Vermiculite Insulation: The Essentials

An all-purpose insulation filler, Vermiculite insulation has been used for over a century as a loose-fill insulation substance. Vermiculite has clear benefits when used as an insulation substance, and some relatively big drawbacks, all of which we’ll explore in this guide from Building Materials Nationwide. We’ll also look at the historic health issues associated with vermiculite insulation, the ways to test loose insulation within your building, and the reasons modern vermiculite insulation is safe for use. 

What is Vermiculite Insulation?

Vermiculite is a naturally occurring mineral, found within mines across the Americas, China, and Africa. When heated vermiculite expands dramatically, creating a natural insulating substance that can be simply poured in to offer thermal and acoustic insulation within buildings. Vermiculite is lightweight and fire-resistant, with a wide range of uses beyond insulation. It can also be used in packaging, concrete screeds, swimming pool liners, and plant potting. Vermiculite is also used to make fireproof insulation boards, used in applications like kilns and high-temperature factories. Vermiculite boards are typically used in industrial settings rather than commercial or residential ones.

Where Can Vermiculite Insulation be Used?

The most common use of vermiculite insulation within a house is as a loft or attic insulation. It can be poured between the joists of a loft, giving a strong layer of insulation. A benefit of vermiculite compared to other insulation substances is that it can be poured into small or difficult areas that other insulation cannot reach. Vermiculite can also be used within cavities and voids inside a house, such as those between floors and under stairs. Another use for vermiculite is for acoustic insulation within internal walls. In modern building designs, vermiculite insulation can be used to top up existing insulation, such as pouring it over loft insulation, helping to plug gaps and increase heat retention. Finally, Vermiculite can be used as chimney liner insulation, being poured around the flexible flue liner connecting a wood-burning stove pipe to a chimney.

The Pros and Cons of Vermiculite Insulation

One of the main benefits of vermiculite is its ease of installation. Compared to other insulation which must be measured, nailed, or sprayed into place, vermiculite is poured into your walls, loft, or gaps, offering a strong level of thermal insulation. This can make it handy for DIY installers. It also works great as a top-up to existing insulation. If mineral wool insulation is already installed within a loft, then vermiculite insulation such as Micafil can be poured over the top of it, helping to bolster thermal insulation and also plug any gaps around your insulation. It can also be used to insulate difficult-to-reach gaps or smaller sections of a property, that other types of insulation may be unable to cover.

The main issues with vermiculite insulation have to do with its comparable insulation strength and price. Micafil, the most common vermiculite insulation, has a thermal conductivity of 0.063 W/mK. This is less effective than most quality mineral wool rolls which offer a thermal conductivity of around 0.044 W/mK (lower scores are better). Secondly, Micafil is usually much more expensive than standard rolls. Insulating a full loft with Micafil would be prohibitively expensive for many when compared to the lower costs, and more powerful insulation of traditional insulation materials. Another issue is that vermiculite insulation can be blown around when installed within a draughty environment, so you may need to reset and rebalance it over time.

The Historic Dangers of Vermiculite Insulation

Vermiculite insulation has historically contained asbestos in certain cases. The origins of this are due to contamination within a mine in Libby, Montana, used between 1919 and 1990, where asbestos had developed alongside vermiculite. This means that historically installed vermiculite insulation in lofts, called Zonolite attic insulation in the US, could be a source of asbestos, and as such should not be touched or disturbed. Asbestos fibres can lead to several asbestos-related diseases, and they should be wholly avoided. Instead, you should engage the services of a professional to test, and potentially remove, your vermiculite insulation. Modern vermiculite insulation will not contain asbestos, and is considered a safe product for use around buildings. Always use the services of a professional when removing asbestos. Exposure to asbestos is a serious health risk, and historic vermiculite insulation is one of several types of asbestos that can be found within older homes.

The Best Uses of Vermiculite Insulation

While vermiculite insulation is too expensive to recommend as a full insulation option for lofts, it has clear benefits as an additional insulation material, or one used in difficult spaces. Using vermiculite insulation to top up insubstantial mineral wool rolls, or to fill in gaps around them, can help reduce draughts and heat loss. Similarly, small nooks or crannies that would otherwise be difficult to insulate can be filled with products like Micafil. As a way to insulate difficult areas or to top up existing insulation, vermiculite insulation is an excellent option.