transition to 16" on center deck joists

Reply

  #1  
Old 11-07-18, 12:12 PM
sgull's Avatar
Member
Thread Starter
Join Date: Nov 2007
Location: AK
Posts: 2,899
Received 1 Vote on 1 Post
transition to 16" on center deck joists

An old deck I have was built with deck joists 24" on center. The joists are 2x12 lumber. I'm wanting to replace the wooden deck boards with the Trex brand composite deck boards which require 16" maximum spacing between joists. This means I'll need to add an additional joist between the existing ones (which will result in 12" on center). Will it be necessary for these additional joists also be 2x12 in dimension, or can they be maybe 2x6 instead? Because that dimension lumber would of course be less expensive. Any comments appreciated.

The title of this thread is misleading but I couldn't edit it after I posted it. I'd actually be transitioning to 12" on center (from the current 24" on center).
 
Sponsored Links
  #2  
Old 11-07-18, 12:23 PM
M
Member
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,972
Received 2 Votes on 2 Posts
What span do you have from ledger/house to beam? This will dictate what size lumber you need to go with. 2x8 would be the minimum I would use, and I believe 11-10" is the maximum span for that size lumber at 16" o.c (southern pine). Whether or not having a 2x12 joist every other joist increases the span of the smaller lumber is beyond me. I wouldn't imagine an inspector would have an answer for this either. He'd probably go by the span tables for the 2x8 to be safe.
 
  #3  
Old 11-07-18, 12:52 PM
sgull's Avatar
Member
Thread Starter
Join Date: Nov 2007
Location: AK
Posts: 2,899
Received 1 Vote on 1 Post
Span from ledger/house to beam is 11' 6". Douglas fir joists. Probably 2x8 minimum dimension for the additional joists then would be fine?
 
  #4  
Old 11-07-18, 12:55 PM
M
Member
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,972
Received 2 Votes on 2 Posts
I would say so, yes. That way you won't have to worry about going against code, even though the 2x12's at 24" are all that is required to support the deck. There would be no doubt that using 2x8 would be fine, but going to 2x6 could be questionable. Plus, 2x8 will give you better support for the Trex.
 
  #5  
Old 11-07-18, 01:00 PM
sgull's Avatar
Member
Thread Starter
Join Date: Nov 2007
Location: AK
Posts: 2,899
Received 1 Vote on 1 Post
Ok that's good enough for me. Thanks mossman for the helpful input.
 
  #6  
Old 11-07-18, 05:22 PM
sgull's Avatar
Member
Thread Starter
Join Date: Nov 2007
Location: AK
Posts: 2,899
Received 1 Vote on 1 Post
Actually, re-thinking about this, I'm considering just redoing they layout with 16 centers; it might be faster and may make for an easier install, and it would seem the cost might be about the same when you consider how many fasteners you probably save with less joist.
 
  #7  
Old 11-08-18, 08:11 AM
M
Member
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,972
Received 2 Votes on 2 Posts
That's entirely up to you. Personally, if a product called for 16" maximum spacing, then I'd feel better using 12" so things are nice and solid. If you are planning on installing the decking at an angle (with respect to the joists), then 12" spacing is required.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: