What makes a good Green Roof Waterproofing Layer?
Well first of all it needs to be made of incredibly waterproof material. Not water-resistant material like your cheap anorak. Typically pond liners or heavy duty EPDM rubber sheets are perfect.
They’re thin, (extremely) waterproof, root resistant – in case any roots manage to worm their way through the root resistant layer – and long lasting. Considering a green roof could last for 50 years, you need a good quality waterproof base layer.
Do I need a Green Roof Waterproof Membrane?
If you value your shed, home or any of the contents in it then yes. Of course you need a waterproofing layer.
Even in climates where it basically doesn’t rain you should still put a waterproofing layer on. Because when it actually does rain and you watch the contents of your shed float away down the A42, you’ll wish you spent an extra £75.
Alright we’re hyperbolising. But if you don’t add a waterproofing layer there’s an excellent chance your roof will rot and you’ll have to a) replace the roof and b) redo the green roof.
Best Green Roof Waterproof Membranes
Danosa Esterdan Plus 40 GP Elast Black Torch On Mineral Cap Sheet
Danosa’s Esterdan GP Elast is – despite the odd name – an excellent flat roof waterproof membrane.
The asphalt sheet is made of reinforced polyester felt, covered on both sides with a bitumen mastic, which provides waterproof, fibrous reinforcement. This mitigates any risk of tearing and increases long-term stability.
Danosa also sells a pre-waterproofing layer membrane to use as a base for additional waterproofing. Recommended for higher rainfall areas or larger projects.
Cromar Vent 3 Breathable Roofing Membrane
Cromar Vent 3 Lightweight Breathable Roofing Membrane is an ultra-durable, long-lasting roll that is incredibly easy to use.
The entire product weighs 7.3kg, which -given it’s 75m² – is ultra lightweight.
Tested in weather conditions much harsher than any we’ll face in the UK, except possibly somewhere around the North Sea. And with durability and tensile strength in mind. Also comes with a 1 year guarantee.
Novia Black Roof Breathable Membrane
Novia’s Back Roof Breathable Membrane is a lightweight, high performance breather membrane suitable for use as a breathable roof underlay.
Suitable for both flat and pitched roofs of any material – timber, concrete, asphalt – it is both flame-resistant and waterproof. The fact it’s suitable for direct installation is perfect for DIY green roof projects.
Butyl & Greenseal Rubber Pond Liners
Pondkeeper’s Butyl and Greenseal Rubber Pond Liners come in a huge array of sizes – from 2m x 2m to 45m x 40m – and, because they’re created with ponds in mind, are impermeable and highly durable.
Starting at around £35, you will be able to find the perfect waterproof layer for your green roof regardless of how large your shed, garage or house is.
You can choose whether you want to purchase butyl – a higher quality, more expensive rubber or greenseal – a slightly cheaper alternative.
Swell UK Deluxe Pond Liner
Capital Valley’s Damp Proof Membrane is a multi-purpose, damp proof membrane that can be used effectively as a waterproof roof layer.
It is thicker than other products on the list, which does increase the overall weight. However it is highly durable and almost impossible to tear.
It comes in multiple sizes, so whilst the 25m x 4m maybe too large or small, whatever size you need will be catered for.
Capital Valley Damp Proof Membrane
Whilst it may seem counter-intuitive to have a pond liner on your roof, they’re thin, incredibly waterproof and highly durable. And Swell UK’s Deluxe Liner is perfect for a budding first-timer (with a smaller roof).
Because you’re buying one-size-fits-all liners, these aren’t as suitable for larger projects. However they’re easy to cut to size and at just £34.99 (in a range of 4 different sizes) and a 25 year minimum guarantee, it’s a real bargain.
Pondkraft Pond Liner
Another cracking pond liner, Pondkraft’s 6x6m offering is rot resistant and has a reversible black / brown finish.
I’m actually not sure what the point of having a coloured liner is if you’re going to completely cover it on a roof, but the 25+ year guarantee and UV stabilisation quality is perfect for a damage resistant UV layer.
