Building a garage over drainage pipe

[[memphis]]

So I purchased my first home
One box that didn't get ticked was the garage but there is a snag.

There is a catch basin at the rear left of the property (viewing from the street). Property is 60x140. The 18" green/plastic feed line to the city sewer runs all the way down the driveway (approximately 100ft).

I would like to build a 2 car garage at the end of the driveway, which is right on top of the feed line to the city storm sewer.

The good news is, according to the city this is private property and no easement was put in place when this storm sewer was installed in 2013. The bad news is, if SHTF I need to repair it because I own it, but I am going to roll the dice and hope that it doesn't fail within my lifetime. I do not plan to live here for the next 50 years.

Has anyone ever come across this kind of situation?
I won't be building anything for over a year but I would certainly like to design the garage that if a repair to the drainage pipe be necessary, breaking up the slab would be contained to a small area of the garage where it wouldn't compromise the structure completely.

Within my design, I would like to have two front doors or a large single (more expensive) and either a single roll up in the rear or a sliding barn style rear wall. Should the slab need to be broken up, I would like to position the garage so that it is a clear shot that could be dug out with a mini ex without destroying everything

 

[firebirdparts]

I have a drain pipe that I own and I would have to repair and I put in, and it's 24", so I can understand what you're talking about. I will just mention this before 50 clueless people get in this thread and say "nobody owns a drain pipe" and just waste a bunch of your time.

In my case there is an easement and I would not build a garage over it.

I think if I were you, I would make at least a passing effort to keep the weight of the garage off it. An ounce of prevention being worth a pound of cure and all that.

 

[DGersic]

I️ won’t say it’s a good idea, but my sanitary sewer hookup runs approximately 150’ to the alley at the back of my lot. Along the way, it goes under part of the house (an addition put on in the 1970s), under the patio, under the detached garage, and under the corner of my neighbor’s yard. It’s a 1940s / 1950s house, and they did things then that you couldn’t / wouldn’t / shouldn’t do now. Oh, and the drain tile was connected to this as well.

When the sewer failed about 10 years ago, we had to excavate about 15’ down in the backyard to get to roughly the middle of this run. We had it sleeved, which can go about 75’ max. So now there’s a 4” PVC cleanout behind the garage. That was a $10K weekend.

A couple of weekends later, another $12K bought a sump pump, pit, and several hundred feet of directional bore 3” pipe to reach the nearest storm sewer, two houses away.


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[TommyK]

So I purchased my first home
One box that didn't get ticked was the garage but there is a snag.

There is a catch basin at the rear left of the property (viewing from the street). Property is 60x140. The 18" green/plastic feed line to the city sewer runs all the way down the driveway (approximately 100ft).

I would like to build a 2 car garage at the end of the driveway, which is right on top of the feed line to the city storm sewer.

The good news is, according to the city this is private property and no easement was put in place when this storm sewer was installed in 2013. The bad news is, if SHTF I need to repair it because I own it, but I am going to roll the dice and hope that it doesn't fail within my lifetime. I do not plan to live here for the next 50 years.

Has anyone ever come across this kind of situation?
I won't be building anything for over a year but I would certainly like to design the garage that if a repair to the drainage pipe be necessary, breaking up the slab would be contained to a small area of the garage where it wouldn't compromise the structure completely.

Within my design, I would like to have two front doors or a large single (more expensive) and either a single roll up in the rear or a sliding barn style rear wall. Should the slab need to be broken up, I would like to position the garage so that it is a clear shot that could be dug out with a mini ex without destroying everything

There are a number of options. The cheapest and easiest of which is of course to do nothing. Alternatively you could concrete encase the pipe or install a sleeve so that the pipe could be replaced in the future without tearing out the floor.

Can you re-route the pipe around the proposed garage prior to construction?

 

[phor53]

Following

 

[Bert_]

Can you re-route the pipe around the proposed garage prior to construction?

Rather than reroute it now just leave it as is and IF it ever goes bad you can always run it around the garage then.

I deal with this issue from time to time usually with underground electrical wires and that is almost always my answer.

I don't think the weight is something to worry about. I'm sure you wouldn't think twice about driving over that pipe. I didn't do any math but I imagine the weight of a pickup is more concentrated than a building.

