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I am replacing my old deck that was completely rotten. The original was non treated lumber so it just was toast. The deck is only about 2' off the ground and 15' out from the house. It extents 30' across the width of the house. I am using 2x8 joists and double joists around the perimeter. There are 3 original footings for caring the load at the end of the deck but I was wanting to run a double 2x8 beam at 8' to help carry the load and get the bounce out of the 2x8s since I think the max span is usually 11' not 15'. I live in north Idaho where the frost line is 2'.

Can I bury pre cast deck blocks 3' down and run 4x4 posts up to catch the beam? The original footings should carry the max load as it did before, these would just help. The photo below shows placement but the blocks are not buried yet footi

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  • I have 4x4 treated posts. My question was can you bury the deck blocks below the frost line and use as intended with the 4x4 and it would be a decent footing. I have only seen those deck blocks above ground for floating decks but read they are a just a normal footing so I wanted it buried to stop frost heave. – Packy May 8 '20 at 16:06
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Sure you can, but they need to be treated for below-grade use. Most 4x4 are not, so you may need 6x6, which tend to be treated to a further degree.

Also, deck blocks are expense overkill if you're burying them, and they don't always meet the area requirement for below-grade footings. Use purpose-built cookies or a few bags of concrete mix.

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  • Thanks! sorry, I must have commented while you were editing. I dont deal with footings too much but what is a "purpose-built cookie". If I do a 6X6 should I do a triple 2x8 beam then too so I can span more (less posts). – Packy May 8 '20 at 16:11
  • Drop-in footing pads (cookies) used to be a common approach to what you're doing. A few years back they were disallowed as inadequate in my area, but for your purposes (I assume good draining gravel) they should do if you can find them. Your second question is out of scope here and mostly a matter of prerogative. – isherwood May 8 '20 at 16:13
  • If you can't find pads with larger base area I'd just be sure yours rest on good gravel or washed/crushed rock. – isherwood May 8 '20 at 16:14

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