currently, I have a basement door leading to my backyard that id like to widen to accommodate a sliding glass door. This wall is load bearing as the floor joists run to it. Currently, there is no lintel/header. My existing door runs all the way up to a double sill plate that runs around the perimeter of the home. Do I still need a header/lintel or will the sill plate bear the weight? Is a lintel and header the same thing? Also, I'm not sure how I would install a header anyway. There's not much space above the door opening. If I used 2x6 header, I might need to have a short door, or cut the sill out (which I figure is a bad idea). All help appreciated.

I thionk it would be safest to get 3 bids from pros and then listen carefully to their plan. Once the bids are in you can think it over and decide if you can handle this type of work or hire one of the contractos. This job would require a permit in most areas and you might not be allowed to make it a DIY project. Failure of a load bearing wall can be pretty serious.

Well if I wanted to do it myself, how would I go about the header situation with my size constraints?

Again,as was suggested,Get 3 quotes from professionals and LISTEN to how they would go about this type of project.Then you can better understand what it is you have to do,Then you can ask for more information from us to help you,we can't see the opening,we don't know the load above,too many factors that we can't guess at.

Hope this clarifies what was posted before.

Tavellar, I think you aren't catching my drift. Installing a door in a load bearing wall is over the heads of 95% of the people I work with, probably me too. Listen to what 3 pros have to say, they may say this is impossible. Also, I think you may be considering trying the work with out a permit. This is a could be a very serious mistake depending on the building codes in your area. Listen to the pros and then come backhere and tell us how they plan to carry the load. One question I do hear from you I can clear up. A lintel , actually it's a header, is no thicker than your current fllor joists. If the floor k=joists are currently 2x6 then the header will be 2x6. The 3rd dimension is thickness and that will complete the load calculations.