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Small Cabin Forum / Cabin Construction / Floor joist assembly ?'s
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WILL1E
Member
# Posted: 8 Sep 2021 08:52
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Joist assembly will be elevated on a post & beam style foundation.

-Do you/ should you always put a vapor barrier between the subfloor and the joists?

-Which is the strongest connection of the joist to the rim board...end nail only, hanger bracket or end nail plus hanger bracket?

-16' joists and 2 beams...which bracket works best to connect joists to beam and should i use one at every point the joist crosses a beam?

snobdds
Member
# Posted: 8 Sep 2021 11:20
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You're never going to get done getting hung up on all these questions. We're ready to see this cabin go up, the anticipation is killing us.

Vapor barrier is not needed on a post and beam subfloor as the underside of the floor is not in a enclosed space. The vapor is carried away with airflow, it will not condense of the underside of the floor. I sprayed foam the underside of mine, which not only dampened the hollow sound of the floor,it added a vapor barrier and insulation. That is the best bang for the buck for performance on multiple levels.

Hanger brackets are used when the joist is set flush with the beams i.e the joists are hung off the beams. No brackets are needed if the joists are resting on top of the beams, toe nailing works. However I have seen some hurricane clips tieing the joist and the beams together. There is really no lateral forces acting on the floor joist, the rim board just keeps them properly spaced and upright.

gcrank1
Member
# Posted: 8 Sep 2021 11:53 - Edited by: gcrank1
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Devil is in the details, hey, Will!
My '83-84 build just sat on the beams never shifted that I could tell, but 'tying' it to the beams is probably a good idea. Easy to do now than later. But really, do you think a wind big enough to shift or blow over the cabin is gonna be impressed by a couple of beams attached?
I used 1"blue DOW styro set flush with the joist tops by using 3/4x1" ledger strips set 1" below the tops; just cut the 4x8' sheets as I went. It went easier and faster after I had enough to actually lay some 4x8 floor decking down as a cutting surface.
Id do that process again but may use 2".
Once my deck was done I was tempted to set a tent up on it and use it but I was driven to get walls up, etc, and get enclosed by winter. Barely made it. The last of enclosing was at about freezing daytime temps.

WILL1E
Member
# Posted: 8 Sep 2021 12:46
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Quoting: snobdds
You're never going to get done getting hung up on all these questions. We're ready to see this cabin go up, the anticipation is killing us.

I know, i know...I spend way to many hours in the day thinking about this project!

Quoting: snobdds
Vapor barrier is not needed on a post and beam subfloor

Does it hurt anything to add it as an extra layer of protection?

Quoting: WILL1E
-Which is the strongest connection of the joist to the rim board...end nail only, hanger bracket or end nail plus hanger bracket?

Any thoughts here?

Nate R
Member
# Posted: 8 Sep 2021 13:16
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Bracket is stronger to connect to the rim... No idea if it's necessary in this case.... You could end nail AND bracket, sure....seems redundant to me...But I haven't studied it in depth.

snobdds
Member
# Posted: 8 Sep 2021 13:32
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Quoting: WILL1E
Any thoughts here?


This is totally predicated on if your joists hang off the beams, making the rim board only applicable on the gable ends or resting your joist on top of the beams with a full permiter rim board.

For you I would use hangers with teco nails, and then use structural lag screws to end nail through the rim. Then all the bases ae covered no matter which way you go.

I just want to see this built so I am suggesting anything to further that along.

WILL1E
Member
# Posted: 8 Sep 2021 13:50
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The rim board on the eave ends will hang pass the beam around 6" so that the concrete blocks and pad are out of the drip line of the cabin walls. The rim board or end joists on the gable ends will be sitting on the 2 beams.

Brettny
Member
# Posted: 8 Sep 2021 15:15
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Quoting: WILL1E
6' joists and 2 beams...which bracket works best to connect joists to beam and should i use one at every point the joist crosses a beam?

Notching the post is the strongest "bracket" yes one notch at every post. Then through bolt it at least 2x.

WILL1E
Member
# Posted: 8 Sep 2021 15:28
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Brettny i think you misunderstood, let me clarify. There will be 2 built up beams running the length of the cabin and will be spaced ~15' apart. Sitting on top of that will be the floor joist assembly. My question was how best to secure the rimboard/band joist/whatever you wanna call it, to the individual joists.

ICC
Member
# Posted: 8 Sep 2021 15:51
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Quoting: WILL1E
I know, i know...I spend way to many hours in the day thinking about this project!


IMO, a neophyte builder cannot spend too many hours or ask too many questions before they start building. How many times have we seen questions asked after something has been done, and done wrong or poorly? Is it easier to correct a problem before or after it is done?

