Need Help With Building a Door or Window Header?

 

It sounds so confusing, load bearing, non-load bearing, span and load. These are all term to describe and calculate door and window header sizes. It's not really that difficult if you break it down into simple descriptive terms.

 

Think of a header like a small bridge. We recently visited the Mackinac Bridge in Northern Michigan. The purpose of the bridge is to "span" the gap in the land and allow the "loads" of cars and trucks to cross without plunging into the water below. The Mackinac Bridge "span" is 5 miles long, with many intermediate support pillars. I'm sure none of your door or window headers will be that long, but the principal is really the same. A door header allows you to create openings, transfer those weights to the studs beside the opening and then to  the foundation, much like the pillars do in a bridge.

 

Now we know how they work, but how do we know what size to use? That's where it can be complicated. There is no standard size header, no one size fits all. It all depends on the width of the opening, the weights resting on the top of the header and the various external factors such as the extra weight of snow, wind and rain. Not to mention those external factors called live loads, change by geographic location.

 

When I first started building over 20 years ago. We framed door and window openings with 2-2x12's with 1/2" plywood sandwiched in the middle over most all the exterior openings. This size worked out well because:

 

  1. The finished 3-1/2 in. thick headers (1-1/2 in. plus 1-1/2 in. plus 1/2 in.) were the same thickness as the 2x4 wall framing.
  2. When we installed the headers even with the top of the standard 92-5/8 in. high studs, it established just the right height for windows and doors.
  3. Architects and engineers who designed the houses had calculated that 2x12 headers were normally deep enough and sturdy enough to span most smaller openings. The problems can occur on the larger openings. Often 2-2x12's are not strong enough to support these wide openings without sagging.

This is where engineered lumber in the forms of LVL'Door and Window Headerss and GluLam's can be useful. These beams or headers each have their own engineering formula, so calculations on these need to be done professionally.

Another resource could be a Building Code book. Many codes have span tables that have pre-determined spans associated with the loads required for your area. These are most helpful for those simple header sizes usually under 6 foot.

 

Here are a few tips:

1.       Engineered lumber almost always can carry more weight than lumber.

 

2.       A sandwich header of 2-2x12's and plywood works for most openings under 3 feet wide, unless you have special considerations such a concentrated load called a point load. This situation calls for a qualified engineer or architect.

 

3.       The wider the opening, the stronger the header needs to be.

 

4.       The wider the opening the more jack studs (pillars) you need to hold up the header.

 

5.       ALWAYS consult with someone qualified if you have any doubt. Sagging headers, or even a collapse is possible if your header is undersized.

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