Designing and building with natural insulation materials

Why what we build from matters

The best buildings are life-enhancing and support our physical and mental health. Great design and healthy products enable the delivery of a healthy internal environment - meaning good indoor air quality, natural lighting as well as excellent thermal and acoustic comfort. In order to do this, we have to ensure we practise good decision making which requires an informed and holistic approach. Products that are low embodied carbon, natural, non-toxic, and healthy such as natural insulation have an important part in delivering better buildings.

But it’s not only what a building is made of that contributes to a healthier living environment,  ventilation also plays a significant role. Where non-sorptive materials (i.e. in this instance ones that cannot absorb and release water as a vapour or liquid as opposed to sorptive ones that can) are used such as Polyisocyanurate (PIR) insulation moisture needs to be ‘managed out’ of a building to prevent poor air quality or potential condensation within the structure, non-sorptive materials are highly prevalent in modern construction methods meaning that the ‘fabric’ itself cannot help buffer and moderate the internal environment and ventilation is the only strategy to remove water vapour or pollutants. However, emerging evidence suggests that relying on ventilation strategies alone to provide healthy air inside low energy buildings is, in many cases, presenting significant risks to the health of occupants as well as the health of the building fabric.[i]

In order to build better, healthier more efficient buildings and taking a holistic approach the inevitable conclusion is that alternative strategies and materials should be seriously considered in order to achieve these elevated levels of performance. This presents a real opportunity to leverage design and natural building materials to deliver better standards. As insulation by volume is a significant part of any build cost, plus it has a direct correlation to building performance and occupant health, this is where the focus of building designers, architects, developers and owners is moving.

The 'Protexion Campaign' to promote natural insulation materials.

To address these issues and help promote the already growing market for natural insulation materials in the summer of 2018 Ecomerchant and Steico UK joined forces to launch a campaign to champion the benefits of using natural insulation products.  The same principles that sit behind the promotion of natural insulation products were echoed by the Alliance for Sustainable Building Products and the Natural Fibre Insulation Group, the members of which, originally proposed that more work needed to be done to highlight the considerable benefits of natural insulation to a market that has largely ignored them in favour of cheap synthetic materials. Despite the clearly defined, tested and verified performance natural insulation worldwide it has not been taken up in the UK as much as in other countries. In the UK the default insulation materials are still mineral (glass) wool and foil backed Polyisocyanurate (PIR) however previous cost savings afforded by synthetic insulation have largely been lost and the price differential assumed before in favour of synthetic insulation has narrowed to the extent that natural insulation options can now be less expensive than synthetic ones plus the increase in timber frame and the desire for better airtightness is driving constructors towards natural solutions. Year on year sales in natural insulations have seen double-digit growth and a widening of the customer base to include modular construction, custom and self-build and social housing.

To help inform potential users of natural insulation materials the Protexion campaign developed a dedicated website www.ecomerchant.co.uk/protexion  where you will find the wheel (illustrated below) the wheel has dynamic segments (links) e.g. health, fire and acoustic which click through to more information on each subject, you can also download wood fibre insulation certifications and find toxicology reports and environmental product declarations, this is the type of clear unambiguous information that allows us to make informed and better design choices.

The Protexion wheel, each segment links to the relevant role with supporting information, the wheel also links to accreditations, EPD's and toxicology reports. Click the image above to link to the Protexion site.

The appeal of natural insulation materials

How we select insulation needs to be about having a real choice and for specifiers to be equipped with the right knowledge to compare materials on a like-for-like basis plus different parts of the building will require different performance criteria no one insulation type will be the best for all applications.

To design a well-insulated building, you need to make informed decisions throughout all phases of a construction project to ensure your building performs as you envisage as mentioned above.

However, selecting the right insulation is about more than just reaching building regulation compliance or ‘keeping in the heat’. It’s about ensuring a building protects its occupants’ entire well-being and comfort, the following list covers most of the core benefits and features of natural insulation and highlights the role they can play in delivering better, healthier and low impact buildings.

How well does insulation keep the heat out?

Summer overheating

High internal temperatures can cause respiratory or cardiovascular problems. Work by CIBSE and Arup suggests that most people begin to feel ‘warm’ at 25°C and ‘hot’ at 28°C. Their report also defines 35°C as the internal temperature above which there is a significant danger of heat stress. For vulnerable occupant groups, the impact of overheating can take effect much sooner with potentially much poorer outcomes.

Low fabric thermal mass leaves buildings more vulnerable to uncomfortably high, and in some instances, dangerously high internal temperatures in summer. This problem of summer overheating has been identified, by the NHBC and others, as a particular problem in buildings vulnerable to excessive heat gain with inadequate ventilation.

In the UK, thermal insulation to protect from the cold is essential, particularly given ever-increasing energy costs. However, as demand for usable square footage of buildings increases, basement and loft conversions are the routes many now take. However, these parts of a home or office, are the spaces most prone to extremes in temperature. They, therefore, need more thought – i.e. how do you keep a space warm in winter but, for a loft, how to keep it cool come summer.

