6" walls on 6" floor on 4x8 beam?

Started by OlJarhead, October 12, 2009, 01:44:56 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

OlJarhead

OK So I built the floor and decided to leave it as a 6" floor -- it's a cabin right? -- and then began to frame my 2x6x10 walls and suddenly thought:  Is this floor strong enough for such heavy walls?

Thoughts?  Am I making a mistake?

John Raabe

#1
Please post a picture of where you are at. That will give us all a better idea of the situation.

Words only go so far...

I ask because I'm wondering if you are doing the Little House lightweight foundation where the walls rest on cantilevered joists... That foundation was not designed for a full two story load or heavy wind or snow. The Builders Cottage plans from the Enchilada plans are better suited to such conditions.
None of us are as smart as all of us.


OlJarhead




Not sure if those show well enough.

I have two walls up so far and just wondered if I was building too heavy of walls for the floor?

OlJarhead

The wow in the wall stud by the way is an optical illusion!  Each time I see this picture I cringe! hehe

OlJarhead

So to recap:  4x8 beam made of 2 2x8's nailed and glued with a 1/2 ply between them (with proper overlaps), 2x6 framed floor and 2x6x10 walls all based on the 14x24 plans (Builder I beleive it's called)...with lofts etc.

I was just wondering if my walls made the cabin too heavy for 2x6 floor joists?



OlJarhead

The silence is deafening...

I was thinking I might go with 2x8 floor joists but then figured this is a cabin in the woods and if the 2x6 floor would be strong enough then why change it?  Now I'm just wondering what kind of load those 2x6 joists can take?

They are on 16" centers and span the beams as per the plans....so I'm hopeful it's fine -- just don't want the floor to shear the joists and become 'shorter' some day!

Hind site right?

OlJarhead

OK, I've been reading as much as I can and I think I might have the answer:

It's fine.

Why?  It seems the real concern isn't the depth of the joist for load bearing but span and load bearing over the span.  Am I right?

In other words you need to span no more then 9'9" for DF#2 2x6 becuase that's max for 40lbs per foot of load right?  So the span maximum is set to prevent the floor from bowing, buckling etc and not becuase of any sheer potential.

The sheer potential and bending potential of the joist is another concern of course but I suspect that becuase these joists are 2'2" from the center of the beam and have 3/4" OSB flooring on them their overall strength is much greater then a single boards strength.  So they should carry the heavier 2x6x10 wall without major issue -- or I'm assuming anyway.

I suppose if it is cutting it close though, I could add an additional beam the length of the floor out near the edge of the deck thus creating an even stronger foundation?

Also, I plan to put a deck off the main floor using posts and piers so perhaps I'll just need to consider that...

MountainDon

Quote from: OlJarhead on October 13, 2009, 10:04:45 AM
The silence is deafening...

I've been silent because I don't have an answer backed by calculations.

John's plan does show 2x6 floor joists on 16" centers. The difference is that you have used 2x6 for wall studs instead of the 2x4 indicated in the plans. Plus your walls are taller. I imagine the roof will be much the same as on the plans so there's no additional weight there?

So, I'm thinking, guessing, that the floor joists probably have enough safety factor incorporated into the design to be able to handle the extra weight of the taller 2x6 wall studs, plus the additional wall sheathing.  But that's a guess, nothing more, nothing less.    8)

Just because something has been done and has not failed, doesn't mean it is good design.

John Raabe

#8
Ah, yes... just checking back on this. You are putting extra weight on the cantilever at the joists. I agree with Don that I think you are within the safety factor (about 8x for DF according to Charlie Wing). For all species the safety factor varies from a low of over 7 to over 9.

However, I am not a sophisticated enough engineer (I'm not an engineer at all) to be able to check your specific situation. In this case for shear on the extension of the joists.

If you wanted to be cautious without having it checked by a local engineer you could add a 4' 2x4 to every other joist. That would increase the section modulus (beef) of the joist
None of us are as smart as all of us.


