Sunday, July 8, 2012

Operation Fenestration

Bay-Side push-out casement window

Friday we received delivery of our windows and, except for a few exceptions, we're almost all installed. Keep in mind this house is used mostly in the winter - and all the heat for the house comes entirely from a wood stove. As such - it's very important  to capture as much passive solar heating as we can during the winter months. So window detailing and layout was something we spent a lot of time and energy on during the house design. After a lot of testing and back-and-forths, we ended up going with Marvin Clad Ultimate Casement windows for the majority of the house. There are a couple awnings for special spots and some fixed triangles for the gable ends - but mostly its big 5'x5' double units punched through our thick walls. 

Since we are trying to gain as much heat as possible, the plan and orientation of the house are driven to a large degree by this solar access. We placed the private bedrooms and entry spaces to the north side of the house, allowing us to open up and add lots of glass to the main living room and kitchen space to the south. The south wall is almost entirely glass and should bring in lots and lots of daylight and heat during the winter months. 

Looking South towards the living room with the lake to the right

The install went very smooth, and I'm very impressed by the Marvin units. They are regular flange-mounted units with Doug-Fir interiors and Aluminum Clad exteriors. The hardware and exterior cladding seem real durable which is a real serious consideration given the harsh climate up here. There is a whole lot to say about why we decided to go with domestic windows instead of importing some true Passive-House certified units. But instead - I'll simply say we've gone the imported fancy-window route in the past, and the combo of schedule, cost and logistics weighed very heavily on purchasing locally this time around. 

John and Jason installing one of the big ones

But - even though these are traditional window units, the install was still complicated by our super-thick walls and our concerns about long-term durability in a tough climate. One thing we really wanted was to be able to mount the windows in the center of the wall assembly. This way we eliminate any super deep window sills on one side or the other. They are still gonna be deep (around 6") - but at least there aren't any 14" deep sills anywhere. 

Additionally - there are real thermal benefits to mounting windows as close to the center of a wall assembly as possible, though I won't go into all that business now. 
Typical window installation details
In addition, by mounting in the center of the wall, we definitely decrease the likelihood that any water will seep its way in - increasing durability (so long as we deal with the deep exterior sills well). We also liked the aesthetics of thick walls with window 'punches' which is created by the set-back glass. 

An inset window from the exterior. The Solitex wraps in under the window flanges as a first level of flashing.  We'll then add insulation and tape to the frame for a second layer.  

So to do this we lined all our window openings with plywood first, then mounted 2x nailers around the center of the window opening. Just compensate for the added thickness when building the rough-openings and thats that. 

Below you can see the finished mounted window on the left, and the prep'd window opening on the right. The plywood also serves to help tie the walls together really well and increase our stability. Its certainly not the simplest detail and not nearly as easy as just mounting the windows to the outside, but I really like how protected and covered the windows now are. 

South-East corner looking toward the bay
regular 2x sill, 3/4" OSB ties the two walls together, then 2x nailers
All this extra wood will get covered by rigid foam insulation and then taped (a topic for another post). We'll then build Doug-Fir extension jambs for everything to finish it off. 

Typical Window Sill detail. Foam insulation over the extra framing. 
The windows on this house are very high-performing units and we selected glazing types to match the specific orientations. The west side units (sort of North-West really) and the north are all 3/4" double-glazed LoE II 272, argon filled. These have a U of 0.3 and and SHGC of 0.29. But on the south, we wanted to allow lots of solar heat to come into the space - so we opted to go with Marvin's triple glazed 1" LoE 180 Argon filled units. These have a better U value (0.25) and a better SHGC (0.39) - but they are a bit more expensive so we only used them where we knew they would have the biggest impact on the overall heating of the space. 

Marvin Double-Glazed unit.
I'll be sure to post more about these window details as we move into the air-sealing phase. But for now, its just nice the be able to keep the rain on the right side of the wall.

South End view - almost done framing the gable-end