What Is Spray Foam Insulation?

If you’re selling, installing or considering using spray foam insulation, have you ever researched precisely what goes into the raw material that creates the insulation? Behind every spray foam installation lies a complex web of chemistry and science that utilises a range of raw materials balanced to perfection. Spray foam insulation is much more than a couple of installers turning up in a van and spraying some chemicals, it represents a detailed, concise and scientific process from raw materials production through to installation.

Comprising a two-part chemical system, spray foam insulation is created from equal proportions of Part A – Isocyanate and Part B – Polyol Resin. Once mixed, spray foam is an expanded polyurethane foam with a low thermal conductivity that helps make it an effective insulator. The chemicals generally arrive with the installer in large, 250kg, 55-gallon metal drums that must be stored at the right temperature and fully sealed to protect them from moisture and contamination.

Most Spray Foam Insulation materials no longer contain HFCs or VOCs and instead use the latest in water-based HFO blowing agents. The ThermoFoam range of Enverge spray foam insulation uses the Honeywell Solstice water-based blowing agent and contain up to 17% of recycled materials within the formulation. In addition our range of spray foams have a Global Warming Potential (GWP) of just 1 and attract LEED points based on being low emitting insulation products.

What is Part A Isocyanate?

Isocyanates are a family of highly reactive, low molecular weight chemicals. They are widely used to manufacture flexible and rigid foams, fibres, and coatings such as paints, varnishes, and elastomers. They are increasingly used in the automobile industry, as well as autobody repair and building insulation materials. Isocyanates are powerful irritants to the mucous membranes of the eyes and gastrointestinal and respiratory tracts. Direct skin contact can also cause marked inflammation. Isocyanates can also sensitise workers, making them subject to severe asthma attacks if they are exposed again. In a nutshell, when mishandled, Isocyanates can be highly harmful to health without the correct PPE.

What is Part B Polyol?

Polyester polyols for polyurethanes are prepared by the condensation reaction between glycols—such as ethylene glycols, propylene glycols, 1,4 butanediol, or 1,6 hexane diol—and a dicarboxylic acid. Polyesters are polymers that allow for enormous structural and property design variations. Part B contains amines, surfactants, catalysts and fire retardants, which can harm health if ingested. Polyols come in different formulations to create plastic-based products, including commonly found polystyrene, polyethene and polycarbonates. Polyols are found in almost every household across the developed world, with furniture, packaging and even shoes utilising the material.

How Is Spray Foam Insulation Produced?

Spray foam insulation is formed from a chemical reaction where Parts A and B are mixed in equal proportions. To ensure the spray foam’s correct yield, density and structure, the raw chemicals are processed through a reactor, filtered and heated before being drawn through a hose using high-pressure compressed air. The two chemical parts remain separated until they reach the gun manifold, and once the trigger is pulled, Polyurethane Spray Foam Insulation is produced at the very last moment.

When sprayed, the polyurethane leaves the gun as a viscous liquid and rises rapidly over the following few seconds to fill and seal the void it applies. Depending on the type of spray foam and density, the expansion process will usually take less than 12 seconds, during which an exothermic reaction occurs where heat is released. Over the following hours, the spray foam will “off-gas”, a term used to refer to the process of vapours, fumes and trapped steam escaping from the foam. Once the off-gassing process is complete, most Spray Foams are generally inert and don’t pose any health risk.

Spray Foam is a liquid, spray-applied version of pre-manufactured rigid PIR sheets commonly used in construction. The critical difference between pre-manufactured PIR sheets and spray foam insulation is the responsibility of the applicator/installer to manufacture it in situ at the job site. Spray foam insulation installers require extensive training to understand the machinery, chemistry, and building science to ensure the completed job performs as intended.

Open Cell

This water-blown material has a 0.5lb density, making it the most vapour-permeable variant of Spray Foam Insulation in the UK. Most Open-cell foams have a water vapour resistance factor of less than 10 (u), meaning water vapour can migrate through with little resistance. Usually, Open-cell foams have a thermal conductivity of 0.037-0.039 W.m.K, making them comparable in thermal performance to mineral wool insulation materials. Due to the low-density, vapour-open nature of Open Cell foams, they should be used in scenarios where the substrate is dry, not at risk of excessive moisture or leaks and where there is adequate building assembly space to meet the thermal requirements of the property. Open-cell foams are generally suitable when spray-applied directly to low-resistance building assemblies. Still, Hygrothermal Analysis should be conducted to assess the moisture load and condensation risks specific to the property, resulting in the possibility of additional vapour control management. Open-cell foams have been used extensively in the retrofit residential homes market, often spray-applied directly to high-resistance, non-breathable, bituminous felts. With all bonafide Open Cell foams in the UK holding either BBA or KIWA certification, additional considerations may apply when using them directly to high-resistance to moisture substrates.

