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Passive House

If you are considering using Passivhaus / Passive House techniques in a project Southwest Environmental Limited can help prepare you sustainability reporting at a planning level to ensure that your projects meets planning targets set by your local planning authority, whether you are in London or Bristol. Please contact SWEL for a quote.

In Germany you will see this phrased as Passivhaus. It is a building standard which is similar to Code for Sustainable Homes, but focuses on different aspects of building design and systems to achieve amazingly low energy consumption figures.

Code for Sustainable Homes focuses on energy efficiency to a point, but in order to achieve TER you can add in renewables. With Passive House the idea is to save enough energy to meet targets. This is achieved using the following methods:

Air Tightness

Perhaps the biggest factor in the passive house design is air tightness. This can be tricky to get right. In the UK we have various entrenched building method preferences, such are floor joists that rest on inner leaves. These areas can be problematic when building to passivhaus / passive house because they are hard to seal around, things get even more complicated with retrofit.

There are various different system elements that can be used for the creation of an air tight barrier, these include OSB, plaster, DPC sheeting or specific membranes. All of these will need special air tight tapes to stick them together.

Super Insulation

It is not only the thickness of insulation applied to a passivhaus build that creates it unique thermal properties, but the way in which the insulation is applied.

As you can see from the diagram to the right, a considerable amount of design effort has to be employed in order to reduce thermal bridging whilst also considering air tightness.

The operational phase of passivhaus project is important, make sure occupants know how to operate in house systems, opt for soft landings.


Passivhaus also considers occupant comfort very highly so in order to provide good air flow in winter it is usually necessary to specify a very efficient MHRV unit.

A ventilation system with high efficiency heat recovery will ensure good indoor air quality whilst maintaining internal temperatures at adequate levels.

Southwest Environmental Limited can help prepare you sustainability reporting at a planning level to ensure that your projects meets planning targets set by your local planning authority, whether you are in London or Bristol. Please contact SWEL for a quote.

(Mechanical Ventilation Heat Recovery) MVHR

Mechanical Ventilation Heat Recovery or MVHR is an essential part of any passivhaus (passive house), it enables the circulation of air within a tightly sealed property without loosing heat to the outside. 

Out going “stale” is passed through a heat exchanger, and series of highly conductive aluminum grills. Incoming clean cool air is then passed over through the aluminium grills, warming it to around 90% of the temperature of the incoming air.

Limitations of Mechanical Ventilation Heat Recovery are that it requires regular maintenance; it can be noisy and through out the heated season requires constant power.

Maintenance – Changing filters is not a difficult task, and for the average owner occupier filter changes in MVHR will not pose a problem. However, for rented properties arranging for entrance to the interior to carry out filter changes may cause problems. The life span of a MVHR unit is around 10 years.

Noise – Noise can be a problem with some MVHR units if not properly installed the passivhaus standard set lower limits for noise for mechanical ventilation and thee should be observed. If noise does become a problem silencers can be fitted between the receptor location, and the MVHR unit.

Power Consumption – During the summer months it is advisable to switch off the MVHR and rely on natural (window) ventilation. It is important that tenants, occupiers of building are educated with respect to the efficient operation of the MVHR. The power consumption for a MVHR for a 3 – 4 bed room house is around 100W, however the true measure of energy consumption is m3/kw, or energy per volume moved. This allows accurate comparison between units.

Passivhaus Soft Landings

Soft landings is a system where by residents, operators or staff members of a new development are helped to adjust to there new buildings in the first few months. Do people really need to be told how to use a passivhaus (passive house). Yes they do.

The soft landing approach not only applies to passivhaus (passive house) but also to other highly sustainable buildings BREEAM, Code for Sustainable Homes etc. These builds may have systems and concepts which are unfamiliar to people, and may results in the miss management of a property effecting heavily it energy performance. 

Site occupiers may require help with systems such as MVHR, or motorized window openers. Control Panels cab be supplied with very poor instruction manuals, and even intuitive control interfaces should not be assumed to easy to use for the intended occupiers. A dinner lady may find a touch screen control panel rather alien, just an an architect may find it difficult to cook a meal for 50 people. 

Most of the above problems can be overcome with signage, education and management. Help should be at hand post occupancy for any one who asks for it, and checks should be carried out frequently over the first few months to check everyone has got the hang of things.

Poor post occupancy management lead to massive increases in energy consumption. For example a malfunctioning bio mass boiler that defaults to a gas back up will not necessarily be a problem for occupiers, and it will be over looked.

Right from the word go architects should look to design with as simple user experience as possible this will ensure a resilient building that performs well. For schools and offices complex MVHR controls should be a voided in favor of simple timed boost switches.