Imperial throughout; ÷ 5.678 turns W/m²·K into Btu/h·ft²·°F.
Glass. You can stack panes and a sealed gap as custom layers, and the Builder will show you why double glazing is warmer on the room side. What it gives you is a center-of-glass U. The window's heat loss uses the whole-unit U from the NFRC label, MEEB Fig. 9.15 or Table E.15, because the frame and the edge spacer raise it, a lot on a steel frame without a thermal break. When it sees glass, the Builder compares against the Zone 5 window line (0.35), and it checks condensation only on the room-side face of the glass, because room air cannot reach the surfaces inside a sealed unit.
It does not do windows (NFRC whole-unit U-factors, §9.5), slab edges (F2 per foot of perimeter, §9.3(f)) or below-grade walls — those are single numbers you look up, and MEEB Chapter 9 says where.