Circular Economy Construction

Learn what the Circular Economy means for construction. On this page find methods to implement circularity, XFrame specific circular design guidance and resources to apply circularity to your own projects.

The Circular Economy

The Circular Economy's core objective is to “decouple economic activity from the consumption of finite resources” (Ellen MacArthur Foundation, 2015).

Drop-down content menu.

Cladding

Vapor Permeable Air Barriers

Rain-screen Construction

Insulation

Internal Wall Linings

Guidance on Circular Cladding Options

Timber Based Cladding Products

Composite Cladding Products

Composite cladding materials employ a wide variety of organic and inorganic industrial residues to produce sheet and board like cladding materials. The most well known variant of such products are wood-plastic composites. These materials use Polyvinyl chloride and wood powder to create an extremely durable, consistent and user-friendly cladding material.

The long life of these products make them very attractive to commercial clients. Examples of such products available in Australia and New Zealand today are:

Many composite cladding products can be recycled into like-for like products. InnoWood declares (as of 2018) that approximately 7.5% of its feed-stock is post-industrial InnoWood material and that this figure would be higher if it wasn’t for their materials long-life performance. Likewise the Weo Composite cladding product reportedly contains “95% recycled content" and is “100% recyclable”.

The difficulty with wood fiber composites and recycling is that once combined with wood powder it is immensely difficult to recover the Polyvinyl chloride or HDPE. This is a barrier to high-value recycling and makes handling the products very challenging for established mainstream plastic recycling schemes. In smaller economies, such as New Zealand, the viability of returning non-standard plastic composites to their manufacturer can be uneconomical.

Fibre Cement and Cement Composite Cladding Products

Fibre Cement Cladding products are well established in New Zealand and Australia under the James Hardie brand name. Fibre cement products are known for their durability, cost efficiency and capacity to create large smooth cladding panels, as well as weatherboard profiles. Fibre cement products are popular in commercial construction as they are inherently fire resistant.

Fibre cement cladding solutions are in most cases nail-fixed to the structural frame, or nail fixed to structural cavity battens. Fibre cement sheet requires specific personal protective equipment to be used safely. When cutting a fine dust is produced that can be toxic if inhaled.

Fibre cement sheet cannot be recycled into a like-for-like product, nor into other high-value materials. For this reason, unless a highly effective circular fixing solution is used, fiber cement cladding products should not be used.

High density fibre cement products are manufactured in Europe and often come with surfaces pre-finished. These products may have improved lifetime performance but ultimately face the same issues at end-of-life.

Aluminium Cladding Products

The use of Aluminum cladding materials has grown significantly over the past two decades. Modern manufacturing methods mean that extruded Aluminium profiles can be created and greatly reduced costs to produce an almost zero maintenance cladding product that is resistant to rot, decay, fire and insect attack. Aluminium can also be recycled time and time again with minimal losses in quality. Recycling reportedly uses approximately 5% of the energy required to create virgin Aluminium. These qualities make Aluminium is an ideal Circular Economy cladding product.

Yet current methods of Aluminium production are hugely energy intensive and produce large quantities of Carbon Dioxide gas. Mining Bauzite ore (the worlds primary source of aluminum) can also be disruptive to natural ecosystems. To put the environmental impacts of Aluminium building products into perspective we have compared these products with engineered timber cladding materials (i.e. finger jointed lumber, thermally modified cladding and the like).

Streamlined LCA Analysis - Engineered Timber vs. Aluminium

Extruded Aluminium: Embodied Energy: 201 Mj/Kg | Global Warming Potential (CO2): 14.15 kg/kg

Engineered Wood: Embodied Energy: 9.5 Mj/Kg | Global Warming Potential (CO2): -1.16 kg/kg

Source: Alcorn, A. 2010. Global Sustainability and the New Zealand House. Doctoral Dissertation, Victoria University of Wellington (pg. 180 and 245). These figures are relevant in the context of New Zealand.

The data on its own is telling. There is a significant increase in the quantity of energy required to manufacture Aluminium weatherboards vs. timber boards. Likewise, there is a 13 fold increase in CO2 emissions per unit of Aluminium manufactured vs. timber. 

You can then convert these generic values into a comparison of the material when actually used on a building:

Engineered Timber vs. Aluminium Cladding Carbon and Embodied Energy (per meter square)

Extruded Aluminium:

Embodied Energy: 1053.2 Mj/Kg | Global Warming Potential (CO2): 74 kg/kg

Engineered Wood:

Embodied Energy: 68.4 Mj/Kg | Global Warming Potential (CO2): -8.3 kg/kg

N.B. In this calculation we assume that 1m2 of Aluminum cladding weighs 5.2kg and 1m2 of Timber cladding weighs 7.2kg. These figures are based on real world products of 200mm wide weatherboards. These figures are relevant in the context of New Zealand.

