Why Alignment Matters
Temperature Movement
Vinyl frames expand and contract with temperature. In Calgary's extreme swings (−30°C to +30°C), that movement is significant. Proper shimming lets frames float without distortion.
Smooth Operation
A window that's plumb, level, and square operates smoothly. Casements close tight. Sliders glide. Awnings seal. Misalignment causes sticking, gaps, and air leaks within the first year.
Long-Term Warranty
Most warranty claims are caused by installation — not product defects. Correct alignment protects your 25-year warranty investment.
The Science of Shimming
The "Float" Concept
CSA-A440.4-07 designs the shimming system so a window "floats" in the rough opening. The intent:
- • Frame can expand and contract with temperature without stress
- • Surrounding cladding can move without putting pressure on the window
- • Building structure can shrink as it dries without crushing the frame
The Reference (R) Point
One double-strength fastener at the sill pins the window in position. All other fasteners are regular-strength to allow frame movement. Think of it like a picture hung from one nail — it hangs steady but can adjust.
In Practice: How GreenFox Does It
- ✓ Frames shimmed at jambs and sill
- ✓ Anchors driven through jambs and shims to clamp firmly — prevents screw bending
- ✗ NO fasteners in the sill (avoids blocking frame drainage) unless window exceeds 64 inches wide
- ✗ NO fasteners in the head — allows the lintel to settle as the structure dries
- ✗ NO shims at the head
- ✗ Corners NOT packed — allows thermal expansion room
CSA-A440.4-07 Clearance Requirements
Gap Tolerances
| Location | Minimum | Maximum | Notes |
|---|---|---|---|
| Jambs | 9.5mm (⅜") | 19mm (¾") | Window centered ±3mm |
| Head & Sill | 12.5mm (½") | 22mm (⅞") | Head gap may be larger than sill |
Shim Placement (PVC/Vinyl Windows)
- • Minimum 200mm (8") from corners (dark colors: add 50mm more)
- • 2 shims per jamb up to 1600mm window width
- • 3 shims per jamb up to 2400mm window width
- • Shims placed below jambs to support weight to rough sill
- • Use opposing pairs of ramped cedar shims to avoid twisting
Shim Material Requirements
CSA-A440.4-07 specifies:
- ✓ Hard enough to permanently support frame without changing shape
- ✓ Good thermal separator
- ✓ Resistant to decay
- ✓ Allow anchoring through the shim
- ✓ Cedar shingles/shakes per CSA-O118.1 or O118.2
What Poor Alignment Causes
Interactive Frame Distortion
Drag the slider to see how misalignment progressively distorts your window frame:
Perfectly aligned — smooth operation, tight seal
Effects by distortion level:
- 0-25%: Minor air gap, slight binding
- 25-50%: Window sticks, visible gaps form
- 50-75%: Major drafts, seal broken, sash locks fail
- 75%+: Hardware stressed, warranty void, frame bowed
Alignment Checklist
1 Before Shimming
2 Shimming Process
3 After Shimming
Alignment is invisible — until it fails.
You won't notice good alignment because everything just works. You'll absolutely notice bad alignment when your window sticks every winter. We measure twice, shim precisely, and check every sash before we leave.