Landscaping Math!

Sammy1980April 17, 2012

I am about to lay a flagstone patio in the 16' X 5' area pictured below.

I would like for the flagstone to be flush with the existing concrete patio. I already dug down to a depth of 5" and the flastone we're buying is 1.5"-2" thick.

I have a couple of questions please:

1. I know that I'm going to have a layer of compacted crusher run, then a layer of sand and finally a layer of flagstone but I'm not sure how deep each layer needs to be so that once everything is compacted, the flagstone is flush with the concrete pad.

2. The patio will be 5 feet wide, is a 0.5 inch drop over the 5 feet sufficient to help keep water from puddling while still being level enough to comfortably walk and sit on?

3. Would it be a better idea to install pavers in that area instead of flagstone? They seem to be the same level of complexity and close in cost but we like the natural look of flagstone better and we love the idea of growing some ground cover in the cracks. Are pavers better for a reason that we are not aware off? We don't have any experience with either.

Thanks for the help.

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You may be able to deal with it later, but when the wood eventually rots away (sooner than you think) there goes your edge retention for the patio addition. Also, you're directing water to the fence and creating a situation where dampness will be retained for a length of time because the timbers are butted up against it. This is bound to invite rot at the bottom of fence. I think it would be better to maintain a 1" gap between the fence and timbers.

I would figure on 6" excavation. This allows for 4" crusher run, 1" sand and 2" (or so) flagstone. Bring it 3/4" above the existing patio on a sand setting bed. Get rid of the excess elevation with the compaction process. You should experiment a little with the actual construction to achieve the intended results. Though you can get by without it, using a woven polypropylene separator fabric between the excavation and the crusher run will add stability.

Because of imperfections in the stone, I'd plan on 3/4" downward pitch (rather than 1/2") across the 5' for drainage.

If it were me, I'd find pavers to be more practical, useful and easier to install than flagstone. Flagstone with gaps between them does not work with all kinds of heels and furniture legs.

    Bookmark   April 17, 2012 at 1:42PM
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deviant-deziner(Oh zone)

Just a thought , but have you considered using a combination of brick and stone or concrete pavers ?
I notice that you have brick on your house and by repeating the brick in the patio addition it could look nicely coordinated vs. introducing a whole new material that doesn't have a relation to the existing materials.
Perhaps a band of brick around the perimeter and a field of concrete pavers ( to match and coordinate with the existing concrete ) would be a nice detail.

In regards to how to set your sub base, we design it to the type of soil conditions that is existing ( highly expansive clay like soils vs stable bedrock )
But an average is about 3 inches of crushed and compacted aggregate , properly sloped, and a setting bed of sand that is about 3/4 of an inch. The sand is used for leveling only so you do not require much if you are working with guaged material. If your material has cleft and is unguaged you may need more sand to handle the uneven surface.

The project below shows a bluestone and brick tiered patio. The house has a partial brick facade so we used brick in the patio to coordinate and tie in with the surrounding context. From portfolioMay08.jpg

    Bookmark   April 17, 2012 at 3:01PM
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I notice that the area the BBQ is sitting on is bare concrete so I make this suggestion: use poured concrete for your patio extension and bring it to the level of existing (there are some construction details to attend to) then tile the whole thing the same.

    Bookmark   April 17, 2012 at 3:33PM
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Thank you for the feedback guys.

Yaardvark, the wood I used said it was rated for ground contact so I was hoping to get a few years out of it before it rots, you still think it will go away soon?

Also, it's hard to tell from the picture, but there is a 4 inch gap between the long run of the retaining wall and the fence. I have a drain at the bottom of that trench. The void was filled with gravel. I can cut back the 3 pieces that are too close to the fence if you think that would help.

The only thing that scares me about pavers is having to cut some of the pavers which seems complicated to me and I'm afraid it will look bad.

1. Can you adjust your retaining area dimensions to match an exact number of pavers? Like if I know that the pavers are 1 foot wide, can I count on 5 fitting across? I was thinking some space would be wasted on small cracks between the pavers.

2. If we did go with flagstone, is it possible to grow some ground cover in the cracks between the flagstone in a shady area if we fill the gaps with sand? I was thinking Fescue seeds. Should we use top soil to fill instead?

Thanks again for the feedback and tips. I will definately post pictures of how this thing turns up next week.

