I am having an argument with an architect about wooden treads for an exterior staircase.  I have always been taught that treads go crown up. Have I been wrong about this my whole life?

That's what I learned when I started woodworking and I have (mostly) stuck with that.  If the stairs will be covered then I would just go with whichever side was the better looking.  I can say that on a swimming pool deck that I had for about 25 years - made from 5/4 PT pine I had no cupping of hardly any of the deck boards.  They were all screwed down and had a good frame underneath.  I am sure there were some that were fastened crown down in that project.

 

And welcome aboard, glad to have you here.  Post up some pics, we like to see project pics!

Edited February 16, 20233 yr by Cal

That's what I've always thought (crown up) though I'm not sure why...I do know I didn't make it up so somewhere somebody told me that. That said, I'm not sure I ever gave it much thought.

Edited February 16, 20233 yr by Fred W. Hargis Jr

What I've always heard and did.

 

Moved to General Woodworking Forum

I think it's simple geometry.  Crown up means there are two points of contact with the substrate surface, which is a stable configuration.  Crown down essentially is one point of contact, and able to roll on the under-surface.  Positional determination has only one solution with crown up, but multiple solutions with crown down.  That's as murky as I can make it?

Thought exercise....  If the crown is up, and deck boards go through several seasons of dimensional cycling with humidity changes, won't the up face be more likely to check/split open, allowing water to seep in and encourage rot?   The redwood steps of the deck that was on the back of my house when I bought it were in assorted states of rot/failure.  Didn't bother checking how they were installed (crown up or down), but some had rotted much more than others.  There was some clear difference between them, suggesting their face up was likely random.  

22 hours ago, PeteM said:

I think it's simple geometry. 

 

Correct Pete, if the board has already cupped... I try to buy them flat

 

18 hours ago, 4DThinker said:

Thought exercise....

 

The flip side of this coin, or deck board... if it is installed crown down and cups to any degree, haven't you just got a natural water basin that will hold water longer and lead to the very sort of problems we're trying to avoid?

Look at the piece on top center and to the left of it.  This is how the board will cup.

 

 

Edited March 5, 20233 yr by kmealy

Anyone accounted for the nails or screws holding down a flat board when it wants to cup or bow up?  It seem the resistance against being held flat by the fasteners is what encourages splitting or checking  when the humidity changes.  I doubt any deck builders use slots for one screw with the other screw fixed to permit the board to expand and contract. 

4D

Edited March 5, 20233 yr by 4DThinker

23 hours ago, kmealy said:

Look at the piece on top center and to the left of it.  This is how the board will cup.

 

 

 

Just the opposite of what I would have thought Keith!  Now I have to go look at my deck, surely some of those boards have some degree to cup occurring...

 

22 hours ago, 4DThinker said:

I doubt any deck builders use slots for one screw with the other screw fixed to permit the board to expand and contract. 

 

Now that would add a couple of hours to the deck build

Most of the decks in our area are made from PT pine and usually quite wet.  A slot might actually make a lot of sense.