---
title: Box Gutter Expansion Joint Installation
description: "**Step 1**: For square ducts, chimneys and skylights: Expand one edge and use separate strips, lapped and joined, to seal around the penetration. **Step 2**: For large round pipes: Flash in one step, stretching the lower edge to fit. Join using…"
url: "https://marcoindustries.com/installation-questions/box-gutter-expansion-joint-installation/"
updated: "2023-10-05"
category: Flashing
---

# Box Gutter Expansion Joint Installation

**Step 1**: For square ducts, chimneys and skylights: Expand one edge and use separate strips, lapped and joined, to seal around the penetration.

**Step 2**: For large round pipes: Flash in one step, stretching the lower edge to fit. Join using fasteners or sealant.

**Step 3**: After installation, and preferably after a period of weathering, Box Gutter Expansion Joint can be painted with any quality 100% acrylic paint after priming with an epoxy resin-based primer.