 

[Vintage Veloce]

if you are putting your foundation on top of anything like sewer lines or other utilities, it is worth the effort to make sure that stuff is new or up to date. You don't want to have to cut up your foundation later to get to it. This is a common situation in the city, often you have to build over something.

But PLEASE don't say, "I'll only be here a few years, so it won't be my problem." That is very uncool. Do it right, or don't do it at all. Think of the times you have pleasantly found the guy who did something before you "did it right", and how lousy it was when you found the last guy "did it wrong".

Put in cleanouts, new pipe, whatever. It's really not that much additional cost compared to the foundation.

 

[m32825]

How sure are you that you know the location of the pipe? We had to relocate the line running to our drain field to build a detached garage. Nothing beats putting eyes on it in a couple places.

-- Carl

 

[6768rogues]

You said it is an 18" pipe. That is pretty big. Don't place your foundation parallel to it and right on top of it. If it crosses the foundation and you see the pipe or are close to it, dig a little more and encase the pipe in concrete. Then put extra rebar in the foundation there so a section cannot break and crush the pipe. It is pretty remote that something would plug a pipe that big such that an excavation outside the building line would not allow it to be cleaned out. If it happens, reroute the pipe around the building if possible.
I doubt it will ever happen, but if all else fails you saw cut a slot across the floor and dig up the pipe.

 

[[memphis]]

There are a number of options. The cheapest and easiest of which is of course to do nothing. Alternatively you could concrete encase the pipe or install a sleeve so that the pipe could be replaced in the future without tearing out the floor.

Can you re-route the pipe around the proposed garage prior to construction?

No I cannot relocated the pipe, but I could definitely shift the garage over. It would look kind of funny being in the middle of my backyard however

if you are putting your foundation on top of anything like sewer lines or other utilities, it is worth the effort to make sure that stuff is new or up to date. You don't want to have to cut up your foundation later to get to it. This is a common situation in the city, often you have to build over something.

But PLEASE don't say, "I'll only be here a few years, so it won't be my problem." That is very uncool. Do it right, or don't do it at all. Think of the times you have pleasantly found the guy who did something before you "did it right", and how lousy it was when you found the last guy "did it wrong".

Put in cleanouts, new pipe, whatever. It's really not that much additional cost compared to the foundation.

I am a total believer in do it right or do it twice... That's why I would design the slab to minimize destruction should any sort of repair rear its ugly head

How sure are you that you know the location of the pipe? We had to relocate the line running to our drain field to build a detached garage. Nothing beats putting eyes on it in a couple places.

-- Carl

I can look down into the catch basin and see the pipe, it is not submerged in water. I am only assuming it runs straight down the middle of the driveway but I am sure I could lay down some marker paint come spring.

You said it is an 18" pipe. That is pretty big. Don't place your foundation parallel to it and right on top of it. If it crosses the foundation and you see the pipe or are close to it, dig a little more and encase the pipe in concrete. Then put extra rebar in the foundation there so a section cannot break and crush the pipe. It is pretty remote that something would plug a pipe that big such that an excavation outside the building line would not allow it to be cleaned out. If it happens, reroute the pipe around the building if possible.
I doubt it will ever happen, but if all else fails you saw cut a slot across the floor and dig up the pipe.

My thoughts exactly... design it so it can be reasonably accessible

 

[Jazz1]

Murphys Law the drainage pipe won't collapse until you hang the last shingle on garage. I would not build on top.

 

[chaosracing]

I was involved with a local Fire Company a few years ago. I used to take care of alot of maint and construction projects. We were renovating the social club and I made a suggestion that before finishing the floor (new VCT tile) that we scope all plumbing drains behind the bar, especially since there was a known problem. When we did, we found a collapsed section of drain pipe. The following week, me and three other guys started jack hammering thru the concrete floor to repair the pipe. Well we opened a large can of worms. When the social quarters was built in the late 60's, it was built on top of the storm drain from the other side of the road. I found a cavern under the club floor caused by a failed steel storm drain. We got the township involved. They replaced the line, but rerouted it behind the club and replaced the entire pipe because of where it drained to originally. It took almost an entire tri axle load of stone to fill the cavern in.