ICC
Member
# Posted: 8 Sep 2021 16:09
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The rim joist does not do much, does not support much load. One of its main purposes is to maintain the proper spacing between floor joists. The rim can also help prevent the floor joists from rotating or leaning over, but installing solid blocking between the floor joists and above the beam does a much better job of that.

Nails into end grain do not provide very much resistance to withdrawal forces, to something pulling horizontally on the rim joist. However, when the subfloor sheathing is nailed down, it is nailed to both the floor joists and the rim joists. That does help hold the rim joist in place against the ends of the floor joists. That is one reason why it pays to think and plan far enough ahead so you do not end up with a narrow strip of subfloor sheathing nailed in place along the outside edge. The width of subfloor panels should be kept to 16 inches minimum width.

Brettny
Member
# Posted: 8 Sep 2021 16:11
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Quoting: WILL1E
Brettny i think you misunderstood, let me clarify. There will be 2 built up beams running the length of the cabin and will be spaced ~15' apart. Sitting on top of that will be the floor joist assembly. My question was how best to secure the rimboard/band joist/whatever you wanna call it, to the individual joists.

O lol yes I did. You just end nail/screw it. The rim board isnt very structural it's mostly to keep the joists inline but it can also help spread the load on the joists.

ICC
Member
# Posted: 8 Sep 2021 16:17
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When building a floor with floor joists that rest on top of wood beams we often liked to use H1 hurricane clips. Measuring out and marking where the H1's would be nailed to the beams was the first step. Then we would nail those H1's to the beams. Then it was easy to drop the floor joists in place and not have to worry about them shifting a little when toenailing the floor joists to the beam.

Yes doing that adds some cost of materials. It also ensures maintaining the floor joists spacing which can make installing the subfloor sheathing easier.

With a 16-foot floor joist span, you will also plan to install blocking somewhere more or at the floor joists center?

Grizzlyman
Member
# Posted: 8 Sep 2021 18:11 - Edited by: Grizzlyman
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+1 There’s no reason to use joist hangers at all. End nail rim to joists. This is how it’s done. Four .131 nails per joist I believe

Hurricane ties where joists cross the beam are good.

As mentioned above I think you’ll want to block between joists too…

ICC
Member
# Posted: 8 Sep 2021 18:36
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And I meant to mention that the H1's will also help with uplifts driven by wind

WILL1E
Member
# Posted: 9 Sep 2021 07:54
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As usual, thanks for the feedback and support fellas!

Quoting: ICC
we often liked to use H1 hurricane clips

Perfect!

Quoting: ICC
With a 16-foot floor joist span, you will also plan to install blocking somewhere more or at the floor joists center?

Plan is to do offset blocking down the center. Subfloor will be 3/4" T&G plywood.

Quoting: Grizzlyman
Four .131 nails per joist I believe

The Wisconsin construction standard calls out 3-16d to secure the rim to the joists. I plan on 2x10"s for the rim and joist so i think doing 4 wouldn't hurt anything.

ICC
Member
# Posted: 9 Sep 2021 08:23
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Quoting: WILL1E
3-16d

If WI does like the IRC, they would call out the nail size by actual dimension as well as the "penny" nail size name. That is because there are nails called 16D that have thinner shanks that what is traditionally called a 16D Common nail size. That is very often done with air gun nails. They are often more like a Box nail than a Common nail. Smaller diameter = less shear strength. Using 25% more nails with the smaller shank generally makes up for that.

WILL1E
Member
# Posted: 9 Sep 2021 09:07
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They have a general notation below their minimum fastener schedule that says "All nails are smooth-common, box or deformed shank except where otherwise stated". And the only place they spec something different is under Panel Sheathing.

Brettny
Member
# Posted: 9 Sep 2021 09:13
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Spiral nails or ring shank really hold tight too. If you dont plan on siding or skirting this rim board I would use galvanized nails too.

ICC
Member
# Posted: 9 Sep 2021 09:21
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Quoting: WILL1E
All nails are smooth-common, box


There is a big shank size between common and box nails so they are not really a case of either/or and both being okay.

EG, a 16D common is 0.165" dia. while a 16D box nail is 0.135" dia. Annular (ring) and spiral are in between at about 0.150"

NorthRick
Member
# Posted: 9 Sep 2021 13:20
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I have a Paslode fuel gun and now a Milwaukee battery powered gun that takes the same nails. The framing nails I buy are dipped in a heat activated adhesive.
The friction from being driven in with the gun heats the nail and causes the adhesive to stick. It works because pulling an errant nail out sucks.

Grizzlyman
Member
# Posted: 9 Sep 2021 20:55
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Quoting: WILL1E
e Wisconsin construction standard calls out 3-16d to secure the rim to the joists. I plan on 2x10"s for the rim and joist so i think doing 4 wouldn't hurt anything.


