Green roofs not only absorb rainfall, reducing storm-water runoff but improves surrounding air quality, reduces the urban heating effect and improves the building’s insulation performance, leading to energy cost savings. The approach to designing and constructing a green roof varies depending on the type of roof, slope, accessibility and the climate.

Types of Green Roofs

Green roof types can be divided into three general categories – extensive, semi-intensive and intensive. What distinguishes them is the depth of the growing medium (soil) and roof accessibility desired.

• Extensive green roofs – Typically featuring a soil depth of less than 200mm, this is the most common type of green roof because it’s cheaper and easier to add to existing roofs. Compared to intensive and semi-intensive green roofs, water retention is limited, and the roof requires low maintenance plants with strong horizontal root systems, resistant to drought and capable of surviving temperature extremes. It is not intended for human access outside of maintenance.
• Intensive green roofs – Typically featuring a soil depth of up to 1000mm, these green roofs can accommodate a bigger, more diverse variety of vegetation. Intensive green roofs can handle much more weight and are designed more like a park or garden with large shrubs, trees, planter boxes, walking paths, tables, benches and small recreation areas. Intensive roofs require a far more complex support structure, making them more expensive and harder to maintain.

Semi-intensive green roofs are any approaches to green roof design that sit between these two categories or feature aspects of both. For example, they might allow for a very limited amount of public access in just one area.

Key Components of a Green Roof

Basic green roof components include the base roof deck, waterproofing layer and the green roof system:

• Structural deck – The roof deck may be flat or sloped or made from concrete, steel or wood. The design of the roof system will largely depend on the amount of load the roof structure can carry. When a vegetative roof is installed on an existing roof, it must be based on the loads that the roof can bear. Existing roofs usually can’t carry the heavy loads required for an intensive roof.
• Waterproofing layer – Located directly above the deck, this layer is designed as the final barrier to water intrusion and can be made of a range of materials including hot-fluid-applied rubberised asphalt, atactic polypropylene (APP), styrene butadiene styrene (SBS) modified bitumen sheets and polyvinyl chloride (PVC). Membranes may be field formed or factory-fabricated sheets, which are either loose laid or fully adhered. Loose laid membranes allow for more imperfections in the overlay material but are subject to movement.
• Green roof system – This layer sits above the waterproofing layer and includes the insulation, membrane protection, root barrier, soil and vegetation. Additional components can be added based on the design of the roof. Extensive green roofs may have very few layers, while intensive roofs will typically have far more to support more complicated water retention, drainage and plant life. Depending on the type of vegetation and the climate of the area, growing mediums may include a blend of gravel, lava rock, synthetic fibers, shale, bark, peat and earth. The appropriate blend will depend on the necessary water retention.

In addition to the above components, other important features may include access boxes for water valves, electrical outlets, roof drains, irrigation systems, additional protection layers for the roofing membrane, maintenance lockers, dividers, public access amenities and lighting.

What Type of Insulation to Use in Green Roofs

The insulation layer is an essential aspect of a functioning green roof assembly. The selected insulation material must be designed for moist or damp environments and have a high resistance to compression. Extruded polystyrene (XPS) foam insulation is recommended for the insulating layer in green roof designs because it:

• Offers excellent thermal performance even while damp or wet
• Is highly resistant to water absorption
• Is unaffected by freeze/thaw cycles
• Can withstand the impact of surface traffic
• Can handle static and dynamic compressive weight
• Provides long-term protection to the waterproof layer
• Protects roof layers from UV and mechanical damage
• Is lightweight, aiding in water retention without increasing the overall weight of the green roof system layer.

XPS foam insulation is highly effective at reducing the amount of heat transferred into the building. The closed-cell structure of XPS foam gives it excellent rigidity and makes its highly resistant to compression. A minimum compressive strength of 300 kPa is required for insulation used above intensive green roof waterproofing membranes.

Technonicol XPS Foam – Ideal for Green Roof Insulation

Technonicol’s Carbon Prof XPS foam insulation boards offer a minimum compressive strength of 300 kPa, making them ideal for inverted green roof installations. Technonicol’s Carbon XPS foam insulation series comes in a variety of sizes, thicknesses and compressive strengths to meet the demands of almost every application, including inverted green roofs on large domestic, commercial and industrial buildings.

At Plastek, we have extensive experience consulting and supplying these XPS foam insulation products, helping to optimise projects by providing the ideal solutions. We can recommend the right Carbon XPS foam insulation product for your specific project, ensuring a functional and high-performance solution for your building.

Related Questions

Do green roofs need drainage?

