Is blocking needed for 8ft load bearing walls?
When using 4×8 sheathing (vertically-oriented) on an 8ft load bearing wall (see attached diagram of what I’m thinking), is any blocking needed or worthwhile? There will be blocking mid-way down the top joists.
I actually plan to have the joists run across the shorter dimension and be attached to the walls with hurricane ties, I’m just showing it this way for discussion as I think this has more shear implications with regards to the sheathing attachment point (i.e. the sheathing not attaching at the very edge).
I’d prefer if there could be a rim joist and then attach the sheathing to that; however, I wouldn’t want to sacrifice 0.75 inch of support of the joists on the tops of the walls and am not sure about blocking the ends of the joists unless toe nailing them (if that would be a good idea).
The siding will be LP SmartSide Series 38 – the shear ratings for it are in the 5/16 row in Table 1 on page 5 of https://lpcorp.com/resources/product-literature/code-reports-certificates/apa-pr-n124
As an additional detail is this will be attached to a treehouse platform that has some sway to it and of course wind exposure, but is in the least seismic zone. There could be a dozen adults on top of it actively moving around.
Also, would the answer potentially change for any other walls? One will have a 32×80 door and 24×36 window and also be 9′ 8″, one will be 11′ long and have nothing except studs 16″ on center, and one will be 11′ long and have two 36×48 windows next to each other in the middle separated by two studs.
Any advice / critiques in general would be appreciated.
Replies
The situation you describe is pretty complex and lacking all kinds of information needed to evaluate your solution. For starters, we need wind and snow load details in addition to the seismic category you provided. Even with that, it’s not enough - the extra stuff you want to attach to this is atypical. Your best course of action is to consult an engineer who can provide some direction on attachment of the treehouse platform you mention. That said, I’ll take a stab at commenting on your drawn wall/floor.
It’s unclear where you’re suggesting the blocking go, but you need lateral support for the joists, which a rim joist typically handles, to prevent them from rolling over. Alternatively, you can block between the ends of the joists/over the bearing wall or partition. Blocking height is minimum 2/3 of the joist depth.
As for bearing, wood joists and beams require just 1-1/2 inches of bearing on wood, which is your situation. I don’t think you’re going to gain anything leaving out the rim joist. People build 2x4 walls with joists and rim joists all the time without any problem. Some other comments/questions:
Cripples should be on your stud layout. Don’t need cripples at ends of rough sills unless that happens to be your stud layout.
Why triple kings at the ends of the wall?
What’s your ground snow load? Answer could mean you need additional jack studs if in an area with high snow loads.
Thanks user-6774315 - here are more details.
Effectively no snow load - annual average is 0.1 days of snow per year but even then in the worst case I've heard of in the past 50+ years it wouldn't exceed 1,100 lbs across the treehouse roof, 2,200 lbs across the whole platform which would be far less than the expected deck occupant load.
The reason for no rim joists is to allow the 1-1/2 inches of joist resting on the walls and also for the sheathing to continue up on all sides. Or are you saying the rim joist plus 0.75" of joists would meet the 1-1/2 requirement? I'm leaning towards blocking near the ends as you mentioned instead and will use full height blocking.
I don't think any cripples are needed on this layout since the header takes up the full height, no? Just the jacks under the rough sill. I put ones at the ends of the sills for ease of nailing purposes (gives an option to nail the sill down into those and attach those laterally). Triple kings on the ends is just for window location reasons rather than having a tiny gap between two studs, not because its needed structurally.
The challenge with wind load is that technically we're in a zone that is rated up to 200mph due to the possibility of tornados; however, we are in a subset of that area that I think because of hills has had maybe only one in decades if even that. My expectation is that if a tornado did hit it'd be toast anyways, and people won't be in it during high winds. Especially of interest is periodic strong gusts. Is the correct way to approach it to look at the cross sectional area and run that through a wind force calculator at the wind speeds I think are rarely possible and see if that exceeds the sheer ratings per foot?
Any thoughts on blocking in any of the walls themselves being needed or not?
Thanks
The reason for no rim joists is to allow the 1-1/2 inches of joist resting on the walls and also for the sheathing to continue up on all sides. Or are you saying the rim joist plus 0.75" of joists would meet the 1-1/2 requirement? I'm leaning towards blocking near the ends as you mentioned instead and will use full height blocking.”
Assuming these are 2x4 walls, the top plates will be 3.5 inches wide. Even with a rim joist (1.5 in. thick), your joists will have 2 in. of bearing. The rim should plane with the wall studs so you can sheathe continuously over both.
“I don't think any cripples are needed on this layout since the header takes up the full height, no? Just the jacks under the rough sill.”
I was using the terminology you used in your drawing. Crips, as you called them, is short for cripples. Cripple is the term typically used for any unusual vertical framing member in the stud layout. Could be above or below a window, or an entire wall (as in a cripple wall - a short wall with short studs). Jacks serve a specific purpose - to support the ends of headers over openings.
“The challenge with wind load is that technically we're in a zone that is rated up to 200mph due to the possibility of tornados; however, we are in a subset of that area that I think because of hills has had maybe only one in decades if even that. My expectation is that if a tornado did hit it'd be toast anyways, and people won't be in it during high winds. Especially of interest is periodic strong gusts. Is the correct way to approach it to look at the cross sectional area and run that through a wind force calculator at the wind speeds I think are rarely possible and see if that exceeds the sheer ratings per foot?”
If the wind speeds in your area are that high, then the IRC likely requires an engineered design. The prescriptive provisions of the code (in other words, the design solutions provided in the model building code) do not apply to areas with very high wind gusts.
“Any thoughts on blocking in any of the walls themselves being needed or not?”
