Technical spec sheet for International Passive House Days – Nov 7, 2014

Nearly finished... Installing the Lunos E2

Installing the Lunos E2

This house is a high performance, low cost, masonry retrofit. The design approach is to “gut” as little as possible, minimize the waste produced, and to use low VOC, natural non-petrochemical products.

Air tightness
Pro clima Solitex Mento 1000, DA, and Intello membranes & Tescon tapes

Exterior walls (front & back)
Redstone PURA, a mineral-based capillary-open board, 4”, R16.25

Cellar ceiling
Roxul Comfortbatt mineral wool, 7.25”, R30

Roxul Comfortbatt mineral wool, 9.5”-25.5”, R30-90

Rieder windows and doors
Douglas Fir Frame, Oiled Finish – 3 layer wood construction
triple glazing, R 10, SHGC-Value 51%, 30db

Lamilux FE skylight & exit hatch
triple glazing, R 9.5, 30% SHGC, visual transmittance 0.60
upstand of 7.9″ (200mm) insulated with 2-3/8″ (60mm) PU foam (0.023 W/mK)

Garden apartment
Mitsubishi DMXZ2B20NA 20,000 BTU heat pump (outdoor)
MSZGE06NA & MFZ-KA09 mini splits (indoor)

Upper duplex
Mitsubishi DMXZ2B20NA 20,000 BTU heat pump (outdoor).
Mitsubishi MSZGE12000 minisplit & SEZKD09 ducted (indoor)

Lunos e2 “through wall” (3 pairs, one per floor)
Ventilation rates: 10/15/20 CFM or 9/18/22CFM
Heat recovery efficiency of 90.6%, humidity recovery: 20-30%
Lunos e-go “through wall” (3rd floor bathroom)
Ventilation rates: 3-12 CFM in heat recovery mode, up to 27 CFM in exhaust mode
Heat recovery efficiency of 85%, humidity recovery: 20%

Hot water
2 GE GeoSpring Hybrid heat pump hot water heaters GEH50DEEDSR (1 per apartment)
50 gallons, estimated yearly electricity use: 1830 kWh per year, energy factor (hybrid mode):2.4

Technical Open House

Windows into the site

Windows into the design process

It’s been a very long time since the last post but we have not been idle. In fact, we have come quite a long way and many of our goals have been or are being met. Between work on the house and our day jobs, there has been little time to post here. However, we are at the stage now where we would like to invite our readers to have a look for themselves. The technical open house is a chance to see the mechanicals and air sealing before the walls get closed up.

Here are some highlights:

  • Wall insulation: Redstone PURA, a mineral-based capillary-open board
  • Roof and cellar insulation: Roxul mineral wool
  • Air sealing: pro clima Intello & DA, pro clima tapes
  • Ventilation: Lunos ego and e2 “through wall” ventilation system
  • Windows: Rieder unpainted Douglas fir frames treated with larch oil, triple pane
  • Skylights: Lumilux FE
  • HVAC: Mitsubishi mini splits/ducted
  • Hot water heater: GE Geospring heat pump

Please join homeowners and designers, Bettina Johae and Daniel Herskowitz on Sunday, June 15 from 12 – 3pm. Harald Hefel of Amnova/Hefel Masonry will be present to answer questions about Redstone PURA mineral board. Send us an email if you would like to attend.



Keeping warm

The three pigs and their building materials

The three pigs and their building materials

When I was a child I read about the three pigs that built their homes – each from a different material. The hero was the pig who favored bricks as his home could withstand the wolf’s best attempts at demolition. While the moral may hold from a structural point of view, the opposite is true when it comes to thermal resistance. In fact, it is the straw-house pig that is sitting pretty from this point of view.

