[MightyDyngus]

I am currently working on framing out some larger windows. The materials list I am working with calls for 4x4 Douglas Fir headers. Is there an issue if I use Pressure treated 4x4's instead?

 

[oh'mike]

two 2x4s with a slice of 1/2" plywood is the usual way to make up a 4x4 header.

I'll wait for an engineer or framer to speak up---do NOT use a treated fence post---

 

[jlhaslip]

The Engineering specifications are different for those wood species.
I once used solid 4 x 4 's as headers for some interior doors as per the design prints and was back in a year to change them to a pair of 2 x 4's with plywood spacers as per the previous posting.
Solid wood headers come with splits, checks and they twist too much for use as headers, IMHO.