Given the design constraint of working with the metal bits, and your preference for materials from the local big box, I'd go with oak. Generally, it's strong and will survive outdoors. If possible, I'd consider the thickest pieces available.

If you broaden your search a little, I'd look at what some of the high-end deck builders have been pushing for the last 10-20 years. Specifically, imported heavy-weight exotics like ipe. Not cheap, but stronger and will last even longer than oak.

 

Best thing you'll likely find at a BORG is going to be PT decking boards. If you have any options outside of a BORG, I'd look for cypress or better yet ipe, but it can be very tough on tools, but also very longlasting

 

most box store woods will not survive for long outdoors without periodic maintenance.
douglas fir, white oak, black locust, redwood, cedar, etc. when properly sealed,
primed, and painted will last much longer than any varnished or clear-coated project.
clear coats have a mandatory maintenance problem. if not cleaned and refreshed when
needed, rot and deterioration will soon follow.

.

 

You can generally fit up to 1" thick wood in there. Increase your thickness to that, and use a hardwood that is resistant to the elements. I used Sapele for the bench I rebuilt.

 

Red Balau or white oak if it was me. You won't find Red Balau (Kayu Batu) at a big box store though.

 

I would use either ipe or black locusts. Both very hard hard and rot resistant.

 

Personally, I'd toss the cheesasauras cast metal part and make the entire thing out of wood, especially if "hefty" people expect to sit in/on it. That way you have complete control over the design and stability. You could cut that pattern into the backrest, if you wanted. When I designed mechanical ground support equipment, it was right in the manual that, "the design should look sturdy". Nothing like workers walking up to a structure unconvinced that it will support them.

 

White Oak.

 

We are doing a very similar project. Wanted to use wood we could get locally that was relatively cheap. Chose Douglas Fir for its high modulus (stiffness).

Our bench requires 3/4" X 2 1/2" actual dimensions for almost all the boards. Ended up buying Doug Fir 4 X 4 from Lowes and making the boards from this.

Everyithing is painted and will go back together this week.

Interesting to note the fasteners on ours were metric - 6mm bolts held the seat boards down. Got truss head stainless replacements from McMaster.

Sorry about the photo orientation. Could not figure how to rotate it. Original on my computer is upright…

 

All oak is not the same. You will get red oak at the box stores. It is no good for outside. As stated above, you need white oak if you want oak.

 

+1 on white oak

-1 on red oak.

IPE decking material is another consideration.

The benches we have are equipped with a metal strap underneath the slats in the middle to distribute the weight.

 

White oak or Ipe, most lumber yard should be able to help you out.
White will be a little more maintenance but less expensive up front. Ipe a little more but almost no maintenance if you want it to age. Both should last a good long time.

Don't forget stainless steel hardware, make sure it's not magnetic or barely magnetic.

 

HI all

Thanks for the replies. Much appreciated.