Archive for July, 2011

Foam, lot of foam!


Last week, we successfully set the foundation walls. Two days later, Peed Plumbing came and completed the ground works in 100+ degree weather!  They did an excellent job despite the heat.

Ground Works

On the same day, Universal Foam made the first of their deliveries.  The driver and I unloaded the foam.  This is probably about half of what we will eventually put on the house.

We have three different specifications. 4″ EPS, 2″ EPS and 1″ XPS (The blue/green stuff).

Here is the idea.  We will insulate under the slab with the 4″ and 2″ to achieve a 6″ under-the-slab insulation.  This foam is treated to guard against termites.

With the 6″ slab insulation, we still don’t have a continuous insulation from the walls to the slab because there is no foam underneath the wall panels.  The 1″ XPS will be laid on top of the concrete slab all the way into the cavities of the Superiorwalls to connect with the wall insulation, thus forming a continuous insulation layer.

See this drawing for our insulation details:

Wall Junctions Slab to Ceiling-02

So, there you have it.

We know there are debates going on about insulation choices.  Here’ re our thought as related to this project:

1. Should we use foam at all?

Some people would prefer not to use foam at all because after all, it is still a product of the oil industry.

The alternatives are:

  • Cellulose (R-3.47/in): recycled newspaper, blue jeans
  • Stone wool (R-3.33): rock-based mineral fiber and recycled slag from steel and copper industries
  • Perlite (R-3.04): mined material, essentially expanded glass
  • Strawbale (R-1.45-2.18)

These all are great insulation choices but cellulose is probably a better material for indoors, we don’t want a house covered in newspaper (no one likes wet newspaper). Although, we may consider it as additionally insulation indoors.  Stone wool and perlite are both mined materials that might not necessarily be better for the environment than foam.  Additionally, we are not sure how we can keep it in place on the walls.  Strawbale is a great one too but perhaps when we actually build a strawbale home one day.

There are obviously others but there are few that matches the versatility of the rigid foam boards.  For our project, we need something rigid that can be used in outdoor and underground environments that can withstand moisture without physical deteriorations or drop in R-values.

2. What type of rigid foam?

We decided to use both, although mostly EPS.  XPS typically has a higher R-value than EPS (5.72 v.s. 4.17).  However, studies have shown that in long-term underground applications, XPS has the tendency absorb water and lose R-value.  EPS absorbs some water too but is able to maintain R-value.  This is why we decided to use EPS for all exterior and under-slab applications.  Above the concrete floor, we wanted a rigid foam board to break the thermal bridge along the entire slab edge and preferably one with a high R-value without the thickness to preserve basement floor height.  XPS seems to fit the bill.

From a sustainability perspective, XPS foam is worse for the environment because it uses hydrocarbon-based gas as blowing agents.

Anyone who is more knowledgeable about this, please feel free to comment.

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How to Build a basement in 3.5 hours


Today was a really long day.  I headed out to the site at around 8 and after fighting through traffic, I arrived at 9.  Weaver Precast’s guys were already preparing the site.  I talked to them briefly and waited for the power company to arrive.  For this set, due to the high pressure power lines in the front of the lot, we had to shut off the power to the entire block (14 homes) to safely install the panels with a construction crane.  Needless to say, this resulted in some very unhappy neighbors, especially because today was very hot.  We had given advanced notice to neighbors 3 weeks ago but our initial date got rained out so today was it.

As you see in the video, the technician used the proverbial 10 ft pole (more like 30 ft) to shut off power.  Then the crane started lifting the wall panels into place. We had two truckloads of Superior Wall Xi panels, one by one, they were lifted and set in place.  It took the Weaver guys about three and a half hours to set the entire basement.  So, that’s how you do it!

Now, I must say here that I feel really bad for the neighbors especially because the power company did not come back to restore electricity for about three hours after the work was completed.  People were without power on a 90+ day for about 6 hours.  I thank the ones who were understanding and I can’t blame the ones who had unhappy words with me.

Why did we use Superior Walls?

  1. We used them before with great success
  2. Speed! Can you build a basement in 3.5 hours on site?
  3. Strength.  Built in a controlled environment means consistency in structural strength throughout the entire wall system of 5000+ psi
  4. Very little on-site waste: the only waste on site were three boxes of spent caulk-type adhesive
  5. Pre-insulated: The walls are pre-insulated to R-12.5 with interior XPS in the panels and EPS on the concrete studs
Superior Walls poses a few challenges for us.  This is mainly because we are attempting to achieve the Passive House standard.
  1.  An R-12.5 foundation walls are not insulated enough for us.  We plan to add another 2 inches of EPS on the outside face of the entire foundation and add more inside to hit R-32.
  2. We cannot have the ideal Passivhaus “continuous insulation”, because the wall footers cannot sit on top of foam.
  3. We cannot insulate under the slab to the edges of the SW walls due to the bearing needs of the walls.
  4. The concrete studs are potential thermal bridges.

