Archive for January, 2012

APHN: Passive Passion not Passive Aggression

The American Passive House Network (APHN) is two weeks old!  See

See for the two week birth announcement 🙂

I personally am extremely glad that such a platform exists now for PH designers, architects, engineers, builders… on the ground just doing their work.  Passive House/Passivhaus no matter how you spell it and no matter how you measure it (metric or imperial) it, is something that needs to be nurtured.  If PH is to become the mainstream building standard as it has become in Europe, people involved in PH in the U.S. and internationally need to work really hard and in solidarity to make it happen.

“The Americans will always do the right thing… after they’ve exhausted all the alternatives.” — Winston Churchill

We simply cannot and do not have time to waste on the alternatives.

I am sure many others feel the same way I do about the break up.  We were the children of two divorcing parents who continue to be aggressive against each other.  The good thing is we really should not feel the need to choose sides, in fact, it probably benefits us the most if we continue to talk to both sides.  More importantly, we have each other.  I benefit loads everyday from all the PH individuals I correspond with.  It a great community of people who share knowledge and experience freely, so let’s continue to share as generously as possible with each other.  It’s a movement that should not be slowed down because of petty disagreements.

For those who are just getting into PH and not familiar with the breakup, don’t bother.   Just skip ahead and know that there are people out there building homes/schools/apartments for the future and join our efforts.  I did not know about APHN until about two weeks ago but I am really psyched!

I think a visual of why PH folks are such an obsessed, fanatical lot is helpful here.  This is a trailer to Charlie Hoxie’s Passive Passion, the official selection from the 2011 NY Architecture and Design Film Festival: check it out!  You should really buy the movie for the full effect.  I did.



A Trio of Window Air Sealing Detail


One of the things we learned from our first unofficial blower door test was that our window sealed with Tremco’s ExoAir Trio alone did not perform perfectly.  This may be a issue of level of expectation than about the performance of the tape.  I think we were expecting it to be completely air-tight but in the end it was not.  It sealed most of the potential air-infiltration but when the home was depressed at 50 Pascal, you can definitely feel a small stream of air leaking in all around the windows.

We decided that this was not good enough and sought out a better solution.  Also, we decided to make some comparisons, so we know what choices we have for future projects.

Window Installed and Sealed with Trio

Window with Trio

Cost: $27 for Trio

Installation Time: 15 minutes

Sealing Time: 0 minutes

Here’s the first alternative, we call it:

Quick and Foamy

Window sealed with GreatStuff sprayfoam

This is the quickest and easiest way to remedy the problem.  Take a can of GreatStuff and carefully seal the entire gap with it.

Cost: $3.00 of foam (Rough estimate, also we have really thick walls.

Installation Time: 15 minutes

Sealing Time: 2 minutes (one minute to spray and one minute to check).  It will probably take another 3 minutes to trim away the excess foam when we drywall.  So, 5 minutes.

and the “Slow and Sticky”……

Window taped with Tescon Tape

This is the most time consuming.  We start with stuffing the gap with fiberglass insulation (next time, we’ll use mineral wool or Roxul).  Then we place the tape on the window frame We had to be mindful of how this will be finished and be sure to only tape 1/4″ or less of the window frame, so when the drywall goes on, the tape won’t show.  The application takes a long time and the tape being SOOOOO sticky does not help.  However, the strong adhesion is one of the reasons this tape performs so well and provides a long-lasting seal.  Finally, we patch the corners to be sure that there are no holes or wrinkles on the tape.

Cost: Tescon Profil ($6.16), Fiberglass insulation ($1)

Installation Time: 15 minutes

Insulation Time: 5 minutes

Air-Sealing Time: 20 minutes

How do they perform?

Jim and Andy of Elysian Energy did another unofficial blower door test yesterday.  We were especially interested in how each of these windows fared.

Andy starting up the Blower Door

Under negative pressure, with the window installed and sealed with just Tremco trio, I felt a small amount of cold air all around the window with the back of my hand.  The Quick and Foamy and Slow and Sticky both performed well, I did not feel any air-infiltration.

We also used an infrared camera to see if there was a big drop in temperature in the installation gap.  Under the scrutiny of the IR Camera, there was a 4to 5 degrees drop in the installation gap with just Trio.  Quick and Foamy showed about 0.5 degree of difference, while Slow and Sticky had a small fraction of degree drop in temperature.

