I have to replace the main beam in a deck at my house. The deck is 10 x 23 and the beam is 6 feet from the wall with the other side of the deck supported from the wall. The deck joists are sistered to the floor joists with lag bolts (about 3 feet of sistered joist section). As per the above there is 4 feet of cantilevered joist going past the beam and 5 feet of cantilevered beam that connects to another beam.

The beam span is 18' and the original beam is a 13.5 x 6.75 glulam. It failed due to dry-wood termites and water causing the laminated sections to separate right over the column connector. I think that a previous owner may have had a plant right over the beam where it joins the column and when watered steady stream of water ended up on the corner of the beam. It never sagged in the center. The deck is ~35 years old and was built with the house. For good measure I am also replacing the posts, joists (many are pretty rotten) and deck boards (which where still there after 35 years so very rotten).

Anyways this size (13.5 x 6.75) while available and not terribly expensive (~$400) would be very hard to get into position to lift into place (lifting wouldn't be that hard). The issue is that the back of the house is situated over a very steep hill (practically a cliff) and not accessible by heavy equipment.

A few alternatives I am considering.

  1. Making a built up beam using 3 2x14's and a 3x14 (13.25 x 7) how would I calculate if this is equivalent to the 13.5 x 6.75.
  2. Adding an extra post (the soil is very hard but I could hit bedrock or a huge boulder within 24" or so).

I am mainly am looking for input on number 1 above.


Download a free pdf Wood Deck Construction Guide from the American Wood Council. It is based on current codes and standards and can help with all aspects of wood deck construction in the absence of specific direction from your local AHJ (Authority Having Jurisdiction).

It will not address engineered construction members (like laminated beams) though...

  • Thanks for the comment, I previously reviewed the deck construction guide as well as the current code and local codes and surprising the decks construction meets even the current code apart from just a few minor things (PT lumber within 36 inches of the dirt for local codes is all I noticed). I have a feeling that if I talk to "AHJ" they are going to say replace it with exactly what is in the original approved plan, and I guess thats the right answer. I supposed I should change the question to ask whats the best way to move a 600 pound beam down a steep hill without equipment. – user103870 Jul 14 '19 at 23:25

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