The Mansion House Dublin...The Mansion House A case study for repairing and upgrading historic windows for thermal efficiency 2 Mansion House Historic Windows 3 Project Summary The

Mansion House Historic Windows

City Architects Division

November 2010

Dublin

The Mansion House

A case study for repairing and

upgrading historic windows

for thermal efficiency

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Mansion House Historic Windows 3

Project Summary

The City Architects Division prepared a carefully-researched proposal for the enhancement of the Mansion House in 2009. One of the objectives of the project was to look at ways that this historic building could be more energy efficient. Dublin is a signatory to The Covenant of Mayors, a commitment by the city to go beyond the objectives of EU energy policy in terms of reduction in CO2 emissions through enhanced energy efficiency and cleaner energy production and use. It is, therefore, appropriate that the home and office of the city’s Lord Mayor should demonstrate best practice in this area. Research on appropriate methods to upgrade traditionally-constructed buildings is badly needed in Ireland. To date we have largely relied on research carried out elsewhere which does not take account of local construction detail or climatic condition. The recently published Advice Series booklet on this topic from the Department of the Environment particularly makes the point that it is essential to include building position and local microclimate in evaluations to assess potential environmental performance. This research project was initiated to respond to one of the common areas of vulnerability in buildings—the performance of windows. The Mansion House is one of Dublin’s premier buildings and the residence of the Lord Mayor during his or her term of office. Purchased for use as a Mayoralty House from Joshua Dawson in 1715, the house has remained the centre of civic hospitality for almost 300 years. Dublin was the first city in Ireland or Britain to have an official residence for its Mayor.

Traditionally the Mansion House has been at the leading edge of innovation providing the platform for the launch of new ideas and concepts. This research project continues that innovative tradition by looking at solutions for upgrading historic windows to improve their thermal efficiency in an Irish context. With financial support from The Heritage Council 2010 grant scheme, we have developed working models for upgrading the historic timber sash windows in the Mansion House for improved thermal efficiency in a manner that is in line with best conservation practice and does not detract from the character of the building. Eight windows of different types and in different locations were selected for detailed study. Their historic features and their condition were recorded on specially designed data sheets. UCD Energy Research Group then carried out the energy rating, analytical assessment and computer modelling solutions required for the project. Necessary repair works to the selected windows, for example re-opening sealed-up shutters and other minor repairs, were also carried out to assist in carry out the required measurements and tests. This work was undertaken by experience joiners in Dublin City Council’s Civic Maintenance team. Project Team City Architects Division Owen O’Doherty, Susan Roundtree, Nicola Matthews, Ciaran Stanley City Manager’s Department Vincent Norton, Fanchea Gibson UCD Energy Research Group Paul Kenny, Zsuzsa Szalay, Donal Lennon, Valentina Marino

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Report commissioned to evaluate the performance of the Mansion House windows


Thermal Performance The study has shown that in general the windows in the Mansion House are well maintained and in reasonably sound condition. They have already been draught-proofed and, in most instances, are fitted with good-quality heavy curtains. Most windows have internal shutters but these have not been used in recent times. Most of these shutters are nailed shut and those that were opened were generally found to be in poor condition. In the overall context the thermal simulation research indicated that the windows account for approx. 14% of the heat loss from the building envelope. The calculated thermal transmittance of the windows was 5.2 W/m²K. In rooms with existing heavy, thermally lined curtains, such as the Lady Mayoress’s Parlour, this reduces to 3.2 W/m²K. With the existing shutters in use this could further reduce to 2.3 W/m²K. Internal shutters exist in all rooms examined except the Dining Room where the shutter cases and internal window surrounds have been altered. In general the shutters are not used and are in poor condition. In many instances they are warped and twisted and have defective hinges and closing devices. Their effectiveness, therefore, in terms of adding improved thermal performance to the windows would depend on carrying out necessary repairs or replacement to bring them back into use, and putting in place a routine of closing them in the evenings and opening them in the morning. There would however be added benefit to using the shutters for additional security for the building.