We figured out some solutions to mitigate some of these issues but they cannot completely be eliminated.  More will be posted as we insulate the basement.

With that said, we still consider Superior Walls to be an excellent wall system for basement walls.

Weaver folks, if you are reading this, feel free to add or comment on why your walls are superior!

Here’s a spec sheet for Superior Walls

SuperiorWalls Xi

Here’s the video of the install today

Passive House Pre-certification Pending


Eric and I decided it was time to actually submit our paperwork for Passive House certification.  So, after a couple of weeks of hard work, we finally organized all the documentation needed for pre-certification and sent it to PHIUS (Passive House Institute U.S.) on Wednesday.  I am sure we will need to make some modifications but hopefully, they won’t be huge.

I then realized we never really discussed what it means to be a certified Passive House.  Here’s what we think it means:

The house needs to meet the three basic but very stringent requirements:

  • Air-Infiltration must be less than 0.6 ACH at 50 Pascal
  • Specific Heat Demand must be less than 1.39 kWh/sqft per year
  • Total Primary Energy Demand must be less than 11.1 kWh/sqft per year

What do those numbers mean?

Maximum Air Infiltration at 0.6 ACH at 50 Pascal:

This means air-tight construction.  You should not see daylight between your door panel and the frame, no air leakages around the windows, no random holes in walls, very few and well sealed wall and roof penetrations. If you think about it, this requirement really means high quality construction and components in addition to paying very close attention to detail.  The way this is tested is using a blower door, which inflates the home to 50 Pascals (Pascal is a unit measure for force 1Pa=1Newton/square meter), and measures the amount of air leakage. 0.6 ACH indicates that air changes per hour due to that air leakage.

Maximum Specific Heat Demand at 1.39 kWh/sqft per year: 

This means figuring out the heat loss from every components of the the thermal envelope (walls, roof, slab, windows, doors), adding any other heat loss from heat recovery ventilation, you have the Total Heat Loss figure for the entire house.  You then add up the heat gains from the sun, home appliances, people breathing out hot air, cooking, baking etc., anything that generates heat without purposely generating heat to warm up the house, you have your Total Heat Gains.  Total Heat Loss-Total Heat Gains=Specific Heat Demand.  Specific Heat Demand is the amount of energy required to actively keep the house warm.  In our case, our house is projected to have a Specific Heat Demand of 1.06kWh/Sqft.  To heat the entire house, we will need 12,609 btu/hr.  A standard hair dryer needs about 6,398 btu/hr.  We can heat the entire house with just 2 hair dryers.

Maximum Primary Energy Demand at 11.1 kWh/Sqft per year:

Primary energy refers to the total energy usage including heating, cooling, water heating, household appliances and transmission losses as the electricity travels from the power plant to the house.  This number really means the amount of energy that needs to be generated to meet the energy demand of the house.  How do you achieve this number? First the heating and cooling loads need to be minimized by building an air-tight and super-insulated thermal envelope.  Second, the heating and cooling equipment must be sized correctly to the minimized demands of a passive house.  Third, the home must be lit with energy efficient bulbs and fixtures.  So, as much as possible LEDs and CFLs are used.  Finally, use energy efficient appliances.  Whenever possible, choose from the most efficient of Energy Star certified appliances.  The Arlington Passive House is projected to consume 5.7 kWh/Sqft/yr in primary energy demand.

Passive House designers cannot dictate how the homeowner will use electricity in their house.  However, the numbers projected are based on average usage data in the United States.  There are a number of different software and hardware monitoring systems available, some of which will allow the homeowner to “fine-tune” the way they live the same way people adopt to driving a Prius more efficiently.

Beyond Passive House:

Theoretically, if the house meets all three requirements, it is a Passive House.  This means great flexibility in design, material selections, building methods, etc.  Even how you meet these requirements is something that you have the ability to decide.  i.e., if you do not like the greenhouse potential of XPS foams, you can use EPS.  If you want to completely stay away from petr0 materials, you can use cellulose.  Or if your insulation of choice is pink fiberglass batts, you can do that too, it just needs to be thick enough.

Interior finishes are designer driven as well too. You can choose to use exotic woods for flooring or you can use bamboo, cork.  You can buy your dimensional lumber from a sustainable source or you can just get the cheapest you can find from your local lumberyard.

A performance based standard like this really allows for various levels of entry.  One passive house may be built as part of a low income house project and another may be built as a speculative home for several million dollars.  Both homes will be constructed to a high construction quality and energy performance.

