Scholarly article on topic 'The Evaluation of a Palette of Low Carbon Measures Applied to a Conservation Area Victorian Terraced House'

The Evaluation of a Palette of Low Carbon Measures Applied to a Conservation Area Victorian Terraced House Academic research paper on "Civil engineering"

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{Retrofit / Low-Carbon / Conservation / Air-tightness / "Solid wall."}

Abstract of research paper on Civil engineering, author of scientific article — Jon Moorhouse, John Littlewood

Abstract There exists a solution gap between the design of new build UK housing and the low carbon retrofit of existing housing stock. Whilst a series of common standards can be reasonably applied to new construction, many factors (such as age, construction type, condition, tenure and planning regulations) affect the approach required for improving existing properties. Conservation issues in particular can limit the opportunity for retrofit and therefore design details appropriate to the character of the dwelling should be considered. This paper reports on findings from a UK retrofit project that aims to bridge this gap by comparing a range of measures applied to a Victorian Terraced property with a ‘control’ property renovated to more usual renovation standards. The efficacy of a palette of solutions is considered in terms of value (cost) and effect on reduction of fuel consumption and carbon emissions. Conclusions are drawn as to the appropriateness of each retrofit measure for future roll-out based on increased energy efficiency and experience from construction. A system for evaluating wider housing stock for suitability of these retrofit details is also outlined and discussed. This paper will be of interest to those considering the larger scale upgrade of existing dwellings (scaling up retrofit) to minimize energy and carbon use when working on dwellings that have challenging planning and preservation requirements.

Academic research paper on topic "The Evaluation of a Palette of Low Carbon Measures Applied to a Conservation Area Victorian Terraced House"

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Energy Procedia 42 (2013) 597 - 606

The Mediterranean Green Energy Forum 2013, MGEF-13

The Evaluation of a palette of Low Carbon Measures applied to a Conservation Area Victorian Terraced House.

Jon Moorhouse1*, Dr. John Littlewood, 2

1 Constructive Thinking Studio Limited & University of Huddersfield, L35TF, UK

2The Ecological Built Environment Research & Enterprise group, Cardiff Metropolitan University, Cardiff School of Art & Design, Cardiff, CF5 2YB, UK.

Abstract

There exists a solution gap between the design of new build UK housing and the low carbon retrofit of existing housing stock. Whilst a series of common standards can be reasonably applied to new construction, many factors (such as age, construction type, condition, tenure and planning regulations) affect the approach required for improving existing properties. Conservation issues in particular can limit the opportunity for retrofit and therefore design details appropriate to the character of the dwelling should be considered. This paper reports on findings from a UK retrofit project that aims to bridge this gap by comparing a range of measures applied to a Victorian Terraced property with a 'control' property renovated to more usual renovation standards. The efficacy of a palette of solutions is considered in terms of value (cost) and effect on reduction of fuel consumption and carbon emissions. Conclusions are drawn as to the appropriateness of each retrofit measure for future roll-out based on increased energy efficiency and experience from construction. A system for evaluating wider housing stock for suitability of these retrofit details is also outlined and discussed. This paper will be of interest to those considering the larger scale upgrade of existing dwellings (scaling up retrofit) to minimize energy and carbon use when working on dwellings that have challenging planning and preservation requirements.

© 2013 The Authors. Published by Elsevier Ltd. Selectionandpeer-reviewunderresponsibilityofKESInternational

Keywords: Retrofit; Low-Carbon; Conservation; Air-tightness; Solid wall.

1. Introduction

This paper discusses findings from studies undertaken as part of a UK Technology Strategy Board 'Retrofit for the Future' competition funded project, through which an un-insulated solid walled terraced property was renovated employing a range of energy saving measures; in Liverpool, UK. An adjacent control property, undergoing

1876-6102 © 2013 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of KES International doi: 10.1016/j.egypro.2013.11.061

simultaneous significant renovation, was observed to provide a basis for measuring environmental performance improvements.

The research forms a precursor to the first author's professional doctorate: Ecological Building Practices Change Project and it follows on from proposals introduced by the authors in 2011 [1].

The Energy Saving Trust suggests that domestic energy use accounts for 25% of UK energy consumption [2]. Low carbon retrofit to dwellings can reduce this energy consumption and, according to the Technology Strategy Board, the retrofit market is worth approximately £200 Billion over the next 40 years in the UK [3].