In conclusion, Slow and Stick is probably the most long-lasting and air-tight detail.  It is also the most time consuming.  Quick and Foamy is not a bad solution, but sprayfoam should not be completely trusted to get into every void you are trying to fill.  Additionally, the longevity of the air-tight seal created by sprayfoam is unknown.

Barcroft and Columbia Pike

A simple fact about real estate is that its value is dramatically impacted by the condition of the immediate area where the property is located.  This is especially true in the case of the Arlington Passivhaus.  This whole journey started with Eric and I driving around in Arlington neighborhoods looking at properties listed for sale.  We came to this  neighborhood to look at another piece of property a block down. We were not familiar with the neighborhood at all except that it “felt like a nice place”.  We decided to drive around every block hoping to learn a little more about the area.  That’s when I chanced to turn my head and saw a small hand-written sign inside of a dusty window of a house stating, “For Sale.”

That “it felt like a nice place” sensation has a lot to do everything in the neighborhood.  We are not from Arlington and will not pretend to be Barcrofters.  We can’t help but appreciate the beauty of the neighborhood.  8th Street is a relatively wide (for Arlington), tree-lined street with cute, distinct and largely well-maintained historical homes.

Our neighbor and award-winning landscape designer Scott’s home has the most amazing masonry walls and of course one of the most elegant gardens I’ve seen.  I don’t think you can get someone to build walls like that anymore.

Scott's Masonry walls

Scott's Front Yard

Scott's Front Entrance

Half a block down sits the Barcroft Community House, which dates back to 1908, a building designated in the National Register of Historical Places.  I love the Gothic windows!  The Community House is currently undergoing restoration.  I can’t wait to see it when the work is complete.

Barcroft Community House

Here’s a map of the Barcroft Neighborhood

Barcroft Map

Columbia Pike is the main drag in the area.  For the last decade exciting developments have been coming down the Pike.  Other than the glitzy new condo/apartment buildings, there are several high-impact developments in progress.

I think the three most exciting developments are

1. Wakefield High School:

S. George Mason Entry

Rendering of the new building from Arlington Public School website

The $91 Million school broke ground last June.  The building is to be completed in 2014 to boast 403,940 gross sqft on four floors, enough to accommodate 1900 students.  The building will be going after LEED Silver.  Although we are are not huge fans of LEED, we like some of the features being included at the school.

  • Solar hot water
  • Rain gardens
  • Low VOC materials for better indoor air quality
  • Using mechanical waste heat to heat the pool
  • Reforestation

For more information on this project, see

2. The New Arlington Mill Community Center

Rendering from

This $24 Million project broke ground last August.  It is expected to be completed early 2013 to feature a 5-story main building (57,000 sqf), an attached Gym (8,700 sqf), a public plaza and two levels of underground parking.

See here for more information:

3. Pike Transit

Future streetcar scenario

Image from

This is a 5 mile modern street car project to connect Pentagon City, Arlington to Bailey’s Cross Road, Fairfax.  This five mile long corridor was slow to develop because it isn’t metro accessible.  With so much development going on on Columbia Pike, the Pike Transit will transform Columbia Pike from a car based growth to a much more sustainable public transportation based one.

I envy the folks who live in Barcroft, with so many positive things going on just a stone’s throw away.

Here is an Emmy nominated video created by the Columbia Pike Documentary Project ( that captures the diverse heritage of the Pike and the changes happening.


Meetup at Arlington Passivhaus/ Passive House Alliance Capital Chapter Meeting

Today we hosted a meetup for the local Passive House Alliance.  We had an awesome turnout.  Around 30 PH consultants, local architects, home owners and folks who are part of this movement.  I am humbled by the passion and the expertise in the house and glad I was able to share something with the group.  Thanks to all who came.  Special thanks to John Semmelhack for conducting an impromptu blower door test.  We were not quite finished with air-sealing the house but we came in at 1 ACH 50.  There’s definitely more work to do but John’s test gave us a clear idea of where we need more work.

John Performing a Blower Door Test

Quick we need more foam!

Today, we’ll write about something lighter and shorter.  We finally got around to insulating the basement some more.