    Bookmark   April 17, 2012 at 3:40PM
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karinl(BC Z8)

The art of fitting pavers (or cut natural stone as in DD's picture) to an existing space might be to select different sizes and arrange your pattern accordingly, as with this patio we did a few years back. You can count on pretty exact measurements of your stone, but you are right that spaces do add up. I should go out and measure the actual length of this patio vs. the calculated measurement. Measure your space, see what sizes of paver you can get, and design accordingly.

True that cutting stone can be a pain, a mess, etc. I'd sooner move the end landscape ties if you can't work out a good fit. Also, a good landscape yard or stone cutter could cut to size for you - for a few bucks.

The reality of growing groundcover in cracks does not always live up to fantasy. But truth is, weeds can settle even in the cracks between pavers if you are not vigilant.

Think mostly about how you will use this space. Will you have the ability to work around gaps into which chair legs might drop, a barbeque might not roll over, etc? In other words, let function dictate whether you want gaps or not. Projecting my experience with various surfaces onto your setting, I think this is a place for a solid surface, not random flagstone. And I think I would go pavers or cut stone (since you like stone, it can be done without cracks) and not poured simply because I am nervous about the lifespan of your edging and the drain pipe underneath - pavers can always be lifted for access and repair, while poured is... there.

Incidentally, to the left of this patio you can see another area of our yard where we have spaces between homemade concrete pavers. Those spaces are too large and are real ankle-turners. Make cracks smaller if you are going to have any!

Karin L

    Bookmark   April 17, 2012 at 4:29PM
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I see your gap now that you mention it. I thought that was another timber. I would not expect to get many years out of them... less than what's claimed. Wherever there is something other than circulating air on the fence, it will shorten its life. So fix any of that you can. If it's only a fence board here or there, that not a major repair later.

Normally, when installing pavers, you install the retaining device after the pavers so there's no issues about them fitting within a pre-installed edge. Here, you have a bit of an unusual situation with the grade change and your solution to it. I would not rule out Ink's idea (whether you tile, or not). If you're planning on leaving the existing concrete slab, a poured extension to it would seem functional and look fine. If you tiled everything, you'd need to leave a joint in the tile where there was a joint in the concrete below (or a crack would develop in the tile). If you did pavers and chose a pattern that required no cutting--like basketweave--then you could eliminate that issue. If pavers, I would consider installing a conventional retaining edge to it while leaving your existing wood edge in place to retain the new grade. Just make sure the wood is concealed when the pavers are finished. However, you'd probably want to expand the dimension of the wood frame (toward the camera view) so that the paver area was not a smaller dimension than the patio.

The nominal dimensions of a standard brick-shaped paver is 8" x 4". (The actual size is slightly less.) It would probably be possible to figure out a pattern that would work very close to whatever dimension you have with very little cutting.

I would heed Karin's advice about the joints.

    Bookmark   April 17, 2012 at 5:33PM
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Thanks so much for all the detailed replies and the pictures guys.

Karin, the reason we were leaning towards natural flagstone with groundcover in the cracks is that this extension won't really be used for anything "functional", it's just for looks. We already have 12' x 12' patio where we have our BBQ grill, tables and chairs. We just wanted the flagstone addition to be something pretty occupy that area since the grass between the fence and the house died as soon as the fence went up, it didn't get enough Sun. If anything, we may put our chiminea there and a couple of potted plants.

So do we need to just give up on being able to grow anything cool in the cracks between flagstone? I saw something about Thyme and was thinking that might work.

Yardvaark, you mentioned installing a "retaining edge" over the retaining timbers, I'm not sure what that is. The only retaining edge we found at Home Depot was the plastic one that used plastic spikes to install directly over dirt. Do they make something we can use as a retaining edge that we can nail to the retaining timbers that we already installed?

    Bookmark   April 18, 2012 at 4:28PM
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"you mentioned installing a "retaining edge" over the retaining timbers" No, not OVER the timbers. You created an earthen "hill" so you must use the timbers to retain it. But WITHIN that retained space, you can retain the edge of pavers using the plastic retainer (or mortar as I show in the diagram... what was used for retention before plastic came about; it's easy to use, though.) You would not nail/attach any paver retention device to the wood. Let me know if you do not understand my diagram. (I am not showing the fence in this diagram.)

If the short "leg" of your timber "L" is sunken a little, it could be covered with dirt or mulch so as not to show.

