How to install windows

Are you just planning to build just using Passive House targets and performance standards or are you going for certification through a Passive House institution? A Passive House designer will be the one to determine the overall design and how many windows can be accommodated and still meet the performance criteria. This page will be helpful I think – 

All you need to know about Passive House certification

But to address your question about windows – there is an overall performance target that needs to be met for any Passive House building, so the more windows you have in your design, the more you will need to beef up the insulation levels of other parts of the home. You mention using ‘high performance’ windows, but that they aren’t triple pane. In any cold climate, a window that isn’t triple pane just does not fall into the category of ‘high performance’, and it would be a smart upgrade in any home but particularly a  Passive House, read  here about windows to make your best selection, triple pane is very much worth the added cost– 

How to choose the best windows for High Performance Homes  

As an example of how the total window surface area and quality of windows affects design, here is an example -  a Passive House we know of that has significant glazing required 24 inches of sub-slab insulation to make up for the loss through windows in order to achieve certification. There is simply no place on this globe outside of besides the North Pole where 24 inches of rigid insulation makes any sense. It is a bit of a glitch in the Passive House system regrettably, where the underlying goal - to reduce climate change causing emissions from buildings - goes right out the window in search of certification. You would be better at that point to forgo certification and reduce the insulation levels since there are more emissions from manufacturing that amount of insulation than it will ever save in the lifespan of a home. So... limit your window use if possible, and try to upgrade to triples! 

There is a lot to consider when you want to install a bigger window, because you will need to lengthen the header. If you’re unfamiliar with the term, it is the support beam across the tops of windows and doors that supports the load and protects doors and windows from being damaged by pressure from above. Think of it a bit like a bridge that transfers the weight to either side of the window opening. And worth noting - replacing windows just to 'save money' or energy doesn't always make financial sense, read more here - 

When to replace windows and when to repair them

In order to be able to carry the load and transfer it to the support members on either side, it needs to be sized correctly for the span to ensure it doesn’t sag. For example, you may currently have a  2x6 header (which would be either doubled or perhaps tripled) that might need to be replaced with a 2x8 header, depending on how much greater the span will be. So there is a bit of engineering that may need to be done depending on just how much you are increasing the span, and that would depend largely on your local snow load.

As you can see from the diagram below, the header (#2 and triple in this case) is resting on what is called the jack post, which is secured to the king post. To enlarge the opening, you will need to remove enough wall section to replace those studs along with the header. Note - this image includes a double bottom plate (#4), which is rather unsual and probably not necessary.

If it is a double-walled building envelope, make sure that you know which of the walls is the supporting wall, but you should see that by the location of the existing header. Sometimes a double wall system will have a 2x6 supporting wall with an additional 2x4 interior wall simply for the purpose of adding additional insulation. Below is a photo of a double wall system that may or may not look like yours, but in this example you can see that the exterior wall carries the load and holds the window, the interior wall is not load bearing, it is for insulation, and wiring is done in this wall as well so as not to compromise the air barrier. 

About the windows, I’m not sure I understand your question about the double and triple pane. If it were me replacing windows, I would certainly purchase triple-pane for efficiency as well as comfort, but you do not need more than one window per opening if that is your question. Just get really good ones. Windows will always be the weakest point in a building envelope, that’s just part of life, and good reason to buy higher quality.

And lastly, I’m not familiar with where SE Wi is off the top of my head, but google is telling that’s Wisconsin, is that right? If so, we don’t know builders in that region, sorry. 

Here are some pages that may also be of use to you, good luck with your renos!