DSJ - SoE - Conservation and Restoration

Question 1

Talk me through your understanding of definitions used in conservation (such as listed building, scheduled ancient monument, conservation area).

Answer 1

Listed Buildings - The Planning (Listed Building and Conservation Areas) Act 1990 creates special controls for the demolition, alteration or extension of buildings, objects or structures of particular architectural or historic interest. Listed building (LB) controls apply in addition to normal planning controls.

Listed buildings are added to a register called the List of Buildings of Special Architectural or Historic Interest. Historic England administers the listing system, but listing decisions are made by the Secretary of State for Culture, Media and Sport.

Scheduled Ancient Monument - A scheduled monument is an historic building or site that is included in the Schedule of Monuments kept by the Secretary of State for Digital, Culture, Media and Sport. The regime is set out in the Ancient Monuments and Archaeological Areas Act 1979

Conservation area - an area of notable environmental or historical interest or importance which is protected by law against undesirable changes.

Question 2

What are the key principles of building/structure conservation?

Answer 2

The document - ‘Conservation Principles, Policies and Guidance’ produced by Historic England identifies six ‘high level’ principles of conservation:

Question 3

What age/styles/materials of building have you worked with?

Answer 3

Victorian Barns Victorian Houses Edwardian Houses Georgian Houses All grade 2 listed.

Question 4

How do you differentiate between conservation and restoration (as well as preservation and refurbishment)?

Answer 4

Renovation: making improvements and/or repairs to a building, externally and/or internally.

Example: addition of an extension to a property, replastering and redecorating.

Restoration: making repairs to a building while retaining materials from the most significant time in a property’s history.

Example: unpicking a building and removing elements which detract from its original character.

Preservation: keeping a building feature from destruction.

Example: retaining the maximum amount of building fabric with minimal repairs or changes to the original building fabric.

Conservation: seeking to maintain and increase the value of buildings by keeping their original built form and architectural elements.

Example: Ensuring the absolute maximum amount of the original material, in as unaltered a condition as possible, is preserved.

Refurbishment - Refurbishment implies process of cleaning, equipping, or retrofitting. So those are the basic definitions of each.

Question 5

What is the lime cycle?

Answer 5

Question 6

What is NHL?

Answer 6

Hydraulic limes (so called because they set under water) are made in the same way as non-hydraulic lime but using different limestone. They are sold as hydrated lime and have an initial set when water is added, followed by hardening while they absorb carbon dioxide. The more hydraulic a lime is, the faster it sets and the higher its final strength, but this means that it is less breathable and flexible.

Question 7

Red lion farm - run through what was included as part of your heritage statement on this project?

Answer 7

Should identify the heritage asset or assets that may be affected by the proposals. The Statement should identify what makes the asset significant or important in terms of archaeological, architectural, historic or artistic interest. Using photographs can be greatly beneficial in identifying important elements or areas of change. It should also reference planning and heritage policy so that any proposals comply with policy or legislation.

Question 8

Where would you recommend the use of lime putty?

Answer 8

Making fine plasterwork and limewash, but also widely used for pointing masonry and making render, daub and other lime-based mortars.

Question 9

What principle legislation surrounds building conservation?

Answer 9

In addition to the planning framework which is primarily set out in the Town and Country Planning Act 1990:

Planning (Listed Buildings and Conservation Areas) Act 1990 provides specific protection for buildings and areas of special architectural or historic interest

Ancient Monuments and Archaeological Areas Act 1979 provides specific protection for monuments of national interest

Protection of Wrecks Act 1973 provides specific protection for wreck sites of archaeological, historic or artistic interest

Historic Buildings and Ancient Monuments Act 1953 makes provision for the compilation of a register of gardens and other land (parks and gardens, and battlefields).

Question 10

What is a heritage statement?

Answer 10

The term ‘Heritage Statement’ can be used to include a Statement of Significance, a Heritage Impact Assessment or a justification statement, and it may also be incorporated into a Design and Access Statement.

Question 11

What guidance is available for conservation?

Answer 11

The bulk of the guidance specific to the protection of listed buildings and conservation areas is contained in section 12, ‘Conserving and Enhancing the Historic Environment’.

Question 12

What are the six ‘high level’ principles of conservation?

Answer 12

The historic environment is a shared resource

• historic environment valued as part of shared cultural and natural heritage.
• The value of this heritage represents the public interest in places, regardless of ownership.
• In safeguarding the historic environment, and thereby protecting public interest, the use of law, policy and public investment is justified.

Participation in sustaining the historic environment

• Public awareness and understanding of their shared heritage should be achieved through learning about sustaining the historic environment by informed and active participation.
• Different generations and communities will perceive heritage’s values in different ways, and awareness and understanding of this should be raised through learning.
• Specialist knowledge and skills should be developed, maintained and passed on as a means of sustaining the historic environment.

The significance of places must be understood

• A place can be considered as such if it is a fixed part of the historic environment with a distinctive identity that is perceived by people. The significance of a place in terms of values tends to grow in strength and complexity over time, as understanding and perceptions evolve.
• Decisions about a place’s future can only be informed by understanding and articulating its values and significance. Any protection, such as statutory designation determined by the degree of significance.