Compared with synthetic insulation materials, wood fibre insulation has a much higher density. This higher density means that natural insulation makes for a better heat buffer as the high midday temperature will only reach the internal side and be lost at night when the temperature is already cooler outside.

High internal summer temperatures are caused by heat from appliances and occupants, solar gain through windows and external heat penetrating through the fabric. It is the latter issue of penetrating heat where the thermal mass of natural insulation systems can delay the arrival of this heat energy so that it is emitted internally in the relative cool of the night. Of course, too much thermal mass will cause this heat to arrive the following day and compound the problem. Perhaps good design with natural systems can hit a ‘Goldilocks zone’ of just the right levels of thermal mass and thermal conductivity.

Thermal comfort

Maintaining internal temperature around a comfortable mean is at the root of good fabric first low energy design. In lightweight constructions, some degree of thermal mass provided by the fabric helps to smooth out the internal temperature fluctuations which may be caused by heating systems or the opening and closing of windows and doors, for example. Natural insulations and systems tend to have high thermal mass relative to other types of insulation. This is due to the inherent physical properties of the cellulose or protein-based fibres and significantly enhanced by the presence of chemically bound water contained in these fibres. Water has a very high heat capacity which is twice that of concrete so its presence in natural fibres adds to the ability of the insulation to absorb heat energy.

How a building’s lack of breathability is hurting our health

A breathable structure is one that allows the passage of moisture.

Those of us committed to the development of natural insulation products and systems view fabric breathability, or more accurately, the dry transport of moisture, as an important component in overall fabric performance. The ability of natural and hygroscopic materials to absorb and release water whilst remaining dry reduces the risk of interstitial condensation and ultimate fabric failure.

Natural fibres constantly adjust humidity levels away from extremes of damp and dryness helping maintain air moisture at comfortable levels, reducing the risk of both surface condensation and the negative health risks from moulds, mites and viruses. Of course, fabric breathability is not an alternative to a good ventilation strategy but should be considered as part of a robust and healthy building strategy.

In a report titled ‘Health and Moisture in Buildings,’ the authors conclude that ‘these risks [moisture in buildings] combine with the other more clearly defined risks to the durability and value of the building fabric. It is relatively easy to see and to cost the damage done to buildings where moisture imbalance occurs. It is estimated that perhaps 70 to 80% of all building damage is due to excessive or trapped moisture’  With such a large percentage of all building construction problems associated with water in some way, breathability is an essential component in preventing the accumulation of harmful water within the building’s fabric.  This is fundamental in reducing health risks from mould and mites that those suffering from respiratory illnesses such as asthma and chronic obstructive pulmonary disease (COPD) are particularly susceptible to.

For effective breathability, there are four essential components that need to be considered:

  • a moisture pathway
  • a driving force
  • a sorptive fabric
  • vapour control.

Natural fibre insulation is most effective as it suppresses potentially harmful water by binding and releasing moisture which helps regulate humidity levels as the moisture moves.

Easy-to-fit insulation

A well-designed building takes into consideration how a material performs throughout the building’s entire life cycle. This includes ease of installation. Steico’s wood fibre insulation is simple and easy to fit (either packed or friction-fitted), eliminating installer error, keeping construction programmes tight and costs low.

How insulation is fitted into or onto the building also has an impact on performance, poorly fitted insulation will allow the passage of air through the structure which can quickly strip out the heat from a building. Tests by Paul Jennings from Aldas featured in the documentary The Future of Housing demonstrated that a building with an air change of 9 m3/hour/m2 @ 50 pascals  (Building Regs stipulates 10) when subject to a modest 20 miles/hr wind will take just 7 minutes to remove the heat from the building, what this shows is that regulatory compliance is not a good indicator of building efficiency, a guarantee of lower bills or occupant comfort.  Minimising air movement through insulation is helped if insulation is designed to help restrict airflow, features such as tongue and groove profiles and dense fibre friction fit batts help to eliminate and reduce air pathways through the building.

Indoor air and occupant health

Creating and maintaining a healthy and comfortable indoor environment is a complex and difficult challenge. Temperature, humidity and carbon dioxide (CO2) must be maintained at safe and comfortable levels. Moreover, the introduction of pollutants such as particulates and volatile organic compounds (VOCs) greatly influences indoor air quality. A robust ventilation strategy is clearly critical to CO2 levels, but the building fabric can play an important role in helping to manage temperature, humidity and pollution levels. Sheep’s wool insulation, in particular, can mitigate and absorb harmful indoor emissions including formaldehyde; the high levels of Keratin based in sheep’s wool are known to react and eliminate formaldehyde test results[ii] showed that Thermafleece sheep’s wool insulation absorbed 90mg formaldehyde per 1kg of insulation.

Internally generated air pollution

Finally, there is a very real and growing problem of indoor air pollution. The problem of poor external air is now well documented with a recent report from the Royal College of Physicians, Every Breath We Take, indicating that air pollution is leading to an estimated 9,500 annual premature deaths in London alone. The report authors recognise the current lack of focus on indoor air. Nonetheless, clients and designers can have significant influence over VOC and particulate levels by selecting low or zero emission products and systems.