Hand nailing 16d is 3. If using a framing nailer and .131 it’s different and is four. In most applications
And nailing patterns it’s usually 1 more for a .131 but that formula is not 100%.

If memory serves the tables usually list a 16d for hand nailing and a .131 for Gun.

WILL1E
Member
# Posted: 10 Sep 2021 07:57 - Edited by: WILL1E
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So to clarify my original point, a vapor barrier is not necessary, but yet won't hurt if i put it on as an extra layer of protection?

Another question comes to mind. Ill be putting 24" diameter by 6" thick precast concrete pads down. On top of that i will be setting 2 8x8x16 concrete blocks. Do I need to mortar the blocks to those pads, or can they just sit on them? I'll be using PT board on top of the blocks for the built up PT beams to sit on.

ICC
Member
# Posted: 10 Sep 2021 14:32
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Quoting: WILL1E
Ill be putting 24" diameter by 6" thick precast concrete pads down.



ON the ground? As in no footing at frost depth?

*****************

I do not believe a floor vapor barrier, with a raised floor is needed or even good.

If you place the vapor barrier next to the warm side which is correct for a cold climate, that would place the VB on top of the joists and under the subfloor. That means you cannot use adhesive between the subfloor and joists. The adhesive goes a long way to prevent floor squeaks.

What sub flooring do you plan on using? We have used Advantech for years because it is darn near waterproof. That is a big advantage before the structure is dried in as rain doesn't have any effect on that stuff. That quality also makes the Advantech act as a pretty good VB itself. And you can still use adhesive. Even standard osb subfloor and plywood subfloor uses exterior grade adhesives which will help slow vapor movement.

I would lay the subfloor sheets on adhesive beads. Caulk seams if wanted. Definitely caulk floor to wall or use the gasket material under the bottom plate. This is to seal against air infiltration. Don't bother with plastic VB for flooring.

WILL1E
Member
# Posted: 10 Sep 2021 14:43
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Quoting: ICC
ON the ground? As in no footing at frost depth?

Correct. Top soil will be removed and the pads will be set.

Quoting: ICC
That means you cannot use adhesive between the subfloor and joists.

Wasn't planning to.

Quoting: ICC
What sub flooring do you plan on using?

This 3/4" T&G plywood with a water repellant coating.

Quoting: ICC
I would lay the subfloor sheets on adhesive beads. Caulk seams if wanted. Definitely caulk floor to wall or use the gasket material under the bottom plate. This is to seal against air infiltration. Don't bother with plastic VB for flooring.

This suggestions holds true even if i plan to insulate the floor?

Brettny
Member
# Posted: 10 Sep 2021 19:34
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That subfloor your going to use is the stuff I'm walking on in my current house. It went down very easy and locked in good. We used no adhesive but screwed it. Its also what I plan on useing for a sub floor. homedepot has the stuff way cheaper. https://www.homedepot.com/p/T-G-Dryply-Plywood-Common-23-32-4-ft-x-8-ft-Actual-0-703- in-x-48-in-x-96-in-673014/202522977. I have seen it at $104 a sheet but the last time I bought it (2011) it was $32 and was below $36 a sheet pre covid.
If you can get the building dryed in quick the osb sub floor also works ok.

WILL1E
Member
# Posted: 11 Sep 2021 20:44
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None of the home depots near me have it Just menards.

I picked up my nails tonight. Since i'm using PT for the built up beam and the rim boards (joist will not be PT) i need to use galvanized. The only options i had were spirals and commons...i bought both...but is one better than the other?

WILL1E
Member
# Posted: 13 Sep 2021 08:15
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Quoting: Brettny
That subfloor your going to use is the stuff I'm walking on in my current house. It went down very easy and locked in good. We used no adhesive but screwed it. Its also what I plan on useing for a sub floor. homedepot has the stuff way cheaper.

The reviews for the DryPly stuff on Lowes website makes this stuff out to sound like garabge with zero water protection. I reached out to a guy i know that's closely tied to the DryPly product and he confirmed it's not the best of the products GP offers. He suggested GP DryMax or their competitor stuff Advantech. He said the water absorption rate of DryPly is almost 5x of DryMax Guess that's why it's double the price!

ICC
Member
# Posted: 13 Sep 2021 09:07
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Have you tried to find Advantech? There are some dealers for the huberwoods product in WI

https://www.huberwood.com/where-to-buy?zip=beloit%20wiscosin&dist=100

WILL1E
Member
# Posted: 13 Sep 2021 09:12
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Yeah, Lowe's carries it. Just trying to avoid paying $80-$90 a sheet for subflooring.

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