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.
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.