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I'm adding an 8' opening to an existing 2x4 wall originally built almost 30 years ago. The wall is definitely load bearing as it currently supports the ends of 30' trusses on 24" centers. I live in central Indiana, and it appears we're in a 20psf snow load zone, and, according to my local inspector, not in an earthquake zone (though I'm not that far from the New Madrid fault line).

Based on this table: Header span table from Southernpine.com Source: SouthernPine.com 5-page PDF with all tables

I believe I can safely use any of the following:

  • 2 @ 2x12 at #1 grade
  • 3 @ 2x10 at #2 grade
  • 1 @ 3-1/2 x 9-1/4" Gluelam/LVL

Am I reading this table correctly?

For my clear span 8' opening, I'd add an extra 6" so it can be supported on doubled 2x4 jack studs at each end. Also, this table accounts for a 24" overhang, but I'll only have a 12" overhang at each end to match the existing structure.

Note: There will not be a garage door covering this opening. This will be an interior opening into a new space that's being built. The ridge line of the new space will be perpendicular to the existing ridge line and will be stick framed (no trusses). The new ridge board will sit directly on an existing truss, so there should be minimal additional load being supported across this opening.

This is a shot from the drawing for the new addition only, showing the existing garage roof, but not the garage trusses or wall. The existing wall sits on the 16' green line added in, and the 8' opening will be centered along the green line.

(Drawing notes:
It shows trusses, but we'll be stick framing instead.
The existing roof plane extends past the new ridge, but in reality, they will meet.
Ignore the "floating" bottom plate - there was going to be block, but we decided against it - I lengthened the studs but didn't move the bottom plate.)

Drawing of existing roof line and addition.

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  • If the existing roof trusses/rafters are the same direction as the new ones, the load bearing should not be as much. The load is more on the sides. Using the header size you marked should be enough, but overkill only hurts the pocketbook.
    – crip659
    Commented Jun 19, 2023 at 23:49
  • @crip659 the existing trusses are perpendicular to the ones in the drawing. The ridge board in the drawing will be parallel to and sit directly on top of one of the existing trusses. I agree that overkill will only hurt the pocketbook, but I'm also looking at the clearance height/headroom and would prefer to maximize that. Of course, M-m-m-max Headroom is of no value if the roof collapses...
    – FreeMan
    Commented Jun 20, 2023 at 11:39
  • That seems reasonable as far as reading the table goes. I guess my question is whether or not you need any additional support for the existing garage roof, for the part of the new roof that extends onto it.
    – Huesmann
    Commented Jun 20, 2023 at 12:14
  • Good point, @Huesmann. While the existing trusses aren't specifically built for storage, we've slowly piled more and more stuff up there. Maybe this is a good excuse to clean the crap out - "can't support the stuff and the new roof"!
    – FreeMan
    Commented Jun 20, 2023 at 12:17
  • @FreeMan if you haven't had the trusses analyzed, it may be worth reinforcing them just for some peace of mind.
    – Huesmann
    Commented Jun 20, 2023 at 12:20

2 Answers 2

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In my home state an engineer’s stamp is required on the plan for the roofing rafters. If that’s true in Indiana asking that engineer may be helpful no matter what answer you get here.

If your preference is to maximize headroom then choose the LVL. They’re also good at not unexpectedly twisting and sagging.

I’m not dissatisfied with having 12” at the ends to resolve the load and the centerline shear in the beam, but what are the jack studs standing on? If you don’t know, find out.

It’s not enough to carry the load across the span. The job isn’t done until the load has been transferred into the soil at a pressure that won’t sink.

If the point load at the bottom of the jack studs will be carried on a thin floor slab it will be a very unpleasant surprise when they punch through the slab. If the slab rests on a 4’ poured concrete frost wall over a footing with rebar it strikes me as unlikely to fracture where I am, but since I don’t know anything about your local soils that’s another reason to ask a local engineer.

The description of the addition is stick framing but the rafter plan is showing a truss. Either spring for the sticks or don’t. A DIY truss is usually the worst choice

Add some fire stops/horizontal studs so that the first 2 or 3 studs of the new addition work together instead of twisting to shed load. My guess is that that first stud needs to be doubled.

I suggest you plan how the power and any plumbing pass through the joining plane. Right now the outside wall is the only option, but that doesn’t work for water

I’m not comfortable with a plan that sets the roof rafters down on a thin wall header without having a wall stud under each rafter. It’s just a problem with the drawing right now, but if that’s what gets built it will be disappointingly weak when it snows.

I’m not sure short shallow eves work well enough for the style shown to be satisfying. The siding gets more wind driven rain and there’s nowhere to put gutters so everything that comes off the roof drops 4” from the siding and splatters so the sill plate is constantly being wetted and it rots. Even modified for gutters and assuming the gutters work perfectly there will still be a lot of wind driven rain hitting the siding starting 4’ down from the gutters. If you’re planning to live there for more than 5 years you could be the one who has to pay to lift the building to fix it. At least flash the lowest 24 inches between the sheathing and the studs and sill plate to block the water and limit the repairs required to the sheathing and siding.

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  • The studs under the header are on the original outside wall of the existing garage and sit directly over the footer - all the weight will be transferred to a ~36" footer. There is a "drawing note" at the end that reads It shows trusses, but we'll be stick framing instead - the plan changed between drawing and implementation. That change included rafters @ 16"OC, directly over studs in the wall below. When originally planning trusses, I was expecting 24"OC as they are on the garage itself.
    – FreeMan
    Commented Feb 22 at 13:15
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I only know how California & Florida does it, as that is Earthquake & Dane County Hurricane Codes. That said the idiots (along with Gates) have been currently engineering the weather since 1947, but weather is at extremes last few years, US & world Wide.Fracking is making some areas (are rich in oil reserves in shale) now earthquake zones... thus are creating structural issues - never were before seen in certain areas.

So, the Best is 4x12" (vs 2- 2x12") with Simpson ties, King Header 2x4" and hurricane straps at Eves & header. Also sheathing is nailed or screwed 12" at periphery and 6" in the field for earthquake stability.

If you have an average of 20lbs/sf of snow load, that is not the Range! The range maybe 50,10,10,10... that is 20lbs/sf. You can go back in an add the structural ties as a retrofit.

We have seen this in Eastern NC in last 6-7 yrs, hurricanes, flooding (more frequent) and earthquakes (rare). We took the siding off a 160 yo house, and besides putting R19 and Painting the insides with BoraCare, we have used 3/4" sheathing plywood w/ Aluminium Coated Polyiso which we foil taped, to stop AIR leaks not just moisture. It was a few extra dollars to strap and side the house this way. A small investment ($500-600) to a $22,000 siding job; and 10-15K mold/termite & insulation job. Wish we would have thought of this before we reroofed the house 2 yrs earlier.

We could not get contractors in the area to do it; so we did it ourselves.

Foundation is next, (bad beams). and encapsulation. Air & moisture barrier upgrades are not really hard or much more time consuming then the initial investment.

We plan to die here, so to us this is investment in our future; not just the current state of affairs.

Watch "The Dimming" on geoengineeringwatch.org

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  • Whether I agree with the political statements or not, this answer would be far better without all the politics. It might also be readable.
    – FreeMan
    Commented Nov 30, 2023 at 12:58

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