Depth of underground gutter drains below walkways?

Discussion in 'Homeowner Assistance Forum' started by Sayn3ver, May 23, 2020.

  1. Sayn3ver

    Sayn3ver LawnSite Member
    Messages: 55

    I'm having trouble finding any technical information regarding the installation depth of sch40 or sdr 35 below a concrete or paver walkway.

    I had my yard graded last week to correct water drainage away from the home.

    The contractor did a great job at fixing the grade as the downpour we had this morning shedded water exacty as he described it would upon completion of the work.

    However I'm concerned regarding the underground downspout drains installed in relation to my plan to wrap a walkway around the home that extends from the foundation out to 4-7 feet depending on location.

    The 4" ads triple wall smooth pipe basically has the top of the pipe flush with grade at the very base of the downspout and follows the pitch of the yard out 20ft with an average depth of soil 3-4" above the pipe.

    My concern is any paver that won't have a proper base below due to the pipe being there will cause heaving, shifting or settling issues long term in the paver walk. There is only foot traffic on this pathway.

    Due to the overall flattness of the property pop up emitters are being used. I plan on modifying where the downspouts tie into the vertical piping by adding a tee fitting in. This will allow me to insert a plug during the summer months in the tee opeing and then swap to a downturned street 45 during winter in case the underground piping freezes and backs up.

    I understand the best method would be a catch basin with grate and air gap at the base of the downspout but I'm concerned it will take up too much space in the walk, add a substantial expense at $55 a piece for 5 locations, and be less adjustable in height as the final finished elevation for the paver walkway has not been established yet.


    I apologize as this post is a bit scattered.

    I have a feeling changes will need to be made and I'm already anticipating me swapping out the triple wall smooth HDPE pipe with friction fit joints for sdr35 with glued joints to prevent future root failure below these walks and the future patio off the back of the house.
     
  2. Mac-s Lawn & Snow

    Mac-s Lawn & Snow LawnSite Senior Member
    Messages: 534

    It sounds like you have a good contractor and let him do his job. I never had any problems or call backs using thin wall as you described. With trying to get the grades right, it never ends up being to deep up by the house. The one thing of a concern to me is the 'air gap' method of downspout transition. I've had people alot smarter than me tell me this is how it should be done only to get call backs the first winter. My choice is to directly dump water to the underground transition and build it so in the winter you can switch the downspout to an elbow and a section of downspout on top of grade. I have also built systems where the down spout transitions into the thin wall runs under a patio and exits to daylight without a emitter that is operational year round. The key here is atleast 2 inches of grade for every 10 feet of pipe and that none of the pipe underground holds any water.
     
  3. OP
    OP
    Sayn3ver

    Sayn3ver LawnSite Member
    Messages: 55

    I'm initially looking for an answer regarding how much gravel base material is needed over underground gutter drains if setting a paver walk or concrete walk around the foundation of the home?

    I assume a more rigid pipe like sdr35,sch40 and sch80 would be preferable to triple wall smooth or corrugated HDPE pipe, especially if the paver only has 3/4" of sand between it and the top of the pipe. I'm neither a mason nor a landscaper. I do commercial electrical construction so I'm only familiar with our underground duct banks and rough concrete work regarding protection of our pvc and galv metal rigid conduits under code required fill.

    I'm not worried about the pitch of the pipework he did. We had 1.5" of rain this morning of rain and everything performed well. My concern is placing pavers over the pipe close to the houses foundation where currently the pipe is flush or just slightly below finished grade.

    My secondary concern is root infiltration of these drains under walkways and a future patio which is why I'm considering digging up and swapping unglued HDPE triple wall smooth pipe for sdr35 with glued joints. Possibly a minor or non existent concern but I'd rather do it now while the yard is dirt than after spending time and $$$ with walkways, hardscaping, landscaping and $$$ on turf renovation.

     
  4. Mac-s Lawn & Snow

    Mac-s Lawn & Snow LawnSite Senior Member
    Messages: 534

    A lot of times these pipes end up not being buried too deep by the house, that was kinda my point talking about grade.
    IMO the thin wall triple layer wouldbe the correct product. Schedule 40 is too rigid and if not buried below the frost line it will heave around, espicially under pavers. The only failure with thin wall I've had was next to a house I buried a 1 foot stub connected to a full piece. I should have put the stub at the other end.
     
  5. OP
    OP
    Sayn3ver

    Sayn3ver LawnSite Member
    Messages: 55

     
  6. OP
    OP
    Sayn3ver

    Sayn3ver LawnSite Member
    Messages: 55

    Here is the worst of the corners. The rest are actually less of a concern as this is the most shallow. The rest are down below grade.

    The actual final grade would be on the side of the home where the swing set is as crawlspace vents on that side of the home dictating max height of the walk so the pipe is going to need to come down no as the grade along the side facing the viewer in the picture will have to come down have the walk meet at the corner.

    I also should preface this with, final grade of the walk, and that any soil in reference pics now approximates the final walkway elevation. I realize the area will be dug out to accommodate the 8" or so of base and sub base.

    20200523_131931.jpg
     
    Last edited: May 23, 2020
  7. OP
    OP
    Sayn3ver

    Sayn3ver LawnSite Member
    Messages: 55

    I decided just to rent a trencher tomorrow and redo the underground drainage myself so I can move on with this.

    I'll expose the runs, pull out the pipe and run the trencher at 12" from start to finish (no drain has less than 3" of drop in 20ft at the surface after shooting it with a laser to verify. Most are 4.5"-6" of drop in 20ft).

    From there I'll tamp the bottom of the trench, dig out additional near the emitter, drop a bag or two of gravel under the emitter 90 which already has drain holes drilled,rerun the drains in sdr35 with the joints glued and verify pitch before back filling and hand tamping.

    The only thing I'm unsure about is adding the extra depth of the trench will add additional water being held in the pipe underground as it'll have a greater distance to the surface since now I'll have a short piece of pipe and a coupling coming to the surface at the pop up to make up the additional depth.

    Do you guys typically fasten your emitters to the fitting with a screw?

    When wall said and done this will resolve my concerns of

    1) inadequate amount of base fill above the pipe at the house for walkway installation

    2) sdr35 with glued joints won't have a chance of separating at the fittings and joints under finished walkways and patio and the solvent welded joints won't allow roots to find their way in (only entrance will be the bottom of the emitter 90 which can be inspected and remediated with from the surface.).

    Thoughts?
     

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