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Stonework and a Good Foundation

3/22/2013

5 Comments

 
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Community Fireplace at our Local Park ...
First, let me be perfectly clear that the pictures you see that accompany this post are not our work. The fireplace you see is a community fireplace that’s located in our neighborhood park about a block from our house.

It’s a great little park with a few little creeks that converge, a network of paths and bridges that wind their way around the park,and a number of small gathering places for picnics and get-togethers, including a few with these nice stone fireplaces which you see in the picture.

The park in general, and more specifically the fireplaces get a fair amount use.  It’s a go-to spot for kids’ birthday parties, scouting events, church functions, community environmental groups and anybody else who wants to enjoy the outdoors but may not personally have the space.

The problem I’d like to address in this week’s post is that the fireplaces are starting to lean.  In some cases significantly.

I don’t know when these fireplaces were first constructed.  My guess is 40 to 50 years ago, but in all honesty it could have been even longer ago.  We’ve been in our house for nearly eight years, and the fireplaces have been there since well before we arrived.

And to be perfectly honest, I don’t recall these fireplaces ever having been perfectly plumb.  But I have noticed that just in the past few years the lean has become even more significant.  My concern is that at the present rate of leaning, these fireplaces may not be around much longer.

So what causes this lean? Well that is the point of this week’s post.

The lean can pretty much be the result of one of two things– either the footing or subgrade work was not done properly, or the location of the fireplaces was a poor choice.  Or it could be a combination of both.

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And the Unfortunate Lean
Not having been around during the construction, I can’t speak to exactly how deep the footings go, or what was used as a base.  But it’s quite clear as you can see that something wasn’t done well enough.

As I mentioned there are several creeks in the park that converge and meander through the park. And wherever there are creeks, there is going to be erosion.  And most likely a series of subterranean springs as well.

The fireplace you see is a good 30 to 40 from the edge of the creek, so erosion shouldn’t be the issue. At least not from the main creek. What is more likely happening is that the small underground springs have softened the surrounding earth, and the weight of the fireplaces has settled unevenly as result.

 If the footing was done properly, it should consist of at least a 3’ deep hole with a concrete base (depth may vary based on geographic region), frost walls around the perimeter of the base, clean gravel fill with more concrete on the surface to build the stonework upon.  There are a few different techniques that will all work fine, but the key is getting that depth so the structure won’t be affected by moving or heaving earth.

So lets just assume the base was done properly – why could this be happening?  
 
As mentioned above, the proximity to the creek and the likelihood of underground springs most likely had something to do with it.  Lets just say there was a small underground spring 5’ to 6’ below the surface.  That never would have been evident with only 3’ worth of excavation.  Once the fireplace was built, that spring would be doing its thing – underneath the fireplace.  
 
And as the spring flows, the area becomes wet, possibly eroding out some more sub-soil, and before you know it you have a big wet cavity under the structure.  Not good.

So what can be done to ensure this doesn’t happen on your next project?  Well to begin with make sure the footer is deep enough to withstand the frostline of the surrounding grade.  Every area of the country is different, but if you’re not sure check your local building codes to see what’s required.  And then just to be safe add an extra 6”.  If you ever have to ask if you’re deep enough, then you’re probably not.

As for the springs, unfortunately there really are no guarantees here.  First, if possible try not to build in an area that may be too close to a creek, or situated in a low flat area that could be prone to occasional flooding.  Some sites don’t offer a whole lot of flexibility, but a good rule of thumb is the higher the ground the better.

If you are in a situation where you have some concerns, the footer can be constructed in a wider footprint than the actual structure.  This will give the entire structure some more stability even if the surrounding sub-grade settles or shifts.  
 
An extra little exploratory digging is another option.  Dig your footing a bit deeper than you had already, and see what you can find.  And if you don’t mind spending a bit more money, some geologic and engineering firms may be able to determine whats going on below the site.  An extra cost?  Sure, but if it ensures the longevity of the structure then its worth it in my opinion.

Built-in fireplaces and other structures are an awesome add-on to any outdoor living spaces.  Spend the time and money to make sure they’ll be around for years to come.  I hope the ones in our local park can be saved.

5 Comments
Dave Marciniak link
3/21/2013 10:13:32 pm

Clark, great post. In a situation like this, if the issue is indeed underground water, would "floating" the entire thing on a structural slab (as opposed to a frost footer) have been a better way to go? When you talk about a wider footer are you talking about this, or down at frost depth?

Reply
Clark link
3/21/2013 10:25:23 pm

I wouldn't sacrifice depth, but a wider footprint would certainly add stability. In this case the whole back half seems to be sinking.

The area where the photo was taken is a flat low-lying area between the confluence of a couple of creeks, and is very prone to soft muddy condtions, if not outrght flooding.

I don't know exactly how this was constructed, but I did poke around a bit and there isn't any fotting I could detect outside the footprint of the fireplace. I'm sure its a combo of poor site selection, and the footing could be wider.

Reply
Anna link
3/21/2013 10:42:54 pm

That's too bad, these are really cool fireplaces! I wonder if they were built during the CCC days? We had some neat old projects up in Northern Michigan like that.

Reply
Matt link
4/1/2013 02:08:50 am

How did I miss this? I love those old ruins..ever noticed how the chimneys and foundations are still standing? Important point you brought out.....the condition of your ground dictates your footing/foundation needs. Very important to understand this when building with stone..there is no one size fits all in stonework!

Reply
Clark link
4/1/2013 11:13:44 am

Thanks Matt. I figured you had a few cents to add on this one.

Reply



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    Clark Kent Creations, LLC is a full-service landscape construction company servicing the Pennsylvania communities of Delaware County, Chester County, The Main Line, and the University City, Art Museum, and Manayunk/Roxborough neighborhoods of Philadelphia.  In addition to this blog page, additional information regarding the company and our services can be found on the subsequent pages of the site.
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    Clark Linderman is the president of Clark Kent Creations, LLC, a landscape construction company based in Swarthmore, PA.  He is a proud graduate of the University of Michigan.  In addition to his passion for all things outdoors, he counts Michigan football, Phillies baseball, Superman memorabilia, Memphis R&B music, and good craft brews among his many interests.  He currently resides in Swarthmore with his wife, Sheila, two sons, his dog Krypto, and a really, really messy garage full of work supplies and toys.

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    Clark Kent Creations, LLC
    Swarthmore, PA
    Design and Construction to Maximize Your Outdoor Experience

    707-290-9410
    clark@clarkkentcreations.com
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