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Jack in the Green

Jack in the Green

Lime Plastering and Conservation Building

Insulating traditionally constructed buildings

Brought into focus largely as reaction to recent government Green Deal initiatives, the appropriateness and efficiency of modern insulation systems (both internal and external) applied to traditionally constructed buildings is at the heart of current debate.

A traditional building is defined as a property built prior to 1919 with solid walls constructed of moisture-permeable materials. It is estimated that traditional buildings, numbering over 6 million, make up around a quarter of the UK domestic housing stock.

Follow these links to SPAB (The Society for Protection of Ancient Buildings) and IHBC (Institute for Historic Buildings Conservation) to read reaction and discussion of some of the issues involved with retrofitting insulation to traditionally constructed buildings.

traditional stone wall holistic system

Traditional Building Materials and Breathability

Across Britain, historic buildings are constructed from a variety of materials; brick, mud, timber and stone being prevalent in different areas. Each material type has its own history of use, and walls not only vary in their thickness and construction, their performance also differs according location and orientation. So, for example, a brick-built Victorian mid-terrace in an urban location will perform very differently (and be subject to much less severe weather conditions) to a detached stone farmhouse in an exposed upland location.

Traditional solid wall construction is a holistic building system. To work properly, this system relies on permeable (breathable) materials. Breathability allows water in the form of vapour or liquid to pass readily through the body of the wall and escape.

Traditional stone walls, for example, are made from an inner and an outer skin of stonework, tied together with through stones, and infilled with a loose rubble core.

Most damp problems are due to water ingress, caused in many cases (especially in western Britain) by wind driven rain. Breathable lime mortars, renders, roughcast and limewash allow the rain to soak into the surface, then dry out in the wind and sun. Any water entering the outer skin dries as vapour within the rubble core, or can filter down to the base of the wall and exit into the ground.

examples of problems when non-breathing products are applied to solid stone walls

If water should reach the inner face, it can enter the internal environment through breathable lime plaster, and dry with the help of ventilation and warm air.

The addition of impermeable materials-modern cement renders and mortars (including bonding and gypsum plaster) damp-proofing agents, modern paints as well as non-breathable insulation- to any element of a traditionally constructed wall- can lead to problems with internal damp when water enters the wall but cannot escape. Although many walls are unproblematic, those prone to wind-driven rain should be properly maintained with attention paid to their rain-protective qualities and adequate rainwater goods!

Where traditionally constructed walls are prone wind driven rain, the application of non-breathing insulation products can trap damp and disguise problems with water ingress.

Insterstitial Condensation and Insulation

Because damp walls are cold walls, it may be tempting to insulate them. However, non-permeable internal insulation fitted against traditionally constructed walls stops heat from exiting the internal atmosphere. This can also make walls cold, and stops them from performing as a holistic system whereby internal heat warms the wall, drying out water vapour within its core.

Where the temperature of the wall becomes too cold the water vapour will condense and return to its liquid form. This is called insterstital condensation. The mould Aspergillus niger thrives on pure condensed water and appearing as black spots is a good indicator of damp problems within cold walls.

Although traditional buildings perform differently in many respects to modern buildings, this is poorly understood in both industry and public policy. Potential problems with damp trapped behind modern non-breathing insulation systems remain a significant issue carrying with it significant risks of moulds, fabric decay and damage to human health created by damp and poorly ventilated environments.

Traditional Buildings and U-values

Although little information is available regarding the U-values of stone and other traditionally constructed walls, research has shown that these perform much better than predictive computer models, and notwithstanding potential problems with trapped moisture, this could mean little payback from some retrofit methods, including solid wall insulation.

In many circumstances specifiers and contractors use information which does not come directly from research or even formal guidance, but from generalised sources including Building Regulations, product certifications and trade literature.

Information about research on the U-values of traditionally constructed buildings is available from SPAB, Historic Scotland (1.6MB download) and Building Conservation online magazine.