“R-value” is how thermal resistance is measured. It is the ratio of the temperature difference across a material under uniform conditions. It’s shorthand for understanding insulation worthiness of any given material. R-value per inch, allows one to compare apples to apples. In many circumstances, such as when internally insulating a townhouse in New York City, space is precious. A weaker insulator means building a thicker wall and that could mean less living space. As you can see from the chart below, common materials differ markedly in their ability to insulate.

r value chart

Thermal resistance of common materials

We took a hole saw to our front and back walls to take a look inside.  As I mentioned in an earlier post, these walls – the external walls – are crucial to the insulation.

Cross section of our front exterior wall made with a hole saw

Cross section of our front exterior wall made with a hole saw

Our existing front wall is a sandwich of (from exterior to interior):

4” brownstone + 11” brick + 2 1/8” air + 3/8” wood lath + 1” plaster

When we add the R values of these materials together we get a total of about 5.5 R.  The rear wall is similar with a little less air and, of course, no brownstone cladding. 5.5 R is not a great insulation value by contemporary standards. But as we shall see in future posts, raising the thermal resistance in an old masonry house is not such an easy task.

A couple of weeks ago we brought together three experts to help us brainstorm on approaches towards a budget retrofit: Thomas Brouillette, a (green) general contractor, Julie Torres Moskovitz of Fabrica718, a passive house architect, and David White of Right Environments, an energy efficiency consultant. It was a productive meeting though we did not come to a final conclusion regarding our approach. David White modeled two possible insulation scenarios: the near passive house approach and the minimalist approach.


Brainstorming about low budget green solutions in the backyard

In the first example, we insulate the house to R13 in the cellar, R6 windows, R16 walls, and R31 roof.  With this scenario, we would be able to use a ductless heat pump to heat the house. The end result is to get the total yearly energy consumption to about 8000 kWh per year and that is more or less what solar panels on our roof could provide. So that seems like a good target.


Near “passive house” approach

The second, and somewhat cheaper approach would be the same except to keep the walls as they are at R5.5 insulation. That brings our energy consumption to about 10,600 kWh. Much more than what it would need to get to “net zero” but not bad compared to the current energy inefficiency of the house. The main drawback of this approach is that it would not be possible to heat a house like this with a ductless heat pump – which is cheap to install and very efficient. Instead we would have to keep the existing steam system (very inefficient) or upgrade to hot water radiant heating (efficient but not cheap to install).

Minimalist approach

Minimalist approach

Both models count on tightening the leakiness of the house to 2 air exchanges per hour at 50 Pascal pressure or 2 ACH50 (that’s far short of the Passive House standard for retrofits – 1 ACH50 but nevertheless a hard bar to reach) . In a previous blog I talked about the airtightness envelop. The air tightness, in practice, is measured by a blower door test and the result of this test is your air exchange value (the number of air exchanges per hour that happen at a given pressure). At this same meeting, David White did a blower door test on our house and results were astoundingly bad (around 20 ACH50). So we have a long way to go in this respect and I will be writing more about this in the future posts.

Windows – keeping heat in, keeping heat out

We knew from the start that we would need to replace the windows. They are universally fogged through and many have cracks in them – which reduces their efficiency tremendously. Although, they are double-pane with aluminum frames they likely were never very air tight. But overall the poor state of the windows represent an opportunity; since they need to be replaced anyway we can explore the relative cost and efficiency benefits of high performance versus run of the mill replacement windows.


An example window from the south parlor floor.

There are many kinds of windows on the market and choosing replacements is not so straightforward. On our house glazing composes 22% of the front and back surface area (for the moment I am excluding glazed doors). The air tightness and insulation value of the windows will have a significant effect on the thermal envelope of the entire house.


Glazing area to exterior wall surface area ratio

Another ratio that is often used to understand the possible energy benefits or pitfalls of windows is south facing glazing/total square footage of livable space. The reason this ratio is interesting is because in certain cases a high ratio of southern glazing can contribute significantly to cold weather heating, decreasing overall energy expenditure. The flip side of this is that a high ratio of southern glazing can cause summer overheating – and increase energy expenditure in order to cool the house. It turns out that 6% south glazing is a pretty good ratio for a cold or moderate climate.


