How to replace joists and repair deck?

[Marshall]

Hi there,

I have a rental property I'm currently doing repair work on a pre-existing deck and looking for some advice. 🙏😊

I didn't built the deck was with the property when purchased over 10 years ago and believe its likely similar age to the property approx 20-25 years old. The deck had some rotted out boards caused by large pots being placed on the deck without any clearance for extended period (though rest of the decking is fine). I came onsite to replace boards and was also looking at sanding and reapplying Intergrain UltraDeck Timber Stain to the rest of the boards (which was overdue). When pulling the rotten boards unfortunately found there was also rot in some of the joists in the subframe in the subframe so looking at also having to replace those. The bearers are fine and still in good condition. There was no flashing or tape applied to the joists so just wood on wood and looks like water has gotten in. The decks also only about 30-40cm off the ground and doesn't get great ventalation. Its open on one side but then butted against house and two fences on the others where it gets some partial ventalation.

Issue is the deck has some unusual characteristics. It's been built using commercial decking boards. 120 x 35 mm thick merbau. Much thicker boards then usual. They have been screwed into the joists with Hex head 14g bugle batten screws. Has been really difficult to pull the existing boards up to be able to get to the subframe due to the thickness of wood and size and age of the screws. The deck dimensions are 4.8m x 4.2m and to pull up all the boards without destroying the deck looks like it would take a huge amount of time. I'm not even sure if I could get them up - as a number the heads on the screws have gone and you would almost need to just cut it up and start again which I'm really not looking to do. 

I was exploring another option which might allow me to not have to pull up all the existing boards. I can snuggly slide through new 90x45mm H3 MGP10 Treated pine joists which meet requirements for my spans. They slide in with only 1-2mm clearance. So I was looking at the option of rather then pulling up all existing boards simply sliding in new joists to replace the ones that have roted. Then pull up the deckboards above the bearers to attach the joists onto the bearers and maybe add a 1-2mm shim at the bearers to bring to level. 

I was interested to know if it would be any issues with doing this and not actually pulling out the old degraded joists  ? Will leaving the old degraged joists in the subframe cause any issues in future ? 

Many thanks for any reccomendations or advice

[Dave-1 · Accepted solution]

Good Morning @Marshall 

I have thought of this a fair few times over the years, How to and what would need to be done to repair/revitilize a deck pretty much from when i first built my deck. I really like your idea but can see a few issues with it.

1 - Not all timbers are equal in size, that 1-2mm free spacing to slide in, I have a feeling as you work through the deck to replace the timber you may find that it dips and rises and that 1-2mm will dissapear fast.

2 - leaving rotted wood insitu is going to help the new timber rot faster. The old rotted wood will retain water/moisture and it will create an ideal enviroment for ot to continue.

3 - The level of rot on that truss may indicate others are wanting to head the same way, a flathead screwdriver pushed hard into the underside if you can get there will help determining if other supports are affected.

4 - Trying to remove old screw/nails/fixings from old hardwood and decking baords... Well I couldnt shift mine, they would sheer off and just burr. Rip up was my only idea for that if I came across it.

5 - Good parts, The stirrups look solid And really thats the base to start with.

6 - Good Part kinda, if you decide that you want to do a proper fix down the track (in the next year or so) then your idea of sliding in supports may be feasablie if only one or two cross beams need doing. You take the loss of the timber underside for a short term usefulness.

Dave

[Marshall]

Thanks for the feedback. 

One item 1. No I already tested with a piece of 90 x 45 I had laying around and was able to get it across the full span without any issue. It worked suprisingly well and I really wasn't optimistic before hand thinking same as you but was pleasantly suprised. Doesn't seem like that will be an issue just enough clearance.

2. Yes figured as much - was really just trying to figure out how bad this would be and how much effect it might have and how quickly. 

3. The rot at a particular end of the deck is quite bad. Worst being in the back corner of the deck. But the joists closer to the house are in much better condition

4. Yes thats kind of what we have found. It was very difficult to get any of the good boards up without destroying them and even the ones we did it took a very long time so it isn't really an option to try and pull up all the boards. 

5. The stirrups and the bearers are fine. No damage at all to the bearers. 

6. This was really my thinking. There is the potential that either me or a family member may move into the house in the next 6 -12 months due to another house build taking place. With tenants in the property currently really wasn't a time I wanted to be doing a full deck build. The slide through joist was really aimed to be just a temporary stop gap option to tide over for maybe a year or so to be able to fix whats there currently quickly and cheaply and make it safe and usable and then plan a full deck rebuild down the line possibly when family are living in the property. The replacement joists are cheap and already picked up some replacement boards from a demolition place before I knew about the joists. So to repair this way would be only a few hundred dollars.

I guess a matter of weighing pros and cons of temp fix vs the full rebuild

[Dave-1]

Morning @Marshall 

I like your thinking and would probarlly go for a temp repair and and then a total repair later on. Having it safe for tennants and usable would be the priority for sure.

Dave

[EricL]

Hello @Marshall 

I believe @Dave-1 has provided an excellent in-depth analysis of the decks condition and proposed solutions. I'm putting my vote to a temp repair so that it can be put back into working order in the shortest time possible. Eventually an opportunity will present itself where you'll have enough time to do a proper repair.

Eric