Framing a window in a larsen truss wall

[Daox]

My summer distractions have been taken care of and/or pushed aside as we're approach fall. I'll be working on the office again soon and one of the next steps is putting up my larsen truss type wall and framing the two new windows in it. However, I haven't really seen any drawings or pictures that really show how to do this. Does anyone have any references or pictures or whatever that could help out?

[Daox]

Of course, now I find it. Builditsolar has some info on it. I don't remember that being there. I've looked at that page multiple times. Anyway, it is here:

Larsen Truss -- Superinsulated wall design

[S-F]

That's one approach. If you truss to the inside as opposed to the outside it's much easier. Put the window in like normal. Make the rough opening on the inside offset to the outside by 30 degrees and bevel those studs at the same angle. Then connect the studs with some cheap wood. This allows a greater viewing angle in a deep window return.

[SimpleManLance]

I love the idea of doing Larsen trusses on the inside. i would love to buy a fix-er-upper house and stip it down to the studs and build it back up using this design.

Does anyone have any info on how he sets up his natural ventilation? I read the info on the link.

[S-F]

All he does is use Panasonic bath fans with Aldes Airlet vents in the rooms. Nothing too complicated there. And it's still not "natural" ventilation. It's mechanical because it's driven by motorized negative pressure. It's cheaper than a HRV to install but there is no tempering of the incoming air. At the level of superinsulation that these natural builders are taking houses it matters little.

[SimpleManLance]

Originally Posted by S-F

All he does is use Panasonic bath fans with Aldes Airlet vents in the rooms. Nothing too complicated there. And it's still not "natural" ventilation. It's mechanical because it's driven by motorized negative pressure. It's cheaper than a HRV to install but there is no tempering of the incoming air. At the level of superinsulation that these natural builders are taking houses it matters little.

where is he getting the makeup air?

[S-F]

The Panasonic vents operate on a 24 hour timer. They turn on from time to time and depressurize the house. The Aldes Airlets open under negative pressure and allow outside air in.

[MN Renovator]

Originally Posted by S-F

All he does is use Panasonic bath fans with Aldes Airlet vents in the rooms. Nothing too complicated there. And it's still not "natural" ventilation. It's mechanical because it's driven by motorized negative pressure. It's cheaper than a HRV to install but there is no tempering of the incoming air. At the level of superinsulation that these natural builders are taking houses it matters little.

Using inverter drive bath fans and passive air inlets is exactly what my energy auditor suggested that I do for ventilation. In the summer I strongly disagree with him in my climate because it would suck outdoor into my walls and condense in the walls due to the pressure pulling extra infiltration through the areas that were missed during retrofit, but I'd be okay with this idea in the winter. In the summer, pluming outdoor air into the return and using a damper to open it on a controlled interval while the air conditioner is running would both pull in cool fresh air and pressurize the house. You wouldn't want to pull more than the exact quantity of ventilation needed to have the right amount of fresh air in the house when temperatures are extreme though.

I do like the Panasonic WhisperGreen fans though, selectable CFM values and it adjusts fan speed against pressure changes to maintain the same CFM.

[Ryland]

Attention to detail is the most important thing when framing! when you have a 2x6 wall the variation in wall thickness are minimal, but as soon as you start building a truss wall your variations in wall thickness can be quite great and that might not seem like a big deal until you have 20 windows in your house and are down to trimming them out and trim isn't fitting because the window is square and the opening isn't, or the outside of the wall is out of plumb but the inside wall is plumb.
Traditional trim is designed to cover up flaws but we have moved away from the layered trim that can cover up 3/8" variations, but if you want to use modern cheap trim you need to make sure that the trim you are using is going to be used within it's capabilities.
I mention this because when I was building straw bail houses we ended up coping every piece of trim to fit, a window that should have taken 15 minutes to trim out took 3 hours and that house only had 12 windows or so, but that is fewer then normal but that was a full work week of just installing trim.

[S-F]

Damn! A week? I'd throw in the towel. There are a couple ways to finish a really deep window return. I think Robert Riversong just uses sheetrock and a wooden stool with an apron. I also don't think he angles the sides of the return like I suggested earlier. Makes some sense since the inner wall on his houses are the load bearing ones. When building to the inside your interior wall is just there to hold up sheetrock and keep cellulose in place so you can make the openings as large as you want. I recently was working on a gut retrofit where they made a new wall on the inside to create a 12" cavity which we filled with cellulose. They didn't use a truss technique. They just built a new wall with top plates, bottom plates and all. The code demands that you have a lateral fire block every 10' so sheetrock was screwed in every now and then between the new and old studs. The window returns were framed with luon or something like that and then covered with some nice oak. Honestly I don't think that in a retrofit situation where you are building a new wall on the inside that you need to tie into the existing studs too much. In a Larsen truss wall you need to tie both walls together so the outside doesn't sag. I've never done a real Larsen truss DER but I hear it's a PITA. Gut renovating from the inside makes all of that sort of thing meaningless. You just toss up a new wall which is anchored to the floor and ceiling joists and fill it with cellulose. Then you stay warm, cool and healthy. Man I wish I had the time and money to gut renovate my house.