Header to supporting the roof and rafters. It was a patio converted to a sun room and I would like to replace two large windows with a sliding door. Currently 4x10x12 header with post in middle. Want to remove post with three 2x8 DF with 1/2" plywood sandwiched between to get my 6" and span 16'.

I'm tight on space, that why I need to use 2x8.

Please advise if this will work?

  • How far do the rafters span onto the existing header? Do you live in a heavy snow zone? What is 6” and why “are you trying “to get my 6” “?
    – Lee Sam
    Nov 5, 2020 at 0:39
  • I believe that you've got a 4" x 10" x 12' header that covers two 6' spans (the post in the middle shortens the span) and you want to replace it with a built-up 6" x 8" x 16' header. I don't think you're going to be very happy with that. I'm pretty sure that any engineering/load span calculator you can find will tell you that 8" deep wood won't support much weight over a 16 foot span, even if you double or triple it in width.
    – FreeMan
    Nov 5, 2020 at 14:09

1 Answer 1


A beam made up of multiple members with plywood spacers can be done, if the fasteners are up to code.

However, that really isn't your question. You want to know if you can reduce the depth of your header while also increasing it's length. For any given condition (loading, length, beam size, material (wood or steel)), the two things that most affect the design are those two (smaller differences have larger ramifications).

Further, for a longer beam, deflection controls not strength. Deflection is many times more dependent on the depth of the beam rather than the width.

Therefore: You CAN NOT make up the difference in depth by widening the beam.

To get a more specific answer will require a site visit by a structural engineer so they can determine the loading and other site specific conditions.

  • Why can’t you “make up the difference in depth by widening the beam” ?
    – Lee Sam
    Nov 5, 2020 at 0:28
  • "Deflection is many times more dependent on the depth of the beam rather than the width."
    – Ack
    Nov 5, 2020 at 1:08
  • Mod notice Deleting comments because they don't follow our code of conduct. Please keep posts to the site respectful.
    – BMitch
    Nov 5, 2020 at 13:36

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