According to the Calcutt Report there are 20 million existing dwellings in the UK and the UK Government still aims to build 250,000 new homes per year from 2013 [4]. From the NERA Consulting report to the Department of Energy and Climate Change, the average heating load for a pre 1990 solid wall property in the UK is 14000 KWH per annum, whereas the average heating load of a post 2010 new build (non detached) dwelling is more than 50% less at 6300 KWH per annum, with a predicted reduction to 4700KWH per annum by 2016 [5]. This suggests that in the UK, the average existing solid wall dwelling will require three times as much energy for heating as a new property in 2016. It follows therefore that great reduction in energy consumption and the associated carbon emissions for heating domestic properties in the UK might be made through the careful energy efficient retrofit of existing solid-wall homes.

Conservation areas exist to preserve the appearance, setting and overall historic aesthetic of unique areas of the built environment and this 'protected status' often restricts the opportunity for low-carbon remedial work. Many UK retrofit schemes involve externally insulating solid wall constructions as a key feature, in particular where rigid insulation is fixed to the existing masonry and is then rendered. [6]. Difficulties arise however in Conservation Areas, or on properties where the external appearance of the building is deemed to be worthy of retention, as it is not possible to add insulation without covering the elevation or changing the building line. Whilst, low carbon retrofit measures are more difficult for such properties, careful design, implementation and evaluation can offer useful solutions and comparatively little fieldwork has been undertaken in this area. [7]

In an earlier paper [1] the authors described a palette of details' and described a methodology for monitoring performance that introduced a range of measures to improve the energy efficiency of and therefore reduce carbon dioxide emissions from a three storey, four bedroom terraced house, in the UK. The architectural detailing was developed by the first author to take account of Conservation Area requirements, which included retaining the visibility of the front elevation brickwork and the appearance of the fenestration. This paper documents the installation of the measures during the renovation of the same house and begins to evaluate the outcomes in terms of improved energy efficiency, cost and usability. Throughout the project, it has been observed that the construction process, liaising with the contractor and observing the supply chain, cost and scalability of the construction process. An approach to post-occupancy

observation was developed that involves the tenants in order to generate feedback on usability as well as collecting empirical environmental performance data. This paper thence describes the implementation of measures including internal and external insulation and improved air tightness, mechanical ventilation and heat recovery, Solar PV slates Solar hot water and thermally efficient traditional sash windows. Lessons learnt through the construction process (2011 to 2012) and their evaluation to date (2013) is discussed.

2. Building condition before retrofit

Prior to the retrofit, both the property and the neighbouring control property had been empty since 1999 and had each been converted into three small apartments. The roof was badly damaged and areas of timber required treatment or replacement and the property suffered with other problems associated with damp ingress. Due to the poor condition of the property it was not possible to undertake an air pressure test prior to reconstruction. It was assumed that the air permeability was between 12 and 15 m3/m2.h @50Pa from Stephens' survey of 471 houses constructed between 1900 and 1930, if the property had been intact to be assessed [8]. For the same reason, thermography images were not captured prior to commencement.

Fig. 1. (a) Retrofit property (centre) with control property to left ; (b) Interior condition prior to commencement of works.

(Photographs by first author)

3. Implementing a palette of low carbon retrofit measures

The scheme introduces complimentary measures including wall insulation (internal and external), Mechnical Ventilation Heat Recover (MVHR), Solar Photovoltaics, Solar Hot Water and reduced heat loss timber frame windows.

3.1. Insulation

The approach was to fully insulate all external elevations of the terraced property (front and rear) and air tightness was a key consideration. For the rear elevation it was decided to insulate externally using a spray-foam insulation to achieve a consistent cover, uninterrupted by floor junctions. The condition of the brickwork warranted consideration, ensuring that the mortar joints and substrate for the insulation was sound. The proposed finish was to be a through colour render. In order to provide a 'screed' depth for the insulation that could be installed around existing features such as window heads and window cills a metal lath (Z rail) was used. This allowed for imperfections in the brickwork to be leveled through and, although metal and therefore a conductor, minimized cold bridging to 0.5% as opposed to 8% were timber to be used. The foam insulation (part castor oil based with no polyurethane) was sprayed to the depth of the frame providing a continuity that would be difficult to achieve with rigid insulation and a potential for a high level of air tightness. The grade of insulation was chosen for its high R-value and its resilience in order to assess its resistance to weather when left exposed for a period of time. A highly stable magnesium oxide board was specified in order to reduce depth and minimise the risk of cracking due to movement. Care in detailing was reinforced by checking the quality of construction prior to handover using thermography as suggested by Hopper et al [9].