As outlined in the summary, the existing windows in the Mansion House were assessed and eight windows of different types and in different locations were selected for detailed study on the ground and first floors. They were selected on the basis of age and style, façade orientation, and location within the house. The Mansion House is a public building and the rooms on the ground floor are used primarily for civic functions. The rooms on the first floor are used by the Lord Mayor as a private residence. The selected windows were surveyed in detail and their features and condition were recorded on specially designed data sheets. UCD Energy Research Group was engaged to examine the windows in their particular context within the house. The team carried out a range of tests to assess existing efficiency in terms of thermal performance, air-tightness, daylight and acoustics, and then prepared computer models to look at the effectiveness of various upgrading measures that could be proposed. Some minor repair works were carried out to the selected windows, for example re-opening sealed-up shutters by skilled joiners working in Dublin City Council’s Civic Maintenance direct labour team. The performance of the selected windows was evaluated by in situ measurements and computer simulations in terms of thermal, ventilation, daylight and acoustic performance, and the possible options for the improvement of the windows were investigated.

Description of Project Activities

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In the tests carried out heat loss through the windows decreases by 12% and 19% with the use of curtains and shutters, respectively. When considering the whole building the reduction is less significant (around 2%) because the windows are only responsible for a small fraction of the total demand, and because the use of curtains and shutters is only effective at night. Nevertheless the use of curtains and shutters is strongly recommended as they provide other benefits, such as improving the thermal comfort by decreasing the radiation losses through the glass, hence increasing the surface temperature. The thermography tests also proved that the internal surface temperature of the curtain can be 5-8 K higher than that of the glazing. The addition of secondary glazing internally would bring a significant improvement to the thermal performance of the windows in all respects. The thermal transmittance of the window would decrease to around 2 W/m²K which would bring the windows up to current building regulation standards. The benefits of secondary glazing are that it is in place both during the day and at night. It also would improve air-tightness and have a positive effect on acoustic performance. The challenge is in relation to its design and in particular how it could be accommodated in a way that would not detract from the character of the existing windows or restrict the use of the existing shutters.

Air Tightness Tests to measure air-tightness showed air infiltration in the high range in certain rooms but the windows generally performed well as they are fitted with an existing draught-proofing system. Reasonable air change and air movement is required to keep historic building fabric in good condition so while improvements could be made in other areas, such as leaky floors and chimneys, the windows do not require work in this area other than routine checking of the draught-proofing system, and sealing of any areas where there might be defects or gaps in the existing system. Daylight With the exception of the drawing room all rooms measured demonstrated poor light levels with daylight factors dropping sharply within a meter or so of the window line. The principal reason for this is the use of net curtains throughout the house. The removal of the net curtains is strongly recommended if this can be done without loss of privacy or impacting on the environmental needs of the interior collection of paintings, furniture and carpets. Increasing natural light in the main reception rooms would reduce what is currently a heavy demand for artificial lighting in these rooms during the daytime. Acoustics The average sound pressure level outside on the street was measured at between 50-70dB which is typical for a busy urban street with traffic noise. The windows do not offer good sound insulation which can be problematic at night especially in the residence.


Recommendations Any interventions to improve the thermal performance of the Mansion House windows must be sensitive to their historic value and character. Ways in which the windows can be improved are in reducing conductive heat losses, reducing air leakage, and improving daylight conditions and acoustic performance. Getting the existing shutters repaired and back in use and fitting thermal blinds and good-quality heavy curtains will reduce the current heat losses and improve the thermal comfort of the building. Adding insulation behind the timber panelling in the window aprons should also be considered and a further option for improvement would be to install a secondary glazing system. As a first stage measure the following improvements are recommended in relation to the eight specific windows examined:- Lady Mayoress Parlour (GW03/4) [North & west-facing façades] Repair existing shutters and put back in working order Replace existing net curtains with thermal blinds Re-hang existing heavy lined curtains Drawing Room (GW08) [North-facing façade] Repair existing shutters and put back in working order Replace existing net curtains with thermal blinds Re-hang existing heavy lined curtains Lord Mayor’s Study (GW19) [West-facing façade] Repair existing shutters and put back in working order Replace existing net curtains with thermal blinds Re-hang existing heavy lined curtains

