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Question DetailsAsked on 10/2/2017

Can a partially rotten rim joist (about 2") be sistered or will it need to be replaced?

I have around 2' of band board that is partially rotted due to a lack of flashing on patio door. It's only around 2" on the bottom of the board and is connected to a deck. It does not appear that the sill plate is rotten at all and the area is accessible as its the unfinished portion of the basement. There is some cracking in ceramic tile above the damage that runs down the subfloor seams. Obviously I would reflash the deck to ensure it does not happen again, but I want to make sure its a permanent solution and not a temporary fix (like the foam spray previous owners used to cover it up). First two contractors went straight to replacing rim joist as well as the upper portion of deck at a cost of $7,000.

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Voted Best Answer

Sounds like they are looking for a down payment on their next fishing boat, assuming your entire rim joist and deck ledger board area are not rotten. Get a repair design from a Structural Engineer - or for only a short section like you are talking I would just get a Carpenter - Framing who is reasonable - like probably about $200-400 range all in depending on how hard access is.

Can be done from inside crawlspace/basement with some back-breaking contortions in most cases - sometimes (especially if long piece) easier to temporarily support the deck (if its ledger board is covering the rim joist), remove joist hanger fasteners for the width of the ledger board covering that area, cut through any decking nails down into the ledger board with a sawzall (or remove screws from above) to free up the ledger board, unbolt it and slip down under the deck joists, exposing the rim joist. Of course, if deck joists are hung directly from the rim joist easier to get at and fix.

Can't say exactly how to repair because depends on exact wall construction and how many stories are overlying it and whether the rim joist (band board) has the overlying floors bearing on it or not, but there are two common fixes for this. (You said 2" and 2' above - I am guessing 2' long section with bottom 2" rotted, but whatever). Whether any temporary support for the walls would be needed depends on detail of the floor framing and the loads from above - full brick wall house or roof heavily snow loaded might need some temporary support during the replacement, normally a standard 2-story house cann easily bridge over a 2' gap in the rim joist as long as the subflooring and joists are good.

1) Remove the bad section as a full rectangular piece, to inside face of adjacent joists on each side (leaving floor joist fully covered by adjacent good rim joist material as nailing/bolting point), sistering to double up the end of the floor joist (typically sister would be 3 times as long as the height of the joist, so 18-24" typically) to double its width (which provides material to fasten the repaired section of rim joist to), put in new treated rim joist piece with code specified nailing or bolting. Can run only one joist bay or several depending on length of bad section.

If not beam-action designed, just simple bearing of the walls on it, can also be pieced if needed joist-to-joist (with sistering for fastening to) to work the pieces into place, especially if needing to install from inside the crawlspace. In some really nasty cases the pieces cannot have joints at the floor joists - in that case sometimes they are installed, then fastened to the floor joists using Simpson angle brackets and structural screws from the inside face. Just be sure they are flush on the outside - not angled in or out.

2) Remove the bad part only (the bottom 2" or so in a uniform height cutout) with skil saw or sawzall and maybe a bit of chiseling as needed, cutting out all the bad section and then putting in a replacement piece of treated wood with structural construction adhesive and toenailing into the rim joist and sill plate. If the rim joist is in vertical bearing only (just weight of floors above) that is all that is needed - if a flexure/sheet rated wall may need a metal Simpson or similar splice plate structural nailed/screwed over the splice - commonly assuming about 2" replacement on the bottom of the rim joist, would be a 4x7" plate or so on the outside, and ditto on inside (crawlspace/basement side).

When doing this, if the deck is bolted into the rim joist then you may have to remove some bolts in the ledger board and prop that part of the deck as necessary if a long piece coming out, do the repair, rebolt the deck into the joists or rim joist as applicable.

If you end up removing the deck board closest to the house, youtube a few how-to's on how waterproofing should go from underneath the siding at the deck level to the rim joist, then out over it (and the ledger board if you have one) and an inch or two further to act as a dripedge under the deck board closest to the house so any water running down the siding stays away from the house, held out and dripping free under the deck by that flashing - Grace Vycor or similar eleastomeric or asphaltic water shield is the easiest to do this with.

I hold the deck board closest to the house free of the house 1/4" and also use 1/8" rustproof washers or rot-proof shims under it on the joist to slope slightly outward from the house and also to leave a drain gap under the deck board at the deck joists to minimize rotting of that deck board from below - then use 1/4 round trim (treated or well painted) to conceal and keep leaves and such out of that gap - caulked at the house wall and at the deck board as a splash guard to keep water out of the gap and to run the siding runoff off onto the deck board and away from the house.

Answered 2 years ago by LCD

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