    Bookmark   April 18, 2012 at 5:54PM
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karin I once gave you a hard time over the way you mixed materials in your garden but this patio is really good and your invention of passing the hose pipe through a drain pipe is clever...tell me that I am forgiven.

As to the patio in question: I see this as a temporary thing and I would use wood over what exist that will be cheap and cheerful until Sammy is ready for something else, then Sammy come here first rather than part way through the job.

    Bookmark   April 18, 2012 at 6:30PM
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bahia(SF Bay Area)

As you have added the information that your existing concrete patio is already of adequate size for how you use it, I'd suggest you skip adding more paving here. It would look much better in my opinion if you backfilled this remnant strip with good top soil and selected plants that like shade. A lower ground cover adjacent to the slab in combination with some shrubs/perennials or ferns would look much nicer than two different kinds of pavers or flagstone brought all the way out to the fence. Since the new fence had made it difficult to keep grass growing well, choose plants that prefer shade. Combining a different material in this narrow strip will just make it look "busy" and obviously installed as an afterthought.

    Bookmark   April 19, 2012 at 6:26AM
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karinl(BC Z8)

You know, Sammy, that is an outstanding suggestion from Bahia. Although for maintenance purposes, I would not do a bed with that particular geometry and access limitation without putting some flagstone IN it for easy access to all corners for weeding and maintenance. (It's like putting a bed in the corner of a room - changing the sheets is a nightmare).

I might add that tallish plants will overcome the shade problem once they get their heads above the fence, and you could have some nice growth there. Mind you, I love low shade plants too.

If you want to go ahead and do flagstone, you will likely have a bit of trouble with planting in the cracks due to shade - you'll have to experiment a bit to find the plants that will do it, maybe Cardamine trifolia (I don't know options for your zone). But I am a big believer in the idea that if an idea is calling you, as the flagstone one obviously is, then go ahead and try it! To an objective eye it might look fragmented, but as Ink has pointed out above, I have something like 8 different forms of paving my small yard (have to try them all) and it works for us - it all has its purpose or scratches a particular design "itch." We don't all have the space for significant garden "rooms."

The neatest thing about flagstone and pavers and such is their utter lack of permanence. If it doesn't work out for you in your conditions, or for a future owner, you pull it up and go to plan B.

In this case, I would say plan B could be to pull up a portion of the flagstone and install some plants.

Karin L

PS Ink, since I was not offended by your initial comments on my yard, there is nothing to forgive. And similarly, I won't risk being cast into transports by this compliment, since I am detecting that your tongue is just slightly tucked into your cheek :-)

    Bookmark   April 19, 2012 at 12:56PM
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If all is "just for looks," I don't know that I would care to contemplate that length of bare fence. I would think that nandina (said to be invasive, but this is debatable) would do quite nicely here, if suitable for your zone, fronted by a few pavers and a low ground cover.

    Bookmark   April 19, 2012 at 1:30PM
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Thanks again for all this information guys. We were still a little torn between flagstone and other ideas until we came across flagstone that we absolutely LOVED! Never seen anything like it here in the South. It's called Pennsylvania Lilac Flagstone and it has a purplish/brownish tone that matches our brick perfectly! Once we saw that, we pretty much made up our mind on the flagstone. I still really appreciate all the other suggestions, this will be our very first landscaping DIY project and I'm sure some of these tips will come in handy in the future.

So far, my trench is dug down, my frame is built, sand was delivered Saturday, crusher run (base) will be delivered Thursday and flagstone will be delivered Saturday.

I have a few followup questions please:

1. Ink said something about this being temporary, I'm not sure I understand what that means. I can live with maintenance tasks such as replacing a few fence boards every couple of years, or having to add more sand and pulling weeds, but does temporary actually mean that I will have to replace everything in a couple of years?

2. Thanks for the groundcover suggestions, I'm going to look into those. We went to a nursery Saturday to look for ideas and one of the managers there felt very confident about Dwarf Mondu, he said it will do fine with 2-3 hours of direct Sun and will grow in the sand between the cracks. He even said that the dwarf won't grow too tall and I shouldn't have to mow it more than once or twice a year.

3. My total depth, trench and edging frame, is 7.5 inches. I have some 57 stone, limestone about 0.75"-1" in diamter, that I need to dump somewhere. Would it hurt if I dumped some of this 57 stone in the bottom of the trench, and then had 3 inches of base on top followed by 1 inch of sand? That would leave 2 inches for the flagtone.

Thanks again.

