Author Topic: 6" walls on 6" floor on 4x8 beam?  (Read 24236 times)

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Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #25 on: January 21, 2011, 12:16:00 PM »
I think what OJ is suggesting is to put this new beam under the house side of the deck thus taking the load off the house foundation and sidewall. This is a good idea and will also allow for good flashing to keep water from the deck side getting into the house wall and floor. When the deck needs to be rebuilt (and it will age faster than other parts of the project) this will be a stand alone project.
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Offline Don_P

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #26 on: January 21, 2011, 01:21:34 PM »
But... use something more substantial than a 4x6, you've got a mill, that dimension is trim.

There was a previous comment in this thread that wood is 7 to 9 times stronger than the allowable design strength. This is kind of misleading. Grading shoots for 95% of pieces being at least 2.1 times design value and 5% of pieces are allowed to be between design value and the 2.1x safety margin. There may indeed be a few pieces in the pack that are many times stronger than the allowable strength rating... but it would not be a good idea for the novice to count on it.


Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #27 on: January 21, 2011, 02:06:28 PM »
I think what OJ is suggesting is to put this new beam under the house side of the deck thus taking the load off the house foundation and sidewall. This is a good idea and will also allow for good flashing to keep water from the deck side getting into the house wall and floor. When the deck needs to be rebuilt (and it will age faster than other parts of the project) this will be a stand alone project.

Yes, thereby changing from two supporting beams underneath to 4.  The last two right at the outer edge and under the floor directly under the wall -- using pier blocks with the 'jack' type cradles the beam could be jacked right up under the floor.  I did this for wood stove support actually.

This would leave a nice beam to hang the deck off of also -- and as you mentioned, it will facility an easy rebuild of the deck in time.

DonP:  I think you're saying mill a 4x8 instead?  That would make a 4x8 at the outside walls (load baring) as well as on 9 foot centers under the floor.


Offline Don_P

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #28 on: January 21, 2011, 03:43:03 PM »
Jarhead, in white pine the log home companies would send a 6x8 is a porch roof carrying beam that can support about 8' of roof at 8' post spacing, floors require more beam than that.  I've rarely been able to get enough info to size parts here, look at the girder tables in the deck guide or code book and go bigger for solid sawn timbers. If you've got a mill you can make real timbers, don't think small, use the tree  ;).

Offline MountainDon

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #29 on: January 21, 2011, 05:00:12 PM »
... unless he's got trees like me.   :(   The ones that would make good 8+" beams are those we want to keep.
Just because something has been done and has not failed, doesn’t mean it is good design.


Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #30 on: January 21, 2011, 07:45:56 PM »
The trees I'm sawing next weekend average around 16" in diameter over 8 feet...I have some that are about 18-20 at chest height.  However I have some I need to drop that are about 60 feet tall and probably over 14 inches above 30 feet!

Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #31 on: January 21, 2011, 07:46:29 PM »
Not sure if I mentioned it earlier but I'm buying a woodmizer Lt10 in the neat future if all goes well :)


Offline Don_P

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #32 on: January 22, 2011, 02:08:56 PM »
As I understand what you are proposing; When you jack up and support the cabin on a beam under the wall, the weight of the main floor half the distance to the existing beam, the wall, half the upper floor and half the roof will bear on the beam, as will half the deck load. For myself, I'd count on a future porch roof as well.

This is BTW a good plan, I'm just trying to smack you into dimensional reality.

My beam and column calcs are here;
http://windyhilllogworks.com/Calcs/beamindex.html
You are probably looking at using the top, simple beam, calc. If you can give me the species you are going to be using I'll give you the design strengths to plug in.

A bandmill will make shorter work than the chainsaw mill, the lt10 is a hobby sized mill. I saw where you were talking about a sideline business with it, you'll rethink that pretty quickly with that mill. Also look at the Norwood, a local retiree is doing a pretty good sideline biz with his. Find an ag show or similar where you can watch or play with them all.