Research undertaken by SPAB and others has illustrated that insulating traditionally constructed walls is only efficient when insulation is applied to property-specific problem areas. Issues of location, orientation, building type, building construction, width of walls, internal linings and openings can all have an impact and should be taken into account when designing insulative schema.

Whilst simply living in a house will demonstrate potential problem areas, the use of thermal imaging cameras can also clearly illustrate specific areas of heat loss. Thermal images often show heat loss through roof coverings and eaves as well as around doors and windows. Before considering expensive and disruptive wall insulation, roof insulation should be a high priority in increasing energy efficiency, as should stopping warm air escaping through windows through the use of thick curtains, thermal blinds, shutters and secondary glazing.

SPAB's Old House Eco Handbook: A Practical Guide for Energy Efficiency and Sustainability (by Marianne Suhr and Roger Hunt) provides step by step advice regarding the insulation of roofs, windows, doors and walls.

SPAB Briefing Energy Efficiency in Old Buildings (7.3MB download) includes advice on insulation, insulation products and secondary glazing.

Historic Scotland's technical series includes a useful guide to 'Keeping warm in a cooler house' (2MB dowload).

Breathable Insulation Products

Many breathable internal and external insulation products are available and can act together with traditionally constructed permeable walls which, properly applied, allow water vapour to escape harmlessly into the atmosphere. These should only be used, however, once problem areas have been identified and external defects allowing water ingress have been resolved.

Natural breathable insulation products available come in many forms and include insulating plasters and renders (based on lime but with additions of hemp and cork), sheet materials produced from wood fibre and reed, blown cellulose insulation made from recycled newspaper, and insulation in rolls and batts made from a variety of materials including sheepswool and hemp. These have a variety of applications and on walls and ceilings can be covered with breathable lime plasters and paints. See below for some links to suppliers and more information.

An important issue to consider when thinking about insulating both external and internal walls is that insulation needs to be relatively thick (typically between 5 and 10cm) to improve thermal efficiency. Internally, floor space will be lost, and skirtings, window surrounds and other internal fixtures (including cornices and picture rails) will have to be removed and/or replaced. External insulation may require eaves overhangs to be lengthened and window sills widened to shed rainwater, and gutters and downpipes will need to be removed and replaced.

As the addition of insulation will change the appearance of a building, if your house is listed or in a conservation area, planning permission or Listed Building Consent is likely to be required.

If you are thinking of applying an insulation system to a traditionally constrcuted wall, SPAB's Old House Eco Handbook: A Practical Guide for Energy Efficiency and Sustainability suggests specific questions to ask potential specifiers and suppliers. The suppliers listed below are just a few of those that we use and many more are out there. This page is intended for general advice only, and we suggest that you make sure to research the appropriateness of products for your building's specific requirements!

Links to some suppliers (many others are out there!)

Ty Mawr Lime natural insulation products

Ty Mawr Lime solid wall insulation factsheet .pdf download

Mike Wye Natural Insulation products

Mike Wye Secil EcoCork Insulation

Eden Lime Mortar hemplime insulating plaster (Cumbria and Northern England).

Internet Resources and Technical Papers

Historic Scotland detailed technical papers on thermal efficiency, insulation, windows, green deal initiatives.

SPAB Briefing: Energy Efficiency in Old Buildings (7.3MB download).

Downloadable report on existing research and guidance on insulating traditional buildings undertaken on behalf of the Department of Energy and Climate Change (DECC) by the Sustainable Traditional Buildings Alliance (STBA) which represents historic building groups in the UK and mainstream construction-related organisations.

The Sustainable Traditional Buildings Alliance (STBA) is a collaboration of not for profit organisations that acts as a forum for sustaining and improving traditional buildings in the UK.

The STBA aims to promote and deliver a more sustainable traditional built environment in the UK through high quality research, education, training and policy. Their website includes interactive, online tools which work together to give guidance for retrofit strategies in traditional buildings. They provide a much needed aid to decision making and learning.

Downloadable articles from Mike Wye website:

Insulation: Meeting the low carbon challenge From Listed Heritage Magazine 2009.

Traditional buildings can be dry and warm From Listed Heritage Magazine 2012.

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