diff --git a/src/components/fabric/QPolygon.js b/src/components/fabric/QPolygon.js
index 29868836..a0fcb57f 100644
--- a/src/components/fabric/QPolygon.js
+++ b/src/components/fabric/QPolygon.js
@@ -2,7 +2,7 @@ import { fabric } from 'fabric'
 import { v4 as uuidv4 } from 'uuid'
 import { QLine } from '@/components/fabric/QLine'
 import { distanceBetweenPoints, findTopTwoIndexesByDistance, getDirectionByPoint, sortedPointLessEightPoint, sortedPoints } from '@/util/canvas-util'
-import { calculateAngle, drawGableRoof, drawRoofByAttribute, drawShedRoof, toGeoJSON } from '@/util/qpolygon-utils'
+import { calculateAngle, drawGableRoof, drawRoofByAttribute, drawShedRoof, snapNearAxisEdges, toGeoJSON } from '@/util/qpolygon-utils'
 import * as turf from '@turf/turf'
 import { LINE_TYPE, POLYGON_TYPE } from '@/common/common'
 import Big from 'big.js'
@@ -120,6 +120,20 @@ export const QPolygon = fabric.util.createClass(fabric.Polygon, {
     this.adjustRoofLines = []
     // this.colorLines = []
 
+    // [1956-RACK-TILT 2026-05-13] 빨강 점선 폴리곤군(가대선/모듈설치면) FP drift 보정.
+    // - trestle, dormerTrestle: createRoofRack 출력
+    // - trestlePolygon: useMode.handleOuterlinesTest 출력
+    // - moduleSetupSurface: useModuleBasicSetting (eavesMargin/ridgeMargin/kerabaMargin 적용)
+    // 가로/세로 edge 의 FP drift 가 저장된 JSON 에 박혀있는 경우 복원 시 라인이 기울어 보이는 문제.
+    if (
+      options.name === 'trestle' ||
+      options.name === 'dormerTrestle' ||
+      options.name === 'trestlePolygon' ||
+      options.name === 'moduleSetupSurface'
+    ) {
+      points = snapNearAxisEdges(points, 2)
+    }
+
     // 소수점 전부 제거
     points.forEach((point) => {
       point.x = Number(point.x.toFixed(this.toFixed))
diff --git a/src/hooks/useMode.js b/src/hooks/useMode.js
index 4bb91ba8..af134ece 100644
--- a/src/hooks/useMode.js
+++ b/src/hooks/useMode.js
@@ -33,7 +33,7 @@ import {
 import { QLine } from '@/components/fabric/QLine'
 import { fabric } from 'fabric'
 import { QPolygon } from '@/components/fabric/QPolygon'
-import offsetPolygon, { calculateAngle } from '@/util/qpolygon-utils'
+import offsetPolygon, { calculateAngle, snapNearAxisEdges } from '@/util/qpolygon-utils'
 import { isObjectNotEmpty } from '@/util/common-utils'
 import * as turf from '@turf/turf'
 import { INPUT_TYPE, LINE_TYPE, Mode, POLYGON_TYPE } from '@/common/common'
@@ -1505,7 +1505,16 @@ export function useMode() {
       offsetPoints.push(offsetPoint)
     }
 
-    return makePolygon(offsetPoints, false)
+    // [1956-RACK-TILT 2026-05-13] trestlePolygon(モジュール配置領域 빨강점선) FP drift 보정.
+    // 입력 polygon.lines 의 미세 drift 가 평균법선 offset 으로 전파되어 가로/세로 라인이
+    // 기울어 보이는 문제 차단. tolerance 0.5mm 보다 작은 dy/dx 만 축으로 스냅.
+    const _snapped = snapNearAxisEdges(
+      offsetPoints.map((p) => ({ x: p.x1, y: p.y1 })),
+      2,
+    )
+    const snappedOffsetPoints = _snapped.map((p) => ({ x1: p.x, y1: p.y }))
+
+    return makePolygon(snappedOffsetPoints, false)
   }
 
