Tag Archives: Ecomerchant

  • 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 the 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. 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 insulation 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 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. 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

     

  • What exactly is a VCL?

    Vapour Control Layer (VCL) Explained

    One of the most commonly used, and widely recognised, acronyms in construction is VCL, which stands for vapour control layer. A VCL is a critical building component designed to protect the building from potential degradation (or poor performance) by managing the passage of water vapour within a building structure. In other words, it is used to manage condensation risk. Condensation is formed when warm moist air condenses into a liquid on contact with a colder surface. A vapour control layer is typically installed on the internal side of the insulation to control the passage of warm moist air (water vapour) entering the structure. However, as a simple acronym, there is a problem because in most applications a specific level or type of performance is required, as a ‘catch all’ acronym VCL is wide open to error.

    Condensation on the internal side of a window, showing that there was plenty of water vapour in the room, which has condensed onto the cold internal window pane. This is a good example of how much water vapour can be available to penetrate and condense within a building structure.

    Unfortunately, and perhaps part of a wider misunderstanding, to many the term VCL is a synonym for polythene sheet, add in only a basic understanding of how condensation forms (as described above) and it is easy to see how the use of the term VCL can cause considerable confusion and anxiety. This is made worse by a large number of alternative terms such as vapour check, vapour permeable membrane, vapour barrier, vapour retarder, ACL, AVCL, vapour diffusion retarder, variable diffusion membrane, monolithic membrane, vapour diffusion barrier, airtight membrane, vapour tight membrane, microporous membrane, breather membrane all used to describe products covered by the acronym VCL …………………frankly it’s no wonder people get confused by all of this. In this article, we will try to bring some clarity to the description and use of internal membranes to help you decide which type to use, where and how. A companion piece is in preparation about external membranes.

    Broadly put there are 3 types of internal membrane.

    Type 1: An impermeable barrier such as polythene, this lets nothing through.  It’s a vapour barrier or a vapour block, has only one function: to stop water, in all forms. An impermeable barrier cannot let water vapour back out of a wall when generated by solar gain - see point below - so this type of membrane has serious limitations in all but a few circumstances. Needless to say, the installation of an impermeable barrier needs to be 100% perfect for it to work.  So, no holes, no gaps at the joints or overlaps, no accidental cuts or nicks and no major scrapes.

    Type 2: A membrane that acts as an impermeable membrane most of the time but has some capacity to allow vapour transfer in certain circumstances.  These are often described as a “vapour retarder” or a “vapour check” and they are designed to work under specific conditions where the inherent properties of the membrane can be relied upon.  Since they only allow the movement of water vapour under these narrow and specific conditions, it is essential to apply them in appropriate situations.

    Type 3: A membrane with variable permeability is often called an intelligent membrane. These are vapour control layers whose ability to allow moisture vapour to pass through depends on circumstances.  Also known as variable diffusion membranes (VDM), most allow vapour movement in both directions, depending upon relative humidity either side of the membrane.

    Some membranes in categories 2 and 3 can be described as breathable, you can read more about breathability here.

    The choice of a membrane can largely be determined by location and build type so a vapour barrier (type 1) can be used under a concrete slab but an intelligent membrane (type 3.) is better to line the inside of a warm roof space.

    The terminology used to describe membranes in buildings is hugely confusing and often ends up being concentrated into the single three letter acronym ‘VCL’ appearing on a drawing, but we know that VCL is a catch-all acronym it means nothing without some context or explanation, for example, we often notice people using the terms VCL and ‘breather membrane’ interchangeably, particularly with regards to pitched roofs. Whilst they have a similar purpose, there are a couple of important differences between the two.

    So why do we need either? Quite simply – the vapour control layer is there to prevent condensation, which can cause a number of problems, including:

    • Structural damage due to rotting timber, whether this be a timber frame, joists or rafters
    • Insulation losing its thermal performance due to having absorbed the moisture
    • Mould, which not only looks unsightly but can also lead to respiratory problems and other health issues

    People generate moisture inside their homes, through breathing, through cooking and particularly by washing themselves and their clothes.  To prevent condensation, we need to eliminate this water vapour from inside the building. We also need to get rid of moisture that is outside the habitable zone but within the building envelope.  This might be water from construction – fresh concrete, for example, takes many months to dry out fully - or perhaps rainwater that seeps through tiled roofs or is wind-driven up under the eaves.