    Bookmark   April 23, 2012 at 3:34PM
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What I meant by 'temporary' is related to the inappropriate use of those timbers for the container upon which the stability and longevity of the whole project depends. As far as I can tell these timbers are not attached to the concrete either which means your new patio will move, the loose material in it will shift and the flags will be uneven. Couple this with rotting timbers that allow the sides to collapse and there you have it. There may be a way to fix this if you want to hear it but I wouldn't want you to go to so much effort and expense for something you will have to do right next time.

    Bookmark   April 23, 2012 at 4:17PM
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Would it help me if I told you that I drilled three half-inch holes in each timber and then hammered a 3-foot rebar through the timbers and into the ground? I was hoping that would give me a little more longevity.

Does your solution require taking out all the timbers or the fence? I'm not too worried about a little extra expense or work if it will help in the long run, I'd just hate to have to dig those timbers out and take out all that rebar now.

    Bookmark   April 23, 2012 at 4:26PM
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Oh, I also have 8 rebars hammered on the other side of the timbers for suport too. I thought I was over-engineering this but I guess no amount of rebar will help if the timber just falls apart. I don't get it though, don't they use similarly treated wood for train tracks?!

    Bookmark   April 23, 2012 at 4:31PM
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Ok, I just had an idea for a possible fix (I hope).

Can I dig a trench right next to the timbers (on the right side) and then fill the trench with concrete and rebar hammered a couple of feet into the ground kinda like a makeshift wall?

If I did that, I would think that the new concrete wall will be bearing the weight of the dirt and it shouldn't rot or move. If the timbers do rot later I would think it shouldn't affect the flagstone and it would also be a lot easier to take them out later since they won't be bearing any weight.

I would really appreciate some feedback on this please, I am having crusher run delivered Thursday and I'm running out of time to change things around.

    Bookmark   April 24, 2012 at 11:00AM
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Sorry sammy I didn't see your response to my post. You arrived at the answer that I was going to suggest on your own though. Either what you suggest or dig out the trench as you suggest and put in a concrete footer for a low brick wall up against the timbers but on the outside. When the timbers rot you can lift a few stones remove the timbers fill with your base mix and put the stones back. The brick should come to the top of the flagstones and the flags fit inside what will be a brick edging. I hope this helps and good luck..but please come back if not clear.

    Bookmark   April 24, 2012 at 11:32AM
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karinl(BC Z8)

That option occurred to me too, of putting concrete inside the timbers. There is an argument to be made that you could just remove the timbers now and build a proper wall - why wait for the timbers to rot? - but then you have to build a form for it, which is tight by Thursday.

The real "right" answer here, for lurkers and for future notice, would have probably been to put a concrete footer under the fence, which could also have served to retain the patio and would have avoided that gap.

There is one other way to look at this, which is that by the time the timbers rot, you (or the next owner) may be ready to rethink the patio anyway - shape or size or even whether you have one - and would be ready to re-lay the patio and reset the fence on a proper footer. Then it would be easier not to have old concrete to deal with, although concrete can be relatively easily sledgehammered out (disposal is a pain though).

By the way, the treated wood you have is not quite the same as railroad ties, and railroad ties are regularly replaced. But even so, I don't see why you couldn't expect 10-15 years out the wood that you have (in my climate, at least, that would be my estimate).

I'm really glad you found a stone that you like. That's the best part!

Also, do a little homework on how to properly work with flagstone. Keep your gaps narrow (I know that's been said) and with flagstone this entails treating them like puzzle pieces where you are designing the puzzle as you go. Be prepared to fit and fiddle, move and try a lot to get the pieces fitting as tight as you can. One "rule" I remember is that you don't want long continuous joints going through but if possible have each joint line lead to the side of a slab. You can get a chisel or (depends on your stone) chip or cut it to size to make it fit.

I know you can find tons of photos of well-laid flagstone on the internet and in books, but I'll put in a photo of flagstone we did in our yard to make the point that you can really play with your pieces to make them do almost anything you want. I did the cross-yard flagstone walkway here without any cutting, just moving around and trying different combinations with the pieces that we had until they made the shape I wanted. It's an advantage if your pieces are not so big as to be immovable, of course!

Karin L

Here is your overload of materials again, Ink :-)
PS it's a work in progress shot, pardon the mess - although to tell the truth, it's still messy now, in a different way!

