Did I do the right thing putting small stones under my deck?

Question

I bought a foreclosure house last year (built in 1987), there is a tall deck at the back, and backyard is slightly sloped away from the house.

• The deck was rebuilt from scratch before put on market (I imagine/guess the old deck might be in unsafe state? and thus need to be rebuilt; deck was painted dark-brown right after install, I saw some legs go vertical cracks from top to bottom)
• During heavy rain, downspout at the back corner of my house was flowing out water (small rain fine, tried to unclog, no much help)

Those two things gave me some worry of water issue. (why the old deck became bad and neighbor's deck was fine? could it be due to watering issue underneath the deck causing the ground soft and old deck sank?) Not seeing any leakage sign at the walkout-basement, but I somehow wanted to do some improvement to keep water away from foundation.

My neighbor got a tall deck, but under it there were a layer of stones (3”). I thought those stones were helping the area under the deck to be dry and avoid any water buildup around the foundation.

So I wanted to learn from my neighbor. But due to some issues, I ended up buying smaller stones (1” round), and I thought it might be a good idea to lay a layer of plastic sheet under the stones to prevent water sinking to the ground, so I did that.

Now my question is:

1. Did I worry too much and did the wrong/opposite thing? Water might actually not flow away due to the small stones keeping water underneath?
2. If I did wrong, what should I do now? Should I remove all the gravels? Should I dig a french pipe along the foundation wall? Thanks so much.

Answer 1

Your downspout extension may be installed incorrectly. It appears that the black pipe coming out of the hill is not sloped properly and is causing water to pool inside of the pipe.

Since the pipe is not draining properly, organic debris such as leaves will clog the pipe and render it inoperable. Since water takes the path of least resistance, it will back up and then come out of the bottom of your downspout instead of out the extension.

The stones are not doing very much, and they are mostly decorative. Many people put stone, or some other kind of ground cover under their decks because it prevents weeds and grass from growing.

If you want to keep the stone there, I would recommend removing the plastic tarp from underneath it and replacing it with landscaping fabric. The fabric will allow water to drain through, and prevent weeds from growing. That way, you would be able to reduce the amount of maintenance in that area.

Answer 2

If your foundation is sound you only need to ensure that the grade allows any surface water to flow away. Earth is designed to absorb water, and foundations are designed to be in contact with moist earth.

The only legitimate application of plastic is as a moisture barrier against poured cement. What you've done here with plastic serves no practical purpose, other than perhaps as a weed barrier.

Likewise there are three legitimate applications of gravel in this context:

1. To reduce runoff erosion on a steep grade, which does not appear to be your problem.
2. As a base for a stacked wall or poured cement, which again is not your purpose here.
3. As a cosmetic covering, which maybe you do want here.

Now you could certainly have had (and continue to have) problems with those deck supports depending on the soil. Only an engineer or local code enforcement officer can evaluate the soil and climate to tell you how deep the footers need to be poured given the soil and water conditions. If the deck piers are sinking or unstable it's unlikely you could halt that with superficial corrections like this. If you're worried about that then take some levels and measurements, and if you see signs of abnormal settlement then you will just have to dig and pour deeper footers.

If I were you my biggest concern would be addressing the downspout's failure to drain. Fortunately it looks like you have a short run of shallow flex pipe you could easily dig up and just replace if you can't unclog it.

Answer 3

I’m not sure that your problem is water related at all. It is possible that it is oriented to north side, and not getting enough sun and therefor never dries out or many similar silly reasons. When it comes to your solution, it doesn't help at all. Putting those tiny stones on a plastic foil, could in theory make things worse because water cannot evaporate cause of the foil, but I doubt that it will make situation worse; but it doesn’t help in any way, that I can tell you for sure since I have been involved in several projects with similar problems. Maybe old deck was made out of poor quality wood, or some sort of wood that is not suitable for this etc.TO cut the story short, so far nothing to worry about (from the looks of it at least) but keep us posted if something changes.

Answer 4

My solution for under a deck is to lay down a very tough 3 layer landscaping fabric (Vigro makes a good one - https://www.homedepot.com/p/Vigoro-4-ft-x-100-ft-Matrix-Grid-Landscape-Fabric-VPNM410085/302802172) and then cover with 2" of 3/8" Bluestone Gravel - https://www.saundersls.com/products/gravel-stone/38-bluestone-gravel/). The 3/8" blue stone gravel is a chipped gravel that is easy to move and laydown and won't move around easily like round river rock will.

Good luck!