Retrofitting for southern winters

This Issue This is a part of the Retrofitting houses feature

By - , Build 105

Health problems for tenants in old Wanaka houses led to a successful retrofitting experiment. This basic research shows that improvements can be expected for a relatively small cost.

Figure 1: Comparison of net temperature differences (NTD) between the living room in house 1 and outdoors for 30 July to 8 August in 2006 and 2007.
One of the retrofitted 1960s Wanaka houses.
Figure 2: Frequency of indoor temperatures in house 1 for July–August 2006 and 2007.

Historically, New Zealand homes have not been energy efficient. The Energy Efficiency and Conservation Authority (EECA) estimates that around 350,000 of the 1.5 million existing New Zealand homes still have poor insulation or none at all, 30 years after insulation of domestic buildings became mandatory through NZS 4218: 1977. With the cost of energy to households continually rising (by 16% in real terms since 1995), owners of thermally inefficient homes are paying more to heat their homes year on year or are accepting inadequate heating to keep the cost down.

Retrofitting homes to be more energy efficient enables them to be heated to higher temperatures for the same cost or to the same temperature for less cost, or sometimes both.

Improving local knowledge

The Sustainable Wanaka Charitable Trust has been advising on sustainable building and energy efficiency for a year and a half. Its research aims to improve local knowledge on appropriate ways of achieving sustainable buildings in the Southern Lakes region.

In 2006/07, the trust monitored conditions in two 1960s Wanaka houses, before and after a retrofit to improve energy efficiency. The houses were rented and in a poor state of repair with little or no insulation. The result was a damp and cold internal environment. The tenants of the two worst houses experienced persistent, recurring health problems over the winter of 2006.

One of the retrofitted 1960s Wanaka houses.
Table 1: Summary of work undertaken to retrofit two Wanaka homes.  
Work undertaken   House 1 House 2
Insulation R5.0 ceiling insulation installed  
  Internal wall linings in living room removed, 50 mm EPS polystyrene fitted, new plasterboard lining
  Polythene laid over the ground underneath the house and around the footings
  Foil faced insulation blanket fitted to underside of joists
Heating and ventilation Heat transfer system installed to transfer heat from the living room to the bedrooms
  Fan heater fitted in bathroom
  Existing inbuilt fireplace removed and relined. New wood burner installed on inside wall of living room
  Extract vent fitted in kitchen
  Thermally lined curtains to living room windows  
  Draught stripping  
Cost of retrofit   $11,515.58 $9,599.73

The houses are typical of old New Zealand houses: small, single storey and detached. Both houses have suspended timber floors but one has walls of concrete block and the other is timber framed. The timber framed windows were single glazed and in a poor state of repair. One house had old, tatty ceiling insulation (likely to be below R1) but otherwise the houses were completely uninsulated. The houses were heated with electric heaters and an inefficient inbuilt woodburner.

Cold and mould = poor health

The project was initiated in the winter of 2006 when the tenants of one house contacted Sustainable Wanaka for advice on how to improve internal temperatures and reduce mould and condensation. The trust was then contracted by the property owners to make recommendations for retrofitting the houses. The contract included a simple analysis to measure the effect of various retrofit options, including a post occupancy evaluation (POE) of the houses, and an energy analysis using the BRANZ thermal design tool ALF3.

Figure 1: Comparison of net temperature differences (NTD) between the living room in house 1 and outdoors for 30 July to 8 August in 2006 and 2007.
Figure 2: Frequency of indoor temperatures in house 1 for July–August 2006 and 2007.

Temperature-sensing data loggers (ibuttons) were installed to measure pre-retrofit conditions. Over July and August 2006, the temperature and relative humidity of the living rooms and bedrooms were recorded. A mould analysis found that a fungal species (Cladosporium) associated with respiratory tract allergies was present.

