Second Story/Loft Support

[smcdaniel345]

My husband and I are building a 20x42 with a 20x18 upstairs.  Below is the master bedroom/bath and the dividing wall is approx 4-5 foot off center.  Above is 2 bedrooms with a dividing wall down the center. 

Question is: what do I use to support the upper story (and thereby the roof) without the load bearing wall below?  I really don't want to move the wall towards the center.

Thanks. 

[glenn kangiser]

Full span 20 footers based on the plan or joist calculator or engineered I joists should work.  The roof could go to engineered trusses. 

[MaineRhino]

My place is 20 x 26, with a 20 x 10 loft.  I ran my flooring joists the 10' way, and used a triple 2x10 hemlock the 20' way. In the center of it all I used a 6x6 hemlock post. Most of the other plans I have seen do it the way Glenn says, using the 20' I joists.  I wanted a more rustic look.



This is before the 6x6 posts went in..


And an after pic...

[John Raabe]

If I have this right, you essentially have a 4.5" x 9.5" beam spanning 10' and carrying a uniform load of 1/2 (5') of the loft live and dead load.

You have plenty of strength there. However, by not running the joists the same as the rafters you do not have as much resistance to the downward and outward forces of the roof rafters. The floor diaphragm still provides some of this and I would make sure the nailing and connections between the wall studs and the loft floor joists transfers this tension load. Perhaps "ledgerlok", framing anchors or some other type of deck screws would help this connection.

This outward force increases as the snow and wind loads increase and as the roof pitch gets lower.

While I think you are probably fine, this type of calculation is outside of my engineering skills.

[smcdaniel345]

The joists will run side to side, as do the rafters.  So the joists are running the same way as the rafters. 

What I am asking about is the support for the joists, from front to back, which is 18 foot.  It is 20 foot from side to side.  What do I use at the midway point to support the upper floor, from front to back, without having to put a wall there and would also allow me to use 2x6x10 floor joists? 

If y'all can help me figure this out, I will figure out how to post pictures and start posting our progress.

[MountainDon]

Photobucket works well for image posting. There is a tutorial in the Forum News section.

[smcdaniel345]

This is the floor plan I want

[glenn kangiser]

If I understand you right - you want use short joists - to come halfway across the room under the central upstairs wall.

It would take two big beams and 3 posts and footings that would likely cost way more than using 20' material such as 2x12's or I joists, and may need to be engineered - or if not at least some good pencil scratching to make sure you cover the loads well and have big enough footings under the posts to support them.

Then again without full length material you could have spread issues as John mentioned above.  Some things just have to be done certain ways to have them done right and all loads supported.

[smcdaniel345]

That's what I am trying to figure out.  How do I need to do the first story ceiling/second story floor so that it will do what it is supposed to do. 

The comment 'some things just have to be done certain ways to have them done right' is what I am trying to figure out.  What is the right way?

We were planning to put a beam lined up with the top of the stairs, from the ground floor (on top of a concrete footer) all the way to the roof.  I was then thinking a beam from side to side, connected to the upright, and then one from front to back in the center. 

So you would recommend 20' floor joists?  Go all the way across?  What about support in the center?

[glenn kangiser]

They won't need center support if they are big enough, but 2x6's are not big enough.

John uses 20' 2x12's on 16" centers for his 1 1/2 story  20' wide or tji's - engineered wood also about 12" .  I would suggest his plans for framing with your floor plan as desired.

The posts and beam lined up with the stairs could reduce the floor joist sizes but with your bathroom wall you are reducing the span from the 20 foot anyway to about 14' it looks like.

From the Free stuff section - http://countryplans.com/smf/index.php?topic=2729.0 Joist and rafter Span calculator -

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Douglas+Fir-Larch+(North)&size=2x8&grade=No.+1+%26+Btr&member=Floor+Joists&deflectionlimit=L%2F360&spacing=16&wet=No&incised=No&liveload=40&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span

#1 and better DF 2x8 looks like 13'4" span  at 16" oc to span the bedroom to bathroom wall if that measurement is close. enough.

What I am saying is that there are variables and they have to be considered.   You can't just say that 2x6 is ok because you want to use it.  Loads have to be considered.

Note that I am not an engineer - just a volunteer here and a contractor.  PEG get's into a lot of this stuff and is a pro -also a volunteer. 

