Window Header Dimension

[Scott MO]

Hello,

I found two, stationary sides of sliding patio doors at the local HFH Restore ($30 each)  .  They are new, double paned, without grids, and might make great picture windows when turned on their sides.

Off topic: This was my first trip to a Restore.  Lots of "stuff," but I was lucky enough to find a few gems.  I'm sure I'll find other bargains when I have time to sift through the aisles and aisles of material.  Can't beat the price, either.

Question: What header dimensions are recommended for that length span?  These will be on a first floor, with a second floor above.  I already built up headers for another use (6x8x8, consisting of 3 2x8x8 with 1/2in osb sandwiched between)...do you think these are sufficient or would you recommend going with 6x10x8 or even 6x12x8?

Thanks.
Scott.

[MountainDon]

An accurate reply would need a few more details... snow load for one. What grade lumber is another. My southern pine charts also make distictions on header size depending upon the overall length of the wall supporting that roof.

Example: 30 psf snow, two story, #2 southern pine, 24 ft wall = three 2x10 for an 8 foot header span.
    28 ft wall = three 2x12

Change the snow load to 50 psf and those numbers become three 2x12's for both 24 and 28 ft walls.


I can't translate your three 2x8 headers into anything (yea or nay) using my tables. Sorry on that. Maybe PEG or John will drop by.

[n74tg]

Your header size depends on the load it has to handle.  That load depends on lots of variables such as number of stories and width of your building. 

I have a library copy of Residential Structure and Framing, by the editors of The Journal of Light Construction.  In there they have an article on the Simple Approach to Sizing Built-Up Headers.  I am not willing to shoot a picture of the table (copyright), but I will tell you what it says. 

For a two story house, using a 50 Load Factor (40 psf live, 10 psf dead), using #2 SYP, for your 8 ft header span, using doubled 2x8 your building has to be 6.5' width or less (ridiculously small), doubled 2x10 will handle a building width of 10', doubled 2x12 will handle a building width of 13'.  Any width bigger than that requires tripled 2x lumber; trip 2x10 good for width up to 15.4 ft, trip 2x12 good for width up to 19.8 ft.

Now that 50 Load Factor assumes no to very low snow loading.  If you have a snow load problem, better to use a 75 Load Factor.  Here are the numbers for that.  Again, assuming an 8' header width, tripled 2x10 up to 8.9' building width, trip 2x12 good for up to 13.2' width.

In either case, the table does not address any additional strength provided by sandwiching OSB between 2x members.

Someone else may be willing to post the table (hint, hint).

Realize here, that I am just telling you what the article says.  I am not a licensed engineer, so take this info with two grains of salt and crosscheck the numbers with someone in your local area qualified to give opinions. 

P.S. this table gives pretty conservative values.  As this is entitled a Simple Approach to... article I think they have built in lots of safety factor.

[Scott MO]

Mt Don / n74tg,

I'm still learning what information is required in these posts...sorry.

I plan to use 2x6 framing and use built up headers to match the 6" depth, on a 32' length wall.  The door laid sideways would not require a full 8' header...I'd need to cut the length down a bit.

There is a small snow load and I believe the lumber is #2 SYP.

In reading the replies, it seems using a built-up 6x12xL header is required given the overall wall length.

Thank you for your recommendations / solutions.

/r
Scott.

[n74tg]

Scott:
The "length" of a wall has nothing to do with header sizing.  A 32' wall would need the same size header as a 320' long wall.  Where the load comes from is the "width" of the building, ie the dimension of the building that is perpendicular to the header being installed.   Similarly, it doesn't matter if the window is one foot tall, or 8 feet tall.  The header is the same size.  What does matter is the window width.  A wider window dramatically increases the size of the header.  If your picture window was installed long dimension up, short dimension horizontal, the header size can be smaller than if you install it long dimension horizontal.

Now, to be completely accurate, each outside load bearing wall has to hold up half of the weight (load) of everything above it, roofing, rafters, trusses, ceiling, junk stored in the attic, etc.  So, load calculation is generally based on half the building width.  However, in the article I quoted to you from, the entering argument is building width (not half width).   

[Redoverfarm]

Your header size depends on the load it has to handle.  That load depends on lots of variables such as number of stories and width of your building. 

Realize here, that I am just telling you what the article says.  I am not a licensed engineer, so take this info with two grains of salt and crosscheck the numbers with someone in your local area qualified to give opinions. 

P.S. this table gives pretty conservative values.  As this is entitled a Simple Approach to... article I think they have built in lots of safety factor.

I usually go for the "bigger is better" approach.  Anything over a 4' opening I would opt for the larger headers.  Your span is rather wide and without any reference to codes or engineering I think it would be only wise to use the header that would transfer the load out of the opening.

[MountainDon]

The "length" of a wall has nothing to do with header sizing. 

I don't want to get into an argument here, but according to what the Southern Pine Council states, it does matter. Not being an engineer myself I don't choose to doubt them. I don't understand exactly how wall length becomes a factor in header size as well as I understand how a second story or roof snow load does. I simply report what the Southern Pine Coucil has published.

Here's a link  http://newstore.southernpine.com/cgi-bin/newsopine/index-us direct to their publications download page. There's a whole lot of useful info there. You probably can't go wrong with the information there, providing you input the right info or use the correct table.

[MountainDon]

Ooops.

I re-read the tables and it is correct that the width of the building is the important extra, not the length of the wall with the header.    Sorry.     

[PEG688]

The "length" of a wall has nothing to do with header sizing. 

I don't want to get into an argument here, but according to what the Southern Pine Council states, it does matter.

I agree with n74tg length of the overall  wall would not increase the size of the header. What length of wall CAN effect is engineered brace wall panels , every 25' of wall that HAS NO interior partitions 90 deg. to the exterior wall will require a BWP to help with racking strenght. To meet code.

Headers longer than 8 ' require two trimmers on EACH end.

Lindal Cedar homes some times , on some models sends out what I'd call a bond beam type header , essentially a 2x8 double header with a 2x6 so it forms a U shaped header that runs over all exterior walls , so windows and doors can be placed just about any where.


I gut says the 2x10 triple header , I really thing a doubled up 2x10 would do as well , will span that glass even as a 6' 10" window , the glass should measure about that length so even if you set  it in a wood frame with a  exterior sill you should be good to go in almost any snow load condition.


There are other factors as well that others have asked about. Fill in those questions and we may be able to answer in a better fashion.       

[n74tg]

Scott:

Here's one more aspect of this question to think about.

Everywhere you have a piece of wood, you don't have insulation.  So, if you fill up a wall cavity with a wood header, instead of building an appropriately sized header for the actual load it has to support, then you needlessly create a thermal bridge where more heat will flow out in the winter and in during the summer, increasing your utility bills during both seasons.   Now, in all fairness, you have this big window under that header, and that is a big source of heat loss too.  But, to fill up the header volume with wood (if it isn't needed) just magnifies the heat loss problem.   

With an appropriately sized header you will likely have some room for insulation, especially with your 2x6 exterior walls.

Over-designing makes us feel safer from a structural point of view, but it does have disadvantages.  And, this temporary drop in oil prices won't stay with us forever.