To recap from where we left off several month ago, the basement has 6″ of EPS insulation below the slab, as well as a 20 mil Stago Wrap as a vapor barrier.  See “Building a Bullet Proof Slab” for a review

On the walls, we used a Superiorwall system which included a combination of XPS and EPS foams as insulation.  See “How to Build a Basement in 3.5 Hours”  We also added more EPS to the outside to beef up the R-value and break some thermal bridges, see “Outsulation”

Now that you have thoroughly studied our foundation, we can move on the to next step of adding yet more foam to this house.  I know XPS and EPS aren’t the more sustainable insulation products to use but cut us some slack here.  We are beginners and need to work with something forgiving.

So, the next step is to complete our continuous thermal envelop by laying foam on the basement floor.

Here’s a before picture

Basement Before

As you can see, the StagoWrap is still sticking out of the concrete.

Salvado and his crew from Leon Home Improvement came to help us out today.

XPS in the stud cavities

They cut small pieces of XPS and filled the stud cavities with it, detached the Stago from the walls and laid them flat on the concrete.

Continuous Insulation

Then, they cut a piece of 1″ XPS to fit along a wall and butt it up against the foam in the wall cavities, creating a thin, cleaning caulking joint.

XPS Floor

A few hours later, the floor insulation was done and the continuous insulation was completed.  They moved on to insulating the walls with EPS foam.

Cutting EPS

EPS Foam Insulation

EPS is easy to work with.  Just cut it to size and jam into the space.

Eric and I decided to get our hands dirty too.

Caulking around spray foam

This penetration already had been sprayed around the pipe.  We decided to caulk around the foam joints as suggested by Sam at 475, then tape around the whole thing.

Wire Penetration sealed and taped

MiniSplit Penetration (Before)

MiniSplit Penetration (After)

I think all these steps are truly a “belts and suspenders” way to seal things.  I can see how spray foam might not create an extremely good seal.  When we trimmed back the bulging foam, sometimes we see voids or areas with only a very thin layer of foam.  Additionally, I think another reason is longevity, I am not sure if I trust the foam to hold that penetration for the rest of the building’s useful life.  The caulk adds another insurance policy between the different materials, i.e. foam and OSB or foam and PVC tubing, etc.  The tape is probably the final coverall.  475 folks, I know you are reading this, tell us what you think?

I have to say, I am not sure how I feel about doing a 3 step sealing process for 1 inch holes, there maybe larger gaps between my SIPs or other building members that I can’t even see.  I guess sealing penetrations are probably the low hanging fruit in a way, mainly because you know where the holes are.  Other potential places of air infiltration, say between SIPs or seams may be difficult to find visually.





Don’t Breath That Air, Breath This Air

Today, we revisit one of my favorite topics, Passive House Mechanical Ventilation.

First of all, we need the ventilation to be balanced.  What does that mean?  Simply, the amount of air leaving the home should equal the amount of air entering the home.  Most homes experience unbalanced ventilation, usually this is resulted from removing large amount of indoor air without a good pathway to replace it.  This often occurs in the kitchen.  For the last decade, with the glorification of celebrity chefs and popularity of cooking shows, many people want to cook in a chef’s kitchen (real home cooks usually just have nice reliable equipment). This means home kitchens are equipped with commercial appliances.  One of these must have appliances is a shiny commercial range hood.  The suction power of range hood varies from 100 CFMs to 1600 CFMs.  At some point, these hoods can suck up objects or small animals ( I kinda want to see a cat… :).  The problem is, when you remove so much air from the kitchen, you create a lot of negative pressure that sucks something else into that space.  Providing clean replacement air is the smart thing to do.  When you don’t, that “something else” is most likely something harmful. i.e. combustion gases from water heater, furnace and other gas appliances, fumes from garage, outside air that flows through moldy cracks in your walls, etc.  you get the idea.  Additionally, more air infiltration into the home in many regions also means more moisture which can cause mold issues and at the very least, add to the latent load that the air-conditioner must work harder to remove.  In a tight home, the backdrafting from gas appliances problem can be even worse.  Now that I’ve scared people from breathing.  We know the reasons why ventilation should be balanced.

