Why Understanding Air Pressure Differences is Key to Designing an Efficient Home

by Rob Shearer

Most people understand the concept of insulation, and why it is important. Heat wants to move from your warm comfortable home to the cold outside, always seeking a balance of energy. Insulation slows that process down, so more is better.

However, insulation is only part of the solution of a comfortable and efficient home. Indeed, there is a point at which adding more insulation is no longer cost effective, because the relationship between insulation and heat loss is logarithmic. The more insulation you add, the less effective each additional inch becomes. The first inch of insulation is extremely effective at reducing heat loss, the second inch is still effective, but less so, etc.

Another, often overlooked way that heat escapes your home is through what is called air infiltration. Warm air finds its way out of your home through the many small, or not so small, gaps and cracks in the walls and ceilings. As this air leaves your home, cold air is drawn in through other gaps, creating cold drafts and robbing your home of its efficiency. Unlike the relationship between heat loss and insulation, the relationship between air infiltration reduction and heat loss is linear. Every square inch of gap that is closed off is as effective as the last. Certainly, there is a point where the methods needed to close those gaps becomes more costly, but a lot can be done with effective gaskets, expanding foam, and caulking. There is a saying in building science circles, “Gaskets are better than foam, is better than caulk, is better than nothing.” This is due to the longevity, effectiveness, and expense of each of these methods.

In order for air to move from one place to another, two things are needed. A pressure difference, and an opening. Thinking in terms of meteorology, wind is caused by air rushing from areas of high pressure to those of low pressure. Without a difference in pressure, the conditions are what sailors would call “dead calm.” No air movement at all, even though there are no physical boundaries to be seen. Now consider a balloon. Using some amount of effort from our lungs, we force air into a well sealed enclosure and pinch it closed with our fingers. Even though there is a significant pressure difference between the air inside the balloon and the air outside, there is no opening, no path for pressure equalization, and therefore, no movement between the two areas. How do we know there is a pressure difference between the balloon and the air outside? Let the balloon go. Air rushes out of the opening, propelling the balloon like a rocket in the other direction.

Air pressure within and around a home is constantly fluctuating. Wind may be blowing on the home, exerting a positive pressure on the windward side of the home while at the same time, the aerodynamic drag exerts a negative pressure on the leeward side. Warmer air is more buoyant than cooler air, so Inside the home, warmer air rises to the ceiling of the second floor. This exerts a greater pressure on the ceiling and walls in the higher areas of the home, while simultaneously creating areas of low pressure in the basement. The low pressure in the basement means that air wants to be drawn into the home, possibly bringing in soil gasses. This is particularly troublesome in areas with high radon content. Since it is not practical to constantly equalize the air pressure between the inside of your home and the great outdoors, sealing leaks is typically the more effective way to control air infiltration.

This is why at evoDOMUS, we painstakingly detail connections and possible weak points in the building envelope with an eye toward air sealing. Major possible weak points, such as the union of two modules, are gasketed to make sure that the seal between them is tight and effective. Areas that are less likely to experience movement over time, such as around windows and doors, are foamed, and finally, small gaps that are too small to receive foam or a gasket are caulked. The net result is a cost effective yet sound strategy for preventing heat loss due to air infiltration.

Each evoDOMUS home is tested at least twice for air infiltration by a certified HERS Rater using specialized and calibrated blower door equipment. Once after the modules are set, in order to find any remaining weak points so that they can be addressed, and once near completion to determine the final result. This equipment measures the amount of air flowing through the fan when the specific target pressure is reached. Air pressure is measured in a unit called “Pascals” (Pa.) The target pressure difference for this test is 50 Pa. With a little math including the air volume contained within the home, the Rater is able to calculate the number of times that the air inside the home is completely exchanged at the target pressure over a given time, yielding a result such as “three air changes per hour at 50 Pascals pressure difference,” abbreviated as “3 ACH (50).” There have been a lot of these tests performed throughout the country, and it is generally accepted that a typical new home built to code will test in at about 6 or 7 ACH (50). A home that is certified under the Department of Energy’s ENERGY STAR® Homes program must test below 5 ACH (50).

