Questions about Cost

Pound-878x1024.jpg

How much more will it cost me to build a Passive House?


The question that everyone wants to know the answer to.  Yes, it will cost you more to build a Passive House than a conventional house. This will vary on the size of the dwelling that you are building. The bigger the build, the more expensive construction costs. It is likely to add 5-10% on to the construction bill. BUT look at the bigger picture. Your bills can reduce by as much as 70% and the pay off period is generally worth the extra expenditure. The value of your property will then in turn increase due to government legislation getting stricter on Energy Efficient Homes. The price of oil is increasing day by day. Is it really worthwhile not building a Passive House?
If you can’t afford to pay the extra 10%, one solution is to decrease the house size by 10% to still come in on budget.

How much will it cost to heat my Passive House?


Again this will vary depending on the size of house and type of fuel used. A typical example for a 200m² (2200sqft) Passive House should cost around £280 (£1.40 per m²) per year. ( calculation based upon conventional gas or oil heating costs).  Cost of heating will depend on energy efficiency of the heating system, heating method and space heating required for your project.

 

Questions about energy ratings

epc .jpg

What Building Energy Rating would a Passive House typically achieve?


This varies from project to project, although surprisingly, a Passive House may not achieve an A1 or even A2 rating. This is because to achieve these ratings requires the use of renewable energy technologies for generation of electrical energy by photo-voltaic panels or hot water by thermal solar panels. These are not necessary for a Passive House to reach its standards although it can be introduced. A Passive House is superb for reducing energy heating costs, whilst the use of renewable energy sources are required for A ratings.

Is a Passive House also a Zero Carbon House?


No. You still need a minimal amount of external energy to provide a comfortable and healthy indoor climate in a Passive House, although in some regions of Europe that amount would be next to zero. A Passive House tries to balance economy and ecology but of course you can turn this into a zero energy house, however this is the most expensive part and it is harder to achieve a payback. It is not a low energy house either as it exceeds these standards.

Do I need thermal mass?


No. Thermal mass is a help in the retention of solar energy. Nice to have, but not necessary as the temperature of a Passive House remains constant.

 

Questions about Ventilation

ventilation.jpg

Can I avoid using the Mechanical Heat Recovery Ventilation System?


No.  There is no point in building a Passive House without this for recovery of heat loss from ventilation. A Passive House uses mechanical ventilation with a heat recovery system which retains 85% of the heat from extracted stale air. If you decide not to install such a system then you will have to install a conventional heating system (such as underfloor heating or radiators) incurring costs which would pay for the mechanical heat recovery ventilation system in the first place. 
It is important to note that it is well proven that ventilation systems are extremely efficient, providing a controlled ventilation rate throughout the house and ensure clean, fresh air is delivered through the use of filters in the system.

Is it unhealthy to live in an airtight house such as a Passive House?


No, because the house provides an abundance of fresh air using the ventilation system. This is a high air quality standard. Typically fresh air arrives into a conventional house via means of ‘hole in the wall’ vents/drafts/open windows. These are somewhat uncontrolled unlike Passive Houses which have on average 8-12 air changes per day. The fine filters in the ventilating system keep out dirt and pollen which reduces allergies and asthmatic conditions.

Are there problems with bacteria, noise and drafts with the ventilation system?


The ventilation system in a Passive House is a fresh air supply system, not an air conditioning system that re-circulates inside air (this is where bacteria growth is a problem in re-circulating systems). This fresh air is also filtered as it enters into the system.
Fan and valve noises in the Passive system are almost completely eliminated by sound control measures such as vibration isolation mounts, low air speed and acoustic lining in the ducts. 
Jet nozzles guide incoming air along the ceiling from where it is uniformly diffused throughout the room at low velocities that are barely perceptible therefore no drafts are evident.

Questions about Heating

thermal.jpg

Does a Passive House need a heating system?


A Passive House needs what is referred to as a ‘back-up’ heating system, which is considerably smaller in comparison to that required for a conventional house. A Passive House may need 3kW of heat at the coldest time of the year whilst a conventional oil boiler produces 20kW.

What kind of heating system is typically used in Passive House?


Typically any additional heating required is delivered using the backup heating system through the mechanical ventilation system installed in a Passive House. The fresh air passing through the house can be heated via different means or methods (such as a pellet burner or electrical heat pump).

What is the difference between a ‘back up heating system’ and mechanical heat recovery ventilation system?


The mechanical ventilation system provides a constant flow of air throughout the house via means of fresh air supply which is heated via the extracted stale air’s heat through means of plates and conduction. When this stale air is perhaps not hot enough to provide the necessary heat required within the system, the backup system comes into play and provides the required amount of heat to supply the constant temperature desired.

Does my Passive House need radiators or underfloor heating?


It is unusual to find these within a Passive House as often they are simply not needed. Of course, if you really want to install these systems, this is possible but you must keep in mind that you are adding costs which in turn unnecessarily increase the cost of construction.

