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Old 11-24-2019, 11:04 PM   #16
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Re: 4x4 floor joists


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Originally Posted by ron45 View Post
You can use this calculator it's free.

https://www.johnbridge.com/vbulletin/deflecto.pl
Thank you. This is the first floor joist span table/calculator I've encountered that handles 4x sawn lumber beams. Since it appears to be designed for tile, I'm guessing it assumes a 40 psf live load and 10 psf dead load, since that is what you must deal with in kitchens and bathrooms.

It confirms that a 3-1/2 x 3-1/2 (actual) Douglas fir beam won't handle a 9.5' clear span. Nor would a 3-1/2 x 4-1/2 beam. Unfortunately, it doesn't allow me to test a 3-1/2 x 5-1/2 beam.

At this point, I'm leaning towards some sort of engineered 3-1/2 x 3-1/2 beam, as long as it can be used as a floor joist and isn't too expensive.
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Old 11-25-2019, 08:52 AM   #17
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Re: 4x4 floor joists


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Originally Posted by Marson View Post
An architect told me once that an LVL was twice as strong as the equivalent sawn timber.
At least twice as strong. Strength is how much stress it can handle before it breaks.

But that is not the only consideration. Stiffness is also a prime consideration in selecting joists (i.e. how much it will bend when you step on it). Pretty sure LVL stiffness is about the same a solid Douglas Fir. (E or MOE from spec sheets)
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Old 11-25-2019, 11:00 AM   #18
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Re: 4x4 floor joists


I'm not familiar with the permitting requirements beyond trailer registration and its roadworthiness, but I'm sure there will be something somewhere. It seems without an understanding of structural design and the use of "rules of thumb," it might be a good idea to hire an architect or engineer to help with the basic structure. A few hundred dollars of time, if no stamps are required, may be a good investment.
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Old 11-25-2019, 12:41 PM   #19
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Re: 4x4 floor joists


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Originally Posted by SPS-1 View Post
Stiffness is also a prime consideration in selecting joists (i.e. how much it will bend when you step on it). Pretty sure LVL stiffness is about the same a solid Douglas Fir. (E or MOE from spec sheets)
Okay, so LVL might not be the answer if I want to keep the deflection to an acceptable level. Maybe LSL or PSL would be better?
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Old 11-25-2019, 01:02 PM   #20
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Re: 4x4 floor joists


Someone at a tiny house forum came up with an outside-the-box (as I defined it) alternative. I was fixated on the idea of running the floor joists the width of our 10' trailer (along the length of our bed). Another option would be to run the joists across the width of the bed. Even a king-sized bed would leave me with a clear span that's only about 6.5'. According to a floor span calculator I was pointed to, Douglas fir 3.5x3.5 (actual) beams should be able to handle that with up to 22" o.c. spacing.

I can foresee two possible issues with this suggestion, neither of which is a deal breaker.

First, my plan is to have a wall of storage drawers and shelving on both sides of the bed. So, putting a ledger board along the top of these storage walls will effectively remove 3.5" of shelf space at the top of the walls. (Is a 3.5" ledger board even practical? I've never seen one that narrow.)

Second, when I sit up in bed, poking my head between the exposed beams, and face forward, then I'll be staring at a beam running directly across my field of view instead of gazing down the length of the beams.

I'll do more investigating of engineered wood and 9'5" clear spans, but it's nice to know I have another option available to me.

Last edited by CanadianRockies; 11-25-2019 at 01:05 PM. Reason: Added ledger board question.
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Old 11-25-2019, 01:12 PM   #21
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Re: 4x4 floor joists


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Maybe LSL or PSL would be better?

Don't think so, according to THIS publication.

I happen to have the costing, so I can share that --- PSL's are 4.3 times the cost of regular 2X's around here. 4x4's were slightly more. (Recently costed that out for a project --- eventually decided to go a different route)
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Old 11-25-2019, 01:29 PM   #22
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Re: 4x4 floor joists


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Originally Posted by SPS-1 View Post
Don't think so, according to THIS publication.
Wow! It looks like sawn Douglas fir beams are tough to beat when it comes to minimizing deflection. Good to know. And thanks, too, for the cost information.

At this point, I can see three options.

Option 1: 6(w)x4(d) Douglas fir beams at 9'5" clear span.

Option 2: Steel tubing (probably 1x3) at 9'5" clear span.

Option 3: 4x4 Douglas fir beams running across the width of our bed at 6'6" clear span.
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Old 11-25-2019, 10:44 PM   #23
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Re: 4x4 floor joists


I can't help but wondering if you're reading to much into this.

Does the trailer frame already have beams.?
And will the floor rest on these beams.?

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Old 11-26-2019, 07:19 AM   #24
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Re: 4x4 floor joists


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Originally Posted by ron45 View Post
I can't help but wondering if you're reading to much into this.

Does the trailer frame already have beams.?
And will the floor rest on these beams.?
The bedroom floor will rest on the trailer beams. The living room will be about four feet above the bedroom floor, so the living room will need floor joists. Unlike nearly 99% of other tiny houses, our bedroom will be below the living area instead of above it (in a loft).
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Old 11-28-2019, 04:47 PM   #25
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Re: 4x4 floor joists


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Originally Posted by CanadianRockies View Post
The bedroom floor will rest on the trailer beams. The living room will be about four feet above the bedroom floor, so the living room will need floor joists. Unlike nearly 99% of other tiny houses, our bedroom will be below the living area instead of above it (in a loft).
Probably not a good idea unless you will be in great shape 100% of the time.

But,
You could use """ Thank you for using the John Bridge Forums Deflect-O-Lator :-)

For joists that are SYP or Douglas Fir, in good condition, 5.5 inches tall, 3 inches wide, 16 inches on center, and 9.5 feet long between supports, the deflection calculated is 0.211 inches.

This translates to a deflection of L / 539.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile, Congratulations! ?


Or

Metal framing.?

Or floor trusses.?
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Old 11-28-2019, 04:51 PM   #26
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Re: 4x4 floor joists


This may give you an idea about the bed/room.

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Old 11-29-2019, 10:16 AM   #27
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Re: 4x4 floor joists


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Originally Posted by ron45 View Post
This may give you an idea about the bed/room.
Thanks for reminding me of this option. We thought about an elevator bed but, for a variety of reasons, opted to go with the bedroom below the living room. I'm pretty sure most elevated platforms wouldn't be able to move a sofa up and down and withstand lots of walking.
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Old 11-29-2019, 02:47 PM   #28
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Re: 4x4 floor joists


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Originally Posted by CanadianRockies View Post
Thanks for reminding me of this option. We thought about an elevator bed but, for a variety of reasons, opted to go with the bedroom below the living room. I'm pretty sure most elevated platforms wouldn't be able to move a sofa up and down and withstand lots of walking.
Did yo ever wonder why that bed will hold over 600 lbs..?
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Old 11-29-2019, 04:01 PM   #29
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Re: 4x4 floor joists


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Did yo ever wonder why that bed will hold over 600 lbs..?
A 400 pound computer hacker and his wife.
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Old 11-30-2019, 03:04 PM   #30
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Re: 4x4 floor joists


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A 400 pound computer hacker and his wife.


I was hinting he could build his floor in the same manner.
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