Learn about Passive Design/Build

It’s like the coat or jacket for your building. In the Passive House standard, projects meet energy efficiency goals by keeping a continuous layer of thermal insulation, without any holes, seams, or breaks at junctions. The thickness of this layer depends on the local conditions and is decided during the design and modeling stage.

Think of a sponge as an analogy – the ability to absorb a certain amount of water (heat), and then release it over time. This is effective when your loads change quickly, and you need to introduce some consistency. For example, in summertime, when there is a a swing in day to night temperatures. In residential buildings, the internal gains provided by the occupants and appliances are fairly constant over time. Thermal mass can help in maximizing the use of passive solar gains and provide some benefit in the summertime. However, proper design of shading, insulation, and summer bypass in the mechanical ventilation unit are much more effective strategies. Non-residential buildings have much more variance in the internal gains during one day. In these cases the impact of thermal mass can potentially be higher. Bottom line? Pay attention to thermal insulation first for highest performance impact for money spent.

A thermal bridge is a weak point in the thermal envelope. It is an area where heat more easily escapes the building, and it is typically where the geometry of the thermal insulation changes, where a material is penetrating or interrupting the insulation layer, or where there are unintentional construction defects.

Because they weaken the insulation and can result in lower localized temperatures on the inside of the building, impacting the comfort level and the potential for the formation of condensation and mold. They can also greatly impact the overall energy efficiency of your project, resulting in higher energy bills and a larger performance gap from the modeled or intended goals.

First, it’s important to know that you can never completely eliminate thermal bridges, unless you made a perfect sphere with no penetrations of any kind… (tricky to get in and out!). One of the primary goals in Passive House is designing to avoid the formation of mold and condensation. The Hygiene Criterion is the verification method in the modeling process to achieve this goal.

It depends. In our training we refer to the ‘mice’ and the ‘elephants’ of thermal bridges. Unless you have an infestation, mice are fairly harmless. An elephant in the room is another thing. Solution? Model it in design phase and avoid construction defects.

The reality is that American window and door manufacturers have historically been behind our European counterparts in manufacturing high-performance products for many reasons. That is changing rapidly, and there are now many homegrown manufacturers investing in R&D to provide windows suitable for Passive House level performance. That being said, there is zero correlation between cost and performance in the America window world, and the spread in pricing can be quite large. For this reason, as well as many others, it is essential that the window and door specification become an EARLY part of the design goals in any project. Not to mention, windows define a lot about our comfort levels.

The human body can only handle a 7˚F temperature difference from one side of the body to another, before feeling discomfort. In typical code compliant windows, there is a much lower surface temperature permitted than in Passive House level windows. This is why we feel cold when we sit near a restaurant window in the winter. By designing to meet the Comfort Criterion, we can achieve buildings with consistent temperatures.

The frame! While much talk in sales pitches is focused on the glass performance, keep in mind that the frame is actually the trickiest bit of the entire product.

First of all, Air is different from moisture. Air exfiltration can carry 30x more moisture into wall assemblies than vapor diffusion. Vapor diffusion occurs through solid materials, regardless of air movement. This vapor drive typically goes from inside to outside. Air exfiltration, on the other hand, is a much more dangerous phenomenon. The moisture traveling with air leaks has the potential to condense inside your wall assembly and cause damage and reduction in the performance of insulation.

About as much as putting a leaky bucket in another leaky bucket. So… no.

A Blower Door Test (BDT) is a 3rd party verification of airtightness. The building is closed up, with one door replaced by a red blower door (pictured below). Through a series of tests, the building is pressurized and depressurized to assess how many Air Changes per Hour (ACH) occur at 50 Pascals of pressure. For reference, a typical existing home can be anywhere from 10 to 15 (sometimes more!). Code requires 3. Passive House require 0.6.

As an exercise for all members of a Passive House design/build team, we recommend that everyone is able to execute The Pencil Rule on a set of drawings. Taking a pencil, and – NEVER lifting it from the page – draw a continuous air barrier around your entire project. Remember, a balloon only needs one pinhole to burst. Air will find a way through a leak!

Yes, via mechanical ventilation with heat recovery. This is arguably the biggest “selling point” of using the Passive House standard as a benchmark. We must remember that buildings are for people. The health and safety that comes with continuous fresh air exchange is not something that most people have ever experienced.

The Passive House standard is, first and foremost, a standard for comfort and health. Buildings are for people. In order to control indoor air quality, mechanical ventilation systems act as the lungs of our Passive buildings. The fact that the Passive House standard requires continuous fresh air exchange means that the resulting indoor environments are often healthier and cleaner than the outdoor air in many areas. Conventional forced air systems, and even manual ventilation efforts like opening windows, do not ensure that fresh air is continually being introduced. Keep in mind – we typically spend a third of our lives asleep in our bedrooms. Continuous, filtered, and balanced ventilation is key to our health.

Balancing & Commissioning. In order to verify that the proper ventilation rates are being delivered to each room of a building, there must be a 3rd party commissioning in the field in addition to the balanced design.

A Heat Recovery Ventilator (HRV) or an Enthalpic Recovery Ventilator (ERV) – sometimes incorrectly called an “Energy Recovery Ventilator” in the US – are the typical mechanical ventilation solutions used in extremely low-load buildings like Passive Houses. It is a very simple technology, where air is channeled through a honeycomb structure. The heat transfers from the incoming to the outgoing air without the air passages actually mixing. Heat and moisture (in the case of ERVs) can be recovered at very high efficiency rates.

Consider this: An adult needs 18 CFM (ft3/min) of fresh air for healthy brain function. In a bedroom of 160 f2, there are around 1300 ft3 of air. 2 people consume that in just over 30 minutes.

Unfortunately, we live in a world where the reliability of fresh air outside is being challenged by pollution, allergens, and wildfire smoke. Providing for continuous, filtered, fresh air exchange is a question of resiliency.