Now part of the reason why I am no longer involved......the higher ups decided to add on to the club for more cooler storage and an office. Guess where they decided to build it? Right on top of the new storm water pipes (and the township allowed it)


Now will this happen to you....probably not since its pvc pipe, not steel or concrete that will fall apart. As for designing to build around it, it all depends on what type of building you are looking at (traditional vs pole building) and how deep it is at the project site. I would definitely avoid putting any kind of load on the pipe itself. Something else you could do to minimize failure due to the building being on top is to dig down to the bottom of the pipe on both sides (I would go past the building footprint by a few feet) and put crusher run (2A modified) stone around it, compacting every 8 to 10 inches, and put that same stone over top of it. When compacted, this stuff is probably as dense as concrete is, but if you need to replace the pipe, you wont need to bust up concrete around it.

 

[firebirdparts]

Do you have any idea how deep it is? If you decide to put a foundation down beside it, or maybe one on each side, that foundation I suppose needs to reach down below it. If you built up a foundation on each side of it, then you could consider pouring the floor in sections so that the part over the pipe is just bridged over that 18" and basically removable. I mean removing it wouldn't tear up the rest of the floor.

 

[Radix2]

If it is good quality plastic pipe, that is a good thing.

One thing to look into if you excavate is to verify that the pipe sections are connected properly. Maybe it is thermowelded which would be best, but if it is sectional, it might be worth verifying it is properly made up and not leaking. A typical failure mode of these pipes is a leak that causes the ground to be eroded around the leak ( usually what happens when the old steel pipes rust out) with the plastic ones, they should last forever, but the weak spot is if the crew did not join the parts properly leading to sinkholes by the joints- so this is what you would be looking for before building.

 

[[memphis]]

Do you have any idea how deep it is? If you decide to put a foundation down beside it, or maybe one on each side, that foundation I suppose needs to reach down below it. If you built up a foundation on each side of it, then you could consider pouring the floor in sections so that the part over the pipe is just bridged over that 18" and basically removable. I mean removing it wouldn't tear up the rest of the floor.

Unfortunately I do not know the depth... as the old say goes **** flows downhill so the catch basin at the rear of the yard is the highest point in the system. I have no idea what the slope of the run is to the street

If it is good quality plastic pipe, that is a good thing.

One thing to look into if you excavate is to verify that the pipe sections are connected properly. Maybe it is thermowelded which would be best, but if it is sectional, it might be worth verifying it is properly made up and not leaking. A typical failure mode of these pipes is a leak that causes the ground to be eroded around the leak ( usually what happens when the old steel pipes rust out) with the plastic ones, they should last forever, but the weak spot is if the crew did not join the parts properly leading to sinkholes by the joints- so this is what you would be looking for before building.

Due to the length it is most definitely NOT a continuous run but I have no idea how it would be connected?

 

[steveo1o9]

Are there any other pipes entering the basin in your yard? 18" is gigantic for just a single yard drain. I know you said you just bought this house but is there any sign that that basin receives a high volume of runoff from the surrounding area? 2013 is pretty new so you should be problem free to many years to come, but I would still be wary of putting a structure on it. Like already said with my luck I would finish the garage and then have a problem with the storm sewer. If possible I would rather put in a few more basins to bend the pipe around the garage. Last thing you would want to happen is that pipe to fail under the garage and create sink hole or something, all it would take is a failed joint and time for that to happen.

 

[chaosracing]

Unfortunately I do not know the depth... as the old say goes **** flows downhill so the catch basin at the rear of the yard is the highest point in the system. I have no idea what the slope of the run is to the street



Due to the length it is most definitely NOT a continuous run but I have no idea how it would be connected?

More than likely its a bell configuration with rubber gaskets in the bell. The bell slips over the end of the previous pipe.http://pacificplasticsinc.com/wp-content/uploads/Sewer-SDR35-Green-Gasketed.jpg

 

[wssix99]

EVERYONE has sewer pipes under their floors and foundations. This one is just bigger.

If a pipe goes bad, the fix is the same:
- Cut slab
- Dig
- Fix
- Repair slab

The bigger pipe means a bigger cut, deeper cut, and more dirt - but it's over a garage, so a potential fix shouldn't be a big deal.