Swell Heavy Duty Pond Liner
Swell make their long-awaited return with another pond liner – but this one’s a heavy duty offering.
Whilst it’s significantly more expensive it’s probably the most damage resistant, lightweight, durable offering you’ll be able to find on the market.
The underlay (typically used as protective layer to promote rot resistance) mitigates almost any chance of rot resistance and deterioration over time.
perfect for damp conditions and longer periods of sustained rain – that sweet British Winter.
Best Waterproof Green Roof Liquid Layers
Acrypol Tech Seal PU Liquid Waterproof Membrane
Acrypol’s Tech Seal Liquid Waterproof Membrane is a seamless, liquid waterproofing membrane made up of single component PU. Why does this matter I hear you ask…
Well single component polyurethane is moisture cured and doesn’t need to be mixed with anything prior to application. Rainproof in 2 and fully cured in 4 hours, this easy to install waterproof layer is top of the line.
ClassicLiquid Waterproof Roof Coating Top Coat
Liquid waterproofing layers are definitely a more advanced method of lining your roof.
ClassicLiquid’s Waterproof Roof Coating is a polyurethane liquid membrane that creates a durable, seamless waterproof layer over existing roof systems. It’s is ultra weather resistant – showerproof in 30 minutes and entirely UV resistant – and a surefire way to protect your roof.
For larger green roof projects, it’s worth also adding some reinforcing fabric to fit between two coats of the waterproof layer.
Flexitec 2020 Roof Resin
Liquid waterproofing layers are definitely a more advanced method of lining your roof.
But if you have a roof or deck with a number of fittings, fixtures or vents then a liquid waterproofing layer like Flexitrec is perfect. It’s rapid curing, super tough finish make it applicable in almost any time of year – although Spring is still the best green roof installation option.
Suitable for almost any roof surface – even balconies and walkways – this fire retardant, liquid waterproof layer is top of the line.
EcoProof 20 Liquid Rubber Waterproof Membrane
Ecoproof’s Liquid Rubber Membrane arguably the most eco-friendly option – which is incredibly tricky to find for waterproof layers because they tend to require noxious primers and solvents.
This water-based system is an easy-to-apply waterproofing layer ideally suited to priming your roof for habitation and greenery.
For bigger roofs there’s also a 20 litre option.
Protec Roofing System
Protec’s liquid waterproofing layer comes complete with a 25 year guarantee and can be applied to a wide range of roof coverings including: asphalt, concrete and felt.
With walk times as low as 30 minutes (i.e. the time it takes to set before you can walk on the roof) and the fact it can be applied to existing roof coverings, makes this a superb no-fuss, low-maintenance option.
Green Roof Waterproofing Layer FAQs
- Both liquid applied waterproofing layers and preformed sheets
- Waterproof and rot-resistant
- Value – not cheap. Good value. Typically coming with a manufacturer’s guarantee.
It should provide a waterproofing treatment – in the form of a liner or a liquid layer – must provide a strong but flexible layer that allows expansion under physical or thermal movements (the expansion and contraction of the fabric of the building due to hot and cold weather) of the building structure, without compromising water-tightness.
Vegetation generally should not be installed over areas such as expansion joints, where regular inspection of the waterproofing will be necessary. Fortunately for most DIY green roof buildings, expansion joints won’t be a problem.
For green roofs there are two major types of waterproofing layers you can apply – liquid applied treatments and preformed sheets – the EPDM and pond liner variety.
Liquid applied treatments are protective coatings – usually bituminous, acrylic, polyurethane or a hybrid combination – that require mixing prior to application. You can literally ‘paint’ a couple of layers onto your roof.
Preformed sheets are asphalt-based or comprised of thermosetting polymers or thermoplastic polymers.
Preformed waterproofing definitely better suit green roofs with a gentle pitch and large uninterrupted areas.
If you have a green roof with a lot of clutter – such as lighting, power cables or ventilation – may be more suited to liquid applied waterproofing that is sprayed or rolled on to form a single layer without compromising other roofing elements.