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I'm renovating a deck. Installing waterproof spline which goes between deck boards. Solution will have center boards in deck with gutters underneath and gutters around the deck. Install guide says to make sure deck pitches by 1/8" per linear foot. This is as much as 1.5 inches across 12ft deck (my deck is an L-shape with 12 ft longest, 8ft shortest). Laser level shows current slope of MAYBE 1/4 drop if im lucky. (Hard to tell with warped deck boards.)

Raising joists near the house not an option because threshold is annoying flush with deck boards (not to mention code says joists tops are supposed to be flush with ledger). Lowering rim-joist/band board/beam is not much of an options because would involve taking apart hardiplank, plywood, many sistered boards cutting posts just to lower.

Rim joist is overbuilt per code.

  • Rim joist: (2)2x12
  • Joist Size: 2x8
  • Joist Span: 16in
  • Beam Span: <6ft

Is there some rule as to how much is allowed to be planed/cut off of a joists or rim joist? I was thinking if I could plane down 1/2in from the rim joist and a tapered 0.5 from the joists I could get 1 in drop and that would help minimize pooling. Or I can just hope for the best with the current water management and live with some pooling post rain.

MD Deck Beam Spam Code Entryway Gutter Areas Post area

2 Answers 2

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You have two considerations: 1) structural, and 2) aesthetic.

  1. Structurally planning a small amount (such as 1/8” or 1/4” per ft) will not make a significant difference. However, for “L” shaped decks a hip is used to keep the edges level, allow guardrails to be installed level, etc. (Bearing, connections, etc. are probably a bigger problem, and don’t forget treated lumber is reduced by about 10% for outdoor use.)

  2. When the deck slopes at different angles the eyes see that as a mistake. Also, if the walking surface is too steep it’s uncomfortable to enjoy. Generally a slope exceeding 1/2” per ft. is noticeable.

Don’t forget that the code now requires steel connectors between the deck and house at each end of the area where the deck touches the house.

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  • Thanks for the tips. It wouldn't be more than 1/8". And it's an existing deck that has been grandfathered in (I assume). I already have footings that are not to modern code, but I will be trying to make sure it's up to code as much as possible without building an entire new deck ;)
    – Joe
    Oct 12, 2021 at 20:50
  • If it’s new structural work, then you’ll need a permit. I’d check with your local Building Department. You don’t want any problems at your next birthday party and it crashes during your “toast”. (If you’re in a high wind area or seismic active area things get crazy all the way to the footings.) Grandfather clause is usually for non structural work.
    – Lee Sam
    Oct 12, 2021 at 21:50
  • Yeah, I dont know where the line is drawn. Say I replace a post with the exact same type of post (or a joist say) for a repair. Do I really need a permit for that?
    – Joe
    Oct 13, 2021 at 1:39
  • That’s called maintenance…just don’t improve the system. Either way, talk to the Building Department.
    – Lee Sam
    Oct 13, 2021 at 3:12
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If I understand correctly, the configuration of your deck should look like below.

enter image description here

If it is correct, then you can replace the rim beam with 2-2x10 (see table below). You will need the table for the 2x8 joist to see whether you can reduce the size or not. But even you can downsize the joists, this approach seems very difficult, as you have to lift up a majority of the deck plates in order to trim the joists and beams.

Therefore, I suggest jacking up the deck and trim the posts instead.

enter image description here

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  • Thanks for your reply @r13 (AGAIN!). (deck length is technically 12'2in (with 2ft catilever?)) So the reason I didn't go for cutting the posts is because there's a lot to remove to get to them. (See new attached image.) I assume cutting in the middle of the post is a VERY bad idea. So I would need to cut at top or bottom, but unfortunately it's a lot to remove (including, MAYBE fragile hardiplank). But I'm 20% considering doing this anyways to replace posts (other question you answered). But 80% wants me to gamble for 10-30 more years on existing posts.)
    – Joe
    Oct 12, 2021 at 20:02
  • I see what you were thinking. But, I would invite a contractor to discuss the difficulty in jacking up the entire deck only to relieve the beam-post joint, so the post can be shortened to build the lowered connection. You may find it is not too big a deal after the discussion. If you are tearing the deck plates, wouldn't be the fragile planks need to be removed too? From the updated information, I wouldn't touch the rim beam anyway. Give this suggestion a 50%-50% chance, then let's see from there :) Good luck.
    – r13
    Oct 12, 2021 at 20:24
  • So I assume cutting 0.5in the the top of the rim joist with a circular saw would take 10 min, planing a tapered 0.5 off each joist would take a little more time, but would be easy (maybe circ saw would be a lot faster). I would have to make sure the surrounding framing (all the sheathing and 2x used to fasten the fragile cement hardiplank). The question if that is more than jacking, removing all sistered boards (or cutting through fasteners with saw, cutting 1 in off the top of the beams and then reattaching. Also I would probably be doing this myself, one or two posts at a time.
    – Joe
    Oct 12, 2021 at 20:47
  • Even it is permitted (which I am not positive) to carve out the rim beams, how about all the joists, they do need slope too. Good luck. (You need 1.5" at the lower end for the 12' deck, and 1" for the 8')
    – r13
    Oct 12, 2021 at 20:51
  • You bring up a good point the 1.5 vs 1 discrepancy would mean that TECHNICALLY I would have to move the ledger on the shorter 8ft side so that everything lines up (not doing that). Vendor says 1/8"/ft and I'll have lots of gutters, and since gutters slope only 1/4"-1/2" for 10 feet, I was hoping that I dont need full 1.5" and I'm just trying to give it a little more slope to help. But since it's impossible to get the same drop, same end height and same ledger height,I might just have to pitch ALONG the house into the centerboard gutters.Thanks for your help @r13, this has been very helpful.
    – Joe
    Oct 12, 2021 at 21:03

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