    Traditionally we have eliminated moisture by ventilation; for example, by ventilating the space between the insulation and the slate or tile on a pitched roof. However, studies have shown that ventilation directly above an insulation layer can reduce its thermal efficiency, which means more and more people are opting for an unventilated roof.

    Some Definitions may help

    • Airtight layer- prevents the movement of air which may/ may not act as a Vapour Control layer
    • Vapour Control Layer- a material which can limit both movements of vapour by diffusion, and air movement
    • Breather Membrane- defined as a membrane with a vapour resistance less than 0.6 MNs/g situated on the external side of the insulation acts as a weatherproof layer whilst still allowing water vapour to be passed to the outside.

    Understanding your walls, temperatures and condensation

    With a plethora of membranes on the market, each designed to do a different job and behave in a subtly different way it is easy to be confused about which membranes are required to create a dry and airtight building structure.

    Starting with the basics, when insulating walls you create a temperature gradient across them with the warmest being on the inside and coolest on the outside during the winter months. You can imagine a graph of the temperature showing a fairly steady decrease in temperature as you move closer to the outer surface of the wall.

    When you take warm, moist air and cool it (as it will moving through a building structure) you find moisture condenses at a point known as the ‘dew point’ or ‘condensation point’.  This will typically be the intersection of an impermeable or low permeability surface with the temperature falling low enough for water vapour to become liquid.  This is how damp accumulates inside the fabric of your walls or your insulation, to the severe long-term detriment of your building.

    Why you shouldn't use a ‘vapour barrier’ (Type 1. Membrane) in your walls

    Different construction and insulation materials cope differently with condensation. Some materials, such as masonry, can absorb and release it again once the weather warms without too much damage. However, when using vapour impervious insulation in timber frame construction, any condensation forming in the walls tends to be absorbed by the timber, a process that can cause rot. Additionally, during the winter months when this condensation tends to occur, driving rain may also enter the fabric of the building, further increasing moisture levels in walls. It is therefore very important to prevent this condensation process occurring in the first place, for the longevity of the building.

    One further complication to the above process can be found in the summer months. The temperature gradient is often reversed and the higher temperature is found on the outside of the wall and the lower temperature on the inside. This creates a situation where moisture is driven inwards and condensation can form close to the inner face of the wall instead.

    In the UK until relatively recently an impervious vapour barrier was used on the inner face of a timber frame and was thought to prevent condensation formation by simply blocking the flow of moisture-laden air through the wall. However, it has since been found that not only are vapour barriers regularly full of holes which let moisture through during the winter months, they also cause the accumulation of moisture inside the wall during the summer months. This was caused by the barrier preventing moisture from escaping towards the interior of the building.

    Water vapour that has condensed against a VCL, in this instance a polythene sheet (type 1) used as a VCL over mineral wool and behind plasterboard. Damage can be seen on the timber stud. This occurred within 2 years of installation. Photo courtesy of SkamoWall.

    The high humidity levels and warm temperatures found in these walls combined to form perfect conditions for mould and rot to thrive. This was problematic to both the timber structure, as it rotted, but also to the inhabitants of the building as mould spores are well known to cause respiratory problems and ill health.

    Vapour barriers are still useful though. One of the few places above ground level where a complete vapour barrier should be used is in flat roofing when using foil faced PIR insulation. In this case, you need to lay a vapour barrier on top of your flat roof deck before you lay the insulation and your flat roof covering.

    Using a vapour control layer to control condensation

    The answer to keeping timber-framed walls and roofs dry is to use a layer to restrict the flow of moisture but not to try and stop it. In other words a VCL (or a vapour retarder). A VCL is always used as close to the inner face of a wall as possible and reduces the amount of moisture passing through the layer to low levels, ensuring only insignificant amounts of condensation occurring within the structure. Additionally, this will allow moisture that is driven towards the interior in the summer months to slowly pass back inside the building. This prevents the conditions for mould forming and ensures the longevity of the structure.

