What is a Green Roof Filter Layer?
Green roof filter layers (or separation layers) are designed to prevent particles of growing medium getting washed into the drainage layer and clogging up the system.
Green roofs rely on sufficient drainage (especially in wetter climates) to avoid over-saturation and allow for proper runoff. If particles begin to block the drainage layer, then your green roof plants will begin to die and the increase in weight could damage your roof’s structural integrity.
The 6 Best Green Roof Filter Layers
Filter layers are generally good value and an essential piece of green roof kit. But we’ve covered something for every style of roof and budget.
Wallbarn Drainage Polypropylene Roll
Best overall filter layer
Wallbarn – another brand with a brilliant roofing heritage – have created a medium-weight, highly-flexible thermally bonded geotextile fabric that’s perfect for slightly larger shed or garage green roofs.
If you need something even larger, there’s a 1m x 100m version too.
If you’re building a DIY green roof on a smaller house roof it’d work brilliantly too.
Wallbarn Drainage Geotextile High Tenacity Polypropylene Roll
Best overall filter layer p. II
Wallbarn
Geotextile High Tenacity Polypropylene Roll-
1m x 100m
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4.6 star rating
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300g / square metre
Wallbarn’s Drainage Geotextile Layer is a high tenacity polypropylene fabric that’s a brilliant filter fleece for living roofs.
Its strength and abrasion resistance is top drawer and because the product has been made with permeability in mind – essential for fleeces – it works on any DIY or commercial project.
Its tensile strength and puncture resistance still allow for adequate water flow. So you can still install a sealing and waterproofing sheet membrane on top.
Hertalan EPDM Geotextile Fleece
Best filter layer for medium sized plants
Hertalan
EPDM Geotextile Fleece-
25m x 1m
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350g / square metre
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50 years of roofing experience
Hertalan’s EPDM Geotextile Fleece is medium-weight, highly protective fleece underlay.
One that not only prevents substrate particles from entering (and clogging up) your green roof drainage layer, but it also protects against any sharp objects that might rip the waterproof layer.
So if you have plants or trees with substantial root growth and want to provide extra protection for your drainage and waterproof layers, Hertalan’s Fleece is a great choice.
Eurovent Breathable Roof Membrane/Felt
Best heavy duty filter layer
Eurovent
Breathable Roof Membrane Felt-
1.5m x 50m
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4.7 star rating
-
Heavy duty protection
Eurovent’s Breathable Roof Membrane Felt is a lightweight (120 g / m2), permeable membrane that’s perfect for DIY green roof projects.
The three layer felt is breathable – allowing for adequate drainage without increasing moisture retention – working effectively across almost all substrates.
In addition to reducing heat loss, this breathable membrane offers long-lasting protection against several threats to your roof’s integrity, including condensation and infiltration by water and air.
Permavent's Black Breather Membrane Breathable Roofing Felt
Best filter layer for all weather
Permavent
Black Breather Membrane Breathable Roofing Felt-
1m x 50m
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4.6 star rating
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Specifically designed for green roofs
Permavent’s Breathable Roofing Felt is a great value, felt-layer that can be used in an weather conditions.
The strong, breathable material is equally suitable for commercial projects – that’s how you know the quality will hold up. The vapour permeable membrane is completely airtight and mitigates any condensation risk.
At 120 g /m2 it is lightweight enough to work on any green roof project.
Spudlica Geotextile Membrane
Best filter layer for small, extensive roofs
Spudlica
Geotextile Membrane-
2.25m x 5m
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4.6 star rating
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1.08kg in weight (100g / square metre)
Spudlica’s Geotextile Membrane (not the jacket potato vendor) has been thermally bonded to provide a durable and tough layer of fabric.
At just 100g / m², this lightweight filter layer is the most common type of non-woven geotextile membrane. One that is perfect for lightweight, extensive green roofs.
It has been specifically designed to provide excellent filtration in all applications and conditions.
HaGa Watering Mat Irrigation Fleece
Best filter layer on a budget
HaGa
Watering Mat Irrigation Fleece-
2m x 1m
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4.5 star rating
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500g / square metre
HaGa’s Waterming Mat Irrigation Fleece is a heavier-duty filter layer that’s ideally suited to slightly more intensive green roofs.
It’s greater load should provide a fantastic filtration layer for any size or amount of growing medium. And it’s completely weather and rot-resistant, with a high capillary absorbency of 4l / m².
An all-weather, all-rounder that’s perfect for larger DIY green roof projects.
Green Roof Filter Layer FAQs
Yes you need a filter layer on your green roof. Without adequate drainage your green roof plants, typically hardy little sedums that don’t require much water, will become over-watered and die.
And a blocked drainage layer will increase your roof’s water-weight. And really the last thing we want to do is test your roof’s structural integrity. I promise you, you won’t want to re-do your DIY green roof.
A green roof filter layer prevents finer particles of growing medium from entering and blocking up your living roof’s drainage system.
Typically a filter layer sits below a growing medium and above the drainage layer to prevent particles from the soil or substrate entering and blocking the drainage layer.
Typically a green roof filter layer weighs somewhere between 100g / m² to 500g / m².
Larger scale living roof – whether it includes trees and larger shrubs for example – and heavier rainfall require a denser, more all-encompassing filter layer.
Generally woven geotextile fabrics are stronger and less permeable, because weaving strands creates multiple, denser layers.
But your green roof filter layer should always be non-woven, because non-woven fabrics have slightly larger holes that allow for greater flow rate and penetration.
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