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Where I live, I've noticed many buildings have a stone/gravel barrier between the building foundation and the lawn or flower bed. Why is this? Does it prevent insect or pest infiltration of the structure?

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Megatron
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  • Picture one shows accessibility as the primary reason to me – Christiaan Westerbeek Jun 28 '18 at 21:41
  • Your Stella d'Oro daylilies are thriving. The skimmia (needs acidic soil) not so much. When replacing look for plants that do not need acidic soils (concrete foundation, lime, alkaline soil pH). – stormy Jun 28 '18 at 23:01
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    Besides drainage, rocks against the foundation lower the amount of periodic lawn maintenance at the edge of the building... no weedwacking against the foundation if there are rocks / weedbarrier there. – Mike Pennington Jun 29 '18 at 03:38
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    "*Where I live ...*" -- Where do you live? It might make a difference in the answer. (e.g. with respect to local weather conditions, local insect populations, local building practices, etc.) – R.M. Jun 29 '18 at 14:27
  • Having them under windows seems to present a natural noise barrier for would-be housebreakers. You can't get close to the window without making *some* sounds. – Valorum Jun 30 '18 at 22:30
  • @Valorum Crushed gravel walks and driveways are seriously great burglar deterrents along with low voltage lighting, no bright light bulbs...and Barberry planted beneath windows! – stormy Jul 01 '18 at 22:44
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    @Megatron Your question was superb. Look at the amount of readers and commenters! Such a simple question yet fabulous for understanding basics of drainage. This question should be reaching some sort of reward numbers! – stormy Jul 01 '18 at 22:48

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You don't want water-retaining soil sitting against the building because this causes damp problems. Creating a porous soakaway like this will mean any water sinks to a lower level than would cause any harm to the building.

David Liam Clayton
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    Does this mean that there is no soil below the rocks to a specific depth? – Megatron Jun 28 '18 at 21:13
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    It probably depends on the nature of the building. If it has a basement then it's a good idea to minimise earth in contact with the masonry. If not then it should have a damp proof course somewhere in the construction, above which it's definitely bad to have wet material in contact with the masonry, but in any case it's sensible to try and keep water away from the foundations. They may also just be decorative. – David Liam Clayton Jun 28 '18 at 21:36
  • The rocks wouldn't prevent the water table to rise above the foundations and cause damp problems. The correct answer is splashing. – Jacques Gaudin Jun 28 '18 at 23:35
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    @JacquesGaudin if the water table is high, it wouldn't help. In most cases though, the water table is lower but after strong rains it takes time for the water to seep down through the soil, while rocks+sand make it much faster and prevent a "swamp" around the house. – IMil Jun 29 '18 at 02:01
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    We recently replaced some sacrificial plywood around the base of one of our buildings, the we now have gravel like this (and dimpled foundation membrane) around the area specifically to improve drainage. – mu is too short Jun 29 '18 at 03:57
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    Obviously depends on your local climate, but this is the answer. My cellar was damp until I dug a trench all the way round and filled it with pebbles like this. Now moisture can evaporate quickly from the walls. – RedSonja Jun 29 '18 at 10:42
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    More details from a UK perspective at http://www.pavingexpert.com/dpc01.htm. – Carl Jun 29 '18 at 11:43
  • @DavidLiamClayton you mean a French Drain? – Mr. Boy Jun 29 '18 at 15:12
  • Depending on climate and soil conditions, at some depth there may likely be a "weeping tile" system, which is really just a circuit of perforated pipes, that collect water and lead away from the building. That may mean a sump from which it's pumped out, or a storm sewer system, or just a "french drain" which is a hole filled with porous material. – CCTO Jun 29 '18 at 18:45
  • Concrete foundations have 3 types of protection; negative drainage so that every drop of water falling on the ground near the home's foundation drains away from the foundation, there should always be a perimeter foundation drain made with landscape fabric covered drain pipe, backfilled with drain rock, the pipe is below the footing and in front of it not on top of the footing. And third a thick coat of asphalt emulsion is painted on all of the exposed concrete of the foundation. Cobble or gravel below the siding is just for splash. Does nothing else. – stormy Jun 29 '18 at 19:40
  • I built 30 custom homes in the North West the wettest place one could hope to find. I also taught grading and drainage...digging a 'french or trench' drain at the base of the siding is not recommended. A swale would work far better after grading away from the foundation then making a 'soft' ditch to ensure any water coming from up hill is directed around and away from the home. Usually lazy contractors will not do the three universal measures for foundations. Who will pull the soil back to check the perimeter drain pipe or if emulsion has been painted on the concrete? – stormy Jun 29 '18 at 19:48
  • @IMil I guess it depends on where you live. In London (UK) the water table is sometimes quite high and varies seasonally, so we build basements with waterproof concrete and a cavity membrane. The soil is usually clay and is in direct contact with the foundations. – Jacques Gaudin Jun 29 '18 at 23:01
  • Now I finally understood why some "roofs" are with pebbles and not used for plants for instance. Many, many thanks. – Rui F Ribeiro Jun 30 '18 at 20:18
  • No home should be built with a foundation below some water table. Clay holds onto moisture better than other soils, as long as the surface is sloped and compacted away from the foundation (having the perimeter drain, asphalt emulsion coated on concrete) one will not have concrete foundation damaged by water. Other little things such as plastic moisture barrier below the compacted 4" of gravel beneath the concrete floor of the basement... – stormy Jul 01 '18 at 22:37
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Perhaps I missed something in the other answers. The one and only reason is because of SPLASHING. Rain over the gutter, a hard sideways rain will splash mud/soil onto the siding. Not good for siding as the mud tends to hold moisture too long and can cause rot as well as a dirty 'skirt' on your siding.

