Passive House Q&A!
We received some great questions this week, from a person considering the purchase of a new Passive House. We thought we would pass the conversation along to you.
-How does the maintenance cost of a passive house compare with a normal house?
The maintenance cost is lower and the projects are easier.
The mechanical system of a PH is much simpler than a typical home, and as a result it is cheaper and easier to maintain. Things like large boilers and central heating systems that use large heat pumps don't exist in our homes, so spending 10k or more every 15 years or so is a thing of the past. The heating and cooling loads presented by our homes are really small, and it follows that the mechanical system required to provide for occupant comfort is small as well.
When a house is sealed up and insulated to PH standards, the energy bill goes down and the indoor air quality gets better. And a huge side benefit is that the house lasts longer and is easier to maintain.
Much of the degradation of a typical wood framed house is caused by condensation within the walls, floor, and roof structure. Moist warm air is moving through the structure, and if the wood is cold condensation occurs and water droplets form on the wood. Over time this can lead to structural damage. This is how old homes can rot even if they are not leaking.
In our homes, we use the best available science to avoid condensation within the structure. We study our assemblies with WUFI moisture management software, and we make sure that our moisture 'planes', the predictable places where condensation may occur, are so well insulated that condensation will not cause moisture to build up on wood components. Air sealing really helps here as well, because if air can't move through the walls or other parts of a home, then moisture is not carried into the structure in the form of humid air. We believe, and with good reason, that if the painted surfaces of our homes are maintained, they may last into perpetuity.
-What happens if the air filtration system breaks down? Will the occupants suffocate?
NO, lol. Excellent question, though. When the HRV system is off for a few hours or more, during a time when all the windows are closed, the home may become stuffy - a little humid, etc. The occupants will be completely healthy, but they will notice. It's like being in a room full of people for a conference, when the ventilation system is not keeping up. When you go on break, the hall seems really nice by comparison. Cracking a couple windows will restore the crisp feeling to the air in the home, and the HRV can be repaired as needed.
-How does the resale value of a passive house compare with a normal house?
Studies in Seattle have shown that deep green homes in that market routinely command resale prices that are 5-15% higher than comparable homes. Marketing time required for a sale is also shorter. As time passes and energy prices increase, this pattern can only become stronger.
-How do cooking odors get ventilated? Will the smells be trapped?
We install charcoal recirculating range hoods to capture the heaviest smoke particles and grease that are in the air from cooking. We also install buttons on the wall in the kitchen that can be pushed to place the HRV on high. This works great, because smells from cooking are collected by one of the large flow exhaust registers connected to the HRV which is always installed in the kitchen. Even better, smelly air that inevitable makes it into the rest of the house is collected by the other exhaust registers in the home, in a short amount of time.
The booster buttons are also located in each shower room, by the way. When a button is pushed, the HRV ramps up to high flow for 30 minutes.
-What, if any, downsides are there to a passive house in comparison to a normal house?
In many cases they do cost a little more up front. Even though this cost is recouped quickly, it's a negative for some people. In the long run a PH makes money for the owners, of course.
Passive Houses are different in our minds right now. Early adopters love them, beta adopters will accept them, but other people that are less comfortable with change may find them to be hard to accept. This of course is a typical situation during a time of market change (and change is always with us!) Randy has a brother that still won't carry a smart phone...
Owners will need to understand their PH's a little more than a typical house, at least for the next decade or so. Repairmen and specialists that can work on the simple but specialized parts of a PH are readily available. But they may not understand the big picture. So it will benefit a PH owner to have that understanding whenever maintenance is being performed.
Posted on August 22, 2014