    Bookmark   April 25, 2012 at 5:48AM
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Thanks guys. I highly doubt that we'll stay in this house for more than a few years but I still wanted to build something that will last a little longer even if we moved out.

I started digging my trench next to the timbers yesterday. The worst part was that I just filled in this trench a few weeks ago! Serves me right for not asking earlier.

I bought some Portland cement and I already have gravel and sand in my backyard.

We're expecting our flagstone delivery today! 3500 lbs of flagstone, 3500 lbs of thin stack rock, 1 yard of crusher run, 15 bags of mulch, 5 bags of top soil and a 20 foot Oak Willow. Anyone wanna come help me move all this stuff to the backyard? There will be beer!

    Bookmark   April 26, 2012 at 12:40PM
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Ok guys, I did end up digging a trench 6 inches wide and 1 foot deep right next to the timbers, then I hammered 3 foot long 0.5 inch re-bar 2 feet into the ground at 1.5 foot intervals, and finally poured a concrete wall in the trench. Hopefully this will give us a little more longevity. The flagstone arrived Thursday and my wife and I worked on it most of the weekend, it was pretty hard work.

Here's a picture of our patio so far, thanks so much for all the advice.

    Bookmark   April 30, 2012 at 10:23AM
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That looks pretty nice, with one exception. The gravel filling in the gap next to the fence is guaranteed to keep the wood from drying quickly after getting wet. It will surely rot out the bottom of the fence in not too long of a time. It would be better to eliminate the gravel and instead fabricate something out of 1/2" hardware cloth (wire mesh)... an upside-down "U" shaped or such, that would keep crud out of the gap, but allow air circulation.

I've lost track of what's been talked about here, but hopefully, you've learned that putting the fence ON TOP of any grade alteration and not incorporate it into the retaining wall system, is the way to go on future projects.

    Bookmark   April 30, 2012 at 10:49AM
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I really like that idea Yardvaark, I think I'm gonna take out a few of the fence posts to let the gravel out and then fill the cavitity with wire mesh to keep it dry.

    Bookmark   April 30, 2012 at 11:13AM
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karinl(BC Z8)

I think that's a lovely job of doing the puzzle!

Regarding the gravel next to the fence, that gap is going to force you to make some compromise or other, and Yardvaark's solution is probably the best idea. But gravel is actually the solution I have chosen myself where I have dirt sloping toward a fence. My husband built the fence and didn't listen (!) when I said a gap at the bottom would be a good thing so I was faced with dirt against the fence, so I walled off a little trench of gravel.

But I digress. I have forgotten your climate, but if it is fairly dry in winter, perhaps, and you avoid as much as possible watering the trench when you water the ground cover, I think the longevity of the fence will still be pretty good - but the bigger the gravel the better, since the air gaps will be bigger. What might also work plus look good is to form the mesh into a shallow channel and fill that with some gravel.

And if you have time on your hands, putting in more small plugs of the ground cover will help you get faster coverage, but hopefully you won't have too much problem with weeds in the shade, under the barbeque, etc. If it gets bad, and the weeding is arduous, mulch over or otherwise cover the gaps wherever the ground cover has not yet grown in.

Overall though, it looks great, and these details are just gravy. Congratulations!

Karin L

    Bookmark   April 30, 2012 at 2:26PM
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Thanks Karin, I wish I could take credit for the "puzzle" but I'm afraid that was my wife's work. I did the grunt work of moving the heavy ones and leveling them while she told me which ones to grab.

We're a little concerned with the Dwarf Mondo now, we'd like for it to fill in all the gaps but it may do so too slowly. Any ideas? We filled the gaps with top soil, that area will get 3-4 hours of Sun a day and we live in the South.

    Bookmark   April 30, 2012 at 3:44PM
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The mondo will do a pretty terrible job of following the cracks. Digging up and dividing will work much better.

    Bookmark   May 1, 2012 at 1:40PM
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Any ideas of what would fulfill this criteria then:

1. Live in South (hot Summers)
2. Stay green year round
3. Would fill in the cracks between the stones
4. Can tolerate a little bit of foot traffic
6. Area gets 3-4 hours of Sun a day
7. I can water as needed
8. Something that flowers would be awesome

    Bookmark   May 2, 2012 at 11:31AM
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would look into Isotoma fluviatilis.

explore link for similar plants.

Here is a link that might be useful: Lawn substitutes, etc.

    Bookmark   May 2, 2012 at 11:56AM
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