Management of significant places is necessary to sustain their values

• Change in the historic environment is inevitable. Conservation is the process of managing change so as to best sustain its heritage values.
• If understanding of the past is increased, or particular heritage values are revealed or reinforced, then intervention may be justified. It is important though that any resulting harm is decisively outweighed by the benefits.

Change decisions should be reasonable, consistent and transparent

• The exercise of statutory controls should be governed by proportionality.
• The least harmful means of accommodating conflicting interests should be sought.
• Where conflict is unavoidable, the weight given to heritage values in making the decision should be proportionate to the place’s significance and the impact of the proposed change on that significance.

It is essential to document and learn from decisions

• It is crucial that records of decision justifications and actions are accessible for analysis and reference. The effects of, and responses to, change should be regularly evaluated by managers of significant places, with the results used to inform future decisions.
• Where any loss is the direct result of intervention, the costs of the work should be borne by those who benefit from the change, or, if it is in the public interest, whose role it is to initiate such change.

Question 13

What is the relationship between ‘significance’ and ‘heritage value’?

Answer 13

Significance is the collective term for all the heritage values attached to a place, i.e. the sum total.

Question 14

There are four different categories to describe how people value historic places. What are they?

Answer 14

EHAC

Evidential value: The potential of a place to provide evidence about historic activity.

Historical value: An illustrative or associative way in which historic people, events and aspects of life can be connected to the present through a place.

Aesthetic value: The sensory and intellectual stimulation drawn by people from a place.

Communal value: The meanings and associations of a place for the people who relate to it.

Question 15

What are the different designations for listed buildings?

Answer 15

There are three types of listed status for buildings in England and Wales:

• Grade I: buildings of exceptional interest.
• Grade II*: particularly important buildings of more than special interest.
• Grade II: buildings that are of special interest, warranting every effort to preserve them.

Question 16

Why are buildings listed?

Answer 16

1. Architectural interest (such as design, decoration or craftsmanship).
2. Historic interest (for example, if the building is representative of a particular type).
3. Historic association (association with nationally important people or events).
4. Group value (part of a larger ensemble).

Question 17

Explain your understanding of breathable building technology?

Answer 17

Old buildings - be they ancient timber framed hall houses, country cottages, stone faced Georgian townhouses or Victorian and Edwardian brick terraces - generally have solid walls. These were built using weak and porous mortars, plasters and renders based on lime, or sometimes earth or clay, that were often finished with simple, breathable paints such as limewash. When it rained, moisture was absorbed into the walls but then the drying effect of the wind and the sun caused it to evaporate. The same thing happened inside, the moisture from cooking, bathing and other activities was absorbed into the surfaces which acted as a moisture buffer but, because these buildings were draughty and had large open fires, the water vapour was drawn out again and dispersed.

Providing these buildings are properly maintained they remain essentially dry and in equilibrium. This delicate balance is upset when modern products are used during repair and refurbishment work. Employing cement based mortars and renders, ‘plastic’ paints and waterproof sealants can prove disastrous. Moisture is trapped, surfaces break down, damp patches appear and rot and beetle infestation occurs. This may be harmful both to the wellbeing of the building and its occupants.

Question 18

Explain the difference between breathabilty and vapour permeability.

Answer 18

Breathability in buildings is often confused with air permeability but it’s important to realise that they’re two totally different things.

Breathability is the water vapour transmission rate, or the speed at which vapour passes through a particular material or construction.

Air permeability, or air leakage, is the uncontrolled movement of air (draughts) through joints and gaps. This means it’s perfectly possible to install an airtight membrane which is breathable.

Question 19

What are the common issues with historic buildings which have been refurbished?

Answer 19

The need to retrofit buildings to make them more energy efficient can compounded problems relating to breathability and moisture. Where airtightness is increased, maintaining controlled ventilation is a must. Equally, careful thought must be given to the choice of insulation. Some modern insulation materials easily trap moisture. Natural insulation materials tend to be better as they’re more breathable and will act as moisture buffers, absorbing and releasing water as the relative humidity within the building increases or decreases.

Question 20

What is a ‘Historic Building’?

Answer 20

‘For the purposes of the interpretation of the energy efficiency requirements of the Building Regulations, Approved Documents L1B and L2B, and this series of documents, ‘historic buildings’ are defined as those which meet at least one of the following criteria:

• Listed in accordance with section 1 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
• In a conservation area designated in accordance with section 69 of that Act.
• Included in the schedule of monuments maintained under section 1 of the Ancient Monuments and Archaeological Areas Act 1979.
• Buildings which are of architectural and historical interest and which are referred to as a material consideration in a local authority’s development plan or local development framework.
• Buildings which are of architectural and historical interest within national parks, areas of outstanding natural beauty, registered historic parks and gardens, registered battlefields, the curtilages of scheduled ancient monuments, and world heritage sites.’

Question 21

How is traditional lime mortar made?

Answer 21

Combination of lime putty (Ca(OH)2) and aggregate (usually sand). Carbonation of the lime i.e. reaction with CO2 in the atmosphere, will form Calcium Carbonate (CaCO3).