Based on this analysis per metre square of cladding Aluminium produces 74kg of carbon dioxide versus timber which sequesters 8.3kg of carbon. All these figures assume a single life/use of the product.

Examining the cyclic use of these products is also important and must take into consideration life cycle potential, reprocessing emissions and transportation. It is frequently reported that recycling Aluminium uses '5% of the energy required to manufacture aluminum from ore' . With that in mind, and by using the previous embodied energy figures, recycling Aluminium uses approximately 10 Mj of energy per kg.

To quantify the benefits of this recycling one approach is to look at the point at which reusing a product with higher embodied energy becomes better than the embodied energy costs of using a new product each time. If we do this for timber vs. Aluminium cladding and assume a lifespan of 25 years it would take (roughly) 750 years (30 use cycles) for you to be 'embodied energy neutral' when using recycled Aluminium products vs. using new timber products every time. And, more importantly, at this stage you would have produced 181kg of C02 per kg of Aluminium used - vs. sequestering 250kg of carbon by using timber. (Although this isn't entirely fair given that timber no longer in use will biodegrade and release the sequested carbon back into the soil and eventually the atmosphere. That said, the above model assumes no timber reuse which is rare). 

With these figures in mind we prioritize the use of timber cladding products over Aluminium at this time. Yet, it is important to note that upon the advent of improved Aluminium production and recycling technologies this balance could shift.

Circular Building Material Guide

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Vapor Permeable Air Barriers

Light timber framing has evolved to use a flexible synthetic material on the outside face of all external walls as a way of achieving air-tightness (and as a secondary defense against moisture ingress).

The use of vapor permeable air barriers (colloquially referred to as building wrap, house wrap, wall underlay and/or building paper) under cladding materials emerged in the late 1800’s (Issacs, 2015). At this time the material of choice was a newly invented tar impregnated paper product (now referred to as bituminous building paper) (Issacs, 2015). At the time of invention and continuing to today the primary purpose of ‘building paper’ is to minimize drafts. And although commonly used in New Zealand and Australia during the early 20th century it’s use wasn't made mandatory until NZS 1900 in 1964 (Issacs, 2015). The specific technical requirements of vapor permeable air barriers are covered in NZS 2295:2006.

SPECIFICATION

The majority of vapor permeable air barriers available today are made from non woven spunbond polypropylene (BRANZ, XXX).

ProClima, who provide higher specification vapor permeable layers, use thermoplastic elastomer-ether-ester (TEEE) between two layers of polypropylene microfibre fleece (ProClima, 2015).

END OF LIFE

DuPoint, makers of Tyvek (possibly the worlds most common building wrap) claim that their product can be recycled at end-of-life. Tyvek, being a category 2 (PP) plastic means that high-value recycling is possible, however Tyvek is not accepted in kerbside recycling schemes. DuPoint only takes Tyvek material for recycling when returned directly to Tyvek’s factory. This makes the recycling of any Tyvek product extremely unlikely outside of major manufacturing centers.

ThermaKraft operates a manufacturing plant in Auckland, New Zealand and distributes its vapor permeable air barriers around both Australia and New Zealand. On almost all of ThermaKraft’s product deceleration literature it is noted that their house wraps are recyclable and do not emit VOC’s (Thermakraft, 2016).

By weight vapor permeable air barriers make up very little of a buildings end-of-life waste (<0.5%).

CONTAMINATION ISSUES

One of the major challenges

Insulation

Polyester is our recommended circular economy compatible insulation material.

Polyester insulation materials are pure in their composition which in turn makes high-value recycling easier and more efficient.

End of life material management has a huge impact on emissions.

All materials, but especially those that are bio-based (wood, cork, wood-fiber), should be reused at all costs before considering landfill (Zabalza Bribián et al., p. 1136, 2011).

Selecting an insulation material compatible with the circular economy can be challenging. Many insulation materials that are marketed as environmentally friendly will often contain chemical or material modifications that restrict high-value recycling. These chemical modifiers are added to prevent rot, decay and reduce the risk of combustion. The result are chemically modified material composites with largely inconstant profiles. In circularity such material profiles are not desirable as they complicate the end-of-life recycling process for end-user’s. For this reason we prioritize materials with less complex chemical compositions.

ROCK/SLAG WOOL INSULATION (STONE WOOL)

Mineral and Rock Wool insulation are produced predominantly from basalt (but can also include traces of Dolomite, Cement, Blast Slag, Ferrite and aluminium oxide). These materials are popular as they are easy to work with, inert, inherently resistant to rot and insect attack and formaldehyde-free.

