Archive for the ‘Lessons Learned’ Category

Monitoring and power outage

We’ve been monitoring the temperature and humidity in the Arlington Passivhaus for about a week now.  As part of a long stretch of heat wave a storm hit (they haven’t come up with a name yet, but let’s just call it the Big One for now), along with the PH, more than 1.5 million homes in VA/MD/DC area lost power, some areas are still recovering from a multi-day outage without air-conditioning.  This actually provided us with an unique opportunity to monitor and report what happens in this situation.

Let’s start with monitoring.

Here are a few constants:

MiniSplit setting: cool 67 F

ERV: Low (approximately 75 CFM)

Transfer Fans: ON


A note on humidity: we noticed the indoor humidity has been consistently high (60s), since we’ve been monitoring.  We attribute this largely to the moisture still in the building materials, especially that giant basement slab and seasonal factors.  However, we also noticed the relative humidity level has about a 7% swings if several windows or doors are open and it is humid outside.  This let us to consult the Bethesda Passive House team (David and Brandon JR.) since they probably experienced something similar.  The advice they gave us was to turn the ERV down while the house is “drying out”.  Because while the ERV dehuminifies the air that comes into the home, it does not take all the moisture out, so in effect, operating an ERV makes the humidity problem worse.  See for more explanation on this.  By turning down the ERV, we’ve been able to consistently drop the relative humidity levels a few percentage points a day from high 60% to mid-50%.  It still likes to go back up on very humid days though…

Temperature Results:

On a Normal Summer Day

We don’t have a large enough data set yet but we can report our observations so far.

We’ve observed the following on a typical summer day (June 27, 2012 Outdoor Temp: 62-89F, Humidity: 23-40%)

At 12 pm when the outdoor temp was 88 F, the indoor temps were: 68F/70F/70F (Basement/1st Floor/2nd Floor)

At 3pm when the outdoor temp was 94 F, the indoor temps were: 68F/70F/72F (Basement/1st Floor/ 2nd Floor)

Two Degree Temperature Differences Between Floors

This experience was consistent with other days with similar levels of humidity and temperature.  The temperature differences are typically about 2 degrees.  Heat rises up so, the 2nd floor usually is the warmest.

Effects of Solar Screens

We have motorized solar screens on the 1st floor south-facing windows.  This picture was taken around noon time and it is illustrative of the need to shade first floor south-facing glazings, the sun hits directly on it, while the 3ft roof overhang protects the 2nd floor windows from the sun.  By the way, shading needs to be on the outside of the windows, or they just become radiant heaters!

Solar Screens

One day, we wanted to see the effects of not shading, the result is that initially, the 1st floor becomes warmer than 2nd floor, then a few hours later, both 1st floor and 2nd floor are 2 degrees warmer than they would normally be.  This makes sense because the lack of shading makes the 1st floor 2 degrees warmer, then as heat rises, the 2nd floor eventually gets 2 degrees warmer too.  The basement is most consistent, the lack of shading on the 1st floor has no noticeable effect on the basement temperature. However, not shading creates a temperature difference of 3-4 degrees between basement and 1st floor.

On an Extra Hot and Humid Day (Outdoor Temp 71-103 F, Humidity: 50-66%)

At 12 pm when the outdoor temp was 95 F, the indoor temps were: 68F/70F/72F (Basement/1st Floor/2nd Floor)

At 3pm when the outdoor temp was 103 F, the indoor temps were: 70F/75F/77F (Basement/1st Floor/ 2nd Floor)

As you see, at 95 F, the indoor temperatures are still able to keep a nice two degree temperature difference between floors.  However, when it hit above 100F, temperature differences widen between basement and first floor to 5 degrees.  However, the difference between first and second maintains 2 degrees.  Also keep in mind, conditions are never perfect.  On this day, we had workers opening and leaving doors open all day long bringing in large amounts of hot and humid air.

Solar screen close-up

3ft Overhang

After the Storm

The storm devastated Northern Virginia, Mayland and D.C.  Here’s a picture of what we are seeing around town.

Crews restoring power

After the storm, the heat wave continued to rage on.  We were curious how Arlington Passivhaus performs in a heat wave with no active cooling.  Here’s what we observed on  after 40 hours of power loss on another scorcher day:

While the outdoor temperature was 92 degrees, the basement was a comfortable 73 degrees.  First floor was a warm but not unpleasant 81 degrees.  Second floor was 79 degrees.