We move on to mechanical.  It would seem kind of funny that a Passive House is so NOT passive in ventilation.  A certified Passive House has an air-infiltration rate of 0.6 ACH 50 or lower.  The home is so tight that it would be nuts to not mechanically ventilate.  Mainstream home building is following this trend too.  The 2012 IRC mandates that any new home with a blower door test result of less than 5 ACH 50 must have a whole house ventilation system.  Given that 2012 IRC also requires any home built in Zone 3- Zone 8 to be tighter than 3 ACH 50, every new home built in a jurisdiction that adopted 2012 IRC will have to have a whole house mechanical ventilator.  I guess we all need to buy stocks in ERV/HRV companies!  This trend toward tighter homes is really a good thing, gone are the days that builders can tell you, “you don’t want too tight of a house, the house needs to breath.”  The truth is, the house does not need to breath, you do!  So, the age of “build it tight ventilate it right” is finally here.  A tighter home brings all sorts of benefits.  See  Mechanical ventilation is also beneficial in many ways, better indoor air quality, comfort, reduced risks of mold and increased durability of home.

In the Arlington Passivhaus, we are doing our best to tighten up the home to our 0.6 ACh 50 goal as you saw from the post yesterday.  In terms of mechanical ventilation, we are using an Energy Recovery Ventilator, which not only ventilates, it also recovers the temperature or energy from the outgoing treated air and it dehumidifies.

We fired it up for the first time today to balance the intake and exhaust flow rates.  Here are some pictures of Michael Bonsby HVAC folks balancing flow rates throughout the house.

Mauricio measuring with an anemometer

Balometer Air Flow Hood

This is used to measure overall supply and exhaust.

Michael reading the hood

Duct tape balancing

Duct tape is used to temporarily reduce air flow to the correct amount, then a piece of metal is cut to the same size to be inserted and permanently fixed in the duct.

Tighten your home so you don’t need to tighten your belt (as much)

Well, that is not to say you should go and blow it all on stupid stuff.  What we are saying is that you can really save a lot of energy and money if your home has a tighter thermal envelope.

This is why the Energy Efficiency section in newer editions of the International Residential Code (IRC) are gradually getting more stringent.  This made me wonder how tight existing single family homes are.  According to a 1998 study “Air-Tightnedd of U.S. Dwellings” published by the Lawrence Berkeley Laboratory, the average SFH in the U.S. has a 1.72 NL(Normalized Leakage) or 29.7 ACH50 (Air Change per Hour at 50 Pascal).  I won’t bore you with the relationship between the two but basically the ratio is 1:17.5 with a 13% standard deviation.  29.7 ACH50 is quite leaky.  The study also showed that there are a few significant factors that causes some homes to be tighter than others.

Number of Stories: multi-story homes (31.5 ACH50) were about 11% leakiers than single-story homes (28 ACH50) .  This makes sense, more stories means more joints, penetrations to seal and more places for failure.

Floor/Basement Type: homes with crawl spaces and unconditioned basements (30.6 Ach50) are 5% leakier than homes with slab-on-grade or fully conditioned basements (28.7 Ach50).  This means a lot of heat loss occurs through floor leakages and highlights the importance of insulating slabs, foundation walls and air sealing all the critical joints in the foundation.

Age of construction: Homes built prior to 1980 were about twice as leaky as ones built after.  The data also shows that from 1980 t0 1998, there was very little improvement in air-tightness.  This maybe the reason for the increasingly stringent air-tightness standards in recent editions of the IRC.

Duct System: Homes without a duct system (15.75 ACH50) were reported to be leakier than the homes with one (12.25 ACH50). Another interesting result is HVAC duct systems account for just under 30% of the overall air leakages of a home.  This explains the need to build air-tight duct systems in homes.

Retrofits: Homes that undergo energy retrofits on average were 25% tighter than prior to retrofit.  This shows that retrofits do work, but I think 25% is probably too low a number.  If you are gonna do it, you might as well go deep!

This is an old study but it explains why IRC seeks to reduce air-leakages of new constructions.  The 2009 IRC N1102.4 which is just beginning to be enforced in Virginia provides builders with two options: Either to comply with a checklist of visual inspections by an inspector or show a blower door test result of 7ACH50.  Here are two interesting articles analyzing this new code provision.

As Martin Holladay pointed out in his analysis, the code writers made a mistake by not explicitly specifying “who” is to perform this blower door test.  This creates a significant loophole which I hope jurisdictions will close before they adopt them.  In any case, at 7 ACH50, this air-tightness standard is still considered leaky but it will probably force builders to start thinking about the issue.