I’m still not clear what you mean by blocking or where it would go, as there isn’t much space on this wall for blocking. But you would want to block behind any edges in your sheathing. You could switch from 4x8 to 4x9 or 4x10 sheathing to ensure the panel edges are supported without the need for blocking.
Thanks user-6774315 - yeah total mental short circuit on the joist overlap. I think your replies clear up all my remaining questions - I have far less knowledge / experience so this has been helpful.
Thanks for all your help thus far Matt. I got the final draft of all the walls together and posted it to https://www.finehomebuilding.com/forum/12x10-treehouse-any-issues-with-the-final-draft-of-these-framing-plans if you had any additional feedback that would be helpful.
I think you would be better off looking at the whole structure, tree, floor, walls, roof, and railings.
I would make the short walls extend to the outside edge of the framing and plan to install them first. the long ends can be made in two parts each, and raised in between the shorter ends. Second top plate will hold them together.
the spacing of the studs should consider the sheathing, so you catch the edges properly. you do seem to have a few extras in the mix. extra weight is not a great idea except where it is needed.
If you plan to install actual operating windows and doors, the structure will need to be very stiff.
blocking would be a good idea, as would sheathing the inside of these walls as well.
It might be better if you can move one or both windows from the shorter end walls to the adjacent longer walls. Smaller windows will be better from a stiffness point of view.
If the deck is already in place, you might want to review the structure, and get an evaluation of the tree and other support for the ability of them to handle the extra weight you will install. If this deck flexes as well as moving in the wind, it will further challenge the rest of your structure.
There are folks who build a lot of tree houses, it would probably be a good idea to find them and ask for specific advice.
Thanks unclemike42. Good thought on the interior sheathing - yes windows and doors are planned.
Why do you recommend making the long walls in two parts - to keep them less unwieldy when raising or some other reason?
Since it's attached to two trees, I do expect some deck flex, though it's 2x12 joists as the base platform with two sets of blocking and rim joists and 5/4 deck boards so is quite stiff; however, to keep the trees from ripping it apart in wind, one end is a sliding end (on UHMW plastic sliders under the joists resting on the spreader beam as the professional treehouse builders say to do), so when that tree blows side to side, I'm thinking it'll cause flex in the platform nonetheless since that creates an angle.
The two parts is to make it easier to erect.
the suggestion to reduce window size, or move to the long walls is to allow for more stiffening area in the short wall.
You also can add some steel strapping at an angle in a couple X shapes to help stiffen up.
I agree with you a tornado would eat this as a snack.
Thanks. As a follow-up question, if we can't move the windows because we already have two windows planned for one of the long walls and none for the other (neighbor privacy reasons), would the best bet be to go with windows on this wall that are less wide (like 2ft instead of 3ft) per your previous note?
Or do you think with interior sheathing plus strapping as you mentioned it'd be good as is? I wasn't sure in this drawing where you'd suggest putting the strapping - an x below the windows (one on each half of the wall), or an x all the away across both above and below both windows together, or something different altogether?
I am thinking of the cases where one corner is lifted in relation to the other three. forces have to transfer to lift the whole thing.
sheathing secured with enough fasteners to the studs will provide support. (more is better within reason)
any time you have a window, it prevents this part of the wall from contributing to the load transfer, and also presents a need for more stiffness.
the drawing you presented of the end wall looked less than optimum to me,
your headers will keep the studs above the windows stiff, but the narrow space between the windows could likely use some help. smaller windows would help.
I would make an X with steel strap suitable for this use on both sides of the studs between the windows, and there is no reason not to extend this beyond this space, to the upper and lower plates (and beyond if it makes sense)
This really is kind of a judgement call. this is not a structure planted on a solid foundation, it is, after all, a treehouse. I suspect you will not let anyone in or near during any kind of wind events (as much fun as that might sound), so the worst case is that under such condition windows and door may not properly operate, or the glass may shatter. Will you make sure the windows are all tempered glass? Or install safety film on all the windows. If kids will play here it is a good idea. ( I used to be a kid....)
Yeah, the plan is to definitely keep people out of / away from it during wind events. I tried finding Simpson's wall bracing straps on the Home Depot and Lowes websites based on the models in the attached catalog page, but couldn't find the strap kind that is for bracing and which is flat for forming X shapes (only the TWB and RCWB kinds which can't be used to make an X or the uplift kind which isn't targeted at this purpose). Do you have a recommended product for this? Thanks
https://www.connectorsonly.com/stg90zico23.html
I found this source of supply.
Looking at the catalog page you listed, it seems to me that you could use TWB and RCWB for the bracing, just have to cut a slot in the studs. for an x one side would be applied to the inside of the wall, the other on the outside.
Also, I was thinking about this, and you may want to leave the inside open, use blocking and the angle braces so that you can examine the structure after wind events to see if any of the sheathing is coming loose from wind or flexing.
Blocking would make handy shelves for beverages, snacks or toys. probably weigh less than another layer of sheathing on the inside.
Since RCWB requires 2x6 and I just have 2x4, I may go with TWB and also do inside sheathing since both the interior and exterior sheathing will be uncovered. The outside is LP SmartSide 38 series and for the interior I'd plan to use a decent looking plywood that is strong enough and forego drywall (though interesting idea on blocking doubling as shelves).
Do you think this would work and then I could just look for nails coming loose? Planning to use ring shank for the sheathing btw and maybe do a closer spacing like 4 inches to bump the shear rating up (1.5x boost per the LP ratings as compared to every 6 inches).
Hi Mike, I was curious if you had any thoughts on if that would be a suitable approach. Also, I just got the final draft of all the walls together and posted it to https://www.finehomebuilding.com/forum/12x10-treehouse-any-issues-with-the-final-draft-of-these-framing-plans if you had any thoughts on them. Thanks