Fig. 2. (a) Dragonboard (Magnesiuym Oxide Board) cladding to the render system; 2012 First author's photo (b) Additional insulation detailing to reveals. 2012 First Author's photo

The same system has been used internal for walls that of stud-work and spray foam insulation, as illustrated in Figure 3. The form of insulation was similar in composition, but applies as a softer foam. This enabled a full seal around the window frames, between the joists and into a constructed return on the party walls. In this way a continuous airtight seal internally from basement to eaves. This would have been otherwise impossible to achieve without removing the interior floor finish and floor construction. The integrity of the insulation was completed with application at roof level and under the ground floor, the properties have basements that are not used and therefore it was elected to leave them outside the insulated envelope. In hindsight it might have been better to insulate the party walls, although the return in terms of thermal and air tightness improvements might not have been worth the additional costs and loss of internal space.

Fig. 3. (a) CAD image showing Internal Icynene Spray Foam Insulation continuous detail at the floor junction (2011 First Author's CAD model) ; (b) Icynene insulation to internal wall after installation. (2012 first author's photo.)

3.2. Windows

A key conservation requirement was to replace the timber framed sliding sash windows with windows of a similar appearance. The original windows were single glazed and counterbalanced with metal weights on sash chords. By replacing the box system with a spring system it was possible to insulate the resulting brick recess, removing much of the cold bridging around the frame. It was also possible to engineer the transom and bead profiles to match the original profiles whilst being able to support a double glazed unit. Whist the system was not able to take the weight of triple glazing, the double glazed units were k glass and argon filled and with the introduction of thermal breaks to the outer frames achieved a U value of. 1.1 W/m2k.The new sliding sashes achieved an unexpectedly high level of air tightness that seemed to reflect the quality of the manufacture. These windows were designed to be manufactured locally

to fit the variations in individual properties and local vernacular in terms of size, proportion and profile. The scalability of this element can be best served at local level to deal with these local differences. Figures 4a and b illustrate the traditional appearance of the window and their thermal performance, following installation.

Fig. 4. (a) High performance timber sash window ; First Author's photo ; (b) Thermographic image illustrating performance taken

by BSRIA

Fig. 5. (a) Chimney containing MVHR ducting; First Author's photo; (b) MVHR modeled through chimney stacks First Author's CAD model

3.3. Mechanical Ventilation Heat Recovery (MVHR)

One of the key conservation considerations was to retain the chimneys. In most Victorian houses each room is served by an individual flue, leading to a combined stack in the loft or at roof level. By limited intervention into the chimney breasts, it is possible to feed flexible ducts into these flues and thus serve each room with MVHR. The heat exchanger and fan unit is stored in the loft. The condition of the flues can vary as quite often the mid feathers that separate flues can collapse. These can be checked in

the first instance by smoke tests that reveal operation or limited failure. By forcing warm air into the chimneys it is possible to check the clarity of the flues through thermal imaging. Finally, following intervention, endoscopy can be used to identify any intrusion into the flues. This method of ducting can be applied to any size of terraced house without the need for creation of ceiling level bulkheads.

3.4. Solar slates

At the outset of the project it was intended to introduce solar PV and two criteria led to the choice of solar slates. In the first instance, the intention was to minimise the effect on the roofline and maintain, as much as possible, the appearance of the original slate roof. Whilst the roof with the most useful orientation on this retrofit project was to the rear the long-term consideration was to find a solution for wider application. Mondol et al [10] suggests that 30° is the optimum angle of tilt for PV installations in similar locations, matching the average angle for roofs of this age. Jardine [11] shows that east and west facing installations may only be 20% less efficient than south-facing installation, suggesting that both roof pitches might be covered on east-west orientated properties. In other cases, the best orientation might be to the front elevation. Initially, this seemed to be an expensive option, but given that the roof needed to be stripped and re-felted, the cost was somewhat offset. There were also security benefits from incorporating the PV into the built fabric. A 2.4KW array facing south-west was installed on this property. A solar-gas hot water system has been installed as the main space and water heating system in this property. See Figure 6a and 6b below.

Fig. 6. (a) Solar slate installation ; (b) Solar slate and solar thermal array

4. Building Performance, Thermography and Air Tightness

Banfill [12] suggests that air permeability (measured at 50PA) must be reduced below 5 m3/m2.h in order to make an overall energy saving and CO2 reduction. For comfort,

ventilation should be introduced below this level of air permeability. The remedial works that assisted in the reduction of air permeability included spray-foam insulation to all external elevations, floor junctions ceilings and roofs, magnesium oxide board cladding, sealed chimney voids and high performance windows with associated installation detailing. Initial air permeability tests were carried out before practical completion in order to check for defects. In this test the retrofit property had an air permeability of 5.2 m3/m2.h @ 50Pa and several serious envelope penetrations were apparent. Remedial work and secondary testing indicates an air permeability of 3 m3/m2.h @ 50Pa with small defects still to be addressed at roof level. A final air permeability of below 2.5 m3/m2.h @ 50Pa should be possible.

