infinity edge engineering and plumbing

shellipJuly 14, 2011

PB has just torn out pool and is getting ready to re-do. Is there a site that details the engineering/plumbing/requirements for infinity pools?

This is first infinity edge for PB.

  1. Is there a site with instructions for infinity edge pools?

  2. Can plumbing be run in the weir wall side of the pool?

  3. How long after shot crete do you have to wait to seal the weir wall? Which Thoroseal product is preferred?

  4. Are two pumps required? The pool area is 14x36 and the weir wall is 34'. The gutter is 3x36.

I am so sorry to keep asking so many questions, but hope to get it right. I really appreciate all your input. You guys have been a GIANT help.


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There is an amazing amount of knowledge required to successfully design and build a properly functioning negative edge pool. To be honest, I'm not sure I'd want someone's first effort in my yard. I built a whole bunch under the guidance of my previous employer before I started my own company and built my first.

    Bookmark   July 14, 2011 at 9:41PM
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And the selected PB is building it because why?

There is no infinity edge site with instructions. It does take quite a bit of engineering know how and experience.

I wouldn't run the plumbing through the weir wall unless extra engineering was done that showed it safe.

Wait till the shell is cured before sealing.

Best practice is two complete filter systems. Anything less than that is just that.The filter system for the weir wall can usually be smaller than the the main one for the pool.


    Bookmark   July 14, 2011 at 10:02PM
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Dittos what cascade said.
Best example is that I disagree with Scott about using two filter systems. Just shows that there are differing opinions about how to build these vanishing/negative edge pools.
Certain things we can probably all agree on are: make sure the weir is properly sized, make sure the auto fill is in the weir, make sure the weir wall is properly engineered, and make sure the weir wall is sealed.

    Bookmark   July 15, 2011 at 10:36AM
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Since skimmers remove over 70% of what falls on the surface, since the weir edge is doing the skimming, it makes sense to filter that water that falls into the catch basin. Is it a must, no, it isn't.

Does it cost more? Adding a smaller filter that the pool's is about a $500 upgrade but the pool will be cleaner and the basin will be cleaner. It's not like I said it needs it own heater. That would be silly.

Can it be built without a filter, sure. Many, if not most are. That, IMHO, doesn't make it a best practice, but a common practice.


    Bookmark   July 15, 2011 at 6:32PM
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When we started this project in Dec. we interviewed 4 PB, and all said infinity pool no prob. We went with a guy we had recommendations on for good pools and honesty/integrity. Has been building for 40 yrs. He seems to be great guy, but the infinity part is causing some issues. I have signed up to get on genesis 3 to see if I can get any help there, and on trouble free Am compiling a notebook of all your suggestions to review when we get to the plumbing stage.

The pool we just tore out was rebar on 9" centers and all the walls were a solid 1'thick, with floor 6". PB is suggesting the re-do with 6" think walls and floor, and 1'thick bond beam. I have told him weir wall must be 1'thick and sealed!

Still waiting for 80+yards of concrete and rebar to be hauled off. Hope to dig and form next week.

Thank you,

    Bookmark   July 15, 2011 at 8:03PM
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The thickness of your weir wall is dependent on engineering considerations rather than simply being automatically 1' thick. Depth of the pool (height of the wall) is an important determining factor. I've built quite a few negative edge pools with 10" weir walls.

The question of 1 or 2 circulation systems is entirely determined by the anticipated use of the pool. In my opinion, the water being drawn from the trough and returned to the pool and then over the weir wall is already being filtered so unless there is a particular reason to consider the pool and trough as separate bodies of water 1 circ system is generally fine.

The most important consideration in negative edge pool design, in my opinion, is trough design, specifically ensuring that it is sized correctly to allow the water displaced by bathers to be captured rather than going out the overflow. Like I said there is a LOT involved in design.

    Bookmark   July 15, 2011 at 9:03PM
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The only compelling argument I've heard to have a separate filter for the negative edge is if the pool is large enough (>50K gallons) to require the use of 2 pumps to get adequate turns per day for chlorination and filtration at lower, more energy efficient speeds.

Our pool is 35K gallons and only has 1 main filter for the infinity edge circuit. We have to run the main circulation pump for 20 hours per day in the summer to get adequate chlorination and filtration at low speed on our 2 speed pump.

If our pool were larger, we would have likely added another filter and chlorinator and it would have been logical to add it to the infinity edge circuit.

Another thing to keep in mind...the addition of another filter and chlorinator doubles the maintenance and replacement expense down the road in addition to initial installation expense.

With only one filter, we've had no problems with the infinity edge pit water clarity or gets turned over 10x per day using another 2 speed pump for the infinity edge which pulls water from the pit and provides water to our waterfalls as well as 4 returns in the main pool.

Agree with the other posters....the engineering of the wall and plumbing is highly dependent on the specific design of each pool and how the pool sits on the site. Also, the sizing of the pit is critical along with the adjustment of the autofill level in the pit.