    Vapour control can be performed very accurately by the many membranes available but it can also be performed at a basic level by OSB, whose vapour resistance (or vapour permeability) is similar to that of some membranes. The benefit of using OSB as a VCL is that it is far more robust than a 0.2mm membrane and does not require the installation of another layer into your timber frame structure if used internally. However, you will need to test the airtightness of the OSB before using it as there is some variation in air permeability. For guaranteed results either use an airtight VCL membrane, such as the ProClima Intello Plus or Constivap or a board such as Unilin Vapour Block or a liquid applied membrane such as Blowerproof. Blowerproof and Intello Plus are both BBA certified.

    It is also advisable to try and minimise the amount of moisture that enters your building fabric during construction.  Much of our construction timber, sometimes including expensive windows, roof joist assemblies and even SIPs panels, are commonly stored on site with little or no protection against rain, especially driven rain.   Once wet, they can take a significant amount of time to dry out, contributing to the internal moisture load a new dwelling has to deal with.  This can even delay and degrade the final stages of construction: for example, airtightness tapes on OSB have been known to come off during airtightness testing, not adhering properly because the timber is still too wet.

    The latest type of VCL membrane is the 'intelligent' membrane, such as Proclima's Intello Plus membrane. These are very useful products that remain very vapour tight (low vapour permeability) during the winter months when it’s important to try and prevent moisture from entering your structure from the interior. As temperature and humidity in the walls rises the pores in the membrane open and allow moisture to migrate towards the interior of the building. This gives the best of both worlds and ensures your structures remain as dry as it is possible to be.

    Watch the video to see how an intelligent VCL works

    Using a vapour-check or foil backed plasterboard as a VCL

    Vapour control layers are always required whenever you insulate, irrespective of the insulation used. They should be used to form a continuous airtight layer and so all the joints and any penetrations must always be sealed with the appropriate airtightness tapes. Without good levels of airtightness the VCL does not work and moisture levels cannot be controlled inside the structures. Products such as vapour-check, foil backed or insulated plasterboard tend to act as a vapour barrier but with none of the joints or penetrations sealed. These products should not be used instead of a VCL or where a VCL is used.

    IMPORTANT REMINDER

    Always refer to a qualified designer if in doubt or ask the manufacturer for technical and installation advice, we are always happy to answer any questions about airtightness or vapour control or point you in the right direction.

     

     

    Thanks to Paul Jennings and Chris Brookman for their contributions to this article.

    Paul Jennings has over 30 years’ experience of airtightness testing, in the UK and around the world, and has been extensively involved in the delivery of onerous airtightness specifications in Passivhaus and other low-energy projects. He tested the first UK certified domestic and non-domestic Passivhaus buildings, both in Machynlleth, on the same day more than ten years ago, and recently led the team that used 8 sets of test equipment to carry out the most complex airtightness test carried out in the UK to date, on Agar Grove Phase 1, in London. He trains airtightness testers and pioneered the development and delivery of airtightness champions training courses. He has been instrumental in improving our processes and tools for achieving good airtightness, as well as training sealing operatives and delivering numerous CPDs and conference presentations to a wide range of building professionals on different aspects of airtightness.

    Chris Brookman lives in a Passive house of his own design which he built based on his own life principles of low impact, low energy living and human health. Chris runs Back to Earth, is a recognised expert on green building and passive construction, he has written widely on the subject and is a keen blogger on the practical and technical aspects of delivering sustainable construction; Chris also curated the first online Wood Fibre Insulation course

  • Adhesive tapes: how do they work, what should they be able to do, and what can they do?

    Why do adhesives stick?

    Considerable lengths of various adhesive tapes are used when sealing buildings. A typical application is seen in the photo where tapes are being used to seal and connect an internal airtight membrane.

    Adhesive tapes are used as bonding aids in a wide range of applications in the creation of airtight building envelopes. Several hundred metres of tape is often used on a single building! Adhesive tapes have become established as bonding agents for these applications (just as nails are the standard solution for timber structures). They have to fulfil their functions for a number of decades to ensure that the building in question fulfils the standards expected by the energy consultant and by the building client. This article provides an overview of adhesive technology and the key properties of adhesive tapes typically used in construction.