The thermography results below illustrate the building's system performance. In Fig 7a the property in the centre is the retrofit property and the property to the left is the control property. Figure 7b shows the external cladding system to the rear outrigger -the positions of the metal laths are clearly visible.

Fig. 7. (a) Thermographic image of the front elevation taken by BSRIA ; (b) Thermographic image of the rear elevation taken by

The effect of the air tightness was approximated in terms of improved energy efficiency by factoring the air permeability into a SAP (Standard Assessment Procedure for compliance with UK conservation of heat and power regulations) calculation for the property. The unimproved property, with an assumed air permeability of 12 m3/m2.h @ 50Pa and no external insulation had an Environmental Impact (CO2) rating of 39. The retrofit property returned a rating of 53 at 5m3/m2.h @50Pa. When the same calculation was made with an air permeability of 3 m3/m2.h @ 50Pa, the Environmental Impact Rating increased to 69 (A higher rating indicated better energy efficiency). In comparison, when the same calculation was made with an air permeability of 8 m3/m2.h @50Pa, the thickness of insulation would need to be increased from 50mm to 100mm to return the same Environmental Impact rating,

indicating a relationship between increased air tightness and reduced insulation thickness. Reducing the thickness of insulation is desirable in order to retain space internally and to minimise the effect on external detailing such as pediments, window cills and rainwater goods. It is noted that the SAP calculations are predictions only. Data is being collected on real-time energy use and this will be compared against predictions in a future paper.

5. Conclusions and further research

The Property has been occupied for three months, since January 2013. The occupants are familiar with the operation of the MVHR and recognise the contribution to their electricity usage made by the solar PV. We are monitoring the energy use and, periodically, the air tightness over a three-year period. During this time we will make qualitative reports on usability and thermal comfort from the tenants perspective.

The initial performance testing has shown that the system as a whole works in a complementary manner, returning an excellent level of air tightness and vindicating the use of MVHR for the property. Further, the project demonstrates a successful approach to the retrofit of Conservation Area properties in an initially void status.

Further evaluation will suggest suitability for application to occupied properties. A matrix will be constructed to assist surveyors with evaluating potential retrofit measures for similar properties in differing states of repair and with alternate tenures.

References

[1] Moorhouse, J and Littlewood, J. (2011) The low-carbon retrofit of a UK Conservation Area Terrace: Introducing a pattern book

of energy-saving details. Session F-Chapter Two. In: Sustainability in Energy and Buildings. Volume Editors: Nacer M'Sirdi and Aziz Namaane and Robert J. Howlett and Lakhmi C. Jain. Vol. 12. Springer, Heidelberg, Germany. pp.307-318. ISBN: 978-3-642-27508-1.

[2] EST (2006) GIR64: Post Construction Testing; A professional's guide to testing housing for energy efficiency. EST, London.

[3] Technology Strategy Board. (2013) Scaling up retrofit of the nation's homes: Competition for collaborative R & D funding

March 2013, Technology Strategy Board, London, UK.

[4] Calcutt J. (2007). The Calcutt Review of Housebuilding Delivery. CLG, London, UK

[5] NERA Economic Consulting,-AEA Technology (2010). Decarbonising Heat: Low Carbon Heat Scenarios for the 2020's. NERA UL Ltd, London, UK.

[6] Strube, J. Miller, A. Ip, K. (2011) Solid wall insulation: its place in retrofit plans, University of Brighton, UK

[7]Stephen, R.K. (1998). Airtightness in UK dwellings: BRE's test results and their significance', Building Research Establishment, BRE London, UK.

[8] BRE. (2010). Building for Change, Press Release, Retrofit for the Future Projects Named: 25th February 2010. BRE, London, UK.

[9] Hopper, J. Littlewood, J. R. Geens, A. J. Karani, G. Counsell, J. Evans, N. I. Thomas. (2012). Assessing the execution of retrofitted external wall insulation for pre-1919 dwellings in Swansea (UK). Paper presented and published in the conference proceedings for the Retrofit for the Future Conference, September 2012. Cited here:

http://www.salford.ac.uk/__data/assets/pdf_file/0006/142377/011-Hopper.pdf , accessed 1st May 2013 (available).

[10] Mondol, J.D (2007) The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system, Elsevier, London, UK

[11] Jardine, C and Lane, K (2003) PV in the UK. Environmental Change Institute Report 27, Oxford, UK

[12] Banfill, P. Simpson, S. Haines, V.Mallaband, B. (2011) Energy-led retrofitting of solid wall dwellings - technical and user perspectives on airtighness.

Paper presented and published in the conference proceedings of the RICS Construction and Property Conference, 12-13 September 2011, University of Salford, Manchester, UK.