Unless you have reason to believe this pipe is going to fail in your lifetime, I wouldn't sweat it.

 

[sberry]

I wonder too about the size. How much area does this cover? I might see if there was a joint under the building, if this is big ole plastic build over it and fix it should it ever happen.

 

[steveo1o9]

I wonder too about the size. How much area does this cover? I might see if there was a joint under the building, if this is big ole plastic build over it and fix it should it ever happen.

There is potential for a few joints under his proposed build, typical sticks are either 10' or 20'.

My concern is if this was a DIY by the previous owner or installed by the town or contractor. My driveway has a 8 feet deep, 40 feet long, 24" HDPE culvert under it. Three weeks after buying the house we got 9" of rain in 3 days. I came home to a driveway with a 6' diameter sink hole in it after the joint under the driveway failed. After digging it up we found that the pipe was sloped the wrong way, had a belly in the middle, and even had logs supporting the joints... I imagine this pipe was installed when the house was built in 2006, it functioned fine for years until that one day. I couldn't imagine dealing with that if it was under my garage. A year ago my answer may be different but after dealing with that mess I would do everything I could to avoid building on that pipe, especially without knowing how deep it is.

If you choose to build on it please do some due diligence and locate it and determine its true depth. Maybe even hire a camera to send down it to check condition.

 

[kbs2244]

First of all, wait that year and watch where the winter/spring water comes from and where it goes.
And how much of it is going into that catch basin.

As said, 18 inches is big, it will drain a lot of water, but a large drainage area can collect a whole lot of water in even a little rain.

2013 is new enough to have the drainage area, and quantities of water expected to be handled, on record at the local surface drainage agency.

They will own the pipe and have drawings about size, route, depth, ect.
They should also have a record if it ever failed to handle a rain/melt.
If there was a surface area set aside for possible basin overflow they will the boundaries of that also.

A garage is an expensive, and emotional enough project to take your time and do your research,

I have seen an open drainage ditch converted to a 36-inch concrete pipe so a typical 50x 100 industrial park building could be built over it.
I may rent that building but I would never buy it.

It sounds like the city is saying you can do it if you want.
But I would take the advice of this guy.

 

[T_R]

I have an 18" plastic culvert under my driveway right in the middle about 500-600 feet from the road. It really only runs during the spring melt. It failed when I was building my garage. I had a load of trusses dropped off. They were on a tilt bed tractor trailer with just a day cab, so not a ridiculous amount of weight. It had been in place for about 25 years at that point.

I guess my point is that they can fail from weight. A slab would probably spread the load better. But then you have to wonder about how good is the compaction around the pipe?

I think if it was mine, I would think long and hard about putting a concrete pipe around the plastic or maybe even excavating down to the pipe and just encasing it in concrete.

 

[[memphis]]

I wonder too about the size. How much area does this cover? I might see if there was a joint under the building, if this is big ole plastic build over it and fix it should it ever happen.

I do know that there is 6" O pipe draining from neighbours on either side of me into the basin; I am not sure if they are going two neighbours over. I will do a good sketch later to explain

There is potential for a few joints under his proposed build, typical sticks are either 10' or 20'.

My concern is if this was a DIY by the previous owner or installed by the town or contractor. My driveway has a 8 feet deep, 40 feet long, 24" HDPE culvert under it. Three weeks after buying the house we got 9" of rain in 3 days. I came home to a driveway with a 6' diameter sink hole in it after the joint under the driveway failed. After digging it up we found that the pipe was sloped the wrong way, had a belly in the middle, and even had logs supporting the joints... I imagine this pipe was installed when the house was built in 2006, it functioned fine for years until that one day. I couldn't imagine dealing with that if it was under my garage. A year ago my answer may be different but after dealing with that mess I would do everything I could to avoid building on that pipe, especially without knowing how deep it is.

If you choose to build on it please do some due diligence and locate it and determine its true depth. Maybe even hire a camera to send down it to check condition.

That sounds awful. This basin was installed by the City. It was part of the "Backyard Flooding Program" which has been discontinued - probably because it was so expensive!