    Aren’t all adhesive tapes the same?

    This illustration shows the various forces that act in an adhesive bonded joint. Cohesion refers to the internal strength of the adhesive. Adhesion refers to the sticking force to the subsurface. As a rule: the higher the adhesion, the lower the cohesion. An optimal balance between cohesion and adhesion is crucial for permanent adhesion. (See information box 1 with regard to adhesive tape tests on construction sites)

    Adhesive tapes might appear similar or even identical at first glance: when you compare different products, they all have a backing material. Depending on the planned application for the adhesive tape in question, this backing material may consist of paper, plastic film or fleece. An adhesive substance has been applied to the backing, and this adhesive substance is covered by a protective sheet or protective paper on the underside of the tape. The various types of backing facilitate different areas of application. For example, a tape that can be used both indoors and outdoors must have a UV-stabilised backing; an adhesive window-sealing tape must have a fleece backing that can be plastered over. The difference is easy to recognise. However, if you consider the adhesive substance itself, the difference is not so easy to identify. A review of data sheets is often of little help in this regard, as they generally only specify limited technical data – and this data is also difficult to compare.

    Adhesive tapes for the creation of air-tightness are generally manufactured using two main production methods. The majority (around 80 – 85%) are produced as dispersion adhesives. In this process, acrylates dissolved in water are applied to the backing material in a liquid state. Emulsifiers are added to the dispersion to ensure that the dispersion remains homogeneous and that the acrylates dissolve in water in the first place. The function of these emulsifiers is to attract water. The water is then evaporated in long drying tunnels later in the production process. The dissolved acrylates bond with one another, form long chains of molecules and become »sticky« as a result. The emulsifiers remain in the adhesive film, but no longer serve any purpose.

    A more exclusive group of adhesive tapes is manufactured using a solids-based adhesive containing pure acrylate. This production technology is relatively new and more laborious from an engineering viewpoint compared to the process used for adhesive tapes with acrylate dispersions. The adhesive is applied to the backing material in the form of a viscous mass and the individual acrylate molecules are cross-linked by the controlled addition of energy in such a way that the desired adhesive properties are created.

    Honey and stone, or adhesion and cohesion

    Honey has high adhesion – it sticks immediately to every surface. However, its cohesion is low, which means that honey drops off the surface under the action of its own weight. Stone is the exact opposite: it has high inner strength, i.e. cohesion, but has no adhesion and therefore does not stick to surfaces.

    Adhesion and cohesion can be demonstrated very well by comparing runny honey with a stone. Honey exhibits good adhesion and sticks to surfaces very well as a result. However, its inner strength (cohesion) is so bad that it runs off in drops under the action of its own weight. A stone has high inner strength, i.e. cohesion, but very low adhesion. Good adhesion is generally associated with poor cohesion and vice versa. A good adhesive tape results from an ideal balance between cohesion and adhesion.

    Why do adhesives stick? Sloths, squirrels and geckos

    These photos show how strength builds up over the course of contact time. An adhesive tape was employed here that can be used for interior air sealing and exterior wind sealing. The initial adhesion – after 20 minutes – can be seen on the left; the significantly stronger adhesive bond after 24 hours can be seen on the right.

    Let us consider the interesting question of how and why an adhesive tape is able to stick things together. The bond with the substrate is achieved using various mechanisms. Sheeting or a pane of glass may appear smooth at first glance, but their surfaces actually look very different – with hills and valleys – when viewed under magnification. The adhesive flows around these structures and claws to the surface like a squirrel on a tree or grips the surface like a sloth wrapped around a branch.

    If the adhesive is in direct contact with the surface, attractive forces – so-called Van der Waals forces – will result between the two elements at a molecular level. The closer the adhesive comes to the surface, the more these forces will come into play and increase the strength of adhesion to the substrate. A similar principle applies with the gecko, which is able to walk upside-down on smooth surfaces such as panes of glass. This is made possible by a large number of very fine setae (hairs) on the feet of geckos, which increase the contact surface and thus facilitate sufficiently strong adhesive forces.