Dining Room (GW17) [South –facing façade ] Replace existing net curtains with thermal blinds Fit new heavy lined curtains First Floor Boudoir (FW23) [West-facing façade] Repair existing shutters and put back in working order Replace existing net curtains with thermal blinds Re-hang existing heavy lined curtains First Floor Kitchen (FW09) [North-facing façade] Repair existing shutters and put back in working order Fit thermal blinds Re-hang existing heavy lined curtains Housekeepers Living Room (FW16) [South-facing façade] Repair existing shutters and put back in working order Replace existing roller blinds with thermal blinds that don’t restrict use of shutters Re-hang existing heavy lined curtains Comprehensive Energy Efficiency Retrofit Works From the research undertaken it is clear that the Mansion House would benefit from a comprehensive package of energy efficiency retrofit works, not just works af-fecting the windows. There are obviously limitations in making changes to the build-ing envelope because of the historic sig-nificance of the building. However there are measures that could improve its per-formance that would not compromise its special character such as additional roof and floor insulation and improving air-tightness. Other improvements are al-ready planned such as the installation an new efficient boiler, additional heating controls, solar thermal panels to provide hot water and LED re-lamping of artificial light fittings throughout.

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Members of UCD Energy Research Group carrying out a fan pressurization test at the Mansion House in July 2010 using a Minneapolis Blower Door Model 3/230 V system

Research & Survey Work


Window survey sheets designed to record window type, condition and detail

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Benefits of the Project

Benefits of the Project The benefits of the research are of immediate value to the Mansion House where the recommendations to undertake specific works to improve the energy efficiency of the existing historic windows will be integrated into the overall management plan for the house. Although the research findings are specific to the Mansion House the report information will be made avail-able on the Dublin City Council web-site and so may prove useful to others who act as advisors to historic building owners. Analysis of Outcomes The project benefit in practical terms will be maintained by putting in place for 2011 an informed programme of upgrading works for the windows in the Mansion House. These works will compliment a works programme cur-rently in hand for first phase energy efficiency retrofit works to the house, which include improvements to the heating system, re-lamping and the installation of solar thermal and PV panels. This project is being supported by a grant from SEAI. In addition to these improvement measures, the thermal modelling of the house carried out by the UCD Energy Research Group using EnergyPlus software pro-vides very clear direction on where further improvements to the house could be made.

Lessons Learnt In terms of energy efficiency it is clear from the research undertaken that the windows can not be analysed in isolation from other factors, such as the perform-ance of the overall building fabric and way the building is used. Decisions about how to improve the performance of the windows must take account of a very wide range of factors including practical housekeeping issues, the times when particular rooms are used, the uses of particular rooms, levels of comfort, con-servation concerns and aesthetics as well as running costs.

Recently published guidance document from the Department of the Environment, Heritage & Local Government, 2010


Statement of Compliance

A statement of how the project complied with the Heritage Council’s Letter of Offer The Heritage Council agreed to offer a grant of €5,000 towards the cost of this project. We were advised that this funding was to-wards the cost of the research element only as capital works cannot be supported under this scheme. A progress report on the pro-ject was made to the Heritage Council on 23rd August 2010. This research project has now been completed successfully and we are satisfied that we have complied in all respects with the relevant conditions of the Heritage Council offer.

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Photographs & Plans


Window joinery from the eighteenth and nineteenth centuries

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North and South Façades Showing the range of window types


Typical window details

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City Architects Division

Dublin City Council

Civic Offices

Wood Quay

Dublin 8

Www.dublincity.ie/cityarchitects

The Mansion House Dublin...The Mansion House A case study for repairing and upgrading historic windows for thermal efficiency 2 Mansion House Historic Windows 3 Project Summary The

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