Timeline for Trying to determine safe header span for clear opening on existing remodel
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| Dec 6, 2023 at 20:57 | history | edited | popham | CC BY-SA 4.0 |
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| Dec 6, 2023 at 20:39 | history | edited | popham | CC BY-SA 4.0 |
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| Dec 6, 2023 at 11:52 | comment | added | Jimmy | I was able to find pg = 30.0 psf for my zip | |
| Dec 5, 2023 at 2:44 | comment | added | popham | @Jimmy, I hear "northeast" and my mind says "substantial snow load." In most bigger cities you can find the snow load by searching "[city name] snow load." If you can't figure it out, then name your state and county. | |
| Dec 5, 2023 at 2:08 | comment | added | Jimmy | Yes the carrier beam on floor one, which is 14' 9" terminates next to the chimney masonry by resting on several 2x4's there. Yes the second floor carrier beam is probably about 13'. I'm not sure about snow load. This is in the northeast, so it does snow though its been mild since I've owned the house. | |
| S Dec 3, 2023 at 23:35 | history | edited | Rohit Gupta | CC BY-SA 4.0 |
new photos of house plan
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| S Dec 3, 2023 at 23:35 | history | suggested | Jimmy | CC BY-SA 4.0 |
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| Dec 3, 2023 at 22:34 | comment | added | popham | @Jimmy, the interior ends of the carrier beams from your schematic irritate me a little still. They have different connection details in the neighborhood of that chimney (I assume that black blob is a chimney)? The first floor header is drawn as 14'-9". Is that right? There's no post to shorten its span length to the 12'-0"? Squinting at the second floor header, I convert the 16'-7" to 13'-0" from the exterior wall to the beam span's interior end. Is that about right? And my assumption about zero snow load? Is that right? | |
| Dec 3, 2023 at 22:14 | comment | added | Jimmy | And where the second story load is coming down from the carrier beam, picture two 2x8 sections of blocking next to each other supported by joist hangers on both ends sandwhiched between the joists directly under where that load is. Then as you say, it should in theory be carried by the joists over to the main carrier beam in that room, which sits atop the 1st floor header. | |
| Dec 3, 2023 at 22:08 | review | Suggested edits | |||
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| Dec 3, 2023 at 22:07 | comment | added | Jimmy | @ popham the loads are applied symmetrically, I just poorly drew them. I did find some older schematics of the home and have added them above. The Floor 1 photo is what we have been discussing. And the Floor 2 photo has the "primary bedroom" which is above that area. The framing layout is the same on both floors, and I marked that up a bit in the photos. | |
| Dec 3, 2023 at 18:59 | comment | added | popham | @Jimmy, whoops, I understand that the roof header load comes down to a floor joist and travels from there to the 1st floor carrier beam and exterior walls. Are these loads applied asymmetrically as shown? 4 ft from the 1st floor carrier beam on one side and 6 ft from the 1st floor carrier beam on the other side? | |
| Dec 3, 2023 at 18:47 | comment | added | popham | @Jimmy, from your description I can't confidently compute tributary area and load positions. For the roof, 10psf dead load and 20psf live load should convert these areas to loads (I assume by the flat roof that you have no snow load, correct?). It sounds like the roof framing layout is perfectly analogous to the floor framing layout. If that's the case, then the roof carrier beam's length is missing from your description. Your drawing is asymmetric. Is that correct? As drawn, the 12 ft header acts as a transfer beam for half the load of the 10 ft header applied 2ft from the 12 ft header's end. | |
| Dec 3, 2023 at 18:29 | comment | added | popham | @Jimmy, what I need is the tributary area of roof that loads the header and how that load is geometrically spread on the header. For the 2nd floor, the tributary area was half of the joist lengths ending in the carrier beam (the other half of the joist psf loading goes to the exterior wall) times half of the carrier beam's length (the other half of the carrier beam's pounds per foot loading goes to its end away from the header). Thus the (12ft/2 + 12ft/2)(12ft/2) = (12ft)(6ft) computation in my answer. | |
| Dec 3, 2023 at 16:33 | comment | added | Jimmy | I edited a photo to reflect the true shape of the house. It is two stories, second story has slanted walls. Flat roof. 2,000 sq foot home. | |
| Dec 3, 2023 at 16:28 | comment | added | Jimmy | It might be best to use LVL beams here. Ideally I would have done that to begin with but removing what is there isn't an option since the house is sided and finished outside. But I wonder if I could build a duplicate header like above out of 2 LVL 2x12 equivalents in front of the old one. I think either codes were more lax "back in the day" or this house was just underbuilt but I am really looking to put my mind at ease and avoid any possible strength related failures since this house will be lived in. | |
| Dec 3, 2023 at 16:25 | comment | added | Jimmy | To further clarify, I would exactly duplicate the existing header assembly in front of the old one, extending into the room. And I would underpin every jack contact point beneath the subfloor by installing 2x8 wood sections on top of the foundation wall and sandwhiching them next to the rim joist, which is the only bearing support on this wall as is. I.e., header assembly bears down through jack studs, which sit on bottom plate, which sits on subfloor, which sits on rim joist, which sits on foundation wall top.) | |
| Dec 3, 2023 at 16:22 | comment | added | Jimmy | To clarify a question of yours, the plan would be to leave the existing header, truss, and 2x4 jack stud assembly as is. I would add to this by building a second header, truss, and 2x4 jack stud assembly in front of the other and nailing, lagging, gluing them together. This would be a functional assembly. The foundation beneath is wide enough that I could fit some sections of 2x8 under the floor where the jacks would come down to essentially create a couple of internal/redundant rim joists. This way, when the rim joists press down on the subfloor, there is actual support under them. | |
