I have a 6' opening in a load bearing wall which is currently supported by double 2x10 dropped beams. I want to convert these into a flush beams.
Do I need to to use LVLs for this?
The engineer told me I don't need drawings if I am leaving the opening the same size and just changing the beam.
A flush beams needs to be carefully engineered as it will usually be held up be a wall itself or joist hangers. Your engineer was right in either can be used but it will have to be engineered to proper load bearing qualities and as to how to properly install it as per the current construction in place (roof, floor etc.) You need to get this looked at 1st.
First off a double 2 x 10 isn't a beam it's a lintel. The Building Code contains tables for sizing of lintels (as well as beams). Dimension lumber beams start at 3-ply & go up to 5-ply in the beam tables of the Code whereas lintels start at 2-ply.
If you're doing nothing other than raising an existing lintel (which previously met Code) and it didn't display any untoward sign of deflection you should be OK without requiring a new design. Note that newer (i.e. 2nd growth) lumber is not as strong as old growth lumber which resulted in the span tables being revised not long ago.
Raising it to flush does carry some risks in that when joists rest on top of a beam or lintel they are usually lapped and nailed together as well as to the support. The structure does lose some strength by altering it in this manner; however as long as you're conforming to all the framing rules contained in Part 9 of the Code it should be OK. It is assumed it is a floor system above and not a stick-framed roof.
Typically anytime there's a structural alteration it requires a building permit which means preparation and submission of drawings showing adequate detail for your local municipality to check for compliance.
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