Inverted roof insulation is a flat roofing technique which employs loosely laid insulation boards on top of waterproofing material, weighted down by either paving slabs or gravel ballast to guard against wind uplift and flotation.
Insulation provides a durable and thermally stable roof surface while also shielding waterproofing membrane from mechanical damage and UV exposure. Green roofs make great use of this feature as it also saves energy – meaning buildings use less power overall!
XPS Insulation
XPS insulation (extruded polystyrene) is the go-to thermal insulating material for inverted roofs as it is less likely to deform and absorb water than other insulation options.
Manufacturers use an ongoing production process to mix and melt polystyrene crystals with special additives and blowing agents that enable their plastic product to expand and shape under heat and pressure conditions. Once solidified, this thick liquid is processed through a die for shaping, cooling and trimming into standard-sized rectangular or square boards with surfaces tailored specifically for applications – smooth, rough or grooved surfaces are possible depending on application needs.
Both EPS and XPS insulation products make ideal choices for wall and ceiling insulation applications as well as below-grade waterproofing systems that use an IRMA membrane to cover them, so selecting the appropriate type is vital to its successful functioning.
Extruded Polystyrene (XPS) Insulation
Extruded Polystyrene (XPS) insulation is created by melting plastic granules together with additives into a viscous fluid, then forcing this mix through a die under carefully controlled temperatures and pressure conditions before being expanded under heat and pressure conditions.
As the end product, rigid foam plastic boards with closed-cell structures and smooth skins on their top and bottom surfaces are produced, using blowing agents that allow expansion while maintaining closed cell effect.
XPS insulation products can also be made using recycled materials to help lessen their environmental impact. Amoco Foam Products uses 50% post-consumer EPS in their Amofoam(r)-RCY extruded polystyrene foam board insulation product as one of the greenest insulation products on the market.
PIR and PUR both utilize chemical additives; by contrast, XPS is made from one renewable polystyrene source and 100% recyclable, meaning it can be reused for future buildings and construction projects.
Green Roofs
Green Roofs are designed to absorb and slow the volume and velocity of stormwater runoff on urban streets and rooftops, significantly reducing flooding risk and sewer overflows, both major sources of pollution worldwide.
Green roofs also help mitigate the urban heat island effect and improve air quality by filtering out harmful toxins from the atmosphere and sequestering carbon dioxide.
Green roofs sequester various amounts of greenhouse gases depending on their species of plant used, but on average it has been calculated that above ground biomass and substrate of green roofs can store between 168 to 107 grams per square meter of CO2.
To convert a PMR or IRMA roof into a green roof, the insulation layer needs to be removed and replaced with a root barrier, soil-based growing medium, plantings and drainage system. XPS foam is an ideal material for this application as it is available in multiple thicknesses and compressive strength grades for load bearing applications.
Inverted Roofs
Inverted roof insulation is a type of flat roofing system in which waterproofing material is installed beneath insulation, secured with ballast or paver slabs to provide maximum protection against UV radiation, weathering, mechanical wear-and-tear and mechanical damage during construction, use, maintenance.
The design ensures insulation remains close to the building’s interior temperature and reduces thermal shock from waterproofing layers, thus minimising condensation risk and ponding water accumulation.
Insulation layers should be durable and rot proof in order to provide long term performance for roof membranes, leading to decreased lifetime costs and increased energy efficiency in structures. This insulation layer meets those criteria perfectly, offering long term protection at reduced lifetime costs with increased energy efficiency benefits.
Warm roof systems are an ideal solution for flat roofs in the UK climate as they provide one of the best ways to increase energy efficiency. Insulation placed above structural decking helps maintain an even temperature on its surface and reduce thermal bridging which could otherwise cause condensation issues.