Think of the pit as a surge tank with widely varying water levels throughout the day....tile the first 12" or so of the top of the pit rather than just 6" as is normal for the rest of the pool. This will allow the level of the pit to be adjusted lower via the autofill setting so that water loss out the overflow is minimized during surges. When surging is not happening, the extra 6" of tile will ensure the plaster is not exposed for long durations when splash out is not happening and the water level is lower.

Surge levels can be minimized by making the pit larger and this is where each PB may differ on how the pits are sized in relation to the main pool area. The larger the main pool area, the larger the pit will have to be sized to accomodate splash out. Think of pit size in terms of inches of water lost from the main pool and resulting volume that ends up in the pit and you'll start to get an idea of how the two are related to each other.

Lastly, surge level can be minimized by running the infinity edge pump at higher speeds. This will keep the water moving faster from the pit to the main pool when lots of splashing is occuring.

Occasionally, we'll turn our infinity edge pump on high speed during parties when lots of jumping, diving and splashing is occuring. The additional people in the pool also displaces water from the main pool into the pit, so this should also be considered when sizing the pit.

Also, remember that filters and chlorinators reduce efficiency of circuits, especially at higher pump speeds. This is another reason not to install a filter or chlorinator on the infinity edge circuit if high speed operation is expected. Some people like the sheeting of negative edges..especially when the water sheet is highly visible (like lakeside lots)...sheeting requires high pump speeds, so desired use of the infinity edge should also be considered in overall design. Our negative edge was primarily for the negative edge reflections and views and not so much the water sheet wow factor...your specific needs may vary.

Hope this helps.

    Bookmark   July 16, 2011 at 10:53AM
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Rack Etear

Not to mention that you are relying on running your negative edge for filtration which can cause as much heat loss as the pool itself.

    Bookmark   July 16, 2011 at 11:35PM
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racket...heat loss is good here in Louisiana this time of year!

When it cools in October, we run the negative edge much less with good results in colder weather...the only reason we are turning so much this time of year is due to the hours we spend's a rule of thumb to always run the negative edge pump on low speed when someone is in the pool to minimize surge.

Your point is good though for the OP...if she is in a colder climate, this could be a factor. Are you suggesting a separate filtration system that pulls and returns to the pit so the infinity edge would not overflow. If so, this seems like overkill to me just to prevent heat loss...maybe in colder climates this is common practice though...

    Bookmark   July 17, 2011 at 12:20AM
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Rack Etear

No, I am saying running it from the pit to the pool will run over they negative edge, and cool the water. The pit to pit systems is overkill, unless you designed the pit to be a kiddie pool.

    Bookmark   July 17, 2011 at 1:21AM
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Just to further clarify what I consider a best practice, I never intended to imply a second filter be used in a pit to pit situation though the scenario of using a larger pit as a kiddie pool would surely require a fully capable filtering and sanitizing system as well as other considerations.

To the original poster:

As you can see, there are a lot of factors to be considered when engineering a negative edge. It requires a lot of communication and people with the right skills.

For someone that has never done it before, having a trusted mentor that has done this and taught others to is crucial so that expectations can accurately be set and met.

There are very few things we teach ourselves. It took someone else to show us. Driving, reading, writing, etc... are examples. Building a negative edge pool is another example. If it was just like any other pool, there wouldn't be such a premium tied to the feature.


    Bookmark   July 17, 2011 at 8:39AM
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racket and scott...Thanks for clarifying...didn't think a pit to pit circuit would be that common unless naturally the pit is used as a secondary swim area.

Heat loss with and without a filter on the infinity edge circuit would be an interesting comparison. Clearly, without a filter, the edge would have to be ran longer for chlorination and filtration..I guess the question would be how much longer and what would be the resulting additional heat loss.

For our design, we can turn our pit in about 30 minutes at high speed. During the winter I turn it about 2x per day and it stays clean and clear.

Not sure where the threshold would be during the summer, but the higher turns are more a result of pool use rather than cleaning necessity. Plus, the heat loss is an added benefit during the summer.

Hope this helps the OP.

    Bookmark   July 17, 2011 at 12:19PM
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I have a 35,000 gallon pool with a 12 foot infinity edge. I put in one of those cartridge filters (the kind used in - line for polaris cleaners). It catches all the big stuff before returning it to the pool. The edge wall acts like a huge skimmer, which I like a lot, so why not catch the crap that it is skimming?

    Bookmark   July 18, 2011 at 7:38AM
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scott, golfgeek,cascade,trhought, and racket;

Thank you all so much for the info in this thread. Have copied all for pool builder.

I am having difficulty finding what Scott talked about "vacuum breaker" to prevent problems with a failing check valve. I read about it in an article on aquamagazine by scott webb, (don't know if you are the same scott). Lew Akins also talks about it.

Can you guys enlighten me on this vac. breaker and who makes the product?

Also, Lew recommended AquRon or Aquafin sealers for the weir wall. Have also read about Xypex C-1000. Any thoughts on these sealers or their ease of installation?

Thank you.

    Bookmark   August 1, 2011 at 3:10PM
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I am not Scott Webb. Writes some good articles though.

I did see the article though. Vacuum breakers are not common and usually are individually designed when used.


    Bookmark   August 1, 2011 at 6:04PM
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