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Question DetailsAsked on 10/10/2017

How to cut a ledger board section without damaging the board or beam behind it

The ledger board supports an outdoor deck with joists. Found wood rot between joists. Suspect that wood has also propagated behind the joist. Would like to cut out the woodrot and some amount of good wood so one can use a fresh section, slip it and use metal plates to to join the old and new boards.

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2 Answers


Most likely you will have to disconnect a couple or few deck joists at a minimum (probe all along the ledger board to find ALL places there is rot) from the ledger board - wherever it is rotten plus a bit into good wood at each end. Pretty easily done if held up with metal joist hangers, tougher if toe nailed or nailed in from behind the ledger board but nails can be cut or the rotten section of ledger board cut in between and then split around the nails to remove it, then the nails (or bolts). Course, the deck joists have to be temporarily supported while they are cut free of the ledger board. Obviously, if doing a lot of ledger board, may be easier to remove the first deck board along the house or two and ALL the deck joists and put temporary supports under the deck joists all along, and push the deck away from the house enough to slip full-length ledger board pieces in and out past the ends of the joists - commonly means swaying the deck away from the house about 3-6 inches. Obviously, you need temporary supports so the deck does not collapse, and if the outer posts supporting the deck are rigidly supported at the base you may not get as much outward sway as you want without risking damage to the posts. And of course keep people off the deck while doing this.

I would first ask if you even have a ledger board (which the deck joists fasten into like a rim joist for the deck) then a house rim joist (aka band board or band joist -may be soild 2x material or in LVL/LSL or plywood TrusJoist type wood I beam construction may be a plywood joist) behind it, which is fastened across the ends of the house floor joists to secure them together - or is the outside joist of the floor system if the floor joists hapen to run lengthwise along that side of the house. (Technically band joist and rim joist are different things, but for this purpose will call them the same - of course, if the outside joist in the flooring system, acting as rim joist, is deteriorated then replacing that means having to support the overlying wall in the interim, which can get tricky at times.

Also, if the rim joist was used as a ledger board (to directly fasten the deck joists to) then it is likely the house joist ends and maybe sill board are somewhat rotten too - or if you have a rim joist and ledger board, a well rotten ledger board commonly means a partly rotted rim joist too - so either way it commonly gets into more repair than you expected. Generally, in my experience, if just the surface has some cracking and dry rot only that board may be affected, but usually if it is cracking apart or readily torn into, the wood behind/under/above it is affected to at leat some extent unless it is treated wood.

Normally, you would have a rim joist as part of the flooring assembly (the "joist box"), flush with the outside of the wall framing, as part of the normal house framing. Then a separate ledger board is fastened to that (and by newer code, fastened with standoffs and also fastened to the house floor joists with tension ties to hold the deck to the house), with waterproofing between them so the deck assembly and water from the deck does not rot the rim / band joist.

New tension tie requirement shown here - if replacing the ledger board technically you should be installing these to meet code requirements too0:

Typical construction (also showing waterproofing between the deck and the house to prevent such rot) shown here:


(in this one the band joist or rim joist is hidden/unshown behind the water proofing and ledger board)

(in this one, the schematic - third image down on the left in the article - shows the band or rim joist behind the ledger board.)

(this one shows rotten rim joist behind brick, but similar situation behind a ledger board or alone if the rim joist was used as the ledger board, as is common with older houses and a lot of DIY construction - this article also has some tips on how to retrofit a new rim joist into an existing wall/floor assembly.)

Here is a recent similar question with answer I gave on replacing a rotten rim joist -

Generally, for the actual cutting, a skilsaw works well if there is room - otherwise a sawzall or jig saw (using a temporary nailed-on piece of 2x as a cutting guide to get a straight cut) - some contractors will use the fancy new counter-rotating blade saws which do close-in cuts better than a skil saw. Depending on clearance, may need to use a drywall or jig saw or chisel to cut through the last bit of wood, especially if using a circular saw blade, which cannot clean cut all the way through at the ends of the cut without damaging adjacent siding. Obviously, make sure you are not cutting sill plate, ends of floor joists, electrical wires, hydronic or in-floor heating, water pipes, etc - normally you want to set to just cut through the ledger board initiallyto be careful. I use a large diameter (about 3") expansion or spade bit to cut an inspection hole through the portion being removed before getting carried away with sawing at depth - and of course if a rim joist is behind the ledger board, don't cut through that unless you are sure it is rotten and has to come out anyway.

If not DIY'ing this, if just the ledger board replacement in thescope of work, then a Carpenter - Framing or Deck contractor can do it - if removing some siding or other similar work is required to do the work, or if the rim joist is rotten and needs replacement along with some floor josit repair, then a General Contractor is a better Search the List category to be looking in.

Answered 3 years ago by LCD


One method I have seen used once or wice FYI - depending on accessibility - is using a guide strip of thin nailed-on material, and using a router with a 1/4" or so extended milling blade (has full-length, except for the chucking end, spiral cutting teeth for rapid removal of material - can get bits for full-size routers, and of course the small drywall cutout routers will work topo (though quite slowly going through 1-1/2" material) but would need a longer bit and make several passes - but probably the tightest quarters option.

Most carpenters would, is not clearance for a skil saw, likely use one of the heavy-duty 12-15 inch coarse tooth wood cutting blades on a sawzall, gently punching into the edge until the blade is in full board depth, then cutting at a quite flat angle to the board so the blade tip cuts in rather than bending and breaking the blade - if a slow speed operation, and of course you nick up the rim joist behind it some because exact depth control is not possible.

Answered 3 years ago by LCD

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