| Dec 3, 2023 at 16:19 | comment | added | Jimmy | This beam terminates into a 2x12 header on the second story, held with joist hanger. And the ends of this header carry down into the floor joist, which was reinforced creatively with some 2x8 sections and joist hangers. This was done retroactively since the original construction carried this load directly into the subfloor, between the joists! At any rate, the second story load from the roof, while not negligible, doesn't anecdotally seem to be too great. The roof is merely some iso board, epdm rubber, 1/2 ply, and 2x6x12's. | |
| Dec 3, 2023 at 16:16 | comment | added | Jimmy | Thank you for your replies. The geometry of the house is confusing a bit. It is a flat roof, sloping wall, two story home. A Mansard style. The roof load is supported by a carrier beam in the middle of the 2nd story room. The ceiling is 2x6, which carries over to the approximately 15 degree slanted walls. The end of the house, which is above the 12' span in question, used to be a balcony (no overhang) which was replaced with a flush dormer window area. So the 2nd story carrier beam terminates centrally above the 1st floor area in question. | |
| Dec 2, 2023 at 6:44 | comment | added | popham | @Jimmy, 3 plies of structural select grade is also probably an option assuming that additional load from the roof doesn't disrupt things terribly. Just a thought if the 4 plies are too thick. | |
| Dec 2, 2023 at 2:45 | comment | added | popham | @Jimmy it sounds like you plan to sister new plies to the existing header without any bearing support below the new plies. Is this what you mean by underpinning the edge of the house? 2x4 jack studs are inadequate for supporting a header with more than 2 plies. Let me know for sure if there's additional loading from the roof so I can iterate the analysis with the 30 psf sleeping room spec and any additional roof load. | |
| Dec 2, 2023 at 2:38 | comment | added | popham | @Jimmy, the analysis is predicated on no roof load and 40 psf live load instead of the 30 psf that would be appropriate for sleeping rooms. Does any load from the roof rafters find its way through the transfer beam? If so, then the geometry of the roof framing becomes important. Technically the 12'-0" span that I used was incorrect. For 1 jack stud at each end, the span becomes 12'-0"+3/4"+3/4". Treating the 4.01 as 4, then, is inappropriate because I cheated on the length and correcting would push the 4.01 up to something like 4.05 or 4.1. The point is moot because your species isn't Hem-Fir. | |
| Dec 2, 2023 at 1:24 | comment | added | Jimmy | What I would wonder about there is how the truss shape wouldn't actually underpin the edge of the house if it was built in front of the existing truss and header. Although it would underpin the tributary 3 board beam and since it would be supported by the foundation below, the additive support should provide what is needed. Wood grade is pine/douglas fir. When you say "I would not cheat with only 4 plies" I am confused since your math suggests 4 would be adequate. Also, house has a flat rubber roof and roof joists are a mere 2x6x12. The room above this area is indeed a sleeping room. | |
| Dec 2, 2023 at 1:14 | comment | added | Jimmy | I found better photos with the wood exposed. It looks like #2 pine/fir with knots but that are about 1inch. Each side has 2 jack studs at the end of the clear opening and one additional near the king stud (3 total each side). I am wondering since your calculations suggest 4 2x12x16's if I could essentially double what is there in front of it. So essentially add two additional 2x12's with the same number of jack and king studs. This way it would essentially become a 4 ply header. | |
| Nov 24, 2023 at 21:31 | comment | added | popham | @Jimmy, hacking that table for 2 plies like your current configuration, you're right at the transition point between 1 and 2 jack studs. Again, that's predicated on grade and species, however. | |
| Nov 24, 2023 at 18:46 | comment | added | popham | @Jimmy, 20 psf is a roof's live load (for construction guys and construction material during roof installation). Interior commercial parking garages get 40 psf live loads (although I suspect that this is currently changing). Libraries get 100 psf live loads. You get about 10 psf capacity for each ply (assuming grade and species), where your 2 plies get you about 10 psf live load capacity beyond the 10 psf dead load. Deflection is good, however, so it feels fine. It has been fine all this time, so I wouldn't hit the panic alarm. First thing should be searching for grade and species stamp(s). | |
| Nov 24, 2023 at 18:34 | comment | added | popham | @Jimmy, I've used a 40 psf live load. It should be 30 psf if those are sleeping rooms above on the second floor. I've used #2 grade lumber of the common species for different US regions. If it is an exotic species (unlikely) or a better grade (quite possible), then I've underestimated its strength. I've assumed zero roof load, where something like a hip roof wrecks that assumption. I think that 40 psf live load goes way back for strength computations. Your beam slenderness makes it decided by strength instead of deflection, so you get deflection control for free. | |
| Nov 24, 2023 at 16:37 | comment | added | Jimmy | Thank you for this response. I think I will follow up with a local engineer and get his input. To summarize my understanding, it looks like I have enough jack studs but the header may be insufficient per code. A follow up question I have then is understanding the delta between modern code and absolute strength of this header, i.e, is it dangerous? Obviously it has stood the test of time and a builder wouldn't install it like this today in 2023 but is it dangerous and at risk of failure? | |
| Nov 24, 2023 at 11:59 | history | undeleted | popham | ||
| Nov 24, 2023 at 11:59 | history | edited | popham | CC BY-SA 4.0 |
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| Nov 24, 2023 at 11:52 | history | edited | popham | CC BY-SA 4.0 |
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| Nov 24, 2023 at 5:45 | history | deleted | popham | via Vote | |
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| Nov 24, 2023 at 4:49 | history | answered | popham | CC BY-SA 4.0 |