A quick look at the issue of fire

All insulations will meet fire safety standards, but this is a minimum rating. Fire protection is a challenging topic and it combines materials (including fire testing and certification) and design in an effort to minimise risk, in all cases it is the mix of these two elements that will determine regulatory and performance compliance. There are also issues to consider in the use of fire retardants which evidence shows can be detrimental to human health[iii] However, there are some inherent properties of natural insulation that should be considered. Most natural insulation materials either resist combustion such as sheep's wool or 'char' quickly creating a carbon layer that helps resist the spread of fire such as wood fibre, additionally when burnt they will not give off toxic fumes such as cyanide as polyisocyanurate (PIR) or petrochemical insulation materials do.

Will the house be standing in 100 years?

Condensation is one of the costliest risks to buildings causing huge maintenance repairs and structural damage. Natural materials are better able to absorb and release water meaning it is better able to protect from and buffer moisture thereby becoming a key part of healthy living and building durability.

Comfort for occupants

Insulation improves comfort by moderating external effects and smoothing out variations. This applies to cold, heat and sound. One of the overlooked benefits of natural insulation is delivered by increased mass. This means it is better at reducing both overheating and noise pollution than synthetic insulation.

Improved well-being

Evenly warm walls deliver more radiant heat. Because people find radiant heat particularly pleasant, it is frequently possible to lower the actual ambient temperature without reducing the internal comfort. This leads to the positive side effect that reducing the ambient temperature by one degree means approximately a 5% energy cost saving.

Effective protection against mould

The humidity in the air will only condense on a cold wall, by creating warm walls, this condensation is eliminated. Without damp patches, mould is unable to grow. Mould is avoided from the outset.

Reduced air movement

Draughts caused by convection can be unpleasant. At uninsulated, external walls the air cools down, falls to the ground and flows to the centre of the room where it warms up and ascends again. This does not occur with well-insulated buildings. The cooling effect is reduced or eliminated. If the air is still, we do not feel these draughts and less dust is disturbed, providing positive side effects, particularly for allergy sufferers.

Cancelling out the noise for a peaceful night’s sleep

The higher density of natural insulations - such as wood fibre - makes them better at reducing noise. Sounds external to the building, such as traffic or music, as well as those from within the building, through walls and ceilings are attenuated better by wood fibre than synthetic equivalents. In providing better protection from acoustic pollutants, occupants often report a building as being more restful and relaxing thereby encouraging better mental health.

When a building is well-designed and well-built, occupants should be at their peak comfort. With the average person spending approximately 80% of their lives in enclosed rooms, an occupant’s well-being is imperative. Therefore, the products used to achieve this should cover all the issues affecting a building’s construction, its impact on both its occupants and nature.

Buildability

During construction, the great British weather inevitably gets a building’s shell thoroughly soaked before the roof goes on and it can begin to dry out. Using insulations that trap moisture and do not allow it to easily escape can cause damage to timber frame buildings and roof structures. Wood fibre sheathing and sarking boards are designed to be exposed to the elements during construction by adding in paraffin wax (candle wax) to the mix during manufacture. This means rain will repel, even when a board is cut, as the wax is ‘through and through’. Additional protection should be considered if the wood fibre is too exposed to prolonged bouts of heavy rain.

Whilst wood fibre insulation can appear to absorb rainwater it dries very quickly afterwards without any detriment to the insulation material itself. Materials such as glass or mineral wool take up water in a similar way but are not able to dry quickly and should be removed if soaked to avoid damage to timbers.

Obviously, you should try and avoid soaking your insulation materials but if the worst happens you know that wood fibre will have no issues.

Wood fibre is clean and easy to use, there’s no chance of toxic dust, fibres or dust. In short, it’s easier to handle and fit meaning that the installer tends to achieve a higher quality job. The snug fitting batts leave no gaps and the tongue and groove profile for the rigid boards ensures a tight secure fit with no gaps. Disposal costs are less as natural insulation requires no specialist waste facilities.

Conclusions

Buildings should be considered not as standalone discrete entities, but as part of a system in constant and dynamic interaction with people and the environment. This interconnectedness means benefits, problems, solutions and consequences cannot be effectively addressed in isolation. If we adopt this broad and holistic approach, the benefits of natural insulation products and systems will come to the fore, and we should then expect the rate of market uptake to accelerate dramatically.

 

Authors note:

Thanks to the following for contributions to this article

The Alliance for Sustainable Building Products

The Natural Fibre Insulation Group

The UK Centre for Moisture in Buildings

 References

[i] ASBP-Briefing-Paper-The-health-and-wellbeing-benefits-of-natural-insulation-products-and-systems

[ii] Eden Renewables ASBP Presentation Healthy Buildings Conference and Expo 2017, February 2017

[iii] greensciencepolicy.org Flame retardant chemicals in building insulation

 

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