What is done to control air tightness of house with respect to sink drain vents?
I want to build an addition that is pretty tight and retrofit existing house to minimize natural ACH. I read and learn alot about it but currently have no hands-on experience with blower door tests, etc. etc.
I know:
–build tight, ventilate right
–no such thing as too tight
–HRV, ERV
–Pasiv Haus 0.6 ACH
–clothes dryer can be eliminated and so is vent to outside
–can’t eliminate kitchen stove vent but can optimize
–etc etc
But I don’t know what, if anything,can be done about sink drain vents. How much ACH contribution does a couple of sink drain vents represent? Is anything ever done to control or minimize their effect on ACH? Are they left open during a blower door test and only represent a small, unavoidable ACH contribution, or are they blocked for such a test?
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Replies
Rick,
Plumbing vents are open to the atmosphere where they penetrate the roof. But unless the water in a sink trap (or a tub trap, shower trap, washing machine trap, etc.) evaporates -- which sometimes happens when sinks are not used for months -- there is no pathway for outdoor air to enter or leave a house through a plumbing vent, because the venting system is sealed by water in the traps.
So the plumbing vent system does not contribute to infiltration or exfiltration.
Martin, thanks. Dah, I don't know and haven't researched alot about plumbing. I know what a trap is, so with a little more thinking, I could have answered my own question.
PS In a world with finite resources, and nearly infinite ignorance of that as demonstrated by the fact that almost no one seems to consider uncontrolled human population as that world's biggest problem,those on the GBA team are quiet heros.
Rick & Martin,
I realize that the level of detail that Passivhaus goes to IS extreme...
But it is all of "these little things" that add up.
The plumbing vent stacks do not add directly to air infiltration...but reducing vent stacks reduces penetrations thru the roof...which is a durability issue.
The vent stack also completes a counduit that connects the underground condition to the rooftop vent.
This low-r conduit transports warm or cold air/gas thru the guts of the house and exchanges heat along the way...so it does affect temperature inside of wall cavities and attics.
This is a little bit like sticking a nail in a potato to make it bake faster.
This is not a big deal....It may only amount to a few btu's a day For The Lifetime of the House.
Our homes are bleeding Energy .. some leaks are small.
Some extreme climate folks are looking at all of "these little things".
John,
As I was answering Rick, I was thinking about this point -- airflow from the municipal sewer system (or septic system) up the vent pipe. Undoubtedly such airflow exists, especially when the outdoor temperature is lower than the soil temperature 4 or 5 feet underground.
A couple of points:
1. Most septic system components are entirely underground, so the source of makeup air consists of air drawn through the soil. This is a weak source of makeup air, because of the convoluted path between the atmosphere and the below-ground components of the septic system. Once the ground freezes solid, even less air is likely to enter from this source.
2. During the summer, when the soil temperatures are usually lower than air temperatures, there will be less of a convective engine driving the aiflow.
I'd be interested to learn if anyone has tried to quantify the heat lost through this route. I imagine it isn't much. In theory, insulating the waste and vent pipes would reduce thermal transfer from the interior air to the air inside the vent pipes.
Martin, I noticed that Passivhaus considers this type of issue and I believe that Thorsten has also brought it up before...
So I say worthy of consideration.
I think that living in an extreme climate as Thorsten has can amplify some of these things and give the rest of us something to think about.
Rick, as far as air tightness goes plumbing vents are not an issue as long as the pipe penetrations are sealed of really well (and long lasting) and traps hold water and are not dried out - like Martin already pointed out. The issue is not air tightness - it is an open penetration through the whole building which lets a considerable amount of conductive heat loss occur...and from my experience this is more than I anticipated it to be when I first looked into this more on my quest to build high efficient homes. Once I really investigated more into this it actually made all sense to me, like with so many things which we just have done for so long one way that one just doesn't even think about it anymore. On a cold day you can follow the vent pipe with a IR camera pretty well in the interior wall. IMO plumbing stacks should be avoided just the same as chimney's -which of course are even worse. I started a long list about 3 years ago on items which I defined as questionable in regards to heat loss and energy efficiency and keep working my way down...and in a way it seems like every time I check of one item of my list I come up with two new one.
