High Performance Case Study - Retrofit
Retrofit
North Rd, Newport
Project Brief:
As a family of 3, the client is looking to refurbish their current dwelling to increase its livability. They also find their current home to be difficult to heat in winter and cool in summer and would like to improve its thermal performance. No works are proposed beyond the existing building footprint.
Site Conditions:
The site is located in Newport with immediate access to parks and public transport. This is not your ideal passive solar house due to a north facing street frontage and living spaces facing a southern back garden.
Existing Building Conditions:
The existing building is a freestanding Inter-war weatherboard with a 90’s rear addition continuing the original tiled hip roof. As expected, this building performs very poorly with single glazing throughout, gaps in sash windows, timber flooring, wall vents (to name a few) plus almost no insulation. Existing heating is provided through a gas ducted system and ceiling fans had been retrofitted.
The building presents the capacity to house all of the functional requirements for this family, however the layout, especially the extension is poorly design, very dated and natural light is an issue. Thermal comfort in a house of this era is a constant battle.
Design Strategy:
Whilst improving the functional layout of the home, incorporate new wet areas and improving connection to outdoor spaces, we are challenged to improve the performance of this home. This is our strategy;
Provide new windows & doors to the living spaces and replace existing windows where appropriate
Alter the existing layout to introduce heating and cooling zones for the north (bedroom) and south (living) wings
Provide new cladding to the the south wing with additional wall, roof and subfloor insulation
Explore options to improve performance of the north wing, where cladding is to be retained
.Baseline Assumptions:
To assess the existing building performance we have input the following values into our software to create an annual baseline heating and cooling load.
Existing Envelope:
Floor: Timber flooring on 100mm joists - no insulation
Walls: 90mm Frame with no insulation
Roof: Pitched roof, R4.0 ceiling insulation
Existing Windows:
Timber framed single glazed (no thermal break)
No additional shade protection
Airtightness:
15 Air changes per hour (10 air changes per hour is assumed by NatHers for 6 star, but given the performance of existing building fabric we believe this is a more realistic and possibly conservative figure)
Energy required for annual operation of the building: 124.63 kWh/m²*
High Performance Strategy:
By using the Passive House tool - DesignPH - in conjunction with a SketchUp model of the building we are able to assess and dissect all of the elements that contribute to heating and cooling loads.
Step by step
The first step is to analyse the existing building as currently constructed. During our initial assessment we decide what sequence of modifications will attain best ‘bang for buck’ for the project, ie maximum energy reductions with minimal additional construction cost.
Our first identifiable issue was the lack of subfloor insulation and the opportunity to increase the roof insulation. Both these changes are affordable and can be implemented with no alterations to the existing building layout. We added R2.0 extra to both these areas which resulted in energy demand reduction of 10%.
The next step was to look at upgrades that could be made to the south wing (living) of the existing as part of the floor plan changes. With the cladding to this section of the building being replaced there is an opportunity to install R2.7 insulation and building wrap to the external walls. Also, new double glazed timber windows are to be installed.
We then looked at the overall air tightness of the building, intending to reduce this from 15AC/h to 7AC/h. This would involve taping all windows, sealing existing walls where possible, penetrations and an air blower test to ensure the quality of workmanship.
The final round of analysis looks at the north wing (bedrooms) of the building for which we currently propose to retain the existing cladding and only refurbish the sash windows and external doors. Our final calculation(#4) shows that completing the final weak point in the thermal envelope make a big difference. We suggest to retrofit blow-in insulation as well as replacing the existing windows with double glazed timber frames. Floor and additional ceiling insulation had already been accounted for in step 1.
As shown in the right hand column on the table below, Specific annual heat demand.
Summary of features
Envelope:
Floor: Timber flooring on 100mm Joists - R2.0 insulation
Walls (South): 90mm Frame with R2.7 insulation
Walls (North): 90mm Frame with blow-in glasswool insulation
Roof: Pitched roof, R6.0 ceiling insulation
Windows:
Timber framed, double glazed throughout
No additional shade protection
Airtightness:
7ACH - Air changes per hour (10 air changes per hour is assumed by NatHers for 6 star)
Results:
We would typically recommend implementing a mechanical heat recovery ventilation system (MHRV) to all homes that are improving airtightness. However in this ‘retrofit’ situation we only anticipate improvements to around 7ACH, which shouldn’t impact the indoor air quality enough to be a health risk.
The diagram below compares the heat balance from the base the the final high performance iteration.
Some early analysis of the results provided the following:
Additional Construction Costs: $53,000**
Annual Energy Savings: 12,893 kWh (approx. 70% reduction)
Annual Carbon Reduction: 13.80 Tonnes***
Annual Savings: $3,868
Payback Period: 14 years
Although still far from a Passive House performance (we’d need to get down to 15 kWh/m2 & 1.0 ACH retrofit) there are some huge benefits from a high performing upgrades, especially at this scale, which we would t-shirt size as a medium-large sized house.
A reduced carbon footprint of 13.8 Tonnes per year is significant enough to make a difference in a time when reducing our carbon footprint is critical.
The additional construction costs include additional labour and materials that would otherwise be above and beyond the minimum spend for this renovation.
Conclusion
Although still far from Passive House certified performance (we’d need to get down to 15 kWh/m² & 1.0 ACH retrofit) there are some huge benefits from a high performing upgrade, especially at this scale, which we would t-shirt size as a medium-large sized house.
The additional construction costs include additional labour and materials that would otherwise be above and beyond the minimum spend for this renovation. However this results in an estimated energy savings of almost $4,000 a year, which will eventually cover the cost of the extra upfront investment. On top of this there is a reduced carbon footprint of 13.8 tonnes per year, significant enough to make a difference in a time when reducing our carbon footprint is critical.
We all know that now is a critical time for us to reduce our environmental impact. We also know that this can be achieved without compromising our living standards. In fact an investment in high performance construction will actually result in an increase in livability!
Additional benefits from HP Building Method:
Comfortable year round climate (20-25C)
No more drafts!
Balanced indoor temp (no hot or cold spots)
Extremely low energy bills
Removal of gas guzzling heating and decommission of the gas meter, moving away from fossil fuel dependency
*Our software makes the following assumptions; a baseline airtightness of 10 ACH; a thermal comfort level of 20-25 degrees is maintained 24/7; energy supply cost of $0.30/kWh; assume all energy supply is via electricity and not gas.
**We are not builders or quantity surveyors, this is an estimate only
***Carbon emissions calculated as per Carbon Calculator
This case study was prepared by Altereco Design in October 2019 to assist our client in understanding the viability of their upgrades. We hope that it assist others understand the cost versus benefit of improving the performance of their home.