The gravel, drain rock, cobble or even the lava rock as pictured in the first picture however needs to be below the siding at least 4" otherwise the rock becomes a moisture problem. That first picture with the lava rock and the trap? That lava rock is touching the siding. The siding appears to be concrete. Concrete foundations need to be coated with asphalt for protection. Concrete is very much harmed by moisture. The picture with the 4X6 holding in cobble? If that rock is as close as I think it is to the siding, that will rot the siding if it is not at least 4" below the siding.

Before the cobble or gravel gets installed this is when landscape fabric is necessary. Not to prevent weeds but to prevent the cobble sinking down into the soil and the soil replacing the cobble.

The following is off topic but hopefully helpful...

I wish I could find a more common mulch people could use instead of chunky bark. This is not for weed suppression it is to unify a landscape by covering the soil with a regular texture. Chunky doesn't work. Fine works far better for aesthetics and for decomposition sometime in the near future.

The only mulch I will ever use in the landscape is human poo mixed with sawdust and completely decomposed professionally. Grins. That 4"X6" (not pressure treated)? is a great condominium for insects and other animals; slugs, snails, earwigs, pillbugs...and many more. Not at all necessary or even beneficial.

I lived and breathed construction in all forms for half a century. The only reason and it works well, for using cobble at the base of an outside wall, is for splash.

If this is your lawn here is the best way to fix those edges. Also look up how to produce and maintain a cool season lawn crop! On our site, not on Scott's or Ortho...Use a hose or string, a center to make a set radius to change when changing point of radius to the outside of the lawn. Keep radius curves consistent for each curve. They can change radii every curve but not during each curve. lawn edging the right way

stormy
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    This answer goes from "totally on-topic" to "somewhat related" to "totally unrelated". Maybe try to remove the unrelated parts? – hoffmale Jun 29 '18 at 17:42
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    @hoffmale or just make it clear that the topic has shifted slightly after 2nd paragraph. "Talking about landscaping the base of buildings in general..." – Jeutnarg Jun 29 '18 at 18:56
  • Thanks for the feedback. Jeutnarg I chose your option. I like giving 'bonus material' and it drives everyone nuts. – stormy Jun 29 '18 at 19:33
  • That's super useful! I do a little landscape design, and I didn't know that. Also find your extraneous info useful. I've had my very helpful answers (according to the people asking the questions) deleted by whoever patrols this site. – Junebugapril Aug 18 '20 at 21:38
  • Junebug, get used to offering seriously sane advice and then getting COLLAPSED or erased. Keep in touch. I've been there and found most humans are clueless about botany, biology, hydrology, chemistry...and done that. This site is just the last site I've found that allows me to simply educate with bonafide truth. I am proud of you that you see these Quora officials PATROLLING the site. big huggs! – stormy Sep 04 '20 at 02:31
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My guesses are that it just looks a lot neater and also prevents weeds from growing near the foundation. If weeds and their roots are allowed to grow there you would have to be constantly digging them out, and roots are already hard enough to get out of the ground without having to dig near or under that area. Another reason, I think, would be because it is a more permanent solution to weed prevention instead of mulching. Mulching has to be (or should be) removed and/or replenished yearly to maintain an attractive appearance. Lots more work to do that way.
Yet another reason may be to keep water draining away from the foundation. And as you say, reduce the likelihood of pest/vermin infestation, since animals and insects have an easier access to the house through soil and grass. Possibly a combination of all of the above(?)

