The loads imposed on a ground floor construction rule out flexible insulation, like mineral wool and stone wool, as suitable products for use in typical build-ups. Rigid insulation boards not only bear those loads with relative ease,  but their large-format sheet sizes can be laid quickly and easily over the floor area.

This blog post looks at lightweight, plastic-based rigid foam insulations: polyisocyanurate (PIR), phenolic (PF), and extruded and expanded polystyrene (XPS and EPS respectively).

Polyisocyanurate and phenolic foam insulation

Both phenolic and PIR foams derive some of their long-term thermal performance from facing materials that restrict the loss of the gas in the foam structure. Protecting those facings is important in ensuring that performance for the life of the building.

That means keeping water away from the insulation boards, regardless of them being closed cell materials with low rates of water absorption.

PIR foam is arguably seen as the most popular choice for domestic or domestic-type floors. It combines thermal efficiency with an economical price point, although the slightly better thermal performance of phenolic foam may justify the increased cost if depth in the floor construction is at a premium.

Whichever product is specified, phenolic and PIR boards should always be installed above the damp proof membrane (DPM). It is never recommended to lay them exposed directly to the ground. Long term exposure to moisture can result in facings – particularly composite ones featuring kraft paper layers – breaking down, to the detriment of the product.

Expanded and extruded polystyrene insulation

EPS has no facings that are susceptible to damage from alkalis or moisture, but its capacity for moisture absorption means it must still be installed above the DPM. While EPS is capable of much greater loadbearing capacity than phenolic and PIR foams, it is also offered in grades with a lower compressive strengths.

This variability means the correct grade must be specified for the correct application.

XPS products for ground floor applications are also unfaced. But they offer an important advantage over PIR, PF and EPS: lower moisture absorption. XPS is tolerant of wet conditions, meaning it can be installed against the ground without concern that performance will deteriorate over time.

Subject to an appropriate build-up being specified, it’s also possible that installing XPS below the DPM means only one membrane layer needs to be installed. That simplifies detailing and saves on installation time and material costs, which is particularly helpful on large commercial and industrial projects. To find out more about the benefits of XPS as floor insulation, contact us to book our new CPD seminar.