What Caused This Wood Deck Failure?

[Runner]

Did the skirting around this deck cause the treated lumber to decompose like this in 13 years? Was I crazy for expecting more time before having this type of problem? Deck was built in 2011 and there is a concrete patio under the entire deck with this solid skirting all around. Note, a couple of the 2x10 joists are rotted all the way through. Main beam, joists and floor boards are Yellawood. Oddly enough the parts that are still holding up (the skirting and guard rail) are plain old green treated wood from Lowes. I started noticing the rot in 2018.

 

[old and tired]

My builder would say yes, you trapped moisture under the deck, that caused the rot...

I have a deck to be replaced, I placed the boards too tight together and trapped moisture, too.

 

[JJT]

Moisture.

Having a solid skirt over a concrete patio simply trapped moisture, resulting in the rot you see.

 

[Runner]

My builder would say yes, you trapped moisture under the deck, that was caused the rot...

I have a deck to be replaced, I placed the boards too tight together and trapped moisture, too.

I guess I naively thought that the purpose of treated wood was to resist rot and decay under such conditions.

No new deck for me, as soon as this one is hauled off in the dumpster, I'm going back to the concrete patio.

On a humorous note, I see a bunch of advertisements for hardscape patios off to the side of this posting right now

 

[sixdogs]

That's moisture coming up from the ground.A plastic barrier with gravel on top would have worked. I've read many times that most decks rot from the bottom up.

 

[Runner]

That's moisture coming up from the ground.A plastic barrier with gravel on top would have worked. I've read many times that most decks rot from the bottom up.

I would have thought the concrete slab underneath would be somewhat of a moisture barrier?

 

[Diggin It]

I did something similar. Initial 6 x 12 deck is basically a porch for the back door, about 18-24" above ground with no skirting/siding of any kind (early 2000s sometime). No rot there. But a few years later, I added an 8 x 12 section to one side, only about 6" above ground. Blocked two sides against digging critter entry. Wasn't long before I noticed various issues and had to replace some boards. I eventually took the side section out and went with patio stones.


Main section is still fine, but have added wire fencing and screening to keep stuff out, but allow full air flow.

But I've also added a full awning/cover over the whole area to keep direct rain off and prevent it from soaking the ground underneath.


.

 

[Runner]

On the brighter side, I will now be able to fit my mower between the corner of the patio and the retaining wall again.....

 

[Tinhack]

If you're going to put skirting around a deck, put vents in it. Treated lumber (most) is for insects not moisture. You need to allow crossflow ventilation.

 

[dodge man]

Ours is doing the same thing and it’s not over concrete. Ours has skirting but it’s far from air tight. I suspect some of its from moisture and some from the fact treated lumber isn’t as good as it used to be. Sometime in the next year or two we will have to redo it and I’ll find out.

 

[Runner]

Something funny I noticed is that the blocking between the 2x10 joists, which is made from the cutoffs from the joists, is all in almost perfect condition. Whereas, the adjacent joists are rotted like crazy.

 

[sixdogs]

That's moisture coming up from the ground.A plastic barrier with gravel on top would have worked. I've read many times that most decks rot from the bottom up.

I would have thought the concrete slab underneath would be somewhat of a moisture barrier?
View attachment 875817

I didn't see the concrete and you're right. I would see concrete as a least a partial barrier. Now I'm stumped as well.

 

[2manyrocks]

I would have thought the concrete slab underneath would be somewhat of a moisture barrier?
View attachment 875817

Concrete may feel dry to the touch on the surface, but has plenty of moisture inside due to concrete acting like a sponge soaking up moisture.

 

[sixdogs]

Concrete may feel dry to the touch on the surface, but has plenty of moisture inside due to concrete acting like a sponge soaking up moisture.

I have seen concrete sweat from the ground up. Would that have been enough to cause the problem? Maybe the restricted airflow combined with the concrete sweating during temperature change?

 

[5030]

You screwed yourself with the solid skirt. Same deal here but I used .40 retention lattice skirting which allows moisture egress as well as air flow and ours is just fine. Like when I use .40 retention fence posts, I always encapsulate the in ground part of the post in hot tar before setting, always.

 

[JimRB]

I have not used this but I did see it in Fine Homebuilding or somewhere. https://trexprotect.com/ A tape to put on the top of deck framing to help shed water and resist rot.

 

[2manyrocks]

My suspicion is the skirting trapped the moisture coming up from the concrete. It doesn't have to sweat for that to happen. The concrete will absorb rainwater and groundwater like a wick.

A properly poured and finished concrete pad will outlast wood decks by a wide margin.

One thing they did is keep the pad below the house framing. That created a step down that is perhaps inconvenient, but the good news is the house framing shouldn't rot due to having a concrete pad poured up against it.

 

[5030]

In my humble opinion, .40 retention lattice looks a heck of a lot better than solid boards anyway. It's cheaper, easier to install as well.

 

[jyoutz]

I have never liked wood decks due to the maintenance issues. When our concrete patio started cracking and spalling, I just covered it with paver bricks. The outside row is mortared to form a solid edge, and the interior bricks are just sitting on the concrete or sand on the concrete where the slab was unlevel. This has been in place over 10 years and sees a fair amount of snow and frost heaving, but since bricks are floating on the slab, it works.

 

[2manyrocks]

Pavers can really upgrade the look of a concrete pad. Yours looks very nice.