Fast forward three more years, hopefully by then the already published 2012 edition will start to be adopted.  The 2012 edition eliminates the visual inspection option, instead requires 5 ACH50 in Zone 1 and 2 (really deep south), and requires 3 ACH50 in Zone 3 through 8 (the rest of the U.S.).  This standard will force builders to come up with an air-tightness strategy.   However, this new edition still leaves the “who” in doubt.  It states, “Where required by the building official, testing shall be conducted by an approved third party.”  This is unfortunate, not only does it leave the question of who is to perform the blower door test to individual jurisdictions, if the state code is silent on the issue, it actually leaves it to the “building official”, i.e. the plan reviewer, field inspector, etc. to decide whether to require the test be done by an “approved third party”.  I can see various compliance problems ranging from uneven enforcement to corruption issues.

All this legal analysis aside (I set that aside four years ago…), how does one actually tighten a building envelope?

We are by no means experts in this field (in fact, we are newbies) but we do have expert/supplier friends at Four Seven Five Performance Building Supply and Small Plant Workshop and all the Passive House designers who give us advice.  Here’s what we’ve done so far to try to reach our goal of 0.6 ACH50.  If you have a suggestion, feel free to comment.

SIPs Joints taped with Rapid Cell tape

This is a vapor-open tape sold by 475.  The adhesion is very good but because SIPs edges and corners can get a little rough, it’s very important to clean up the OSB a little bit before applying the tape.

Floor Joints Caulked

Ideally, we would have taped these joints above and below the plate too. But because the joists were already there, taping it would have been very labor intensive.  Here we opted for a good sealing caulk.  The lesson here was to do air-sealing as we build the structure instead of air-sealing after the build.  But then I guess we will need to ensure the work is not exposed to rain.

Basement to SIPs Joint

Here, the the joint between the SIPs and plate, we caulked.  Between the plate the Superiorwall is a larger gap, which we caulked and sprayed foam.  For the larger cavities, we used high expansion foam.

Windows installed with Tremco ExoAir Trio

For the windows and doors, we installed them using Tremco ExoAir Trio (you can get it from Small Plant Workshop).  I think it is a good product for installing windows.  I hope it will eliminate having to come back with a can of Great Stuff to go over the gaps (Only the blower door test/Thermal imaging will give us the answer).  It’s also important to caulk the corners prior to installation as an insurance policy.  I have my reservations about it when it comes to installing doors, especially at the threshold.  Because it is expansion foam, it can potentially push up the threshold if the opening is large, like in a French door, causing the doors to not operate properly.  Additionally, don’t trust it be weather tight as the literature claims.  When we noticed our French door threshold bulging, we pulled the trio out from under the threshold and the Trio was soaking wet.  Basically, we don’t recommend it where water can potentially accumulate.

ERV Pentration Sealed

For the exhaust and supply points of the ERV, first, we made 10″ diameter round holes for the 8″ ducts.  We sleeved the ducts through a Roflex 200 Gasket, using Tesco No.1 tape to tape the connection and taped the gasket to the SIP panel.  Finally, we made sure the duct is positioned in the center of the penetration (not touching the sides), then sprayed foam from the outside.  This is my favorite seal!  I must be a real geek to have one…

Plumbing Penetration Sealed

For all plumbing penetrations, we made sure the penetrations are larger than the pipes, position the pipes in the center of penetration and sealed around them.  We will most likely trim off the foam, caulk and then tape around the pipes to ensure the seal holds over time.

MiniSplit line set sealed

The MiniSplit line set is basically sealed the same way as the plumbing pipes except with the insulated coolant line.  We cut back the black insulation for the portion that is in the wall and sprayed around the line set.

SIPs Chases Filled

This is less of an Air-tightness but more of a insulation issue.  Our SIPs (except for the roof panels) came with electrical and plumbing chases.  These chases cut into the insulation value of the walls.  We weren’t sure at the time we ordered the panels whether we would need to use them.  In the end, we did not use even one of them.  We basically drilled holes along the chases every foot and filled each hole with 2-part foam.  The work is not difficult but unnecessary if we had ordered roof panels for the entire house.  So, we learned our lesson.  Also, don’t believe it if anyone tells you the chases have a negligible impact on the overall performance, we emptied at least 6 tanks of foam into the walls.

Oh, if you survived reading this post, check out our video, it’s a lot more fun


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