 

[sberry]

It might be worth a look at city or county plans. The lot size is small but the drain basin /watershed could be way larger. But a clear 18 inch pipe will drain a lot of water, a lot. Especially that short. Maybe the city had future plans up hill from there.
The garage is downsteam the way it sounds, sou could collect run off and drain it to the basi I spose depending on elevations.

 

[01-7700]

The weight of a garage will cause some consolidation of the soil surrounding the pipe. This will cause tension on the pipe and could slip one of the joints apart. It's very likely that you have a joint within the influence zone of the garage you're planning.

 

[wssix99]

The weight of a garage will cause some consolidation of the soil surrounding the pipe. This will cause tension on the pipe and could slip one of the joints apart. It's very likely that you have a joint within the influence zone of the garage you're planning.

A properly designed foundation will spread out the pressures of the building to just a few psi above the pipe.

Proper foundations shouldn't move or sink. If the soil under the building consolidates, then someone screwed up.

 

[T_R]

A properly designed foundation will spread out the pressures of the building to just a few psi above the pipe.

Proper foundations shouldn't move or sink. If the soil under the building consolidates, then someone screwed up.

I don't think you can say that without knowing how or what the backfill around the pipe is. No way of knowing if it was compacted gravel or they just threw dirt back in the hole and left.

Also you don't know what kind of foundation and that is going to matter. A frost line foundation wall sitting a foot above the pipe is going to put a lot weight on it than a floating slab 6 feet above it.

If I was going to put big money into a "show" garage over this thing, I would dig it up and find out. Maybe I would risk it for a cheap no frills unfinished deal where I didn't have a lot of money in it.

 

[wssix99]

I don't think you can say that without knowing how or what the backfill around the pipe is. No way of knowing if it was compacted gravel or they just threw dirt back in the hole and left.

That's a fair point and may probably worth digging a test hole to see what's on top of the pipe.

Another thing that can be done is an engineer can design the foundation to bridge that area, assuming it's suspect and has zero bearing capacity. (Additional rebar would just be needed locally.)

I had to do this with my house when we uncovered a 100 year old cesspool full of horse s&#@ under one of our foundation walls. That was a less-than-awesome discovery, but we were able to adapt the foundation wall and the house is still standing fine. (on top of the soft ****)

Also you don't know what kind of foundation and that is going to matter. A frost line foundation wall sitting a foot above the pipe is going to put a lot weight on it than a floating slab 6 feet above it.

It wouldn't be a big problem. The forces don't radiate directly downward to the pipe. They spread out and dissipate with a square of the depth. So, by the time the force of the building gets all the way down to the pipe, the forces are much less than they are at the surface of the slab.

 

[01-7700]

It wouldn't be a big problem. The forces don't radiate directly downward to the pipe. They spread out and dissipate with a square of the depth. So, by the time the force of the building gets all the way down to the pipe, the forces are much less than they are at the surface of the slab.

You seem to be assuming that the pipe is buried at some depth. How do you know that?

 

[wssix99]

You seem to be assuming that the pipe is buried at some depth. How do you know that?

The pipe would be below the frost line, which should probably be deep enough, in itself. Since the OP mentioned the pipe is for a storm sewer, it must be much lower. The inlet to the pipe would be at a low point on the property or subdivision. From there it would start at least at the frost line. The garage would be on a relatively elevated area and then the pipe would need to slope away from that low point at least 1/4" per foot.

So, unless the garage is going to be in a gully and right on top of that sewer inlet, the pipe must be several feet below ground level where the garage is going to go.

 

[01-7700]

The pipe would be below the frost line, which should probably be deep enough, in itself. Since the OP mentioned the pipe is for a storm sewer, it must be much lower. The inlet to the pipe would be at a low point on the property or subdivision. From there it would start at least at the frost line. The garage would be on a relatively elevated area and then the pipe would need to slope away from that low point at least 1/4" per foot.

So, unless the garage is going to be in a gully and right on top of that sewer inlet, the pipe must be several feet below ground level where the garage is going to go.

He did say this was part of a backyard drainage project. So it sound to me like low land with not much elevation to drain - so that would take large shallow pipes to remove the water (if I were assuming).