Mineral Wool insulation products, do however, come at great environmental cost.

Flury & Frischknecht found that to produce 1kg of Basalt based rock wool insulation material 1kg of greenhouse gas emissions are released and 15 MJ of energy are required (2012) (Zabalza Bribian et al., 2011 puts this at 3.6kg). The majority (70%+) of these emissions and energy are centered around the extraction and processing of raw materials into rock wool materials. Most importantly to note here is that the production of rock wool insulation causes sulfur dioxide and nitrogen oxide to be released (key contributors to acid rain) (Flury & Frischknecht, 2012). It is also estimated that as of 2012 less than 10% of the energy required to produced rock wool came from renewable sources.

Many report that used Mineral/Rock Wool can be entirely recycled into a new like-for-like product, yet as of 2012, it is estimated that less than 1% of all rock wool produced is recycled into new rock-wool.“The rest is disposed in an inert material landfill” (Flury & Frischknecht, p. 14, 2012). Thus, although mineral wools is comprised of ‘an average of 75% post-industrial recycled content’ the cradle to cradle of such a product is very low. Vantsi & Karki note that the key reasons for a lack of rock wool recycling is “include economic questions and issues related to the purity and health effects of mineral wool waste” (p. 62, 2014).

No rock or mineral wool recycling services exist in Australia and New Zealand (as of 2020) and therefore Rock Wool should not be considered an appropriate circular economy insulation product.

FIBREGLASS INSULATION (GLASS WOOL)

Fibreglass based insulation materials dominate Australia and New Zealand’s insulation markets. Manufactured from molten silica (specifcally sodium, calcium and magnesium silicates as well as quartz and recycled glass) Fibreglass insulation is a inert material that is inherently fire and rot resistant (XXX).

Fibreglass insulation should be considered a technical nutrient under Cradle-to-Cradle design guidelines as the material will not break down over time. A major concern in respect to circularity is the presence of “Phenol–formaldehyde resin…” as “…the most commonly used binder,”…” account(ing) for up to 10 % of the final product mass” (Väntsi and Kärki, 2014). Fibreglass insulation also has traces of Boron in it due to manufacturing processes but these levels are so low that they do not pose any risks to human health.

Recycling of Fibreglass insulation materials is uncommon (especially in Australia and New Zealand). It is reportedly possible to shred old batts and then blow them into new buildings/renovation projects as a loose fill insulation product (XXX).

Large scale recycling facilities for fibreglass batts are established in the USA, taking the waste product and turning it into rigid insulation sheet materials (read more here).

(NB. Brand names like ‘Glasswool’ are based on the same base fibreglass insulation materials).

CELLULOSE INSULATION (RECYCLED NEWSPAPER)

Cellulose insulation is typically considered one of the most sustainable insulation products you can use. It is however combined with ammonium sulfate and borate modifiers to prevent it from rotting and burning and these additives complicate how the material can be processed at end-of-life. Recovery is further complicated by the loose nature of the material and reuse is not recommended as the effectiveness of fire-retardants for a secondary install is unknown. Read more here.

Cellulose insulation should be installed with a continuous air-tight barrier between the insulation and the living area.

NATURAL FIBER INSULATION (SHEEP’S WOOL)

Woolen insulation materials are also generally considered highly ecologically sensitive insulation solutions, comparable to Cellulose. However, like Cellulose, Wool requires chemical modifications to protect it from insect attack. Boron (disodium octaboratete trahydrate added at a weight ratio of 100:3) is the most common chemical used to prevent such attack (Corscadden et al, 2014. Murphy and Norton, 2008). Under ECHA definitions Boron is not classified as a toxic material, however, it is noted that if ingested directly and in large quantities there is some risk to fertility and unborn babies (ECHA, 2012).

Wool is also typically twice the cost of fiber-glass based insulation for the same effective thermal resistance (NZ Prices 2019). A study by Corscadden et al in 2014 identified that if produced on a commercial in the same quantities as fibre-glass insulation woolen products could be cost competitive.

HIGH DENSITY RIGID WOOD FIBRE INSULATION

Composition: Made from softwood fibre’s spun and thermally pressed into rigid sheets (learn more here).

Circular Compatibility Issues:

  • Paraffin wax is used as a water repellent and is a petrochemical derivative.

  • The manufacturing process is typically high embodied energy due to heat and water requirements.

  • As of 2020 wood fibre insulation is not manufactured in New Zealand or Australia (this adds to embodied energy).

  • Rigid boards can be fragile and difficult to use on site.

Key Advantages:

  • High Density Wood Fibre Insulation does not require chemical additives to resist fire in most instances. If fire treatment is required (usually only for medium and low density wood fibre insulation materials) ammonium phosphate is commonly used.