Can I control the temperature in my Passive House?


Of course you can. A Passive House is designed to deliver a constant 20°C throughout the dwelling although different people have different comfort levels so this system can be designed in such a way that the temperature can be changed via means of conventional room thermostats.

Is it true that a Passive House can’t have an open fireplace?


Yes unfortunately this is true. This is due to the air tightness which is completely necessary in order to achieve the Passive House Standard. An aesthetically pleasing compromise is the installation of a wood burning stove as this has a sealing door or a bio-ethanol fire to produce that real flame effect in the home.

If the house is unoccupied will the house cool down?


Yes but very slightly and definitely nothing like a conventional house. The heat loss in this case, due to the quality of the insulation, will be minimal. The temperature changes only very slowly – with ventilation and heating systems switched off. A passive house typically loses less than 0.5 °C (1 °F) per day (in winter).

Questions about Windows

windowcolour.jpg

Can you open windows in a Passive House?


Yes, without a doubt.  A Passive House must be built to a high level of airtightness, meaning no air leakages through the windows, but of course these specially designed windows can open. People usually open windows in their homes to let fresh air in and foul smells out, although there is no need to do so in a Passive House. 
A Passive House is fitted with a heat recovery ventilation system that provides an abundance of fresh air, much more than opening a few windows and more constant with no drafts or chills. 
Be sure to note that leaving windows open in colder seasons, such as winter, will mean a higher use of energy needed to heat the house, just as you would in a normal house.

Can you only build a Passive House on a sunny south site?


It is ideal to have south facing windows to make plentiful use of the free energy provided by the sun. However it is possible to achieve the Passive House standard if your site does not have south facing windows (more insulation may be needed to compensate). All designs have to be tested and verified in the PHPP software to ensure that they will indeed meet the Passive House Standard, north facing or south. This standard is not as strict as people think.

General questions about Passive Houses

thermal.jpg

What is it like to live in a Passive House?


A Passive house provides a great environment for life with extraordinary low heating bills and excellent indoor air quality. It provides a high comfort level and is low maintenance to the user as well as dramatically reducing your carbon footprint.

Why should I bother building a Passive House?


Why should you not? In the next 2-5 years, it is the ambition and highly likely that the European Parliament will ensure that Passive House is the base standard of construction across the EU. Think in the longer term about how energy efficient your house will be in 5 years time as building standards are forever improving. The value of your property will of course follow the trend.

What if my Passive House doesn’t work?


Your Passive House will work. It is essential that your passive house is properly designed through speciality software such as PHPP (Passive House Planning Package), which shows how your Passive House will work, all before building commences. It is important that accuracy on site is maintained in order to achieve this standard of airtightness and low thermal bridging. There are currently 17,000 Passive Houses across Europe reaping the benefits of high levels of comfort in climates that are a lot colder than the UK & Ireland. If these houses didn’t work, they wouldn’t keep building them!

What is the most challenging aspect of Passive House construction?


The most likely is the onsite construction in regards to the airtightness of sealing difficult junctions. The construction team need to be fully aware of the need to achieve this onsite, including plumbing or electrical installers who may innocently tear the membrane to fit the necessary services. It is important that a project manager is onsite to ensure that the building is constructed in such a manner to achieve the Passive House Standard, as any inaccuracies could result in your Passive House under performing.

Can an existing building be upgraded to Passive House Standard?


Yes. Although generally this is expensive. A retrofit solution is possible and the Passive House Institute  (Passivhaus Institute ) have developed a new approved standard for retrofit called EnerPHit - the Passive House Certificate for old buildings.  This standard does not achieve the same energy efficiency as the Passive House Standard (25KWh/m2a retrofit as opposed to 15KWh/m2a new build). Perhaps replacing the dwelling with a brand new design will prove more worthwhile and cost effective depending on circumstances.

Is it possible to surpass the Passive House Standard?


Yes. It is very possible to build an even better insulated home but it is well proven that the cost of doing so is not generally economically sensible. It is possible to introduce renewable resources such as photo-voltaic panels to generate the electricity required and produce a ‘net-zero carbon’ home (where the amount of energy that you consume per year is equal to or more than the energy produced).

Can any architect design a passive house?


Yes, provided it is designed to Passive House standard. It is vital that the building design is tested and verified using the specialist software PHPP (Passive House Planning Package). At present, there are few consultants throughout the UK & Ireland with this specialist knowledge.  It is recommended that, as a minimum, a Certified Passive House Designer would be appointed to oversee the design and build.

Does a Passive House always have to look boring to be efficient?


No. There is a common misconception that Passive Houses have to be boring, simple shapes with no windows on the northern side and the southern side fully glazed. It is obviously more efficient and ultimately cheaper to construct a compact shape with optimal solar gain, typical of any construction. The house designer should otherwise be free to create any bespoke design according to the clients’ desires in whatever style they wish.