OlJarhead

Quote from: John Raabe on October 13, 2009, 11:10:31 AM
Ah, yes... just checking back on this. Let me do some calcs and check this out. You are putting extra weight on the cantilever. What is your snow situation? Are you doing the steep pitch (12:12) roof?



12:12 roof per plans -- I considered doing 2x8 roof rafters and would like to....hadn't thought of the weight I'm adding.

Snow load?  Depends on Global Warming I guess...except that it was 5 degrees Saturday morning and I predicted we could see a 30 year cooling trend now....so, bearing that in mind (*chuckle*) I just read that:

Quoteminimum roof load of 40lb will stand up to the snow load in most areas of Okanogan County, however if you are placing the home at higher elevations that get more snow you may need to order your home with a heaver roof load rating.


John Raabe



Here's one idea.

Another stiffener would be to angle a short 2x6 brace from the rim joist to the beam. Nail it to the joists. Might be easier.

None of us are as smart as all of us.

OlJarhead

Quote from: John Raabe on October 13, 2009, 12:08:30 PM


Here's one idea.

Nail a 2x4 to each joist under the wall and extending over the beam?  Never thought of that but it certainly would add to the shear and bend factors right?


OlJarhead

One thing I'm wondering is how much difference does the deck make?  I'm figuring on putting hangers on the rim joists and then 4' out a beam on post and peirs using PT 2x6 for the flooring just like the cabin floor.

My question is:  does this change anything?

MountainDon

Snow load: What type of roofing material? A steep pitch metal roof will  not accumulate much snow before it slides off. Shingles will accumulate some before it slips off.

Deck: with a roof? I think a row of posts and a beam at the cabin wall to support the deck without placing additional loads on the cabin structure might be a good idea.
Just because something has been done and has not failed, doesn't mean it is good design.


John Raabe

I'm with Don. Let's not add more weight to the cantilevered wall and floor joists. Make the deck self supporting.
None of us are as smart as all of us.

MountainDon

Quote from: OlJarhead on October 13, 2009, 11:30:30 AM

12:12 roof per plans -- I considered doing 2x8 roof rafters and would like to....hadn't thought of the weight I'm adding.


2x6 rafters will be more than adequate when on 16" centers. Of course 2x8 would allow for more insulation in a cathedral ceiling.
Just because something has been done and has not failed, doesn't mean it is good design.

OlJarhead

Tin roof -- and if 2x6 will do then we'll go with that!  Save the weight/loads!

Like the idea on the deck too thanks! 


OlJarhead

Just re-read this again -- cool!

I've got lots of information here so I think I'm good.  I'll do a little of both perhaps (going to borrow an air nailer to assist).

Thanks again for your replies!

OlJarhead

Getting ready to go back and get the walls done and try to complete the roof!

The weather is supposed to be cold and rainy/snowy but I'm hopeful it isn't too much!

OlJarhead

Quote from: MountainDon on October 13, 2009, 12:24:10 PM
Quote from: OlJarhead on October 13, 2009, 11:30:30 AM

12:12 roof per plans -- I considered doing 2x8 roof rafters and would like to....hadn't thought of the weight I'm adding.


2x6 rafters will be more than adequate when on 16" centers. Of course 2x8 would allow for more insulation in a cathedral ceiling.

Just re-read this thread (looking for something else) and saw this post....how did I miss this? :(  I went with 2x6 rafters on 24" centers.

Of course the 12x12 pitch means no snow load and 6 months of being installed (without all collar ties) and the roof seems to be holding just fine.

I'm hopeful that this cabin doesn't start to sag on me in the near future but I'm thinking it will be ok -- I once had to peel the sheeting off someones roof (after removing roofing) and 'shim' the sheeting with wedges cut to the sagging rafters to clean up the roof line for a customer.

I'd advised them that they needed to replace the rafters and put a new roof on but they weren't interested, they just wanted the roof of the old house to match the new carport roof I'd built for them (with trusses) so I complied with their wishes.  Their rafters were 2x4's!  But after 35-40 years they were still hanging in there though I anticipate their collapse some day (to that note we did add a little extra bracing here and there to try to shore of the ridge beam and rafters but their roof is doomed sooner or later).