An evoDOMUS home is typically below 2 ACH (50) because we want the air that you have paid to heat and cool to stay in your home as long as possible. Another benefit of this is that the air within the home has time to equalize itself in terms of temperature. A more constant, lower powered HVAC System provides smaller amounts of conditioned air into the home, which naturally wants to find thermodynamic equilibrium. The tight envelope gives this process more time to occur, letting the natural process quietly equalize energy throughout the home instead of simply rushing out through gaps and cracks. The result is a more evenly comfortable home, where all rooms are closer to the same temperature without having to move around large volumes of air with big furnace fans.

If, after reading this, you are wondering if a home can be too tight, stay tuned for our next blog, “But a House Has to Breathe, Right?”

Posted in Uncategorized | Leave a comment

Stuck in the Fifties?

About better ways to build homes

by Mike Farinacci

Would you trade in your smart phone for an old-fashioned rotary phone? Would you rather use a typewriter than a computer? How about you quit listening to music on your mp3 player or iPod and go back to eight track tapes? Those devices did have their time and place, however, something always comes along that makes our lives better, easier, and more efficient. If you agree with that, then answer this question: Why do we settle for the same building methods that have been using since the 50’s?

“Building Science” has made leaps and bounds over the past 60 years. Today we understand more about advanced framing, air and thermal barriers, and how to control moisture better than ever before. However, all these advances give way to the “building standards” that have been used since the 50’s. Homes are still being built with 2×4’s @ 16″ on center (o.c.) with double top plates, three stud corners, jack studs, cripples, double headers, and batt insulation. Some builders replace these standards with a thicker wall (2×6), studs spaced farther apart (24″ o.c.), while using better insulation that fills the entire cavity along with a single top plate, two stud corners, no jack studs, no cripples, and single headers.This method is cheaper, faster, and saves energy. It’s cheaper because it uses less lumber and fewer pieces, which is faster to assemble. The deeper cavity allows the builders to use more insulation, which cuts down on air infiltration. The increased spacing and reduced framing members also minimize thermal bridging.At evoDOMUS, we are upping the ante even more. Our Bensonwood OBPlus ™ wall panel has Huber Zip Sheathing on the inside and out with 9-1/2″ engineered I-studs (TJIs) @ 24″ o.c. with dense-packed cellulose insulation for a total R-value of 35. Also, on the interior we assemble 2x3s @ 24″ o.c. with 5/8″ drywall to provide a utility chase. This ensures that we do not compromise the integrity of our wall. Along with our triple pane windows and minimum R-50 roof panel, our homes are green, sustainable, energy efficient and incredibly airtight. Now, that’s the kind of building envelope you deserve in your home!

With our depleting resources and rising energy costs, it only makes sense to build better homes with better methods of construction. We shouldn’t settle for anything less. We owe it to ourselves, our kids, and our environment to constantly push the envelope and develop greener, more sustainable, and more efficient ways to live. We always want the next best phone, computer, car, or gadget; why don’t we want or expect excellence in our homes?

Posted in Uncategorized | Leave a comment

Windows – The Achilles Heel of Green Buildings

By Alexander Kolbe

For many years, the construction industry did not care enough about the quality of the windows available. What a mistake. Even the most advanced thermal envelope is useless if the windows are not up to par. Along with general construction leaks, they are a major source of energy loss.

The most energy efficient homes use the best windows in the market. At evoDOMUS we go even further. We advise using European windows because of their superior build quality and performance. We love Unilux windows because they close like a Fort Knox vault. A triple layer of seals and incredible 2″ triple-glazed panes make these windows remarkable. We have done a lot of research in this field because high quality windows are vitally important. Although there are very good North American windows which we offer as an alternative, that are similar in terms of insulation quality, we must acknowledge that European, and especially German windows, offer unbeatable quality at an only slightly higher price. Triple-glazing comes at a premium, but in terms of the energy efficiency of the total project, it is money very well invested. If you would like to find out more about these windows just visit their website. You’ll be amazed.

Posted in Uncategorized | Leave a comment

Why We Prefer Panelized Construction

By Alexander Kolbe

When people talk about prefabricated homes they usually refer to them as “modular” homes. Increasingly, the terms modular and panelized have been used interchangeably, however, distinct differences exist between the two types of homes. We would like to explain why panelization is our construction method of choice.

