What is Passive House?

Passive House or Passiv Haus, started in Germany, is a certification program targeting 75% percent reduction in heating and cooling demand in your building or home. It requires high quality construction techniques paired with an emphasis on occupant comfort and indoor air quality. It was originally created with the idea that a house could be a “house without heating” for central Europe. Unfortunately, “without heating” isn’t quite possible. However, a house without a central heating plant, radiators, or large distribution systems is possible. And the way you achieve this is by a concentrated reduction targeting a couple of really dynamic principles in building.


These principles are:

1.     Low energy use

2.     No Condensation Risk

3.     Comfortable Surface Temperatures

4.     Cost Effective

5.     Air sealing for durability

Along with the great principles that surround passive house. There are a couple of myths I’d like to debunk!

1.     You can’t open the windows! Yes, you can. These houses (or buildings) are not hermetically sealed petri dishes.They have very tightly controlled building envelopes which leak very little, but outdoor air is introduced to the spaces with ventilation systems. And in climates such as Maine and Germany, summers are mild and breezes from correctly placed windows can keep the homes cool and comfortable. If you have seasonal allergies, there is nothing keeping your from closing the windows and providing fresh air through your ventilation system year round. However, if you like to throw open the windows and breath in the fresh summer air, by all means, go for it!

2.     Air quality in tight buildings is awful! A properly installed and ducted ventilation system will provide much higher quality indoor air than a traditional leaky building.  My favorite saying “people need to breath, buildings do not” It’s a common misconception that the air filtering through your building is healthy, fresh outdoor air. Where do you think the air comes from? If you haven’t thought about it, i’ll clue you in. The air comes from weakness in your building structure. Gaps and cracks in the foundation, around windows, and though the ceiling into the attic. I spent years climbing through peoples dusty attics doing energy audits, and let me tell you, we always wore masks! Between the dust, and the other “things’ we found in attics, I’d call that a far cry from fresh air. The air drawn in from wet basements, littered with mold? I wouldn’t call that fresh either. The air filtering through the fiberglass stuffed in around your windows (oh yeah, that’s totally doing nothing by the way) I wouldn’t call that fresh. If you won’t touch the fiberglass insulation without gloves on, why would you want to breath it in. Okay, okay – tangent – but I think you’re starting to follow my thought pattern.

3.     Passive Houses (or buildings) are Ugly – Wait, what? Okay, okay, so in the 70’s when building science just started to become a thing, there were some pretty awful structures. But we’ve grown up since then, and with a really good architect, there is no reason why you can’t have the most beautiful house and still be comfortable, efficient, and durable. There are a few things to take into account when designing any energy efficient building, but the details are what make the house beautiful. Spend the time (and money) in the design phase, and reap the benefits of a truly beautiful and sustainable building.

4.     It’s too expensive to build! Does it have to be? Absolutely not. It’s called trade off. We are going to trade the expensive heating system for insulation and ventilation. We are going to offset the monthly bills by more than the increase in the mortgage. We are going to pick and choose window locations to take advantage of the views and the landscape and only put them where we need so you can afford more expensive windows, but not more of them. In Germany it’s actually cheaper to buy a triple pane window then to buy a standard double pane window. The US will catch up, in the mean time, we will work with proper orientation to take advantage of passive solar and lose less through heat loss.


Now that we have described what is passive house, and what is not passive house, let’s talk about how to build one in Maine and more specifically, with Mottram Architecture.

If you’re hear because you’ve gotten on board with the passive house movement and you want to understand not only how to get one, but the science behind it, go HERE! Instead of re-inventing the wheel, we will let you dive into the science directly from Passive House International. And then we will sit and discuss the science and building techniques with you, for hours, maybe over a glass of Wine.

The specifics of building a Passive House in Maine are as follows:

·       High R-value roof, walls, and slabs with a thermal resistance of at least R-38, but we aim for R-40 Walls, R-60 Ceilings,    R-38 foundations/slabs (this will typically mean 9″-12″ depth in your walls. It gives you the opportunity for deep window sills, but less interior square footage. However, we’d love to show you how great our spaces come out, you won’t miss the square footage, we promise! That’s what happens with a really detailed house that works exclusively for you and your family!

·       Triple Pane, high R-value windows: R-7.1 or as you are more accustomed to seeing: U-0.14. Triple pane windows have higher thermal resistance which keeps the interior surface temperature more comfortable, but also resists condensation on the glass which can lead to moisture and mold problems. These windows also need high solar energy transmittance (SHGC) 50%-55% to take advantage of passive solar heating.

·       One continuous air tight envelope: Though a series of tapes, skins, vapor barriers, and construction techniques, passive house buildings must maintain 0.6 air changes per hour or less. That means minimal leaks, drafts, and heat loss.

·       Ventilation system with heat recovery: Since Maine is a cold climate, we want to capture as much ventilation heat before it leaves the building so we can preheat the fresh air coming in. This becomes important for 2 reasons. First, it reduces the amount of energy you need to heat the incoming air. Second, it doesn’t introduce cold outdoor air into the space. In February when it’s -15 degrees outside, you don’t want -15 degree air filtering into your home. Not only does the ventilation system need to recover the heat, but it needs to be at least 75% efficient to qualify for passive house.

·       Efficient electrical appliances are used. No energy hogs here!

·       Exterior shading is used. This can be as simple as landscaping with trees for shade to exterior overhangs and shading devices.

If you love all the ideas of the principles we mentioned above, but you’re less concerned about understanding all the ins and outs of the science. (Since that’s our job, and really what else are you hiring us for! ) Then this is how you move forward with Mottram Architecture on building your dream passive house.

Answer these questions:

We don’t require any information for you to reach out to us about your project. But during our first phone or email conversation we will ask you the following questions, so it will help if you have thought about these before you contact us.

·       What are you looking for?

·       Why do you want this?

·       On a scale of 0-100 how motivated are you to finish the project?

·       What is your budget for this project? Or do you need help determining what your budget should be?

·       When do you want this project to be complete?

·       Apart from you, who else is involved in the decision making process?

·       Let us know you’re interested in Passive House Certification

Once you’ve answered the questions, give us a call. We do an initial 1HR consultation at no cost to you. It’s a great way for us to introduce ourselves, go into more detail on who we are and how we work, and find out your project budget, scope, schedule and really what you need from us.

After our first introductory meeting, we will put together a proposal for you on what it will be like (and cost) to work with Mottram Architecture based specifically on your project.