A Passiv Haus does not have any plumbing stacks penetrating the conditioned space with an open connection to the environment - and one of the Golden Rules of the standard certainly is to avoid any penetration of the building envelope as much as possible. The new 2009 Plumbing code now makes provisions for the use of air admittance valves (AAVs), but at least here this is not adopted as of yet. Be prepared for lots of arguments and discussions with plumbers, inspectors and code officials...this took some effort for sure, like so many other things we are doing by now. And of course the plumbing vent system needs to be designed accordingly and correctly with and integral design with the use of AAVs in mind. Happy building - TC
First, I need to say I am extremely impressed by the quality of individuals that have responded. I have browsed the writings on GBA a lot, and I know the names here, and others, keep showing up with quality responses. TC, I know the crowd here seems especially happy to hear from you, due to your good efforts and "interesting" climate. Thanks to all!
Second, this trail of responses shows some snapshots of points along the "green spectrum." How green are you building? How green should you or can you build, or live? When my brothers and I have hiked and camped out overnight on the Appalachian Trail in Virginia, the rule is "Leave No Trace" that you have negatively altered that natural environment. To me, a simple extrapolation indicates that humans are headed toward that rule within the world as a whole (unless something quicker and stronger intervenes), particularly since "green" and "human population control" have never (to my knowledge) ever been used in the same sentence.
I don't believe that the level of detail that Passivhaus goes to is extreme, at all. I don't believe that using AAVs is extreme, either. They are considerations for each of us in determining where on the green spectrum we need to be, and can be. In about 2006, I was slapped with a 72% increase in my electric bill in an all-electric house--the slap caused me to see green, but mostly just with respect to kwh and btu management. Mainstream building and most of the public have felt a slap too, but the momentum of such a huge mass is hardly changed--the revolution is a quiet one.
Although fundamentally fairly simple, to build "right," even just for btu and kwh management, is immensely different from what most people and builders are used to seeing. You should have seen people walking by my house, with mouths open and staring, when I had the entire perimeter of my suburban house on slab dug up in order to retrofit slab and frost wall insulation. "Do you have a water problem, or something?" "No, but I'm determined to stop those ants, once and for all."
I tried to use AAVs on my house and my plumber just wouldn't go for it. He played the fear card, "they would fail", "that you couldn't rely on them", etc.
I just gave up in the end and let him add to the holes in my building envelope. To be honest, I was tired of trying to get yet another trade to think differently, and to change their hard held belief that I would be wasting time and money, and besides, that was the way they always did it.
It may have also beeen noted above but AAVs also provide another benefit other than reducing the number of holes in the building envelope, they can greatly reduce the amount of vent piping needed for the house.
All that said, I do recall reading that if you are on a septic system that you should at least have one vent to the outside. But it's not uncommon for a house to end up with more than one vent exiting the house, and there is no reason that AAVs couldn't have been used instead.
I got my plumbing license over twenty years ago in order to get better control of my schedules and of details such as discussed here. Our current code allows a home to be vented with a single 2" vent and to use air admittance devices, commonly called "studor-vents" at other locations so long as they are accessible for inspection and replacement. The main vent is mostly for releasing methane when anaerobic digestion happens in the septic line as well as for allowing incoming air to prevent traps from siphoning esp w/ toilet and washing machine surges.
My experience has been that when they fail they get stuck in the closed position rather than open (as compared to check valves which typically fail in a half open position) To protect the vents and minimize failure potential just don't screw them to their PVC pipe adapters until all the gluing is complete, including the gluing of the trap adapters, so the fumes of the primer and glue won't impact the rubber seal.
Also, always keep them dry by placing them as high above the trap they serve as possible. If inside a cabinet place them at least up under the counter top.