Staircase to loft
EDIT: Link in comments to show loft plan as described in my question.
I have been talking to Grok about this but thought I would also see what real human feedback I might be able to get.
We’re building a 16×24 studio cabin. Single slant shed roof, 3:12 pitch.
There will be a loft in one corner of the high roof side. Loft is supported by 8×8 beams stretched across the whole 16 ft width of the cabin, positioned at each end of the loft.
loft width will be in in range of 7-9’. 4×8 rafters (essentially loft floor joists) are attached to the beams.
Loft plans currently call for ladder. We want a staircase.
There is enough space for a staircase to run along the 24’ long high side wall and meet up at the edge of the loft with one of the 8×8 loft beams.
(we will integrate storage into stairway. IRC 2018 Appendix Q for tiny houses applies to staircase design.)
Current plans call for the 4×8 rafters to be notched into the beam so that each rafter end sits in a 3.75d x 3.5w notch. Considered a timber frame technique I believe.
Grok is calculating a lot and saying the notches are too big- they decrease the strength of the beam and even more so if we want to also attach a staircase to the beam.
But Grok suggests if we use Simpson hangers for the 4×8 rafter connection to 8×8 beam, instead of notches, then the beam is strong enough to also support the staircase.
Generally speaking – do you agree with Grok that we should NOT attach stairs to a notched beam but that we COULD attach stairs to the loft beam via ledger if we use hangers for the rafters instead of notches?
I understand the official answer could be to consult a structural engineer but wondering outside of that what experiential feedback I might be able to get from people here.
Thank you!
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Note that Grok is not a licensed engineer in any of the 50 states as far as I know, and I imagine the Canadian authorities would also frown on having "Grok" as your project engineer...
Can you provide a drawing of what you're planning here? There might be a prescriptive way to do it that doesn't need to be engineered.
Bill
Yes I understand. Using Grok for a start on a time efficient way to pull some ideas and information together.
I do think there’s a prescriptive way to do this. Will be working on a sketch. Will update later with picture.
There's a sketch on the website at the link below. That is if you are building it according to those plans.
Yep, using these plans as a starting point but increasing size, changing some windows and creating our own amended sketchup plan.
Loft constructed as shown here. We are increasing cabin size slightly. We want to attach a staircase to the loft beam.
https://www.elevatedspaces.ca/products/redwood-cabin-plans
Looks like there are a couple of metal tube steel hangers that are also supporting the loft from the roof framing.
Yes the metal is not necessary.
This guy said he did it just for extra insurance and because it looked cool.
We’re not using the metal brace.
So, the notch would be in the top of the 8x8 and would be 3.75"Dx3.5"Wx7.25L? Yeah, notching a beam on top or bottom like that significantly reduces the capacity of the beam. I don't think that would be a good idea if you want to span 16' and use this as a beam to support your joists. You'd be reducing the beam by about half it's original depth so it would act more like(5) 2x4s sandwiched together than an 8x8.
What about structural screws? You could place your 4x8 and 8x8 at the same level perpendicular to each other, drill some holes about halfway though the 8x8 in order to countersink the screws and then run the screws into your 4x8s. Depending on the size of the screws would determine now many you need so you'd have to figure that out. Then you could use wooden dowls to fill the holes and give you the timber frame look avoiding the joist hangers? Or, you could just use wood dowels for that matter but you'd need to read about how many you need to support the structure.
Section 507 of the IRC might be of help here? https://codes.iccsafe.org/content/IRC2021P2/chapter-5-floors#IRC2021P2_Pt03_Ch05_SecR507
Thank you, will review again once I can get back on my computer.
Thank you. The 4x8s as in the plan are designed to be cut somewhat at an angle to fit into the notch reducing the 8” portion by half where the rafter sits into the beam’s notch.
The plan as is, according to the designer who himself also built this design…is designed to irc code, including CA code. But does not account for a staircase.
Loft construction plan as shown here. We’re increasing cabin size slightly and want to attach staircase to loft beam.
https://www.elevatedspaces.ca/products/redwood-cabin-plans
I'm going to bow out of this one since I'm not a structural engineer but if it were me, I'd be adding a column under the 8x8 beam and incorporate it into the storage under the stairs. Just looking at the code this doesn't appear to meet code but I don't design structures like this every day but maybe someone here can provide more insight.
Well, if someone else has already built it adding a staircase adjacent to the high wall likely won't cause any issues since you'd only be supporting the additional dead weight of a fraction of the staircase. You could attach one stringer to the wall and use the studs in that wall to carry a portion of the weight. Also, if you incorporate a column or wall that goes under the beam into the storage under the stairs, that would more than compensate for the added weight of the stairs. A 4x4 or 8x8 column would probably match the look.
The strength of a beam is based on the height of the beam raised to the third power so if the beam is notched it reduces the capacity exponentially. σ = My/I; I=(w*h^3)/12
Yes this all makes sense. I appreciate the input.
Several people have built a version this plan and shared pictures. We’re the first ones I am seeing who want to add stairs rather than ladder…
We will be building the version of the plan with a small bathroom framed under part of the loft so the loft would end up having a cantilevered look over the framed in bathroom.
Seems like wall studs for bathroom underneath loft would also ultimately help distribute loft weight distribution.
We’ll keep consulting and researching…..
A drawing would help immensely. I know it's clear to you but your description is hard to follow. At least mark up a photo to show what you want.
I believe you're talking about notching the beam that goes from eave wall to ridge wall. That beam is very likely already undersized. I certainly wouldn't notch into it and I see no reason to do so.
(I'm not a licensed structural engineer but I have a degree in it and have done most of my own engineering for 20+ years.)