This is a shot at the end of the day today, we've begun playing with the timbers on the job. These are 6x8 beams and 6x6 posts. Simplifying the layout a bit, there will be a floor above, joists spanning about 15' from the window to the beams, the posts are about 6' apart there is no floor on this side bearing on the beams. They are pretty much maxxed in white pine with just the upper floor load.

The mountain of rocks outside the front is some of what we've gathered from the field edge piles, the mason is using them for porch walls  [cool]

Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #33 on: January 23, 2011, 07:35:33 PM »
Thanks Don.

My intent is to continue to use the original beams also thus having 4 beams rather then two.  The initial two are in accordance with the plans at ~9' apart (I'll have to check exactly but I think it's 9' on the nose on center) so the next two would be under the outer walls about 13'6" on center.


Offline Don_P

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #34 on: January 24, 2011, 02:55:24 AM »
Yes, the load path shifts, think about what I described and it should make sense.

Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #35 on: January 24, 2011, 12:10:36 PM »
The 4x8 beams in the lightweight 14x24 plan (from the Little House plans kit, not the 14x24 Builder's cottage which has a perimeter concrete foundation and engineered I-joists) are only spanning 4' - there are 6 piers on each side under the beams and the floor joists span a bit over 9' between the beams. In the first photo you posted it looks like that is what you have built.

In the first page of this thread I think we decided you should not be adding new weight to this foundation and that the deck should be free standing and not adding to the wall load with hangers. If I understand what you are suggesting, you plan to use much the same foundation plan for your deck as you used for the house?

Decks should be designed to carry even more load than house floors (typically 60 psf rather than 40) because they can have very heavy loads during a party or such. Not that there aren't thousands of existing decks that are built less strong than house floors - there are. Usually this will not be a problem if lightly used. But a failure, especially when the deck is high in the air and loaded with a bouncing crowd at a party, can be devastating.
None of us are as smart as all of us.


Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #36 on: January 25, 2011, 06:00:57 AM »
The 4x8 beams in the lightweight 14x24 plan (from the Little House plans kit, not the 14x24 Builder's cottage which has a perimeter concrete foundation and engineered I-joists) are only spanning 4' - there are 6 piers on each side under the beams and the floor joists span a bit over 9' between the beams. In the first photo you posted it looks like that is what you have built.

In the first page of this thread I think we decided you should not be adding new weight to this foundation and that the deck should be free standing and not adding to the wall load with hangers. If I understand what you are suggesting, you plan to use much the same foundation plan for your deck as you used for the house?

Decks should be designed to carry even more load than house floors (typically 60 psf rather than 40) because they can have very heavy loads during a party or such. Not that there aren't thousands of existing decks that are built less strong than house floors - there are. Usually this will not be a problem if lightly used. But a failure, especially when the deck is high in the air and loaded with a bouncing crowd at a party, can be devastating.

I'll have to go back to the beginning of the thread but this sounds correct, which is why I decided to increase the strength of the foundation itself.  My thinking was that 4 beams supported as you stated (on 4 inch centers) would be twice as strong as two.  However, if i understand DonP correctly then in reality the new beams would really be taking the load leaving the old beams to take only the load in the center of the house -- which is ok.

So, if that's correct I'll be looking at heavier beams which I'll toss into DonP's calculator to see how well they work...so maybe some 4x10s to start -- and of course since they would be Pine they might need to be heavier still.   But I have LOTS of tall pines :)

Just need to order an extension bed for the LT10 when I get to ordering :D

Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #37 on: January 25, 2011, 11:07:59 AM »
If you are putting new beams under the wall line and parallel to the beams about 2' inside the walls, then yes - those new beams will be carrying a bit of the main floor load (about 1' wide) and all of the wall, plus 1/2 the roof and loft loads. The existing beams will now support most of the main level floor loads. This would be a good way to carry the taller 6" walls and the extra weight of a loft.
None of us are as smart as all of us.

Offline OlJarhead

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #38 on: January 26, 2011, 01:35:17 PM »
If you are putting new beams under the wall line and parallel to the beams about 2' inside the walls, then yes - those new beams will be carrying a bit of the main floor load (about 1' wide) and all of the wall, plus 1/2 the roof and loft loads. The existing beams will now support most of the main level floor loads. This would be a good way to carry the taller 6" walls and the extra weight of a loft.

