As a building contractor it is my job to assemble the house to meet the specifications from the architect and the structural engineer. I do this by looking at the building plans and installing the specified lumber sizes. I can take it upon myself to install a larger size wood beam or window header adding an additional cost to the job of course. I don't think so.
It's not uncommon for a framing contractor that has an additional 5 foot scrap piece of 4 x 8 left over that he now has no use for. He can then choose to use the 4 x 8 instead of a 4 x 6 for the window header. This type of building is common and acceptable.
If the structural engineer calls out for 4 x 6 window and door headers do not take it upon yourself to replace the 4 x 6 with a 4 x 4. I have seen too many framing contractors or carpenters make an on-the-job judgment like this.
A good example would be a single story house with 2 foot wide windows that require a 4 x 6 window header. As the carpenter builds homes over the years he can come to his own conclusion that a 4x4 will work fine for this application. Again keep this in mind as a framing contractor and a carpenter you are assembling the home not designing it.
Do not change the sizes of any headers or beams.
A long time ago carpenters used a standard rule of thumb, you could go up two sizes larger than the window opening for your header. Let me give you an example of what I'm trying to explain.
A 4 foot wide window opening would require a 4 x 6 window header. A 6 foot window opening would require a 4 x 8 window header. This should give you an idea of what I mean by going up two sizes larger than the window opening to figure out the lumber necessary to use for your window header.
This rule of thumb does not necessarily apply in today's building industry. The reason for this is structural changes from earthquake damage. The structural requirements that are required for building a home require a lot more metal bracing and strapping. Therefore some of the lumber requirements for beam sizes and window headers will be different.
This message is for general contractors, framing contractors and carpenters. When installing a window header and you take it upon yourself to change the size you also assume the responsibility if the building fails. This type of mistake is common and you guys know what I'm talking about.
It's not worth it. Keep in mind you are the assembler and not the designer of the building you are working on.
Greg Vanden Berge is working on the internet to promote the education for creating simple to follow guides and home building books to help professional building contractors as well as the weekend warriors. He is currently working on more Building and Remodeling Library and adding useful content to help solve problems created by the lack of construction knowledge in the building industry.
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