Miss Tinker'smom
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    After looking at the picture again, there appears to be what looks to me like a rat trap in the corner, the black thing sitting on top of the brick paver. Maybe that homeowner had or knew of rat problems in the area? – Miss Tinker'smom Jun 28 '18 at 20:25
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    Speaking as someone who has rocks 3/4 of the way around my house, weeds still grow in rocks... just in much lower densities. Weed barrier under the rocks helps you pull them out, but you get them no matter what. My primary reason for using rocks was drainage and no lawnmowing / weedwacking on the sides of my house. – Mike Pennington Jun 29 '18 at 03:35
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    From experience, rocks around a foundation do not prevent weeds from growing. They just make them harder to remove, because you can no longer use a tool like a hula hoe (a.k.a. stirrup or scuffle hoe.) – StackOverthrow Jun 29 '18 at 22:05
  • Oh. Like I said, it was just a guess. It looked denser in the picture to me. My humble apologies. – Miss Tinker'smom Jul 01 '18 at 02:41
  • But wouldn't it make sense to lay a weed barrier under the gravel to prevent them in the first place? That's what I would do. – Miss Tinker'smom Jul 01 '18 at 02:42
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    There is no such thing as a 'weed barrier'...landscape fabric was designed to be used between gravels, rocks and the soil so that the large pored spaced materials don't sink into the ground as the fines are allowed upwards. Someone thought they could sell more of this stuff as 'weed fabric'. Putting a plastic barrier between the organic layer and the topsoil only slows water, soil life and decomposed nutrients to be eaten by the soil life and mixed down into the topsoil. Great housing for pests including mice, cockroaches and earwigs. Just dump soil on top of weeds. 2" plus. Done. – stormy Jul 01 '18 at 21:45
  • @MikePennington That rock is NOT for drainage. Just splashing. Three requirements are critical for drainage of your foundation; negative drainage away from the foundation, no sloping soil towards the foundation. Asphalt emulsion painted on concrete before backfilling. Perimeter foundation drain that is 'daylighted' or contained in the city sewer system. Gravel next to the foundation is simply for splash. You do not want to 'attract' water using a trench drain towards concrete foundations. – stormy Jul 01 '18 at 21:48
  • The water flows much faster through rock than grass. If the point where the rock is located is sloped, it definitely helps drainage (that comes from a civil engineer in licenced in Texas). Around my house it helps drainage. YMMV – Mike Pennington Jul 01 '18 at 21:50
  • Ummm, I taught civil engineers Grading and Drainage. That rock certainly isn't causing harm to your foundation UNLESS water is directed towards your foundation by slope. It would be better than nothing but the three things I listed should be checked off the list. If you've got water running off the surface towards your foundation I hope that trench is as deep as the foundation with a perimeter drain slightly below and in front of the footing. How long have you owned your home? In Washington State warranty is 12 years, 6 for discovery and 6 for repairing. – stormy Jul 01 '18 at 22:11
  • I wasn't talking about a plastic barrier, I was talking about the mesh type of weed barrier that allows water to drain through. Ive used that in the past and it worked quite well as a weed barrier. – Miss Tinker'smom Jul 03 '18 at 16:35
  • *placed under mulch. – Miss Tinker'smom Jul 03 '18 at 16:40
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Some jurisdictions require non combustible mulch i.e. gravel next to the structures. Several buildings have had fires started from discarded smoking materials in combustible mulch.

Jose Periut SR
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It’s mainly so termites don't get in to your walls as they require moist ground cover to travel and mulch against your home would provide that to them.

Stephie
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Ben
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  • Thank you for your answer; if could include suggestions for width and gravel types could also be helpful. We encourage you to take the [Tour], and browse through the [Help], to learn more about how the site works! Thank you! Welcome to the site! – M H Aug 18 '20 at 12:24
  • Having studied architecture, it was all about protecting the wall from water damage. In some regions, termites may be a problem, but there are lots of areas that are completely termite-free and still have a strip of gravel or rock. – Stephie Aug 18 '20 at 22:01
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I was also told by an exterminator that this will reduce rodents by removing a potential habitat right next to the home. I didn't see that answer here so I'm starting to wonder if he knew what he was talking about.

Adam Wise
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