The houses were retrofitted during the summer of 2007 and were monitored over the winter of 2007 to gauge the impact of the measures on the internal temperature. The retrofitting concentrated on the thermal envelope surrounding the living areas and addressed the walls, windows, ceilings and underfloor regions (see Table 1).

A second POE was conducted to assess whether there was a change in the comfort and health of the tenants. The monitoring and analysis was intentionally kept basic and non-technical.

Improved health and energy savings

The tenants in house 1 were noticeably healthier in the winter of 2007. During the winter of 2006, they were sick frequently and suffered particularly from respiratory infections. The tenant had attributed this to an allergic reaction to the mould. The tenant’s young daughter didn’t have a cough during 2007; in 2006, she had a chronic cough for 8 months. The throat infections the tenant suffered have not recurred. Her heating bills have remained more or less constant between 2006 and 2007.

In house 2, extensive mould, damp and condensation in both heated and unheated rooms were causing the tenants discomfort and possibly illness during the winter of 2006. The tenant was ‘in and out of hospital’ and suffered from a chest infection for the whole winter while her daughter had constant colds. Following the retrofit, the tenant says her daughter has not had a cold.

In 2007, the tenants of house 2 used approximately 6 m3 of firewood, compared with 16 m3 in 2005. In 2006, they used electric heaters, having decided that the inbuilt wood burner was too expensive to run. Electric heaters were not used in 2007. New thermal curtains were hung in the living room and they ‘make a big difference’.

Before the retrofit, the tenant had shown little pride in the house. She now has plans for redecorating when the retrofitting is completed. It is possible that this change in attitude is a result of feeling comfortable and warm (and therefore happier) but it could also be attributed to her feeling more valued because the landlord has spent money on the house.

Temperature assessment

Although NIWA considered the winter of 2007 to be more severe than that of 2006, the average outdoor temperatures during monitoring were fairly similar (2006 = 5.3°C; 2007 = 5.6°C). Monitoring was between 27 July and 18 August, with temperatures recorded every half hour.

The average temperature in the living room of house 1 increased after the retrofit. In 2007, the average living room temperature was 17.5°C compared with 12.3°C for the same period in 2006. The temperature in the main bedroom also increased, from 9.1°C to 14.0°C.

In 2006, the modal temperature values were between 10 and 12°C, compared with values between 14°C and 16°C in 2007 (see Figures 1 and 2). There were significantly more counts above 18°C in 2007.

Comparisons of the net temperature differences (indoor (living room) temperature minus outdoor temperature) for 10 days in August show significant differences between 2006 and 2007 (see Figure 2).

Good results for small cost

The results of the monitoring show either an improvement in comfort and health or a combination of improved comfort and energy savings. The effect on the internal temperatures at house 1 is significant; the average temperature is now above the recommended threshold for health of 16°C.

It was anticipated that there would be considerable take-back (where the occupant chooses to maintain higher internal temperatures rather than make savings in fuel costs), close to 100%. That energy savings have occurred in house 2 is a bonus.

The POE provided a useful gauge of the tenants’ comfort in the houses before and after the retrofit. Evidently, the retrofit had a positive psychological affect on the tenants: improved perceived comfort, actual improved health, as well as pride in their rental property.

The energy assessment conducted by Sustainable Wanaka found that an inefficient heating system (old inbuilt woodburners and electric radiant heaters) and poorly insulated building envelope were the biggest contributing factors in the poor internal environment of the houses. Although basic, the research shows the kind of improvements that can be expected for a relatively small cost (approximately $10,000 was spent in each case).

Before the 2008 winter, all remaining walls will be insulated and relined and ceiling insulation will be added to house 2. The results will then be monitored again.

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Articles are correct at the time of publication but may have since become outdated.

Figure 1: Comparison of net temperature differences (NTD) between the living room in house 1 and outdoors for 30 July to 8 August in 2006 and 2007.
One of the retrofitted 1960s Wanaka houses.
Figure 2: Frequency of indoor temperatures in house 1 for July–August 2006 and 2007.

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