South facing glazing area to total floor area ratio

High performance windows are designed to have either a high or low solar gain coefficient. A high solar gain coefficient means that a high percentage of solar radiation in the form of heat can be transmitted through the window. Alternatively a low solar gain means you can get all the light without the heat. In an ideal world we would have super smart windows with a high solar gain in the winter and low gain in the summer. But that doesn’t exist of course so instead we will choose moderately high solar gain in combination with some sort of summer shading. Shading is a great and much under-appreciated technology. We will use deciduous trees and, maybe, awnings. Both of these will allow open window air flows to passively cool the house while blocking summer solar radiation.

The leaves of deciduous trees provide shade in the summer and in the winter–when the leaves are shed–solar radiation (and therefore heat) can pass through.


The “smart” shading technology of deciduous trees

We have such a tree in front of our south façade (luckily). Obviously, a tree like this takes years to grow. It’s a good argument for being proactive in planting deciduous street trees throughout the city.

Summer pic from google maps showing off our tree shading technology

Awnings take advantage of the difference between the angle of the sun in summer and winter. In New York, the sun is at 73 degrees at summer solstice, when the sun is most intense, and 26 degrees at winter solstice. The projection of the awning should be great enough to block high angle solar mid-summer radiation allow low angle mid winter sun in.


Awnings projections and the summer/winter sun

We have to address the question of what kind of awning is aesthetically appropriate for the building later. Here is an inspiration photo I found of a masonry townhouse with new awnings.

inspiration shutters

Awning inspiration – a little cheesy though – still exploring better solutions.

The other key metric of high performance windows is their u-value. U-value measures the level to which the windows are able to keep the heat (in winter) or the coolness (in summer) inside. The lower the u-value the better insulated the window is. In general we are trying to get the lowest u-value window that we can afford. But as always there are trade offs. At some point the cost of the window may be higher than the energy savings for any foreseeable time horizon. And even if it does pay off in the long run, maybe that extra money would be better spent on “active” technologies such as solar panels. I don’t have the answer to these questions yet. But I have been playing with some window modeling software and came up with some very broad figures.


High performance window savings over time

For the baseline, I modeled average aluminum frame double-pane windows. Vinyl-framed decent high quality windows (blue line) had about $1,400 savings over 20 years. The super high performance triple-pane windows (orange line) had about $5,040 savings over 20 years. Now we have to spec out the prices for these windows and find out if the total incremental cost of superior windows is less than the savings. These numbers are preliminary because the software could not model exactly for our house and our proposed thermal envelope. I am hoping the cost savings will be even higher when we get some more precise modeling. But if you want to try this on your own you can download the software for free at

Inside the “envelope”

The “envelope” is the continuous air barrier that is formed by the shell of your house: the external walls, the doors and windows, the slab or cellar ceiling, and the roof. Green builders in cold or moderate climates consider the building envelope the first and most important “passive” strategy of an energy-conserving house.


The tighter the envelope (the less air leaks) the more control you have over the atmosphere of the house and the less you are forced to use active systems to heat or cool the house. The graph below shows how much homes can differ from one another in terms of tightness.

envelope chart2

Almost everyone agrees a tighter home is better from the standpoint of comfort and energy efficiency, but exactly how tight a home needs to be is more controversial. Making a house super tight, especially a retrofit, takes a lot of money and resources. After you have filled up all the easy air leaks, it gets harder and harder to find the really small leaks. So there are diminishing returns on your efforts. Some engineers say that it’s better to make just a fairly decently tight house and spend the saved money on an “active” systems like solar panels on the roof – which at certain point might more than make up for the lost energy through air leakage.

To complicate matters more, when the envelope reaches a certain level of tightness, you need to supply some sort of mechanical ventilation to provide airflow. In a leaky old house mechanical ventilation is not needed because the tremendous amount of airflow through cracks and porous walls. The great thing about a mechanical ventilation system is that they can include a heat recovery system. This is a mechanism that absorbs heat or coolness from the air before expelling it and then applies it to the incoming air. They can be a very efficient way of allowing your house to “breath” without paying the price of lost energy. Mechanical ventilation is, however, an “active” system, and it consumes some energy just to operate – so this needs to be brought into the equation as well.  For more on this read Martin Holladay’s analysis and critique. 