    Take your time: the build-up of adhesive force

    It can take some time before an adhesive has flowed into a subsurface fully and established a strong bond with it. Adhesive strength is generally built up over a period of hours. The reason that all manufacturers recommend that their adhesive tapes should be pressed into place can be explained by the mechanisms described above: an adhesive must be brought into close contact with a subsurface to be able to flow around and surround it.

    A drop of water brings clarity – The influence of surface tension

    There is a commonly held myth that an adhesive should be able to stick to every surface. And if an adhesive bond doesn’t hold as desired, then it’s always the adhesive agent’s fault! However, this assumption is false. Nobody would think of taking two pieces of sawn timber, applying wood glue to them, pressing them together briefly and then pulling them apart again immediately, and then saying that the glue was responsible for the fact that the bond didn’t hold.

    Surface tension of foils: the low-energy surface has few attachment points and a low surface tension. It is not able to pull the water drop out of its shape. The more attachment points there are, the more energy the surface has and the more the water drop will be pulled out of its round shape as a result. High-energy surface: The liquid spreads across the material.

    The quality of a given bond is always dependent on the bonding agent, the subsurface and the method of applying the bond. The release films used are evidence that not all foils are suitable for adhesion: some adhesive tapes can be easily removed from their release films. On the other hand, there are films that tapes bond well too, but which then become detached under tension. Finally, there are also films that adhesive tapes cannot be removed from at all. The surface tension of membranes is responsible for all of this. This tension describes how well a given membrane can be ‘wetted’ by an adhesive – in other words, how well the adhesive can get close to the surface of the membrane to be stuck. The surface tension of a membrane cannot be seen, and this value is specified in data sheets by a few limited number of manufacturers.

    Water drop test

    Silicone paper: Surface tension: < 30 N/mm. Very poor surface wetting. Very hard to stick for this reason.

    Weak wetting and a poor adhesive ability for this PE airtightness membrane: approx. 35 N/mm

    Double-layered airtightness membrane: Very good wetting and good adhesive ability, as the surface tension is greater than 45 N/mm.

    How can one estimate surface tension on a construction site? One possible method here is the water drop test: a drop of water is placed on the surface of the membrane and it is observed how well the drop of water spontaneously wets the surface. The greater the surface tension (surface energy) of the membrane, the greater the likelihood that the water drop will be pulled out of its “drop” shape. This indicates a stronger and more reliable adhesive bond with an airtight membrane.

    Of course, this test does not provide precise information, but it has proven useful in practice over a long period. Membranes with a surface tension of > 40 N/mm are recommended for permanent airtight adhesive bonds. Membranes with surface tensions significantly below this value are often used in building practice. In order to supply the market with adhesive tapes that can still stick to these lower-quality surfaces, large quantities of resins are added to acrylate dispersion adhesive tapes, in particular. These resins stick aggressively to poor surfaces. However, the problem here is that resins can oxidise with oxygen, become brittle over their service lives and lose their adhesive strength. To prevent this from happening, it is recommended to ensure that adhesive tapes that only contain pure acrylates are selected.

    As well as being used for adhesive bonds for membrane overlaps, acrylate adhesive tapes can also be used on joints to adjacent building components consisting of timber, stone, wood fibreboards, plaster and concrete. This is possible as long as the surface is generally even, free of dust and resistant to abrasion. If all three of these prerequisites are not fulfilled by a given surface, it can be pre-treated with a primer. Primers for acrylate tapes are applied in liquid form and differ from undercoats in terms of their mechanism. An undercoat penetrates deep into the surface and strengthens it. A primer for an acrylate adhesive tape is designed to penetrate into the subsurface and also to form a film on the surface that levels out any unevenness. These primers have proven themselves in practice. It is critical that the primer is suitable for the adhesive tape: i.e. one should always think in terms of overall systems.

    Resistance to moisture – why are there differences?

    Adhesive tape after storage in water for 24 hours: Top: a conventional acrylate dispersion adhesive tape, re-emulsified with water; the adhesive has lost its strength. Bottom: pure acrylate on a solid basis is absolutely water-resistant.

