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Posted 07/04/2020 in Basic Help

DIY Deck Repair - Main Header Replacement


DIY Deck Repair - Main Header Replacement

DIY Deck Repair - Replacing a rotten header beam on your deck.

If your deck was mad of a wood product, sooner or later the support system will need to be replaced. It might be the joist or the main beam that holds up the joist system. 

In this blog article we will show you the safe and best way to replace the main beam with out tearing down the entire deck system.

A main beams or headers are usually a 4x8 piece of lumber, sometimes it's just standard fir not pressure treated. You want to use pressure treated lumber on your deck support system.

As years go by the rain water will drip down between the decking boards and just sit on the top of the header, it will start to rot the board the first time it rains. It will take years for it to destroy the beams integrity and strength, but it will happen.


This is a very dangerous project! We do not advise you do this! 

Hire a Professional Contractor!


Replacing the main header beam in the deck sub framing system.

  1.  The first thing you will want to do is close off the deck to any and all traffic.
  2.  Make sure the ledger board is properly attached to the house and that it is not rotten also. If it is not rotten, it will need to be lagged into the house framing system. Not just into siding. If it is rotten STOP!


Next we will build the temp header beam that you will be using to support the deck while you are replacing the main header beam.

  • We will call this the "T" Header - Get a couple 2x8 pieces of lumber. It does not need to be pressure treated as it is a temporary header. The length should match the length of the main header, you should make multiple smaller temp headers. use decking screws to tie the two 2x8 together like a "T". 
  • Next screw the "T" header in to the bottom of the joist system behind or in front of the main header beam. Give yourself some room to work around the main header beam. You will need a sawzall (reciprocating saw) to cut the nails or fasteners away later.
  • You will want to jack the deck up just a little. Use a floor jack with a 4x4 post to jack up the deck as you install the temp posts. Jack up one area and set temp post, then move to the next temp post and repeat.
  • You can now place the temp posts under the "T" header. You will want to screw properly cut to length 4x4 temp posts into the "T" header. To attach the post to the "T" header use decking screws and screw through the vertical part of the "T' header. You may also want to put a small 2x4 between the ground and the bottom of the 4x4 post, as it will help to plumb the post if you need to hit with a hammer. Place temp posts every 6 to 8 feet apart.

Once the temp header system is in place, you can now start to remove the rotten header. 

Make sure the temp header is set up properly!

Again Very Dangerous!

  • If the posts are in good shape, and concreted in, leave them in place. start cutting the fasteners away from the rotten header beam and the joist system. Put in a few screws as you go, so the beam does not move until you want it to move...
  • Once the beam is free from the joist system, you can start cutting the beam into manageable sizes and remove it.
  • With the rotten header now removed, it is time to install the new one. It is best to have a floor jack to help lift the decking a little bit if needed to install the new header beam. Many things can go wrong here! Make sure post stay straight up and down. You will need multiple people to help with this part.
  • Remember you may have jacked the deck up a little, so allow for that if you are putting in new posts.
  • Attach the new header to the posts.
  • Once the header is in place you can lower the decking system back down onto the new header.
  • Once the deck is lowered attach the fasteners to the header and the joist system.
  • Now you can completely remove the temp header system.

Find A Professional Deck Builder Here.