   /**
@@ -5115,6 +5124,7 @@ export function useMode() {
 
     roofs.forEach((roof, index) => {
       // const offsetPolygonPoint = offsetPolygon(roof.points(), -20) //이동되서 찍을라고 바꿈
+      // [1956-RACK-TILT 2026-05-13] trestle name 으로 QPolygon.initialize 가 축-스냅 처리
       const offsetPolygonPoint = offsetPolygon(roof.getCurrentPoints(), -20)
 
       const trestlePoly = new QPolygon(offsetPolygonPoint, {
diff --git a/src/util/qpolygon-utils.js b/src/util/qpolygon-utils.js
index dccd3414..5fc1a2e7 100644
--- a/src/util/qpolygon-utils.js
+++ b/src/util/qpolygon-utils.js
@@ -405,6 +405,57 @@ export function cleanSelfIntersectingPolygon(vertices) {
   return vertices
 }
 
+/**
+ * [1956-RACK-TILT 2026-05-13] 거의 축에 평행한 edge 를 정확히 수평/수직으로 스냅.
+ * 빨강 점선(가대선/모듈설치면) edge 가 FP drift 누적으로 미세 기울어져 보이는 문제 보정.
+ * **각도 기반 판정**: |dy|/len < sin(angleTolDeg) 면 수평으로 간주.
+ * 절대값 tolerance 가 아닌 각도 임계를 쓰는 이유 — 긴 edge(예: 576mm) 에 작은 누적
+ * drift(15mm) 가 실려 closing edge 가 흡수하면 절대값은 크지만 각도는 작음(1.5°).
+ * vertex 단위로 인접 edge 의 축 목표값을 적용해 코너 어긋남 방지.
+ * 대각(hip/ridge, 45° 등) 은 임계 2° 보다 훨씬 크니 무영향.
+ */
+export function snapNearAxisEdges(vertices, angleTolDeg = 2) {
+  if (!vertices || vertices.length < 3) return vertices
+  const n = vertices.length
+  const sinTol = Math.sin((angleTolDeg * Math.PI) / 180)
+
+  const edgeY = new Array(n).fill(null) // 거의 수평 → 목표 y
+  const edgeX = new Array(n).fill(null) // 거의 수직 → 목표 x
+
+  for (let i = 0; i < n; i++) {
+    const a = vertices[i]
+    const b = vertices[(i + 1) % n]
+    const dx = b.x - a.x
+    const dy = b.y - a.y
+    const len = Math.sqrt(dx * dx + dy * dy)
+    if (len < 1) continue // 0-length edge 안전장치
+    const absSinDy = Math.abs(dy) / len // sin(angle from horizontal)
+    const absSinDx = Math.abs(dx) / len // sin(angle from vertical)
+    if (absSinDy < sinTol && absSinDx >= sinTol) {
+      edgeY[i] = (a.y + b.y) / 2 // 거의 수평
+    } else if (absSinDx < sinTol && absSinDy >= sinTol) {
+      edgeX[i] = (a.x + b.x) / 2 // 거의 수직
+    }
+  }
+
+  return vertices.map((v, i) => {
+    const prev = (i - 1 + n) % n
+    let nx = v.x
+    let ny = v.y
+    const yPrev = edgeY[prev]
+    const yCur = edgeY[i]
+    if (yPrev !== null && yCur !== null) ny = (yPrev + yCur) / 2
+    else if (yPrev !== null) ny = yPrev
+    else if (yCur !== null) ny = yCur
+    const xPrev = edgeX[prev]
+    const xCur = edgeX[i]
+    if (xPrev !== null && xCur !== null) nx = (xPrev + xCur) / 2
+    else if (xPrev !== null) nx = xPrev
+    else if (xCur !== null) nx = xCur
+    return { x: nx, y: ny }
+  })
+}
+
 export default function offsetPolygon(vertices, offset) {
   const polygon = createPolygon(vertices)
   const arcSegments = 0