Recent content by BPP

You will want to google “lintel”. You should have an existing one that is almost certainly steel angle or an I or T-type beam.

If you go with 13/16, which as pointed out, will fit 21mm typically, just a bit tighter, which is actually in your favor roundover-wise, you should be able to find a number of used ones on ebay of the Proto, Armstrong, Mac, Williams, Snap-on variety. But, if your cars have 2 pieces lug nuts...

As already mentioned, with that joist spacing you will need to add either more joists or blocking placed between your existing ones. If you can get by with less R value, 1” Polyiso foam board will give you R6 and because it is so light, it wont sag under its own weight if attached on 4’ centers...