How they Differ

A modular home is one type of prefabricated home that is built in a factory in sections. These sections, or modules, consist of whole or partial rooms which are delivered to the construction site, placed on pre-made foundations, joined together and completed by a builder. Panelization is a second type of prefabrication, where the manufacturer pre-constructs the walls, floors, and roof panels. Often fit with doors and windows in the factory, the panels are then delivered to the construction site, placed on pre-made foundations, joined together and completed by a builder.

Panelization vs. Modular Construction

The main advantage of the modular prefabrication method is the higher degree of factory prefabrication which results in shorter on-site construction time. Wall finishes, floors, ceilings, windows and doors, and even sometimes wiring and plumbing can be installed in the shop. The method of inspection can be viewed as neither pro nor con as the factory usually receives a third party certification in combination with on-site inspections.

In our opinion, the most considerable disadvantages of modular homes, in comparison to panelized homes, are size and design limitations. The modules need to fit on a flatbed truck, and hence can not be wider than a reasonable oversize load, as regulated by the relevant state laws. Those size limitations, in turn, have a direct impact on the design of a house. The maximum transportation width limits the width of the rooms. It is not easy to add a couple feet to make your room larger. The volumes tend to be boxy, while the layouts typically follow standard interior patterns. Often, when you look at modular prefab homes you will note a certain uniformity which derives from the specifics of this construction method.

Our Choice

At evoDOMUS, we have been aware of this situation for many years. We had the opportunity to learn from the leading German home manufacturers over a period of 20 years in our role as designers of over 300 homes for their world wide clientele. Because of the indicated disadvantages, the vast majority of prefab manufacturers in Germany utilize the panelized method.

Because our goal is to create individualized, site-specific homes that provide the highest degree of energy efficiency, we prefer the panelized construction system, by far. We build single panels, up to 48 feet long, which form walls, floors and roofs. This panelization gives us utmost freedom to build exactly the home our clients desire. There is no length or width limitation for walls, and ceiling panels can easily span 24 feet and more. Another advantage is that these panels are usually straight and flat which enables us to stack them side-by-side or on top of each other and shrink wrap them for weather protection during transportation.

As with modular construction, we can fit doors and windows in the factory, sealing them properly and making sure that all panels have been built with the greatest precision. In this way we achieve an incredible level of air tightness, the number one criteria for energy efficiency.

Once they arrive on the construction site, the panels are winched into place with the help of a mobile crane. It takes only a couple days to assemble a house, making it airtight, watertight and lockable.

This freedom from system-inherent aesthetic restrictions enables us to design our homes individually, while still taking advantage of the resource-saving, and healthy off-site construction merits. All this results in fabulous benefits for our clients.

Posted in Uncategorized | Leave a comment

On The Right Track

By Michelle Kolbe

Stepping back to consider where I am today, and why I am here, absolutely confident and excited to grow our company evoDOMUS, I can offer the following background:

Back Then

As a young American architect in Europe, I remember many frustrating visits to the States. I specifically am reminded of being saddened at the sight of a number of large retailers from my childhood on a familiar road in Warren, OH, that had recently gone out of business and whose empty buildings and vast parking lots were left behind as lonely reminders more prosperous times.

The attitude that prevailed then was that land is cheap and plentiful, so just leave the old and develop the land across the road, creating even more enormous big box stores with many more acres of paved parking lots. To witness the razing of beautiful homes and forests to accommodate future shopping plazas, parking lots and endless fast food restaurants was depressing. Though the financial justifications were probably warranted for each individual company and developer, it was hugely damaging for the community, creating an increasing number of visual eyesores, as well as an environmental burden. The word sustainable was in no one’s mouth at that time, unless it preceded ‘growth’ in a business plan.

The idea of conservation, in terms of land, resources and energy that I had become accustomed to in Germany seemed to be as foreign to my fellow Americans as Kaisersülze. Of course this was due, in part, to the fact that the European countries I had visited were much more densely populated than America on the whole. The effect on the general population was that everyone recycled, built responsibly and worked to reduce dependence on fossil fuels. The government made it easy to do so by, for example, requiring apartment buildings to provide recycling containers for no less than 5 different types of refuse, and by creating very stringent building codes. Land use was strictly zoned to protect the countryside to benefit of the local retailers and inhabitants.

