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What is passive house retrofit?

What is passive house retrofit?

Retrofitting is the process of converting an old house into a new one by renovating to a high energy standard. A passive house is an environment responsive house design which ensures a healthy lifestyle. That means you are renovating your conventional house to an environment-friendly passive house with reduced carbon emissions, in pursuit of a zero carbon lifestyle. Instead of relying on non-renewable heating and cooling resources developing a sustainable building design that can automatically use the sun and wind to heat or cool the house is the passive approach [1].

When compared to normal designs, passive house principles can lower energy expenditures by 80 to 90 percent, saving the owners money, minimising the building’s carbon impact, and making the house more comfortable. The payback period makes these houses’ operations cheaper. A passive house behaves like an electric car with no CO2 emissions [2].

The cooling and heating load of the passive house should be lessened to a point where using electricity seem inexpensive to cool/heat the space. It needs 80-90% less energy to heat up the space, instead it can use the heat coming from the human body, and appliances.

Passive house retrofit goals

  • Providing a stepwise cost-effective retrofit to make the existing houses with addition to exterior insulation, new façade, and roof [3].
  • A passive house should be evident by producing almost 100 % of the building’s net electricity by itself [3].
  • It should have the heating demand and electricity consumption value mentioned in the international Passive House Standard [3].
  • Achieving a constant indoor temperature by lowering the risk of draughts [3].

The passive house has essential features including massive insulation, no air leakage to/from the environment, no thermal bridges, the orientation of glass windows towards the sun, and ventilated heat recovery units. The first three are the major points to be emphasised. Proper insulation makes the house temperature comfortable in winters and summers without using a conventional heating. Figure 1. Showing the retrofitting components.

Figure 1 Retrofitting components for converting a typical house to a passive house

Passive houses can be retrofitted by using the guidelines from the International Passive House Association (IPHS) [1]. The logic behind the passive house retrofitting can be complicated because of various factors to be focused but it is understandable. Passive housing is a trending phenomenon to mitigate the global warming potential by adopting the passive standards so every stakeholder needs to implement this strategy. To make the existing house passive/environment friendly, stakeholders need to focus on economical solutions depending on building elements to be fixed like walls, floors, and roofs.

Retrofitting of walls: Airtight layers of insulation are required to be installed to make the behavior of the wall passive. Providing a cavity wall can also be an option because air present within the cavity can act as insulation [1]. Insulation can be provided at either interior or exterior end. For that wall, finishing needs to be detached depending on how costly the exterior or interior finishing can be. The selection of insulation (thickness and no. of layers) is done based on weather conditions. Standardised windows and doors’ materials are also selected as per the heat coming through them.

Retrofitting of roofs: the thermal barrier type depends upon the roof space usage. If the home has an attic area, then extra insulation along the ceiling side is provided creating a warm roof space. If not then along the ceiling of the floor below insulation is added creating cold roof space. If the clear height limitation is encountered then vacuum type insulation can be an option to avoid the drop in clear height. For cathedral ceiling design a new ceiling design can be built for a specific R-value [1], [3].

Retrofitting of floors:  provision of a floor cavity can act as an insulator if the basement floor is inaccessible. In another case, a vacuum panel option will be utilised to make the space passive as a vacuum will lead to no drop in height [1].

Let’s briefly explain the three main features of a passive house that needs to be renovated to make the house climate responsive.

No air leakage:

Minimising the heat loss through the infiltration of air has prime importance. This can be defined by air changes hour (ACH). The ACH is associated with the replacement of interior air volume with the exterior air and it is observed to be 3 to 5 times per every hour. This actually is the loss of heated/cooled air which can transfer the energy in the wall envelope and ultimately convert the space to an uncomfortable zone by releasing it to the interior. The standard ACH rate and retrofit standards are 0.6, and 1.0 respectively, for a newly constructed passive house [2].

Infiltration was assumed as ventilation in old school thought but in reality, it is unfavourable due to the mold problems linked to this. To be honest modern methods (e.g., mechanical ventilation heat recovery  (MVHR)) did not exist in the past to change this scenario. Currently, building codes provided this MVHR system for homes but the inefficiency in terms of leaking air still exists.

Thermal bridges

R22 wall insulation (the bigger the R value, the better the insulation), R32 roof insulation, and R10 below slab insulation are currently required by the standard building code for new homes. Newly constructed passive homes in our location, on the other hand, require R75 wall insulation, R110 roof insulation, and R40 below slab insulation.

As a general rule, dwellings renovated to the passive standard require R48 insulation in the walls, roof, and floor.

Windows orientation

It’s critical to utilise a passively approved window for thermal comfort. These are triple-glazed windows with R12-rated insulated frames. This may not seem like a lot, but it’s a lot when compared to a non-certified triple glass window. It’s difficult to find a non-certified equipment with a rating higher than R4 [2].

A high-temperature interior pane in certified windows improves comfort. When it’s 25°C outdoors, the interior glass must be at least 17°C in the passive scenario. Under the same conditions, non-certified triple glass windows might be as cold as 12°C on the inside [4].

Solar gain

In the winter, windows are sized and placed to make use of the sun’s energy (e.g., south side orientation of windows). During the summer, roof overhangs provide shade for windows. Expect costs to be roughly 10% to 15% higher than conventional renovation charges at the outset. Fortunately, high-tech materials and procedures allow for the use of smaller heating and cooling equipment [5].

However, a passive home is more than just energy efficiency. A passive house is silent when you walk in. You won’t hear much if you don’t have access to fresh air from the outdoors. The air is also quite pure because it is filtered. It turns out to be a pleasant way of life.

The majority of passive house designs are for new construction, but existing houses can be retrofitted to accommodate high insulation levels and other passive house techniques, the majority of the projects are entire gut-to-exterior-walls projects.

References

[1] Ekobuilt, “Retrofitting an older home to Passive House standard.” https://ekobuilt.com/2019/04/24/retrofitting-an-older-home-to-passive-house-standard/ (accessed May 17, 2022).

[2] Sweeten, “A Guide to Passive House Renovations.” https://sweeten.com/advice-and-faq/a-guide-to-passive-house-design-renovations/ (accessed May 17, 2022).

[3] D.-E. A. (Emulsionen) Zack Norwood, Ingo Theoboldt (Passivhusbyrån), “Step-by-step deep retrofit and building integrated façade/roof on a ‘million program’ house.” https://passipedia.org/planning/refurbishment_with_passive_house_components/step-by-step_deep_retrofit_and_building_integrated_facade_roof_on_a_million_program_house (accessed May 17, 2022).

[4] Passivhaus Trust, “Research Report – Passivhaus Retrofit in the UK.” https://www.passivhaustrust.org.uk/guidance_detail.php?gId=51 (accessed May 17, 2022).

[5] Eva Vahalova and Benjamin Krick, “Windows in a step-by-step retrofit,” Passipedia. https://passipedia.org/planning/refurbishment_with_passive_house_components/windows_in_a_step-by-step_retrofit (accessed May 17, 2022).

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