Anyway, I'm finding I've forgotten more then I imagined possible and have rushed past the rest in the attempt to avoid weather :(

Note to self:  slow down, do it right and forget the weather.


John Raabe

#20
Be sure to get the collar ties in place as they will stiffen the rafters, triangulate the forces and cut down the working span. Also spend some time reinforcing the connection between the rafters and the wall. Use a metal framing anchor or strap.

Do that and you should be fine.
None of us are as smart as all of us.

OlJarhead

Quote from: John Raabe on June 03, 2010, 01:06:41 PM
Be sure to get the collar ties in place as they will stiffen the rafters, triangulate the forces and cut down the working span. Also spend some time reinforcing the connection between the rafters and the wall. Use a metal framing anchor or strap.

Thanks John.

I used Hurricane ties on the walls to the rafters though with my installation (rafters) being so tight I couldn't get them inserted up the wall to the rafter so I had to lay them on top of the walls and push into the rafter.  Which, when I think about it might even be better -- or at least exceptable.

I plan to get collar ties on this weekend as well as additional blocking etc.

Also have to work on the foundation as one beam is bowed a little as if one pier raised up or two outside piers have sunk.

Anyway, my plan is to install a post and pier at each end of the 24' beam (the kind of block with the bolt saddle that you can ajust height with - to tighten into the beam).  I'm thinking this will add additional support.

OlJarhead

https://i290.photobucket.com/albums/ll257/loonlakebound/DSCF1310.jpg
I wanted to revisit this thread with a question:

Why could I not go ahead and nail 2x4s to the inside of my 2x6 rafters using this method (plywood/osb sheeting to tie them together)?

To clarify something:  I went with the 2x6 rafters after much debate because of the cantilever floor and 6" walls.  I was worried that I had too much weight on the cantilever.  However after much consideration I've realized that I can solve that problem when I build my deck :)  All I really have to do, correct me if I'm wrong, is put a nice heavy beam (say 4x6) down the length of the cabin under the cantilever and jack it up to the floor -- then I can hang the porch off the beam with joist hangers.  This has the added benefit of removing the cantilever as well as eliminating the need to separately frame the inside wall of the surround deck (something we figured would be wise because of the cantilever).

Bear in mind that once my LT10 arrives I'll be able to mill my own 4x6 beams (I have a Fir I'm eying now) for this so cost won't be an issue (which it was previously).

Why would I want to do this?  I just don't like the options for insulating my roof now and really wanted more then the R19 I'm likely to get now and by doing this I also eliminate the shelf on top of the wall as well as better tie the roof into the walls.

I'm still just pondering this and if I'm insane in thinking I need to do any of this please smack me back to reality!  It's just something I've been thinking about for a long time now and I kinda thought I had the answer now :P

MountainDon

Quote from: OlJarhead on January 20, 2011, 01:55:38 PM
https://i290.photobucket.com/albums/ll257/loonlakebound/DSCF1310.jpg

Why could I not go ahead and nail 2x4s to the inside of my 2x6 rafters using this method (plywood/osb sheeting to tie them together)?

The biggest difference between your roof and the other roof is you used a ridge board and the other ses hand built trusses. The peak has a sandwich around the rafter points/tips made from plywood. I believe John's 20' wide has an option for owner built trusses and those were engineered if I'm correct. But they are much the same as what is used in that image you selected. Something like that, to increase the space for insulation, should work I think. The plates would be better if plywood rather than OSB I believe. Waterproof glue should be used as well as a well developed nail pattern. Would you redo the cross ties you have as well?
Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

The beam under the side... I'm not clear on what would be supporting it and if you mean it would be under the existing main cabin side wall. I think that is what you mean and you'd have a set of posts to support it. Then you would ledger off that.   ???


Just because something has been done and has not failed, doesn't mean it is good design.