Fast forward to Now

Recycle Reuse Reduce. A quick Web search of those three words today turns up over of 35 pages of links. Actually, that number might be much higher, but I grew tired of clicking next… Ditto for Green, Sustainable and Eco. I don’t know exactly when it happened, but believe me, I am thrilled and relieved to see that America has jumped on board.

When I returned to the States in 2009, with my husband and young son, I was apprehensive. I didn’t know how we would find a community that would have similar ideals and expectations to ours. Moreover, how in the world would I adapt professionally, after a 17 year absence, to a country where the construction industry was so resistant to change? Imagine my relief when I began online research into companies and products and found interest in passive solar design, environmentally safe products and sustainable building methods. Yes, the movement had arrived!

So, thank you Building Science Information, Sustainably Built, Fine Homebuilding and the numerous other incredible websites committed to sharing knowledge, ideas and to offering professional support. In the dedication to writing environmentally valuable and timely articles, and the corresponding comments of readers, whether contractors, homeowners, architects or manufacturers, it is apparent that America is on the right track. In fact, most of the people who contact us to discuss our homes are as interested in our sustainable benefits as they are in creating a modern home.

Through evoDOMUS, I am proud to be a member of this community and I look forward to contributing in every way possible. The road ahead for us all is long, but interest is growing. It can be difficult to prod a land of 300 million into action, but when they start moving, look out!

Posted in Uncategorized | Leave a comment


By Michelle Kolbe

So, it is the beginning of the New Year. Out with the old, in with the new. Firming up, slimming down, running a tighter ship. Many of you will use this time to get your health and bodies into better shape. I, too, try to keep up with that. Some weight training, a couple spinning classes a week and fair-weather running all help me to maintain balance in my life. Add to this my most recent clutter purge and I feel prepared with the power and energy to manage anything.

Sometimes this need to optimize can become a bit addictive. Anyone whose family car is a hybrid, or who has a close friend who is a Prius driver, has probably become competitive in seeing who can get the best gas mileage. AK and I engage in this more than either of us is willing to admit. I’ve also seen this with clients who have PV systems, and who proudly report how much the electric company owes them.

I liken this need to compete with our obsession to create optimal homes for our clients. For example, when searching for the ‘best’ products and materials for the wall and roof systems, cladding, windows, finishes and appliances of our homes, we pour over websites, testing studies, consumer reports, and meet with endless representatives before taking only the fittest, best value for money items onboard. Then, we categorize the results into standards and upgrades complete with our own internal Green Star rating system. The time invested in pre-selection streamlines what can easily become one of the more time-consuming, resource burning phases in the delivery of a home. Inform yourself early, increase predictability, reap the rewards later.

To help organize and focus the decision-making process, we use a short, but helpful matrix of identifiers:

What is the client’s budget?

This will actually lay the groundwork for all of the options and decisions during the entire project. From the amount of glazing, to finishes, to the utilization of alternative energy systems, understanding the client’s financial comfort zone will aid in the value engineering of the project.

How environmentally minded are the clients?

Are green aspects fringe benefits, or are the clients serious about choosing the most environmentally sound selections available? Or, perhaps they find themselves somewhere in between. R-35 walls and triple-glazed windows are our standards, but depending on the climate zone the process of value engineering might lead to the possibility of lesser thermal qualities in return for the investment in a small PV array. One of our most jaw-dropping experiences came when an interested party informed us that he didn’t give a hoot about our eco-credentials, he just liked our homes’ appearances. Wow.

Which station in life?

Young family, professional couple, golden agers, jet-setters, entertainers, patchwork in need of flexible space, or keeping up with the Joneses? There are as many familial situations and lifestyle preferences as there are stars in the sky. Understanding how your client structures his or her life today, as well as how that routine might change in the future, will aid in the entire design and specification process. Should every bathroom have a tub, or are tray-less showers preferable? Is wool carpeting desirable in the baby’s room? Office today, guest suite tomorrow, granny flat in 5 years? Efficient and creative planning makes the most out of  available space and funds.

What is their attitude toward maintenance?