    Nobody wants moisture on a building site, but regrettably the reality often very different! Adhesive tapes have to be able to reliably withstand the challenges of moisture after they are installed. The first protective layer is the backing material that is used. A film is clearly more resistant to water than paper. However, moisture does not always come only from the outside, but often from the subsurface too. In this case, the advantage of the external protective effect of the film is reversed, as the moisture cannot escape through the film and builds up instead between the adhesive and the film.

    As already described, acrylate dispersion adhesives contain emulsifiers in their adhesive film after production. A characteristic of emulsifiers is that they store water, and they are still capable of doing this years later. If an acrylate dispersion adhesive comes into contact with water again, the adhesive re-emulsifies often assumes a white colouring and can lose adhesive strength. Pure acrylates are fully water-resistant, as they do not react with water – in this way, their adhesive strength is preserved.

    See yee, who join in endless union – Durability: experience and laboratory tests

    Cohesion adhesion test with 47 adhesive tapes: 40 adhesive tapes failed within two years in a long-term test with low loading.

    Reference is often made to the positive experience observed over the last 20 years with regard to the durability of adhesive tapes. When we plan and build a house nowadays, clients expect the built structures and the materials used to have a service life of 50 years or longer. As a result, it is even more important when selecting adhesive tapes to take into account long experience in the marketplace alongside ageing tests that confirm the high durability of bonding agents.

    Consistent rules are coming: a new standard for bonding agents will create a basis for comparison

    The forthcoming standard DIN 4108-11 will specify laboratory tests that have to be carried out for all adhesive tapes. This will create consistent quality standards and provide a basis for users to compare products.

    Presently, adhesive tapes are not regulated by standards and there are no uniform minimum requirements that have to be fulfilled by-products. The draft of DIN 4108 Part 11 that is soon to be published will fill this gap and specify uniform and comparable minimum requirements for adhesive tapes. This standard contains various tensile strength tests on standardised subsurfaces such as wood and membranes, as well as the possibility of having systems (membranes and adhesive tape) tested by manufacturers.

    Many of the requirements demanded from adhesive tapes described above are formulated in this standard. For example, the tapes are pressed into place in a defined manner before conducting a pull-off test, and the test is carried out with a low pull-off speed so as to simulate the long-acting, low tensile stresses that occur in real applications in this test. Ageing will also form part of the scope of the standard. It is not yet possible to state exactly whether and when the standard will be introduced and become part of construction law. However, the standard will form a good basis for comparing adhesive tapes with one another and will help installers and project planners to make informed decisions.

    Summary: permanent adhesive joints are only possible with good systems and the right handling

    Soft adhesives perform better in the ‘finger adhesion’ test, as they are better able to wet the surface of the thumb. This can lead to problems in practical construction applications, as soft adhesives generally have low cohesion forces.

    Actual loading in practice on site: the adhesive joint is subjected to low forces over a period
    of years, so sufficient cohesive strength is important.

    Permanent adhesive joints on construction projects are feasible and can achieve reliable performance; nonetheless, damage to structures often occurs when joints become detached. Knowledge about the fundamentals of adhesion technology and about the loads that will actually be acting in practice is crucial in order to be able to carry out reliable project planning and testing too. An optimal end result can only be achieved with good handling, a high-quality subsurface and a suitable adhesive tape. All three of these criteria should be carefully considered by the specifier and the energy consultant on site. Manufacturers who make statements about the surface quality of their membranes and about the production technology used in their adhesive tapes (solid acrylate or acrylate dispersion) and who offer long market experience, 3 rd party accreditation by reputable bodies (i.e. PHI, BBA, NSAI, BRANZ etc.) appropriate ageing testing and engineering support should be preferred over suppliers who provide little or no information about their products.

    See the Pro Clima range of airtight tapes here

     

    This article was written by Jens Lüder Herms, Dipl.-Ing. (FH), Jens trained as a carpenter and then studied construction engineering. He develops practical solutions for sealing buildings as part of research and development at Pro Clima.

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