How to Build a Green Roof on a Shed

Sedum green roof on your shed? Absolutely possible, but only if done right. This guide explains how to prepare your garden building for it and build it yourself.

First Things First: Can Your Shed Handle a Green Roof?

Wet substrate and matting add significant weight when added. A shed roof on its own, in most cases, isn’t enough. Refer to this checklist to see if yours is up for it:

• Roof frame strength: Check that rafters or trusses can support 60 to 80 kg/m² when the roof is fully saturated, carrying the maximum water weight the sedum and substrate can hold.
• Joist spacing: Reduce the distance between joists so the roof does not sag under the wet load.
• Roof deck condition: Make sure the deck is flat, smooth, and free from rot before adding any layers.
• Edge containment: Install trim or raised edges to retain the substrate and sedum mats.
• Access for upkeep: Ensure you can safely reach the roof for watering, weeding, and inspections.

If you don’t reinforce the shed, the roof could sag or collapse under a wet green roof. Most warranties don’t cover damage from added weight. Failing to strengthen the structure may void it.

Note: these instructions are for information only. Structural modifications to our products may void the guarantee.

Shed Green Roof Installation Guide

Step-by-step instructions for preparing your shed and installing a lightweight sedum roof.

1. Prepare the roof deck

Let’s keep the roof level and solid so all the layers sit evenly.

1. Remove any existing roofing felt or debris to make room for the EPDM membrane.
2. Sand down rough edges and fill gaps or cracks with exterior-grade wood filler.

2. Install heavy-duty waterproof membrane (EPDM)

EPDM will act as the main waterproof barrier to protect your shed from leaks.

1. Cut EPDM sheet to size, leaving at least 10 cm overhang on all sides.
2. Apply adhesive as per manufacturer instructions.
3. Smooth out air bubbles and ensure full contact with the roof deck.
4. Seal edges with EPDM seam tape or flashing to prevent leaks.

3. Lay the fleece

This part protects the membrane from being damaged by the substrate above.

1. Roll out a fleece layer directly over the EPDM to protect the membrane from sharp substrate edges and root penetration.
2. Overlap seams by 10 cm for continuous protection.

4. Place plastic drainage board

To channel water off the roof and prevent it from pooling:

1. Fit a lightweight, corrugated plastic drainage layer on top of the fleece.
2. Move on to the water channels and make sure they’re facing downward to facilitate drainage.
3. Cut boards to fit edges and around roof penetrations, such as vents and chimneys.

5. Add filter fleece

This step stops fine particles from entering the drainage and supports the substrate layer.

1. Place a second layer of geotextile filter fleece over the drainage board to prevent blocking drainage.
2. Overlap edges by at least 10 cm.

6. Apply a lightweight substrate

Time to lay the lightweight base so the sedum can root without overloading the roof.

1. Use an extensive sedum-specific growing medium: lightweight and low nutrient.
2. Spread evenly to a depth of 50 to 80 mm.

Do not compact too tightly; sedum needs airflow at the roots.

7. Create a pebble border

Before laying your plants, you need a vegetation barrier around the perimeter to keep the roof secure and well-drained.

• Leave a 10 to 15 cm gap around the outer edges of the roof (and around any drainage pipes).
• Fill this gap with washed river stones or pebbles (usually 20 to 40 mm in size).

This crucial border stops wind from lifting the sedum mats, prevents the lightweight substrate from washing off the edge into your gutters, and keeps the plant roots from sitting in standing water.

8. Lay sedum matting

At this stage, the sedum layer establishes itself on the substrate.

1. Roll pre-grown sedum mats onto the prepared substrate.
2. Place the edges of each mat against the next without overlapping.
3. Press the mats gently so the roots make full contact with the substrate.
4. Water lightly to help the mats settle and start rooting.

All layers are installed and the green roof is live!

How to Maintain Shed Green Roofs

Sedum is drought-tolerant, so very little upkeep is needed, including:

• Weeding once or twice a year
• Occasional watering during long dry periods
• Inspection on drains, edges, and plant health once or twice a year
• Checking on membrane edges annually for signs of wear or displacement

Round-up

Sedum is the lightweight option for a shed green roof. Even so, you’ll want to account for the added weight and confirm that the structure can bear the load. If it can, the steps above will guide you through the installation.

A pent roof is ideal for this setup, though apex and flat designs can work too. Planning to upgrade your shed before starting? We have options for you here:

Shop Pent Sheds

FAQs

Why is a pent roof preferred for DIY sedum roofs?

A pent roof features a single slope, allowing water to run off in one direction. This reduces the risk of pooling. It’s also easier to layer the membrane, drainage boards, and substrate.

Is apex shed suitable for a sedum green roof?

It can work, but there should be reinforcement at the ridge. Water drains off both sides, so the layering must be applied to avoid leaks at the apex.

Can I put sedum roof on a flat shed roof?

Yes, but the roof needs a slight pitch (at least 1 to 2°) and excellent drainage to prevent water pooling. Reinforcement and adding additional drainage channels might also be necessary.