Are the clients hands-on in terms of periodic oiling of the Ipe cladding? Would Trespa rain screen panels appeal to them if the budget would allow it? What about the wood deck? Would the naturally occurring patina on the Richlite countertop be acceptable? Or is Silestone the better choice? Oiled hardwood floors, or would porcelain or stone be more appropriate? Especially when dealing with the greenest of materials, understanding your clients’ feelings toward upkeep is very important. It’s not sustainable if it is torn out and replaced in 5 years time.

Materials, systems and products will continue to improve and evolve. Our trusted network of consultants, contractors and representatives, is invaluable in filtering information down to the most useful elements. In the end, the goal is for the client to be as happy as we are in creating an individualized, beautifully sustainable home.

Posted in Uncategorized | Leave a comment

The Joy of Being Green

By Alexander Kolbe

When I studied architecture in Berlin in the eighties I had absolutely no clue about sustainability and energy efficiency.

Like many students, my only goal was to become an outstanding designer. My role models were famous architects like Le Corbusier, Mies van der Rohe, Walter Gropius and Erich Mendelsohn. More current influences came from the contemporary architects Norman Foster, Renzo Piano and Richard Rogers, among others. I read a lot about these icons of modernism and I adored (and still do) these big names. Their portfolios made a great impression on me and I studied their work quite intensely.

Nevertheless, after graduation I quickly began to understand that there was more to architecture than just great design. I noticed that many of the big name practices also focused on using smart technology and design in order to make their buildings energy efficient and sustainable. I found it fascinating that beautiful buildings and structures could do more for the environment than just look great. I was hooked instantly. If it was possible to design buildings that served their purpose, looked aesthetically pleasing and needed less energy for heating and cooling, I wanted to do nothing else in my career.

One piece was missing in my picture: my clients didn’t necessarily share my passion and eagerness for sustainable buildings. I learned the hard way that the mechanisms of the real estate market did not really appreciate green designs. I remember one of my clients listened to my presentation, and obviously understood the benefits of an energy efficient approach. Sadly, he concluded that my ideas sounded great, but that his tenants would not pay a higher rent to cover the extra costs for a better building.

I found that experience very painful and rather frustrating. Although I ended up building a conventional house that time, I did manage to convince new clients of the benefits of environmentally friendly buildings. Luckily, I came across Georg Huf, the owner of Huf Haus, a leading German manufacturer of green luxury homes. We hit it off and he asked me if I was interested in designing homes for his customers in and around Berlin. This was 1991, and the beginning of an interesting journey toward more sustainable and user-friendly built environment.

Years later, after moving to the UK and completing over 250 Huf homes in Germany, England, Scotland and Ireland, including a 50 bed nursing home in Sligo, which turned out to be one of the most energy efficient buildings of its kind in Ireland, we started designing homes for Baufritz, another well-known, German high-end manufacturer. This was indeed a great experience! Their company philosophy, design flexibility, green manufacturing techniques and passion for building science greatly influenced us. In 2008, however, my wife Michelle, who is an Ohio-native, and I decided it was time to move on and relocate to the US.

This period of my career was extremely exciting and an invaluable source of inspiration, education and knowledge. Maintaining my independence as an architect, I was able to meet many interesting people who were extremely passionate about sustainable home building.

Coming from 20 years of experience in the field of manufacturing and in the design of energy efficient homes, we were absolutely stunned by the strong green movement in the US, which demonstrated incredible momentum and pace.

When Michelle and I began our business here in the States, we noticed an overwhelming demand for green homes. Many people were drawn to us because of the contemporary designs we have to offer. Most, however, were interested in the combination of energy efficient homes and modern aesthetics. It seemed out we had hit the nail on the head. Green and healthy homes, well designed, with a European edge and clear lined designs are very appealing to many people who are looking to build their dream home.

We found this so very motivating and exciting that we resolved to create custom homes as premium prefabs, which led to the formation of evoDOMUS. In doing so, we have developed the most incredible homes we could imagine. Our focus is on energy efficient, sustainable, healthy homes, carefully designed in order to provide optimal usability, based on passive house standards and beyond. And we enjoy every minute of it. This is the most inspiring endeavor I’ve ever undertaken in my career. It is fulfilling and delightful to meet so many inspiring people and potential clients who respect and love what we do, people who share our visions and goals.

Our aim is to contribute in making this world a better place with the collaboration and dedication of our clients.

Posted in Uncategorized | Leave a comment