Proper drainage is crucial to the function and overall life expectancy of a green roof. If too little water is retained, vegetation will wither and die. If too much water is retained, excessive weight can damage the roof structure. In the case of sloped roofs, drainage occurs naturally due to gravity and as such, drainage mats are not typically used. Instead, a gravel perimeter on the roof directs excess water to rain gutters.

Can you put a green roof on an existing building?

Yes. However, waterproofing must be in good condition and ideally it should be no older than 5 years. An existing roof can usually only support an extensive green roof as intensive roofs require too many heavy layers for an existing roof to support without being specially designed for it. It is essential to carefully consider and appropriately design the type of green roof an existing roof deck can support.

How do you control the risk of roof collapse resulting from weight?

Green roofs add both static (from the added layers above the roof deck) and dynamic weight (from retained water and public access) to the building structure. When new green roofs are designed, the supporting roof structure is designed to address these loads. However, when a green roof is added to an existing roof deck, it is crucial that a structural engineer evaluate the roof to determine what, if any, additional loading the roof will bear.

Extensive roofs typically have a weight of 60 to 200 kg/m2. Intensive roofs typically have a weight of 180 to 500 kg/m2. Designers need to calculate total roof loading based on these weights, any accessories, and retained water at super-saturation. Care should also be taken to avoid altering the static loading of the roof, e.g. from changing soil or plant type or adding accessories, such as benches and tables. In severe cases, excessive loading can result in total roof support failure. Likewise, the dynamic loading of a roof must be closely monitored.

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Multi-storey car parks are an essential part of every modern city. While they seem like simple constructions, a well-built, safe, clean and long-lasting car park requires particular materials and design approaches. A key part of this is preventing water ingress through the car park deck, which can lead to damp, cracked, spalling concrete, slippery floors and damaging alkaline salts dripping onto car paintwork. Good design, including using the right insulation materials, is key to ensuring a car park is well constructed.

Car Park Deck Design

A car park deck is essentially a type of warm flat roof. In a warm roof construction, the insulation layer is installed above the structural deck and below the waterproofing layer. A car park deck is a warm roof where the imposed loads from vehicle weights are significant, meaning the design requires an insulation material capable of bearing heavy loads while maintaining its integrity. 

Extruded polystyrene (XPS) foam has a number of key characteristics that make it ideal for car park decks, including superior load-bearing performance, water repelling qualities and a flat, strong and dimensionally stable base for the deck overlay. In many car park deck constructions, the insulation layer is covered by a separating layer, screed and mastic asphalt or liquid-applied waterproofing. 

Benefits of XPS Foam in Car Park Decks

XPS foam has a high compressive strength for specialist applications such as car park decks, heavy duty flooring and inverted roofing. It also resists water absorption and provides excellent thermal performance. Other benefits include:

• XPS foam boards have a high strength-to-weight ratio, making them robust and highly durable while at the same time lightweight and easy to transport.

• XPS foam boards are long-lasting with a service life comparable with that of a car park, building or structure.
• XPS foam is durable enough to withstand the stress of heavy surface traffic and mechanical damage that may occur during installation and maintenance.

If the waterproofing layer is damaged in a car park deck, the XPS foam won’t be damaged by exposure to moisture or water. An important part of flat roof designs are the detailing and construction of suitable upstands around the roof edge. XPS foam boards limit heat loss due to thermal bridging where the flat roof joins with the external wall. 

Meeting Car Park Deck Load Requirements With XPS Foam 

The closed-cell structure of XPS foam gives it excellent load-bearing qualities. The material is extremely rigid and capable of withstanding both static and dynamic compression. Technonicol’s Carbon Prof 300 XPS foam offers a minimum compressive strength of 300 kPa and 500 kPa with Carbon Solid 500 XPS foam. This makes these XPS foam boards appropriate for car park decks

Technonicol XPS Foam – Ideal for Car Park Decks

Technonicol’s Carbon XPS foam insulation series comes in a variety of sizes, thicknesses and compressive strengths to meet the demands of almost every application, including car park decks.

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When designing an inverted flat roof, the primary consideration is where thermal insulation is placed in relation to the roofing membrane (waterproofing layer). Choosing the right insulation ensures the final construction is durable, waterproof, long lasting and provides the necessary thermal performance. Extruded polystyrene (XPS) insulation features unique properties that make it ideal for inverted flat roofs.

Cold vs Warm Roof Construction

Depending on where insulation is placed, a typical roof construction can be described as cold or warm. In a cold roof construction, insulation lies below the structural deck and remains cold. This creates a risk of condensation which is commonly reduced by placing a ventilated space above the insulation. However, this approach is rarely used in temperate, humid climates such as those found in Australia.

