Upgrading 12 long by 16 foot wide deck to code

[illanrob]

This northern Alabama, USA home has a deck 6 feet above ground (2 story house is 2 feet below ground), the 16 foot wide side is attached to a ledger board and onto the first floor cement block wall. I lived in the house built in 1965 for 20 years and just now completed to upgrade the railing to code (40 inch railing, and 3.5 inch spacing on aluminum balusters, the railing looks great!). I may have to sell the home soon and will replace the deck planks as well.

I removed the very shaky stairs 8 years ago and added a very sturdy stair design with a landing leading to a new patio below. I added brackets to the 2 by 8 joists at this time. The deck got little or no use, so I let it be until now.

The 12 foot long deck built circa 1975 rests on 2 by 8 joists with 16 inch centers and 4 by 4 posts at the 2 corners. I found out recently that the joist spans are not to code 2 by 8 joists should only span 10.5 feet not 12 feet.

The deck does shake some when compared with the stairs. I am hoping that by adding a beam to the deck it will vibrate less. The question is should I sister some of the existing 2 by 8 joists now or wait for the beam to be in place first?

Code says I may add beam with spans of 11.5 feet, 10 feet from the ledger board using three 2 by 10 on 6 by 6 posts on 12 inch round by 16 deep cement pad. This design has 2 and 2.5 foot overhangs on the 3 sides.

Robert Illan

[pushkins]

Why not add a set of bearers 1/2 way out from the home approx 6'. If you add 2x 2x10 material as bearers under the existing joists the entire length of the deck, it will solve your problem your span will be reduced to approx. 6'.
Set your posts in 2' at either end that will make a 12' span for the bearers so your posts will be 2'....8'....14'. Bolt the bearers to either side of the posts.

[Fischer]

Originally Posted by pushkins

Why not add a set of bearers 1/2 way out from the home approx 6'. If you add 2x 2x10 material as bearers under the existing joists the entire length of the deck, it will solve your problem your span will be reduced to approx. 6'.
Set your posts in 2' at either end that will make a 12' span for the bearers so your posts will be 2'....8'....14'. Bolt the bearers to either side of the posts.

This is what I would do, and I'm into overbuilding everything.

[Wgoodrich]

The discription I am picking up is horizontal shaking movement not vertical flexing of spanning lumber. If this is true corner braces installed from bottom of post to top of next post at each corner is the type bracing you need to address horizontal movement much like wind bracing of a house.

Just my opinion

Wg

[illanrob]

Thanks for your reply and for sharing some of your ideas. I think that my first intent is to meet the deck railing and deck structure International Building Code 2003. So far I have redone the railing and the 4" ball test is now OK.

The 4by4 posts at the 2 corners is not to code since the joist span is 12' and should be 10.5' for the 2by8 joists.

I was thinking more of removing these two 4by4 posts altogether or if keeping them then they would be an auxiliary/extra support. If I add the new beam half way 6', I can see how vibrations would be reduced but then I would need to keep the 4by4 for support at the full 12' length. Then I would have to replace the two 4by4 with 6by6 posts.

This deck is built without a beam. The stairs that I added 8 years ago to the rim joist are supported independently of the deck. The stairs are probably reducing some of the vibrations that I had then. Do not remember.

The vibrations that I have now may be from a lack of a beam anywhere. I figure that no matter where the beam is placed half way 6' or 10.5' vibrations will be reduced. Once I add the beam it would be impossible to sister 2by8 joists.

Question: Should I sister some 2by8 joists before placing the one and only beam?

Thanks for your time,

Bob Illan

[pushkins]

If you reduce your span there is no need to sister anything, in fact if you already have joists hangers in place it will be almost impossible to sister anything correctly anyway. A set of bearers across the middle of the span will remove almost all if not all movement up, down or sideways. As for the posts on the two corners at the front, leave them there and add 1 more in the center of the span to break it down to an 8' span