That's the plan :)  Kinda feels good to have one!


Offline Don_P

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #39 on: January 26, 2011, 07:01:46 PM »
You got it  ;)

Offline small cabin dreamer

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #40 on: April 05, 2013, 12:31:37 PM »
I am going to resurrect this topic:
If I beefed up the entire floor could I build what oljarhead has built? larger beam than 4x8, and larger 2x8's or 2x10 floor joists?

Offline MountainDon

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #41 on: April 05, 2013, 12:48:17 PM »
Could you describe what it is you want to build;  L x W x height, # of floors and so on?  That would probably result in a better, more accurate and clear answer. We'd have to re read what OJH has done anyway, at least I would as I don't remember all the details of his project.

New topic of your own would be fine too.  :)

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Offline small cabin dreamer

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #42 on: April 06, 2013, 03:34:00 AM »
ok, I am trying to build something relatively small, something between OJH 14x24, or rick's in vermont 10x16. I am thinking 12x18 or 12x20 with 10 foot sidewalls to have a sleeping area upstairs big enough to put in a real bed, even if not on a real bed frame. I am in the UP of MI where there is a considerable amt. of snowloading. I want a 12/12 pitch roof (metal). I have come to find that the ground is a crummy loamy soil, not good for much. most neighbors have very old cottages on slabs built on/ or built up off grade, not dug down below. I am thinking that if I use a shallow base, foundation piers, or dig down 3feet or so and backfill with gravel and then put these pirs on top that will eliminate frost heaving. I am not sure if burying 4x4's in this loamy soil is a good idea, like rich in vermont did. I have asked about beefing up the foundation to have the taller walls, I dont need the beams cantilevered, I can run the beams all the way to the edges if need be. This is why I am asking about beefing up the original little house plans (12x18 or 12x20)

Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #43 on: April 09, 2013, 06:39:00 AM »
Dreamer:

I think your suggestion of getting down 3' (I assume this is below frost depth) and building a crushed rock footing is good. You could do concrete tube or block piers or 6x6 foundation grade PT posts (see this article). Brace these piers to sturdy built-up beams and use 2x8 or 2x10 joists @ 16" o/c for your floor (assuming a 12' span). You should be good to go on your platform.
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Offline small cabin dreamer

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #44 on: April 10, 2013, 08:01:17 AM »
What size should the beams be, or is what is listed in the little house plans good enough?


Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #45 on: April 10, 2013, 08:53:14 AM »
They would need to be deeper than the Little House design since you have more loft load if I understand correctly. To be accurate you should do a load trace and consider the snow loads as well. Don_P has some links to beam calculators if you want to do this yourself. If you just want to have plenty of beef you could use built-up beams of 3 laminated 2x10's. If you are using 6x6 posts you could shim out this 4.5" wide beam with a couple of 1/2" ply shims to fit a 6" saddle for the pier to beam connection. You can then bolt in 4x6 braces between beam and post.
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Offline Press

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #46 on: April 10, 2013, 02:29:44 PM »
Does it matter if those spacers for the beam are plywood, or just cut from a 1 x 10? Other references to this technique also mention plywood. Thanks.


Offline John Raabe

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #47 on: April 10, 2013, 03:11:11 PM »
Those spacers add little to the strength of the beam and don't have to be continuous for the length of the beam. In other words you can just use small pieces of what ever thickness needed to fill the open space at the brackets. You run your screws or nails through these spacers and into the beam.
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Offline MountainDon

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Re: 6" walls on 6" floor on 4x8 beam?
« Reply #48 on: April 10, 2013, 03:23:00 PM »
I was typing and interrupted myself   :D

So, I ditto what John just said. The plywood or whatever is simple spacing material. Strength of the beam is calculated on the lumber used and that's it. Place any splices in the dimensional lumber over the supports.
Just because something has been done and has not failed, doesn’t mean it is good design.

 

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