are existing joists for a new deck acceptable???

jaansuFebruary 28, 2012

I'm going to replace my deck with something this summer (wood, composite, aluminum, not sure yet). After I pull off the old PT boards and remove the nails, should I in some way treat the existing 20 yr old joists before the new boards are attached? Such as fill in the old nail holes to minimize water infiltration? Of course, any major damage will be repaired but just wondering. I read others talking about filing nail holes, putting down waterproof membranes etc.

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If your deck is 20 years old it's likely it was built to a code less stringent (and safe) than now. Like 4x4s instead of 6x6s for posts, or end-nailed joists instead of joist hangers. I'd take the opportunity to upgrade those at the same time. And the PT framing is about the cheapest & fastest part to replace.

Can you post photos so we can help you evaluate?

    Bookmark   February 29, 2012 at 8:40PM
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A 20 year old deck that is failing is failing. Period. The whole thing needs to be replaced. Pressure treated wood isn't eternal. It has a finite life and it is a big waste of time and money to put new decking on an old decaying deck frame. Tear the whole thing out and start over.

    Bookmark   February 29, 2012 at 11:54PM
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Thanks guys. I've crawled under the deck a few times and I have to admit I didn't notice any signs of decay or trouble. I shall go take another look to be sure - thanks for the heads up. I'd really want to be sure it requires replacement before destroying a possibly useful structure.

I bought the house 9 years ago and the deck could well be only 15 yr old. Tell me, if the supports look solid, should I continue with my idea of replacing only the deck or is it possible to miss signs of decay? Is it that easy to replace the whole thing?

    Bookmark   March 4, 2012 at 7:50PM
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Ease of replacement depends on the design. I helped a friend replace a 10x10 PT deck (complete teardown + replacement) and did it in a day. Our 660 sf 3-level garapa deck with pergola took us 3 months to build from the ground up.

Pictures, pictures. Then we can help you decide.

    Bookmark   March 6, 2012 at 8:33AM
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Sophie Wheeler

It's always a false economy to put new over old.

    Bookmark   March 6, 2012 at 12:45PM
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Treated lumber has a 50 yr warranty , if they look in good shape use them, one thing I would check is for crowns or dips in each joist. You can use a string and some help and slide the string from outside to outside down the deck to see if they are sticking up or down. You can try to turn them over or just replace the few that need it. For PVC decking this is important as it will show dips and crowns much more than other types of decking.

    Bookmark   April 9, 2012 at 8:46PM
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Where I live, the county requires a permit whenever more than 50% of a deck's materials are replaced. If you want to keep the framing, they require you to tear off the decking and then they come and inspect it.

This may not be a requirement where you live, but it makes a lot of sense. The other thing to consider - if you have any future insurance claim involving the deck (someone falls from it, it gets damaged by wind, etc.), most likely the insurance company will deny your claim if you reused existing framing without having it inspected.

    Bookmark   April 12, 2012 at 8:39PM
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If the substructure is in good shape, you can go ahead and just change the decking. Once you remove the old decking, check for rot. If it's attached to the house, make sure that connection is strong, and that the ledger board is flashed. It should be fastened with bolts, not nails. As weedyacres said, look for joist hangers, and add them if there aren't any.

It would help if you would post some pics.


    Bookmark   April 14, 2012 at 6:25AM
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thanks guys. I've had a couple of contractors bid on the job and neither has suggested the joists need to be changed. Once the deck is torn up,it will be easier to look for rot, improper attachments, etc. Thanks for the heads up on the permit - I shall check.
I'll a little confused by what is meant by 'ledger board flashed.' Is there a picture on the web that shows what that means?
I'm 99% sure I want to replace with ipe or massanduba. The contractor said that since the joists are 16" OC, I can't lay them diagonal as the old PT deck but need to go at 90 degrees. This length is just below 15', the length of the lumber I can buy. To avoid buying 16' and cutting, I was wondering if OK to attach a 2X6 PT piece to the exterior support member to avoid screwing too near the end. Or does predrilling make it OK to screw within 1/2" of the end?
I can post pixs but what exactly so you wish to see? I can take a shot from a corner that shows part of the support network. Or I have exterior shots of the overall design.

    Bookmark   April 14, 2012 at 9:30AM
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Post pics of the guts of the deck. Crawl underneath and take photos of all the framing. How joists are attached to ledger, joists to beams, beams to posts, posts to ground, etc. And a couple overall pics.

    Bookmark   April 16, 2012 at 3:45PM
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My back had some surgery so I couldn't get entirely underneath, but here are some shots from the opening. I hope they answer some questions.

    Bookmark   April 22, 2012 at 7:44PM
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I would add joist hangers as other have suggested on ends of the joists. As fas as the "ledger flashing" is concerned, do a web search. You are essentially protecting the existing structure of your house where the "ledger board" (the board that is attached to the house) attaches from moisture penetration. The flashing depends on the type of siding you have. Look underneath the deck on the house side. Do you see the heads of bols or lag screws that attach the ledger board to the house?

My deck is free floating, and only pinned to the house at a bump-out by the back door.

    Bookmark   April 25, 2012 at 2:00PM
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The posts are on steel bases on concrete. That's good. (sunk into the ground or wood on concrete=bad). The one looks like it's up off the post base, though, which isn't good. Needs to be replaced or re-nailed.

Posts are 4x4; 6x6 is current code, but these are so short, it's probably not a big deal.

I can't tell from the photo if the beams are resting on top of the posts, or sandwiching them. They should be on top.

Also can't see where the joists connect to the rim joist. They should have joist hangers, not just be nailed. Hurricane ties from the joists to the beam(s) is a good idea too.

Got some overall pics?

    Bookmark   April 25, 2012 at 7:11PM
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