Header Span Limit

[optionguru]

I'm planning on building a 14x24 and have some windows that are approx 5 ft wide and 3 feet tall.  I wanted to put two of them almost side by side in one of the 24 ft walls to have a nice view of the lake.  Is there a general rule regarding the size lumber needed for certain spans in a header?  Do I need to use beefier framing for the whole house?

Thanks,
Peter

[T]

Hello Peter,

I am sure the experts will chime in on this.
So for what its worth...

I have a case where there is no building code so I too recently needed to calculate this question based on some "almost free material" that was available and some ideas bouncing around in my head..

IMHO, there is much more to just using a general rule for 'span' as you mention. The folks I had worked for in the past "had general rules" for header size, span number of jacks needed etc.. but it was mostly based on code experience. Therefore, generally speaking your local building code should give you some idea based on your individual specifics/area what you can do. Otherwise, there are several factors that come into play. Take a look at this calculator for example, note the that load (snow, etc), header placement, type of material, etc.. all play a role on this span.

http://www.cwc.ca/design/tools/calcs/SpanCalc%5F2002/span_calc_headers.php?member_type=999&species=0&grade=1&height=2&width=6&spacing=24&load_id=0&result=&span_type=1

This not to mention a header can be perhaps beefed up (again code dependent) with something like.... http://toolbase.org/PDF/DesignGuides/flitchplate.pdf

In this venue, I would error on the side of 'too-much' than 'too-little'.

[okie-guy]

I'll chime in too. My framing book says that the header is as follows:
Spans for a one story house(two story houses are a different deal)
1)up to 4 ft.- Two 2X4
2) 4 to 6 foot- Two 2X6
3) 6 to 8 foot- Two 2X8
4) 8 to 10 foot- Two 2X10
5)10 t0 12 feet- Two 2X12

Of course this is standing them up and then you add in a piece of 1/2" plywood between them to achieve the 3 and1/2 " wall thickness.

[optionguru]

I've seen that some people are framing their walls with 2x6 instead of 2x4.  Is this just for added building integrity or is there more to it than that?

[Chateau Prideaux]

the 2x6 framing allows for thicker insulation and therefor higher R values. As to whether it is beefier, that depends on the spacing. IIRC, 2x6 is 24" OC and 2x4 is typically 16" OC. You could space 2x6 ad 16 and have a stronger wall, but I'm not an expert on whether there are cases where it would be necessary.


The 2x6 also allows you to lay in a 2x for the 2nd floor floor joists in balloon framing.

[Amanda_931]

The serious professional builder among us will tell you that 16" on center with 2x6 is the way to go.  Advantages of insulation, and the walls tend to be a lot straighter than 24" on center.

He's probably right.

6"-12" round wood, peeled, and possibly shaved a bit to make for less chinking, stood side by side would make a nice wall too.  

[optionguru]

Is there a thread that explains the 2x balloon framing you mentioned for the loft?

[glenn kangiser]

Here is one

http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1114976901/4#4

Also - there is quite a bit more if you go to the search button above and search the word "balloon".  Set the date option to all posts to bring up a good response.

[PEG688]

Is there a thread that explains the 2x balloon framing you mentioned for the loft?

How to plus more about letting in than anyone should ever need ::)Here:

http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1144724922

On your header question there is more than just span to consider , on a normal height ceiling (about 8 ') a  dbl. 2x10 header with a 2x6 on the flat under it (like L sort of ) will work out for a 6" 10" RO which workers nicely for doors it also lines up your headers around the house (generally there are things that can happen that throw that line up off , so this a a general rule) '  On a situation like your thinking about I'd use one continous header MTL a dbl 2 x10 , or 4 x10 with the 2x6 S/R backer "L"( if your walls are 2x6 ) which to meet energy code they will / should be 2x6 that is . I'd use 2 at least,  maybe 3 / 4 "trimmers " between the two windows , these "trimmers " would make a mullion "look" between the two windows and provide bearing for the header. As you want more view the two vertical 2x6's nailed together would provide support for that header.   Of course many variables to this situation , roof load / foundation / # of floors all could make this advice poor advice . More info on your building would be required for good / better / best advice . So this is basically a shot in the dark . G/L PEG


MTL TMI in this post.      

[optionguru]

Great links and great information.  

My plan is to do the 14x24 on a post and pier foundation.  I would like to use 12 foot high walls to give the lofts more room.  I also have a great local lumber yard that sells rough cut lumber and beams very inexpensive but I'm worried about all the troubles I might have using full dimension rough cut versus traditional dimensional lumber, any thoughts.  

[glenn kangiser]

I don't like full dimension rough cut - it's a special order item if you ever have to work with it later.  See if they will cut it in standard sizes so you can replace parts or add on with regular lumber yard 2x4's etc.  I always cut mine t the standard finished size.   Per Ken Kern - even 2x4's are over strength in most cases anyway.  You can throw out a bad mill cut board just as easily as you can throw out a bad graded board.  Make sure you are not required to have stamped lumber by any building department if they have any say on your project.  Some will give you a variance - some will not.

[John Raabe]

All good advice - especially the continuous header (could be a built-up girder). Make sure you leave enough wall space on the sides to handle lateral bracing (4' normally).

Also, because of the post and pier foundation, consider where the heavy loads from the post in the middle of the twin headers will land. This will be a pretty good point load.

[optionguru]

I ordered the plans yesterday so I should just be patient and wait to see if these questions are answered in the plans themselves.  I've just been day dreaming about this project for a few years and now that I'm finally closing on the land and ready to start I'm getting very anxious.

Unfortunately in my area the winters are dead time.  Currently the lot has a very rough right of way so my pre-winter project will be to turn that into something closer to a road with some drainage.

I was planning on using 6x6 posts in the foundation, should this help with the loads from the long header?

[PEG688]

I was planning on using 6x6 posts in the foundation, should this help with the loads from the long header?

 The post size in this 14x24 post and beam cabin I'd say should be 4x4, when  you go bigger on posts  , generally ,it's due to length as that post could flex under the weight if it's to spindey/ small to combat the deflextion the weight could cause.

This is "general" infomation / rule of thumb so no chapter and verse from a manual.

Some of these questions are a trap in a way as no "rule of thumb " works for every situation many variables are / can b stated.

On a cabin of this size "point loading / loads " would be hard to add up to signifcant weight / ## to worry to much about. Point loads "generally " come /are involved in multi storey buildings with large roofs , and potential snow loads . If your beams and post are right out at the primeter of the building , not set back 18" or so , your box sill / joist system should tranfer the load of that header , if your worried about it and the beam is right under the exterior wall just put a post and pier right under the three points of the trimmers , I doubt it is a issue thought.

BTW John most of my advice is good  , generally , if it's about building    

[glenn kangiser]

If I recall correctly, fiber stress on wood is about 1000 lbs per square inch -- my rule of thumb stuff out of my head---
various sources--- the issue is not so much the wood strength - a 4x4 = 3.5x3.5"- 12.25 sq inches or 12250 lbs support strength if not too tall.  The footing under that post has to be big enough to support whatever load you put on it.  Many times they allow 1500 lbs per square foot -- 6000 lbs roof area - snow load - material weight - etc on one post would require 4 square feet of footing with reinforcing to keep it together -- just for an idea of where information like this is coming from or going too.