I am working on a 1980’s chalet in upstate NY. It is a two story, single gable home (second story is a loft which spans half the house)and measures roughly 25×35. The homeowner would like to put a 55″ window on an exterior wall, on the first floor, about a foot away from the corner of the house. After laying out the window and demoing Sheetrock and insulation I found metal strapping running from the top corner of the wall at 45degrees down to the rim joist. The wall has a wafer board (?) sheathing on the studs and t-111 on top of that. Above is a loft with floor joists running perpendicular to the wall in question. A header will carry that load but I am concerned with the horizontal force the rafter may exert on the exterior wall after strapping is removed. The rafters run parallel to the wall we will be putting the window in and they rest on the floor above not the top plate of the exterior wall. Can I remove the strapping and rely on the t-111 for lateral stability or do I need to add additional support? There are no rafter ties but their is an intermediate beam (4×10) between the ridge and the seat cut of the rafter with about 7′ of rafter on each side. What can I do to eliminate the strap and still have adequate support against horizontal thrusting of the rafters under snow load,etc?
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Not sure I fully understand what is where here. But I'll start w/ a comment. The steel strap is for shear resistance in the wall ... i.e. preventing the wall from racking along its length. It has nothing to do with e.g. vertical loading or horizontal loading perpendicular to the wall. Maybe the strapping was used because of the T1-11. Is the T1-11 8 inch or 4? I think there may be a structural difference.
You may well be able to reconfigure your shear structure to accomodate your window. The window may not meet shear wall code. You might consider having a chat w/ the local BO about this. By all rights, this should be structurally 'right'. Prescriptive structural code says you have to have 24 inch to 48 inch walls at the corner ... but there are a number of alternatives, so that is by no means the last or only word.
Food for thought to start it off, here.
The strap is shear bracing, to keep the wall from racking. Not generally needed if the wall is sheathed with rigid sheet goods, though whether the fiberboard sheathing is "rigid" is always subject to question.
In terms of actual safety, many homes (including ours) were built without such straps (or rigid sheathing), and most are amazingly still standing.