Standard rough-opening shim & jamb allowances
Typical published planning values / code minimums — NOT a certified design or a compliance sign-off. Actual egress compliance and energy performance depend on your local building code (AHJ), climate zone, the exact product’s NFRC-rated U-factor & SHGC and the installation; confirm against local code and the manufacturer’s NFRC label, and consult a pro. Structural headers for enlarged openings, whole-building heat-load / HVAC sizing and code certification are set by code and a professional — not engineered here.
The rough opening is the framed hole — a bit larger than the unit so you can shim it plumb, level and square. These are the LABELED standard allowances: about ½ inch of shim per side for a window (so +1 inch in each dimension), and about +2 inches wide / +2½ inches tall for a pre-hung door (jamb + shims). Confirm the exact rough opening on the manufacturer’s spec sheet. Use them with the rough-opening calculator and the door rough-opening calculator.
| Unit | Allowance | Effect on the rough opening |
|---|---|---|
| Window (shim per side) | 0.50 in each side | +1.00 in width and +1.00 in height |
| Pre-hung door (width) | +2.0 in | Slab width + 2.0 in (jamb + shims) |
| Pre-hung door (height) | +2.5 in | Slab height + 2.5 in (jamb + shims) |
LABELED standard allowances — the common starting point. Confirm the exact rough opening on the manufacturer’s spec sheet; it varies by product and brand.