Things to Consider:

  • Manufactured using the ‘hot’ process high density wood fiber insulation is heated to 170 degrees.

CORK INSULATION (BOARD AND GRANULATED)

Cork based insulation materials are lauded for their ecological sensitivity. Raw cork bark, being an entirely renewable and carbon sequestering material, is processed using heat and steam to create rigid sheet insulation boards (Sierra-Pérez et al, 2016). An Life Cycle Analysis of cork insulation sheet material undertaken in 2011 found that to produce 1kg of Cork Board insulation 0.8kg of CO2 will be released. This is for a Spanish use case and transportation to the Southern Hemisphere is estimate to double that emissions level. Thus, one of the major concerns with cork based insulation materials when used in America, Canada, Australia and New Zealand is the associated environmental costs due to transportation.

Small quantities of Polyurethane is added to cork granules during manufacturing to enhance the binding strength (Sierra-Pérez et al, 2016). No chemical additives are required to resist rot, insect attack or prevent spread of flame as these are all natural qualities of the cork material.

It should be noted that although cork is an excellent circular economy insulation product the constrained supply chain means that the cost of using cork in New Zealand and Australian construction is extremely high. An R1.5 equivalent 50mm insulation sheet product is NZD$66.30/m2 (ThermaCork, 2020) (vs. NZD$12/m2 for Wool Blend and NZD$4.10 for Fibre Glass).

As of 2014, quantitative LCA information for end-of-life performance of cork insulation materials is unavailable.

RECYCLED ALTERNATIVES

Insulation materials are one of the few building products in which low-grade recycled materials and bi-products can be re-utilized as their visual qualities are not important. Providing the material is resistant to the spread of fire, does not easily rot and acts as an insulator by trapping air than the material can be considered an appropriate material. The aforementioned Cellulose recycled newspaper is one such recycled insulation alternative.

Shredded used denim clothing is another popular alternative. The leading industrial brand for this product is ‘UltraTouch’ (a subsidiary of BondedLogic Group) whose batts contain approximately 80% ‘up-cycled’ post-industrial waste denim. Unfortunately, however, just as with Cellulose a Borate additive is needed to make the product resistant to fire and rot (source). BondedLogic Group do accept waste material back to their manufacturing plants and can reform the waste into the same insulation batt (some new borates are added for QA purposes). Therefore, as high-value recycling is only available locally such products should be used only if manufactured in the same region.

STRAW, HEMP & JUTE

Another popular and much talked about category of sustainable insulation products are bio-mass type materials made from waste agricultural processes. Straw is the most well known of these materials and has been used in timber frame construction for hundreds of years. Trapped air in the cells of dried straw stalks and air trapped between the cells when straw bales are compressed create a bulk insulation block. Straw is entirely biodegradable and can be used in residential construction up to five stories without the need for chemical fire suppressants. Straw insulation and associated building methods work well in terms of circularity for one-off buildings in which some of the labor costs can be absorbed by end-users. A case can be made when straw-based systems are prefabricated, however these also suffer from cost and spatial limitations (also note that no Prefabricated Straw Bale house building systems is operational in New Zealand as of May 2020).

One of the draw-backs of Straw is that thicker walls are needed to achieve equivalent insulation R-Values to that of glass wool or polyester (Straw is approximately R1.7/100mm vs. R2.4/100mm). To ensure that moisture doesn’t cause rot in the straw mass a lime-based plaster is used (generally on both sides). This allows moisture vapor to pass right through the assembly and also acts to limit surface flame spread.

Hemp as an insulation product has gained significant popularity over the past 10 years (XXX). The husk of hemp can be used in a variety of different ways to produce an insulation material. Traditional methods involved mixing the chaffed (chopped/shredded) husk with a lime based binder to make ‘hemp-crete’. This material can be packed into a timber frame when wet and then will form a rigid insulation mass. Depending on the mixture and how the structure is designed hempcrete can also be used in a load bearing capacity. Although both lime and hemp are natural materials and would biodegrade hempcrete is not considered an appropriate circular insulation material. The main issue is that typically the process of extracting lime is more intensive and environmentally destructive then just using a light-weight and directly recyclable material like polyester.

CONCLUSIONS

This collated list of the advantages and disadvantages of different insulation materials in respect to material circularity highlights the complexity of specifying building materials in today’s current building material supply market. For mass-production housing we recommend polyester insulation products due to their material purity. In low volume housing situations the use of natural insulation materials such as straw or feathers excel in a circular context.

Given the associated complexities of specifying an insulation material we recommend that you undertake your own research to determine state-of-the art practices that may be more circular economy appropriate at your time of construction.