In a warm roof construction, the insulation is installed above the structural deck and below the waterproofing layer. This succeeds at reducing the risk of condensation, but it means the waterproofing layer is thermally isolated from the rest of the roof construction. This exposes it to wide temperature fluctuations, potentially leading to premature failure. An inverted roof design overcomes the problems of both cold and warm roof constructions.

What is an Inverted Roof Design?

Inverted roofs, which can also be called upside down or protected membrane roofs, resolve the problems of cold and warm roof designs by installing insulation above the waterproofing layer, keeping it at an even temperature close to that of the building interior. This also protects the waterproofing from UV radiation, weathering and mechanical damage during construction, use and maintenance.

The waterproofing layer in an inverted roof design acts as a total vapour control layer and can be maintained above dew point temperature since it is on the warm side of the insulation, minimising the risk of condensation. For this design to work, you must use XPS foam insulation as it has the necessary characteristics to withstand the conditions above the waterproofing layer.

The Importance of XPS Foam in Inverted Roof Design

XPS foam insulation offers excellent thermal performance and features unique properties that differentiate it from other types of foam insulation such as EPS foam. For example:

• XPS foam is resistant to rain, snow, frost and water vapour, enabling the material to withstand repeated freeze/thaw cycles.
• XPS foam is resistant to acids, salts and fungus, as well as being clean, odourless and free from dust.
• When properly installed, XPS boards have a service life comparable with that of the building or structure.
• Due to its homogeneous closed-cell structure and uniform density, XPS foam can be cut very accurately and to very close tolerances.
• XPS foam is durable enough to withstand surface traffic and is resistant to UV and mechanical damage that may occur during installation and maintenance.
• The boards have a high strength-to-weight ratio, making them robust and highly durable while at the same time lightweight and easy to transport.

XPS foam is ideal when higher compressive strength, higher water resistance and higher thermal resistance in the presence of water are required. XPS foam insulation boards can be loose-laid on top of the membrane and then weighted down with paving slabs, gravel ballast or soil medium if creating a green roof.

Technonicol XPS Foam – Ideal for Inverted Roof Insulation

Technonicol’s Carbon XPS foam insulation range comes in a variety of sizes, thicknesses and compressive strengths to meet the demands of almost every application, including inverted flat roofs on large domestic, commercial and industrial buildings.

At Plastek, we have extensive experience consulting and supplying these XPS foam insulation products, helping to optimise projects by providing the ideal solutions. We can recommend the right Carbon XPS foam insulation product for your specific project, ensuring a functional and high-performance solution for your building.

The post How to Insulate Inverted Flat Roofs appeared first on PLASTEK.

However, there are important considerations to factor in when planning to include one in a residential, commercial or industrial building. Below we look at some of the features, benefits and approaches to green roof design including how XPS foam insulation can help maximise its performance.

Types of Green Roofs

Green roof design, construction and vegetative cover will vary depending on the roof type, roof slope, roof accessibility and climate. Green roof types are generally divided into three broad categories – extensive, semi-intensive and intensive. The key difference between them is the depth of the growing medium and the degree of intended roof access.

• Extensive green roofs – This is the most common form of green roof and typically features a soil depth of between 75 and 150mm. This limits water retention and requires low maintenance plants that have strong horizontal root systems, are resistant to drought and can survive temperature extremes. This roof design is the cheapest as it requires less structural support, less maintenance and is not intended for public access.
• Intensive green roofs – These typically have a soil depth of between 250 and 1200mm, allowing them to accommodate a wider variety of vegetation including large shrubs and trees. In some cases, intensive green roofs will have recessed plant wells or planter boxes to allow for vertical root growth of trees. Intensive roofs are designed more like a park or garden and are maintained in a similar way. These roofs often allow for public access and can feature walking paths, benches, tables, and small recreation areas.

Intensive roofs require a much more complex supporting structure, making them more expensive and harder to maintain. Semi-intensive roofs describe any designs that are between these two types of roofs or feature aspects of both. For example, they might allow for a very small amount of public access.

What is an Inverted Roof?

An inverted roof is a type of design used when constructing green roofs. It uses the same materials as a conventional roof but instead places insulation on the top of the membrane. Inverted roofs are only possible by using XPS foam insulation, which is moisture-resistant and durable enough to withstand exposure to the environment as well as the weight of human footfall and the garden itself.

