The bottom line on floorboard insulation

Rob Firman of Polyfoam XPs highlights the key differences between floorboard insulation products, thereby illustrating the importance of correct specification in housebuilding.

Both product specification and the housebuilding sector are constantly evolving. Changes to the planning system are designed to accelerate housebuilding to ensure developers deliver 300,000 new homes a year by 2025 – a stringent target set out by the Government. Not only this, but ongoing budget restraints, land shortages and the ever-changing political climate are putting more and more pressure on housebuilders.

With all these strains, it is important to ensure specifiers make the right decisions during product selection right from the start, and floorboard insulation specification is a key factor in this decision making.

Poorly specified and installed insulation at ground floor stage can create risks onsite, and potentially threaten the effectiveness of the entire build.

Poorly specified and installed insulation can have a detrimental impact on ground floors in residential developments. At best, the floor could be sound but won’t meet its intended U-value, and potentially not comply with Building Regulations. At worst, the flooring installation could fail, compromising the sustainability and quality of the entire project.

Installing the ‘wrong’ insulation board or switching the specification may seem like a small risk, but housing developers should not underestimate the potential impact it could have – especially at a time when the construction industry is being scrutinised on how it delivers projects, and its quality.

Misconceptions are a big part of this problem, including an assumption that there is a minimal difference between the different types of rigid insulation for ground floors, and that a more thermally- efficient insulation offers better performance in other respects.

In fact, different rigid insulation boards offer different combinations of characteristics, so if one material is specified, but an alternative material is offered, purchased and installed, that other material may not offer the same performance – that’s why it’s so important to specify and install the correct one. In general, rigid insulation materials are mainly lightweight, plastic-based rigid foam insulations.

In recent years, vacuum insulated panels (VIPs) have begun to offer an alternative to the more common board stock materials. However, these products are best suited to refurbishment projects where the depth of insulation is constrained.

Both phenolic and PIR foams derive some of their long-term thermal performance from aluminium foil facings that restrict the loss of the gas from the foam structure. Protecting those facings is important to ensure they perform 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. They should always be installed above the damp proof membrane (DPM), and never laid exposed directly to the ground.

Although expanded polystyrene (EPS) insulation has no facings that are susceptible to damage from alkalis or moisture, its capacity for moisture absorption means it must similarly be installed above the DPM.

EPS is capable of much greater loadbearing capacity than phenolic and PIR foams – but is also made available in lower compressive strengths. Even with compressive strengths exceeding 120 or 140 kPa, manufacturers of phenolic and PIR products can be extremely cautious about offering their insulation for anything more than domestic and light commercial applications.

Extruded polystyrene (XPS) is an increasingly popular insulation option for specifiers seeking a material that can be used in demanding conditions and applications, and still deliver good thermal performance. XPS insulation is not only thermally-efficient, easy to install and lightweight, but moisture tolerant too.

With a moisture absorption as low as 0.6 per cent by volume, XPS products can be installed below the DPM, and in conditions where moisture is present, such as below damp proof course (DPC) level, or against the ground and to the external side of tanking membranes – all with negligible impact on the performance of the product.

Sustainability is of course an important factor, so housebuilders and developers should look for XPS insulation produced using a blowing agent with zero ozone depletion potential (ODP) and low global warming potential (GWP), and manufactured in a factory with an ISO 14001-accredited environmental management system. Products should also comply with BES 6001 sustainable sourcing and offer Environmental Product Declarations (EPDs).

It’s not hard to see why confusion can arise regarding insulation specification and installation. However, a greater awareness and understanding of insulation products can significantly reduce risks onsite and make installation easier.

It’s important to value the thermal and loadbearing performance of materials over how much they cost, to ensure ground floor construction performs as expected. And, if a product substitution can’t be avoided, make sure the same material type is used with an equivalent performance.

Rob Firman is technical and specification manager at Polyfoam XPs