Closed Cell

The closed cell spray foam insulation variant differs from the open cell thanks to its 2lb density. With a lower vapour permeability than Open Cell, Closed Cell is still a breathable material yet has a much lower thermal conductivity of between 0.026-0.028 W.m.K to make it one of the most thermally efficient types of insulation available. Closed Cell is commonly used in newly built residential, commercial, industrial and agricultural environments but can be used as a retrofit solution in residential settings provided the roof assembly is low-resistance or a vapour control layer is used when installed to high-resistance substrates. Commonly relied upon as an anti-condensation treatment or asbestos encapsulant, Closed Cell has strong adhesion to just about any substrate and should provide extensive performance for the surface’s life. Unlike Open-cell foams, Closed Cells should be installed in several layers to achieve the required thickness due to the exothermic reaction that occurs as the foam expands to its final state. Closed Cell is solid and unlike Open Cell, is not easy to compress which helps to make it a popular choice in many buildings throughout the UK.

Historic Use Of Spray Foam Insulation In The UK:

Spray Foam Insulation has been available in the UK for around 30 years, migrating across the Atlantic from America and Canada, where it has become a mainstream insulation solution. When it was first introduced to the UK, Closed Cell Foam was used primarily in residential settings to provide a roof stabilisation solution in homes where roofing membranes were absent, and the roof tiles were visible from within the attic space. Due to its exceptional bonding strength to most substrates, closed cell foam was often used as an unofficial insurance policy to buy the homeowner up to 25 years of peace of mind that the roof tiles wouldn’t slip. Still, of course, a bonding solution such as closed-cell foam should never be used as a long-term fix to the need for a roof replacement. Now an unaccepted process, roof stabilisation using Closed Cell Foam causes considerable concern for mortgage lenders and building surveyors as there is little ability to assess the roof’s condition and structural timbers. In addition, should moisture drive through any penetrations in the roof tiles, it can become trapped within the closed-cell foam to degrade and rot the structural roof timber.

During the 2010s, Open Cell Foam became a primary solution for the discerning homeowner looking to reduce energy costs. Spray-applied directly to roofing membranes, Open Cell Foam is a vapour permeable insulation system that enables moisture migration through the roof assembly. When the primary roof covering is a low-resistance, modern membrane, it promotes an entirely breathable roof assembly, meaning moisture can migrate through without becoming trapped. However, most of the existing UK housing stock was constructed using high-resistance bitumen felt membranes impermeable to moisture which can trap interstitial condensation within the outer layer of the insulation. Mortgage lenders and building surveyors are concerned that Spray Foam Insulation, when applied directly to high-resistance membranes, can trap moisture within the roof assembly, leading to rot and decay of structural timbers when moisture content breaches a threshold of 20 kg/m3. Despite these concerns, scientific and hygrothermal data shows that neither Open or Closed Cell spray foams pose any risk to the structural elements of the building where the property is subject to a low moisture load or vapour control layers are used on the warm side of the insulation.

Elements of the Part L Building Regulations and BS 5250 for the Management of Moisture in Buildings can support the concept of spray foam insulation thanks to its airtightness, thermal performance and their ability to reduce or eilimnate surface condensation. Although some mortgage lenders and surveyors may have expressed concern or reservation about spray foam, it is important to note that any insulation material can cause damage to a property when installed incorrectly or without consideration for BS 5250. It is important to mention that spray foam insulation remains an important product in the UK as we seek to meet net-zero by 2050. Over the past three years, the spray foam industry has worked hard to establish Best Practices, better installer surveillance, proper installer training and the provision of better system designs and handover documentation. Additionally, the five main brands of spray foam available in the UK all hold BBA or KIWA Certification following extensive testing to support the quality of scopoe of use for the product. When considering spray foam insulation, it is essential to choose a product that holds certification as there can be vast differences with the quality of cheaper unregulated and uncertified spray foams.

You can find out more about Enverge Spray Foam Insulation here or browse our website case studies to learn more about its use and suitability in a wide variety of projects.

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