This tells me two things:

Insulation Really Works

First, all the insulation in the walls and roof is effectively isolating the indoor environment from the outdoor elements, slowing down the effects of extreme outdoor temperature changes, i.e. after 40 hours of power loss, the first floor only warmed up by 6 degrees (75F -81F) and second floor by 2 degrees (77F-79F).

Shading is Crucial

I think the 6 degree increase in temperature on the first floor can also be attributed partially to the lack of shading on the French door on the middle of the wall (see first picture above), which explains why the second floor only increased by 2 degrees.

We still have no power…

We anxiously await the power to return.  This would be an opportunity to monitor how quickly a system like this recovers to desired indoor temperature and relative humidity level.

Hopefully, the next time we post, there will be power and interesting observations to report.



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.

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


Lesson 2: How to turn ashes to gold

Previously posted on our FB Page:

I couldn’t believe it when I received the county real estate assessment notice a couple of weeks ago.  A miracle had occurred!

As some of you know, we donated the house to the ARL Co. fire department for a controlled burn exercise.  Now, the house before the burn was definitely uninhabitable.  I think back then, you could potentially argue that the parts, if taken apart and sold for scraps, may be worth $48,700 (Assessed value 2010).

The FD burned it in October 2010 and therefore, turned it into a heap of burned remains of a house.  I actually think it should have a negative value due to the various potential liabilities this heap now represents.  The RE assessment department turn my ashes to gold!  The assessment for the improvement (house) actually came out to be $52,200.  That is a $3500 increase. Amazing!

Lesson 1. Donating a House

We purchased the property in the summer of 2010.  This is what it looked like:

There was really no way of saving it.  This house sat on a charming, pristine, tree-lined street in Arlington.  We thought this is a great property to redevelop.  There was no question about tearing it down.  One of our friends heard that you could donate tear-down homes to the fire department for training exercises.  We thought, “great! if we are going to get rid of it, we might as well do something useful in the process.”  We called the Arlington FD to donate it.  They were very happy to get a house to train in.

The FD told me they will probably not burn the house due to the closeness of the houses in Arlington.  It was about one week before the actual exercise, they told me that they plan to burn the house, but “just a small portion of it”.  I thought maybe they can just burn a small portion of the attic or something.  I asked two questions: 1. Do you have permits to burn?  2. Do I need to contact the neighbors?  They told me a permit was pulled and they will contact the neighbors.

At the appointed time I showed up as a spectator and of course as the homeowner.  The street was blocked off and the entire neighborhood was out.  I spoke with several neighbors and found out that they had just been notified of the burning 16 hours before!  I was quite shocked by this.  One of the neighbors asked me if I got the TV crew to come.  I asked, “what TV crew?”  There was a camera crew which I thought were just part of the FD filming it for training purposes on site getting ready to film. I spoke with the FD and was told that they were a national network news team filming the burning as part of their October fire safety month program.  I was a little disturbed that no one in the FD let me know about this or asked my permission to film but I kept quiet.  I do believe in fire safety and was hoping the program will benefit from this.

Here’s the footage of the burning that I filmed:

When it was all done. I asked the FD if I needed to do anything to secure the house.  They told me they will take care of it.  I waited around to see what they do to secure it.  When I saw a truck pull up with a bunch of OSB boards, I felt good that they were going to board up the place and left.

The very next day, this was posted on a local blog:  I commented that I had no knowledge that CBS was filming the burn and it wasn’t burned “for TV”.  Then I heard that the neighborhood got together and petitioned that the FD never burn in Barcroft again.

With some much negative ramifications that resulted from this.  We decided that we needed to move our demolition permit ahead of schedule.  Truth be told, after the burning, the boarded house was more secure than the state that it was in pre-burning with most windows broken (the house was in this state for years).  However, we knew neighbors probably didn’t want to live next to a burn-out house, we decided to make a separate demolition permit application ahead of our building permit application.  At the time we were about three months away from finishing up with the design.  The demolition permit still took about 2 months to get.  We removed the house as quickly as we could.  We also had to excavate out the old basement foundation, which left a large hole on the lot.  We did neglect to fence off the lot for a few weeks.  However, as soon as one of the neighbors voiced his concern, we installed a fence to secure the lot.

During all this time, we completed out designs and submitted our building permit application for plan review.  The process took another 2 months.

Lessons learned:

1. Donating a house is fine but make sure they agree to NOT burn it

2. Always be sure to secure the site

3. Talk to neighbors

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