A bit about our windows



Turn function of the window

In a Passive House the windows are like an appliance that performs a specific task efficiently. They are an integral part the passive solar function of the house. The windows capture solar energy into the house and then must help the house retain that energy,  i.e. not let all that good heat go right out the window, a one way valve.  We decided on Intus Eforte windows manufactured in Lithuania, http://intuswindows.com/passive-house-window.html

While the windows are not officially certified by the Passive House organization, their performance metrics are comparable to windows that are.

There are 3 main metrics for analyzing window performance.  U-value is a measure of a window's ability to keep heat from escaping the house, lower is better.  It is the inverse of R-value, a metric commonly used with insulation.  SHGC is Solar Heat Gain Coefficient, a measure of the fraction of heat from the sun that makes it into the house.  VT is visual transmittance, a measure of the amount of light from the sun that makes it into the house. 

The eastern and western windows have U-values of 0.088, an SHGC of 0.4 and a VT of 0.58.  The northern and southern facing windows have U-values of 0.105, an SHGC of 0.5 and a VT of 0.74.  Originally, the SHGC of the southern facing windows was going to be higher, but there was concern about too much solar gain in the spring and fall when the sun is lower in the sky. 

Why did we choose Intus?  There are no American-made windows that meet the performance requirements of our Passive House, so we had to look at European manufacturers.  Wood framed windows were too expensive.  That left us with UPVC.  We looked at Intus, Shuco and Unilux.  Since we have no idea which if any of these companies will still be in business in the US 10 years from now, it ultimately came down to cost.  Intus was 25% less expensive than the second place finisher, Shuco.  We ended up paying about $50/SF of glass, but that includes a large slider and two doors.  I was surprised at how affordable these windows were. 

You can see the "tilt" function in the top left window. The windows are nicely shaded in June.

 We're very happy with the windows.  They seem to be really well made.  The windows are a little different that what we are used to in the US.  They are in-swing windows which are popular in Europe.  They have a really cool tilt-turn function that enables you to tilt the window in just a little for ventilation (see top left window in the picture above) or swing the window all the way open like a door.  They seal up very tightly when closed.  We were able to get some really large panes of glass for an uninterrupted visual frame of the trees and beautiful garden I'm still dreaming about.

Our architect Jamie also designed a beautiful curved overhang like the brim of a hat on the south side of the house to provide just the right shading for the first floor windows for the time of year and position of the sun.  We have been at the house during these hot summer days and have seen the upstairs windows perfectly shaded by the roof overhang and the large slider in the dining room perfectly shaded by the hat brim as well.  I  look forward to feeling the sun shining in brightly in the colder months to warm our New England winter bones.

Finishing the wall insulation

The insulators were back last week putting in the final layer of dense pack cellulose between the studs of the inner stud wall.  This completes the EPS/Polyioso sandwich with dense pack cellulose bread.

The video below shows the cellulose being blown between the studs and the cloth batting.  Behind the studs, you can see the aluminum foil cover on the sheets of Polyiso from the middle layer of insulation.

This brings the total wall insulation of our 1' thick double stud walls to R 48.  Is this a lot of insulation?  The framer has commented that we could have insulated standard 4 houses with the amount of insulation in our Passive House and that was before this last layer of dense pack went in.  The CT Energy Efficiency Fund gives rebates for "High Performance Insulation".  Their minimum requirement is R 21.  We have more than double the insulation of what is considered a very well insulated home.  One of the fundamental principles of Passive House is super insulation.  We're definitely meeting that requirement.

The basement walls (where we'll lose less heat) are insulated with 2 inches of Polyiso up against the foundation walls and dense pack cellulose in between 2x6 studs.  These walls have a combined R-value of R 32.  Underneath the basement slab is 5 inches of EPS at R 28.  The slab doesn't meet the foundation walls creating a thermal break that prevents heat from being conducted from the slab to the foundation.

The attic is going to be insulated with loose pack cellulose to R 83.  This should do wonders for keeping the heat from escaping to the roof during the cold months and infiltrating from the roof during hot months.  Again, the CT Energy Efficiency Fund requirement for ceilings is R 40, so again, we have more than twice this amount of insulation.

According to our builder all this extra insulation costs about $10K more than insulation would on a standard house.  We think that the upfront cost will more than pay for itself over the house's life.  In addition the extra insulation will provide a more comfortable place to live.

Walls like a sandwich, Insulation Information

The wall construction of a passive house is one thing that makes it very distinct from a standard building.  Our architect Jamie Wolf told us when Passive House "geeks" get together, their line is "What are your walls?" meaning what are the materials and construction you use in the Passive Houses you build. In my last blog entry, I described the first blower door smoke test to check for air leakage in the outer wall structure. We have come to the next step in wall construction, the insulation.  Jamie describes his walls as a "Sandwich Wall".  Basically, it is a double stud wall with several layers of insulation. Outside to in, an outer stud wall with dense pack cellulose blown in between the wall studs retained by a mesh batting (the bread). 

Dense pack cellulose being blown in between the wall studs

Next is a 4" thick layer of EPS, then a 1" layer of Polyisocyanurate (Meat and cheese).



Three layers out of the four done

Finished off with an interior stud wall with dense pack cellulose blown in between the studs and the interior wall board (bread again).  Insulating and appetizing. Great care is taken to eliminate air leakage and thermal bridging which is heat loss through conduction.

I have been a little remiss about blogging in real time. A lot of progress has been made at the Green Box.  I'll catch up in the next couple of entries.

Currently, the interior stud wall is partially constructed but will not be closed in with wall board until all the electrical, plumbing, ventilation, and heating/cooling lines are finished being installed in all of the interior walls so they can all be closed up together.  In addition, the windows are in, the roof shingles are on, and the screen porch and front porch are in the works.  More details and photos soon to come.



I love our windows

In other news, our green box is an official participant in the CT Zero Energy Challenge for 2012. Check out our entry and the competition at www.ctzeroenergychallenge.com/.We are entered as WolfWorks - Harwinton,CT.