Globalization of windows and doors (Mostly Europeanized)


Just got an email from our windows and doors supplier, the manufacturing have completed and they will ship next week.  Where are they shipping from?  Lithuania.  People don’t usually think of Lithuania as the destination for windows and doors but I think our friends at Intus Windows have put it on the map.

Windows manufacturing have globalized just like automobiles, computers and everything else.  The parts are sourced all over the world and assembled in a plant somewhere and shipped to an end user somewhere else.

In our case, the profiles (frames) are made in Germany by Innoutic, which is now part of Deceuninck, a Belgium company. They are the world’s leader in UPVC (Unplasticized PVC) window construction.  Our glazings (glass) are made by  Guardian in the United States.  They are the maker of most glazing you see on large commercial buildings.  The spacers are made by SGG Swisspacers, a Swiss company.  In my opinion, they make the best window spacers.  Well, there you have it, a tour of America and Europe and now, they are being loaded on a ship to come back to America.

For a more technical discussion on super-efficient windows and doors, see: http://www.finehomebuilding.com/how-to/articles/understanding-energy-efficient-windows.aspx

Passivhaus Envelope and HVAC


If you talk to any Passivhaus designer, invariably, he/she will tell you that there are two crucial components that makes a house a Passivhaus.

1. Envelope

In order to drastically reduce active heating and cooling of a house, the envelope is the first thing that needs to be optimized. A houses envelope includes walls, roof, foundation walls, slab, windows and doors. Generally speaking, passive house walls will have much higher insulative value than a code home. According to IECC, a new home in Arlington, Virginia needs to have R-16 walls, R-38 roof and the window U value of 0.49 or less. Our home is designed to have an R-42 wall, R- 50 roof and window U value of 0.11.  This tells you that a passivhaus is insulated about twice as much as a conventional home.  The numbers will change depending on the climate, in some very temperate regions, passivhaus performance does not require a significant departure from code requirements.

Another aspect of Passivhaus is the air-tightness of the home. Passivhaus requires an air-infiltration rate of 0.6 ACH at 50 Pascals or less.  This makes the house extremely air-tight. This requirement is both a quantitative and a qualitative one. Such air-tightness means no drafts and minimal radon infiltration.  This level of air-tightness is also an important indicator of building quality (it’s difficult to build that air-tight without paying extreme attention to every detail).

What do we achieve by building such a robust envelope? We minimized heat loss. By reducing heat loss to next to nothing, the temperature inside of the home responds very slowly to exterior conditions.  This means on a hot day, the interior heats up very slowly and on a cold day, interior temperature drops very slowly.  This also means drastically reduced need to actively heat or cool the home.

Here are some pictures of what our envelope will look like.

thermal envelope

2. HVAC

The typical HVAC system is designed to deal with heating and cooling needs first.  This is necessary in a conventional home largely because it does not have a robust enough thermal envelope. When approaching a home, the HVAC designer frequently assumes the house is not well insulated and not built tight. Without further data to properly engineer the HVAC system,  the engineer “over-engineer” the heating and cooling loads to avoid insufficient heating or cooling, this leads to unnecessary over-sizing of equipment.  This sounds too much like guessing to us.

Additionally, in conventional HVAC design, ventilation is even less precise.  The reason is the builder “intentionally” built the house not air-tight to allow the house to breath.  This “breathing” is done through the various cracks, gaps, holes, etc. in the house’s envelope, as I wrote in a previous post, breathing though your skin.  Others in the Passivhaus movement have called this”breathing through your underwear.”

The Passivhause HVAC design approach is completely different.  First, we assume the envelope is air-tight.  Then we figure out the ventilation strategy. An adequate ventilation strategy is very important in providing the highest indoor air quality especially in homes so tight. A dedicated Energy Recovery Ventilator (ERV) is typically utilized to continuously remove stale air and bring in fresh air.  Additionally, as the two streams of air are exchanged, temperatures are transferred from the outgoing to the incoming, eliminating the need to completely reheat or recool the replacement air.

Even with the robust thermal envelope and ERV, on the hottest and the coldest days, a little active heating and cooling are still necessary in many regions of the U.S.  Designers have come up with many different solutions to satisfy these needs.  In our design, a point source 1.5 ton reversible Mitsubishi MiniSplit (15000 Btu/h) is used to meet the heating and cooling needs.  Our HVAC guy (Mike Bonsby of Michael Bonsby HVAC) told us that in a conventional home of the same size, a system that delivers 150,000 Btu/h would be necessary to heat the house.  Our modeling indicates to us that when built, the active heating load will only be 10% of the equivalent conventional home.

Mike and us also devised a simple strategy to eliminate the potential for temperature stratification when bedroom doors are close.  We will install transfer fans to blow air between different rooms and floors.  Link to transfer fans:http://www.tjernlund.com/Tjernlund_Aireshare_Lit_8500730.pdf

Here’s what our HVAC design look like

A-241

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