XPS foam insulation is distinctive because it:

• Resists water absorption
• Offers excellent thermal performance
• Is unaffected by freeze/thaw cycles
• Withstands the impact of surface traffic
• Can handle long term compressive weight
• Provides long-term protection to the waterproof layer
• Can be ballasted to prevent flotation
• Protects roof layers from UV and mechanical damage

Inverted roofs are utilised for green roof design because it best facilitates the establishment and maintenance of a green roof environment while mitigating the risk of water damage to the membrane. The inverted roof design also prevents possible damage caused by garden work, such as irrigation or using tools like a spade and hoe.

Key Features

All green roofs have a layered structure built upon a roofing base structure. This can be built on site or arrive in pre-constructed modules that are joined together once raised onto the rooftop. Basic green roof components include the base roof deck, waterproofing layer and the green roof system. The latter must include subsystems for:

• Drainage – Drainage design must both maintain ideal plant growing conditions while managing heavy rainfall without sustaining damage due to erosion or water ponding.
• Plant nourishment and support – The green roof must be carefully designed to facilitate plant growth and health and ensure minimal damage from wind, direct sun and rain. Of course, this also largely comes down to selecting the right vegetation for the climate and application.
• XPS foam insulation – Critical for saving energy and ensuring comfortable temperatures inside the building can be maintained efficiently. XPS foam insulation is the ideal solution as it can withstand moist and damp environments while offering the necessary weight and compression resistance.
• Protection of underlying waterproofing systems – The design must ensure protection of the underlying waterproofing system from human activities (footfall and maintenance activities) as well as biological attack and solar degradation. A capillary break immediately above the membrane is required in most cases.

The structural deck can be made from concrete, steel or wood and may be flat or sloped. Much of the design of the roof system will depend on the load the roof structure (deck) can carry. Existing roofs usually do not have the weight-bearing capacity for intensive green roofs.

The waterproofing layer is placed directly above the deck and is designed as the final barrier to water intrusion. It can be made out of a variety of materials including hot-fluid-applied rubberised asphalt, atactic polypropylene (APP), styrene butadiene styrene (SBS) modified bitumen sheets and polyvinyl chloride (PVC).

How XPS Foam Insulation Supports Green Roof Design

While the soil and plants on a green roof offer some insulation on their own, it’s not enough to maintain optimum comfort and energy efficiency in a building. Green roof insulation solutions like XPS foam boards are highly effective insulators for the building that also function as a membrane barrier between the soil and the roof itself. XPS foam insulation is highly effective at reducing the urban heat island effect, reducing the amount of heat transferred into the building as well as providing thermal protection for the membrane.

Using XPS foam this way can be compared to house wrap placed between the sheathing and the siding of a newly constructed house. The closed-cell structure of XPS foam makes it resistant to rain, snow, frost and water vapour, enabling the material to withstand repeated freeze/thaw cycles.

XPS Foam is Ideal for Green Roof Design Load Requirements

In load-bearing applications, the closed-cell structure gives XPS foam excellent rigidity and makes them highly resistant to compression. A minimum of 300 kPa compressive strength is required for insulation used above intensive green roof waterproofing membranes. Technonicol’s Carbon Prof XPS foam insulation offers a minimum compressive strength of 300 kPa and up to 500 kPa with Carbon Solid XPS foam. This makes these XPS foam insulation boards well-suited to inverted green roof installations.

Technical XPS Foam – Ideal for Inverted Green Roof Insulation

Technonicol’s Carbon XPS foam insulation series comes in a variety of sizes, thicknesses and compressive strengths to meet the demands of almost every application, including inverted green roofs on large domestic, commercial and industrial buildings.

At Plastek, we have extensive experience consulting and supplying these XPS foam insulation products, helping to optimise projects by providing the ideal solutions. We can recommend the right Carbon XPS foam insulation product for your specific project, ensuring a functional and high performance solution for your building.

Related Questions

Can you put a green roof on an existing building?

Yes. However, waterproofing must be in good condition and ideally it should be no older than 5 years. In most cases, an existing roof can only support an extensive green roof.

Do you need planning permission for a green roof?

Green roofs on sheds and other separate outbuildings are usually fine without planning permission. However, if the building is occupied or is attached to one that is, you should contact your council’s planning department

How long does a green roof last?

Green roofs can last up to 50 years or longer depending on how it is maintained. By protecting the roof membrane, a green roof can actually extend the life of a roof by two or three times beyond its typical lifespan

The post Using XPS Foam to Insulate Inverted Green Roofs appeared first on PLASTEK.

Extruded polystyrene XPS foam meets all these requirements, making it the ideal choice for inverted roof constructions. XPS foam boards are loose-laid on top of the waterproofing layer and below paving slabs, gravel ballast or soil in the case of a green (vegetative) roof. Inverted roofs offer a range of benefits over traditional roof constructions, explored in greater detail below.