Question 22

Explain the difference between types of lime used in construction?

Answer 22

Hydraulic (Natural Hydraulic Limes) or non-hydraulic (lime putty).

Hydraulic lime is made from an impure limestone and sets through hydrolysis, a reaction caused by water.

Non-hydraulic lime is made from a pure limestone, pure calcium carbonate, and tends to be in the form of a putty. Non-hydraulic lime sets by carbonation (re-absorbing carbon dioxide from the air).

Question 23

Explain the practicalities of non-hydraulic lime?

Answer 23

Arrives to site as a lime putty (usually in plastic tubs). Must remain air tight to prevent carbonation.

Softer and sets much more slowly than hydraulic lime and remains softer for longer as the carbonation process is very slow.

The fatty nature of lime putty lends itself especially well to plasters and renders and its flexibility allows for the subtle movement common to older buildings constructed with little or no foundations.

Question 24

When is hydraulic lime used?

Answer 24

Hydraulic lime provides a faster initial set and greater compressive strength compared to non-hydraulic lime and will set in more extreme conditions including under water. Because of their more robust nature, hydraulic limes are most often used for exterior work

Question 25

What types of hydraulic lime are available?

Answer 25

Three different grades; NHL 2, NHL 3.5 and NHL 5.

The number relates to compressive strength in MPa (Megapascals) or N/mm² (Newtons per square millimetre) at 28 days under the current British Standard.

These grades were historically associated with the terms feebly hydraulic, moderately hydraulic and eminently hydraulic respectively. These terms refer to each grade’s degree of hydraulicity, that is their ability to set under water without exposure to air

Question 26

What guidence exists for hydraulic lime mortar?

Answer 26

BS EN 459-1 is entitled: Building lime: Definitions, specifications and conformity criteria.

Question 27

How would you specify mortar on a historic building?

Answer 27

Typically NHL 3.5 for external work.

Question 28

What is the difference between NHL and HL?

Answer 28

• Natural hydraulic lime (NHL): This is produced by burning more or less argillaceous or siliceous limestone and then reducing it to a powder by slaking with or without grinding. The hydraulic properties result from the chemical composition of the raw materials.
• Hydraulic lime (HL); This is a binder consisting of lime and other materials such as cement, blast furnace slag, limestone filler and other suitable materials.

Question 29

What is formulated lime?

Answer 29

Formulated lime (FL): Formulated lime consists of air lime and/or natural hydraulic lime with added hydraulic or pozzolanic material. Inclusion of any cement or cement clinker must be declared.

Question 30

What mix would you reccomend for NHL 3.5

Answer 30

1 part lime to 3 parts sharp sand

Question 31

What is SPAB?

Answer 31

The Society for the Protection of Ancient Buildings (SPAB)

Founded by William Morris in 1877, the SPAB was established in response to the work of Victorian architects whose enthusiasm for harmful restoration caused irreparable damage.

Question 32

Breifly summarise the SPAB approach.

Answer 32

• REPAIR not RESTORATION
• Carefully considered inaction
• The SPAB Approach is based on the protection of ‘fabric’ — the material from which a building is constructed.
• the SPAB Approach generally
• rejects arguments that original design or cultural associations
• are more important than surviving fabric.
• care and maintenance. Some deterioration of a building over time is almost inevitable, but maintenance helps slow the rate and lessens the need for larger campaigns of work.
• The SPAB Approach calls for an understanding of history, design and construction.

Question 33

Explain traditional timber frame construction.

Answer 33

Question 34

When planning to undertake works to a building in a conservation area, what would you consider?

Answer 34

Property alterations - May need permission for minor alterations, usually allowable under the GDPO. LPAs tend to overide GDPO with an Article 4 directive.

Trees - For cutting down a tree (even without a TPO), or undertaking pruning works, you must notify the council at least 6 weeks in advance.

Demolition - Demolition or substantial demolition of a building will usually require permission from LPA.

Question 35

What is non-hydraulic lime?

Answer 35

Non-hydraulic lime (CL or DL 70-90) is sold as either hydrated lime or putty lime; they set and harden through drying out and absorbing carbon dioxide from the air. This means they have a very slow set: CO2 is only absorbed when certain conditions are met. They are the softest, most breathable limes available.

Question 36

What is Hydrated lime

Answer 36

Hydrated lime simply means that a controlled amount of water is added to quicklime to make a powder that is more stable and safe to handle. This can be done to hydraulic lime or non-hydraulic lime.

Question 37

What is Wattle and Daub?

Answer 37

Wattle and daub is a composite building method used for making walls and buildings, in which a woven lattice of wooden strips called wattle is daubed with a sticky material usually made of some combination of wet soil, clay, sand, animal dung and straw.

Question 38

What is Cob?

Answer 38

Cob, cobb or clom (in Wales) is a natural building material made from subsoil, water, fibrous organic material (typically straw), and sometimes lime.[1] The contents of subsoil naturally vary, and if it does not contain the right mixture it can be modified with sand or clay. Cob is fireproof, resistant to seismic activity,[2] and uses low-cost materials, although it is very labour intensive.