John's plans have the loading calculated, and there are varying ways to do things in them. 

[John Raabe]

smcdaniel:

Now that I see your floor plan ideas, you may be able to work with full span joists as we have in the 20' wide 1-1/2 story and Universal cottage. These can often allow you to eliminate interior bearing walls.

It will be helpful if you study these two houses and the various version of them that have been posted to this forum and the Gallery. Many of the folks trying to help others here are building houses using these plans and ideas.

To keep costs under control and to minimize frustration you are better off starting with a straight-forward structural layout and then designing your floor plan to use that space efficiently.

In your design you appear to have a two story house with full height walls at the upper bathroom and bedrooms. This would be like the Universal cottage plan.

However, if you do this then you have a very tall open area above the great room on the main floor that is wasted space and now needs additional support since the sidewalls are 15' to 17' high.

The 1-1/2 story layout works better for what you are showing on the main floor but you will not be able to get two bedrooms and a bath up there - at least not in the configuration you have now.

A compromise solution is to have a two story house that then steps down to a one or 1-1/2 story at the main floor.

[smcdaniel345]

It will be a 1-1/2 story.  The upstairs will have 4 foot walls.  I know the current layout isn't right, it was just there. 

And it's the structal part I am trying to figure out.  Basically, what I am getting, is the best option is to use 20' floor joists that don't have a center support, right?  And if so, what would the best options be?  The I joists?  The open web floor joists?  2x12s?

Thanks.

[Zavoot]

The Ijoists will be about 11 1/4 inches high and the 2x4 web truss will be about 16" - gives you 5 more inches of headroom to use the ijoists.

[davidj]

It will be helpful if you study these two houses and the various version of them that have been posted to this forum and the Gallery. Many of the folks trying to help others here are building houses using these plans and ideas.

To keep costs under control and to minimize frustration you are better off starting with a straight-forward structural layout and then designing your floor plan to use that space efficiently.

As someone who just spent the weekend making sure I didn't make a mistake cutting $45 chunks of LVL for my center beam, I'm living proof of John's advice.  We started with the basic 20x30 plans but then had a local designer bring it up to the detail required for a CA permit submission.  Whilst doing that, we added some tweaks based on floor plan and design issues, and she did the structural stuff her preferred way.  Now I seem to be spending half of my time (and money and brain cells) working on things that weren't on the original plans despite the final layout still being a 20x30.  I'm sure the end result is going to be great, and fortunately our budget isn't too tight at this point, but the wisdom of these words seems so much more apparent seen through a haze of sweat and $ bills!

To add some numbers, our arguably-gratuitous center beam cost something like:

LVL beams - $240
Posts - $15
Concrete (approx 1/3 yd) - $50
Forms - $40
Hardware - $30
Backhoe time - $20
Dobbies and rebar - $30

Total - $405

And some photos:


Maybe two or three days work all in, too, at slow-amateur pace.  Using bigger I-joists would probably cost less and would be zero days work.

I'll update everyone on  the extra cost of our full-load-bearing ridge beam once we've finished, but it's definitely in the thousands (6x18 glu-lam and associated cranes don't run cheap!).  Quite a steep price to remove a few rafter ties...

[rwanders]

I have a 6x16x36' glulam ridge beam----forgot the beam price but the lumber yard delivered it with a crane truck and as long as we were ready to set it there was no extra charge to unload it directly into place----love the unobstructed cathedral ceiling look.  Price was certainly not in the thousands though.

[davidj]

I have a 6x16x36' glulam ridge beam----forgot the beam price but the lumber yard delivered it with a crane truck and as long as we were ready to set it there was no extra charge to unload it directly into place----love the unobstructed cathedral ceiling look.  Price was certainly not in the thousands though.

That's a good idea - thanks.  I guess I should start looking for other lumber yards as our local one doesn't have a crane truck.  Maybe spending a bunch more for delivery will save me a separate crane or fork lift rental.

Perhaps I'm being a bit pessimistic about the cost and hassle, but apart from the beam itself there's also all the other stuff - 4x6 and 6x6 posts, glu-lam and LVL headers (because the posts are over doors), lots of concrete where the posts sit (I think the main support has almost 1/2 yd) and individual pieces of hardware that start heading towards 3 figures.  It's also a lot harder dealing with this big stuff with a small crew (typically just me!).  But it's good to hear it's all worth it in the end...