1. Increased Durability and Lifespan

Cold and warm roof constructions are both traditional roof building approaches. In a cold roof construction, the insulation layer is placed below the structural deck. This creates the risk of condensation, which can be mitigated by adding a ventilated airspace above the insulation. However, this is unsuitable for temperate, humid climates. A warm roof construction involves placing insulation above the structural deck and below the waterproof layer, reducing the risk of condensation. However, the waterproof layer is still exposed to temperature fluctuations due to its thermal isolation from the rest of the roof construction, increasing the likelihood of degradation and premature failure.

An inverted roof construction solves both these issues by placing XPS foam above the waterproof layer, ensuring it is kept at a consistent temperature similar to the building interior. This also protects it from UV radiation, weathering and mechanical damage during the construction process and maintenance work. By protecting the waterproof membrane, the roof is more durable overall and has a much longer lifespan.

2. Reduce Costs Over the Roof’s Life

Roofs are a significant investment and how well they function has a big impact on the rest of the building. The potential cost-savings of an inverted roof are massive because of how much longer they last compared to traditional ones. Deferring a roof replacement by 10 years can save hundreds of thousands of dollars.

Inverted roofs also have significantly lower maintenance costs because the XPS foam layer protects the roof membrane from mechanical damage and weather. This enhanced durability, combined with the much lower annual energy costs offered by the thermal performance of XPS foam, can reduce total costs over the lifespan of a roof by up to 22 percent.

3. More Eco-Friendly

The cost savings an inverted roof offers through energy efficiency and longer life are also beneficial for the environment. A well-insulated, long lasting roof means less energy use for decades, drastically reducing the carbon footprint of the entire building. Since materials like the ballast and XPS foam are loose-laid in an inverted roof design, they are much easier to reuse at the end of the building’s life, meaning less landfill.

An inverted roof design also offers the opportunity to create a green roof, terrace or garden on top of the building. This provides further insulation and reflects less of the sun’s energy back into the atmosphere, alleviating the urban heat island effect and reducing contributing to global warming. Having a green roof also benefits local wildlife, helping to protect biodiversity in urban areas.

4. Protects Roof Membrane Against Thermal Shock

In a traditional roof construction, the waterproofing layer (roof membrane) is subjected to the full onslaught of weather and the insulation is sandwiched between two membranes that creates a water trap. Rain, sun, snow, hail and condensation all reduce the functional lifespan of the membrane. However, thermal shocks from temperature changes are among the most important factors contributing to early ageing and fatigue for waterproofing membranes.

The waterproofing layer in an inverted roof construction is protected from such thermal shocks and acts as a total vapour control layer. Since it’s on the warm side of the insulation, it is kept above dew point temperature, minimising the risk of condensation. The reverse layer design means the life span of built-in waterproofing can be several times higher than if those exposed to weather.

5. Better Stormwater Management

Stormwater is having an increasingly drastic effect on urban environments as, with rainfall overwhelming drainage systems in cities that are expanding and increasing in density. This results in overflow polluting local waterways and damaging infrastructure. An inverted ballast or green roof construction can help manage stormwater better by absorbing rainfall and reducing runoff. Green roofs typically retain between 40 and 90 percent of storm water runoff from the roof. This has environmental benefits as well as reducing stress on the building’s drainage system.

Technonicol XPS Foam – Ideal for Inverted Roof Insulation

Technonicol’s Carbon XPS foam insulation range comes in a variety thicknesses and compressive strengths to meet the demands of almost every application, including inverted green roofs on large domestic, commercial and industrial buildings.

At Plastek, we have extensive experience consulting and supplying these XPS foam insulation products, helping to optimise projects by providing the ideal solutions. We can recommend the right Carbon XPS foam insulation product for your specific project, ensuring a functional and high performance solution for your building.

Related Questions

Why is XPS foam insulation used for inverted roofs?

Inverted roofs are only possible by using XPS foam insulation because they feature a closed-cell construction, meaning there are no tiny gaps between the polystyrene cells. This makes them impervious to water and durable enough to withstand exposure to the environment as well as the weight of human footfall and plant life if used in a green roof construction.

How long does an inverted green roof last?

An inverted green roof can last up to 50 years or longer depending on how it is maintained. With XPS foam insulation protecting the roof membrane, the life of a roof is extended by two or three times beyond its typical lifespan

Can an intensive roof design support a rooftop terrace?

Yes, intensive roof construction is ideal for creating highly functional and economical rooftop terraces so you can fully utilise rooftop real estate for human activities.

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