How to Slope a Pergola?

To slope a flat-roofed pergola, one common method involves creating a pitch using graduated furring strips attached to the purlins.

If you have a pergola with a flat top and wish to add a minor slope, particularly for drainage or aesthetic purposes, you can achieve this by cutting graduated furring strips and nailing them to the top of your pergola's purlins.

Method: Adding Slope with Furring Strips

This technique essentially builds up one side of the pergola's top structure, creating the necessary angle. Here's a breakdown:

• Materials Needed: Furring strips (lumber), saw, nails or screws, measuring tape.
• Process:
  1. Determine the direction of the desired slope.
  2. Calculate the required height difference across the width or length of your pergola based on the chosen slope angle.
  3. Cut furring strips to varying thicknesses or stack them to create a gradual increase in height.
  4. Nail or screw these graduated strips onto the top surface of your existing pergola purlins (the beams running across the main support beams).
  5. The top surface of these added strips will now form the sloped plane onto which your roofing material (if any) or shade structure will be attached.

Recommended Slope Angles

According to the reference provided, the minimum recommended slope for a flat-roofed pergola, especially when adding a slope this way, is:

• Minimum Slope: 1/8 inch per foot (equivalent to approximately 0.6 degrees).
• Better Slope: 1/4 inch per foot (equivalent to approximately 1.2 degrees) is generally preferable as it allows for better water runoff.

A steeper slope can improve drainage and reduce the likelihood of water pooling, which can extend the life of roofing materials or prevent sagging in fabric covers.

Why Slope a Pergola?

Adding a slope is particularly important if you plan to add a solid or semi-solid roof covering to your pergola. It helps:

• Water Drainage: Prevents rainwater from pooling on the roof surface.
• Snow Load: Aids in shedding snow in colder climates.
• Longevity: Reduces stress on roofing materials and the overall structure from standing water or snow.

By using graduated furring strips, you can effectively transform a flat structure into one with the necessary pitch for proper water management.