Our house has a fairly simple envelope. It is a cuboid shape without any jutting appendages or cutouts – which would make the envelope less efficient and harder to seal. Two walls are party walls – that’s the massive advantage of the townhouse. These walls still need to be part of the envelope, but on our very modest budget we will opt to do the minimum amount of work on them. They are covered in plaster and plaster, if it has an un-cracked surface, is an air barrier. There will need to be a lot of detail work of sealing and caulking along these walls but no demolition or construction. As you can see the from the diagram, the cellar ceiling will form the lower barrier of the envelop and we will exclude the cellar itself. The roof forms the upper boundary of the envelope. If we opt for a new roof it will make this part of the job easier. The front and back walls form the really hard part of the equation. Partly because they could end up being the most expensive area to seal and partly because there are some nice architectural details on the internal walls that we want to keep.  In future posts you will hear more about how we will deal with each of these surfaces and the tough trade-offs that we will have to make.

The darkness and the light

We decided to have a little get together in the garden to kick off the renovation last Sunday. We thought this would be a good time to show everyone what we are up to and at the same time “crowdsource” some solutions to our design and technical problems. Unfortunately, the house had other plans. We came in on Saturday morning to do some minor demo and found that the power was off. It did not seem to be a fuse problem. Slightly more disturbing was the fact that after a week of rain the cellar was pretty damp. We had never seen it before like this. There was no standing puddles but there were plenty of spots on the floor that were wet to the touch. Ground floor above the cellar also smelled musty and damp. We called Con Ed and by the end of the afternoon they were in our cellar cursing at the state of our medieval electrical system. It’s not unusual for technicians and inspectors to gasp when the see it for the first time. The electrical wiring consists of years and years of amateur ad hoc patches on top of the original 1920’s cloth insulated cables. Bettina kept the Con Ed guys entertained with jokes and questions. Eventually they fixed the problem by laying a new
“gap” cable between the (internal) meter and the panel. The old one had shorted because of the rain water.

Our "medieval" electrical meter and panel before the storm.

Our “medieval” electrical meter and panel before the storm.

The next day the sun was out. We aired out the house and began cleaning up. By 3 o’clock we changed just in time for our first guest to arrive. Bettina and I gave some mini tours of the house and chatted with our neighbor’s contractor in between serving lemon thyme infused prosecco. The party was a hit. Our guests were charmed by the house. It was a terrific pick up for us!

Mingle in the backyard.

Mingle in the backyard.

Charming friends.

Charming friends & neighbors

Meet the house!

Since this is the first posting, I think it’s only fair that we give an overview of the house we are working with. We closed on the the house last Tuesday and last weekend was the first time we had the house to ourselves. We were really excited about being able explore and brainstorm without someone looking over our shoulders!


The house is situated on a modest block of 3-story townhouses in the Stuyvesant Heights section of Bed Stuy. It has a footprint of roughly 19.5′ x 43′. It has a brick structure with brownstone cladding on the facade. The house has fairly high ceilings on the parlor floor (10.5′) and on the second floor (10′)


There are a few nice details on the inside but there are also many parts that appear to have been more recently modifications.


And of course the wonderful rear garden with lots of potential.


There are plenty of problem spots in the house that show areas where the house was not properly maintained or where there was water damage at some time in the past and these may indicate larger structural problems.


Here is what we know about the inner workings:

Mechanicals: Gas boiler with steam heating. Boiler has not been maintained and may not have much life left in it.

Electrical: Electrical panel circa 1920’s. Ad hoc, amateur patches throughout the house.

Plumbing: Original brass pipes with amateur repairs.

Structure: Several joists have termite damage and need sistering. Supporting beam held up by temporary posts.