Basement wall finishing around perimeter drain system

Because the hive knows all...

With wfh most days in my future I plan to make a more permanent and comfy basement office space and eventually do more adds over time. 

One of my laeger hurdles is figuring out how to deal with this

its maybe 1.5" wide full of gravel  at the bottom but plenty of spiders as well. Thse all lead to a sump that never seems to take on additonal water. We have a wet yard but so far no water problems inside. 
 

For finishing I want to use some foam insulation behind the walls to take the edge off the temps and only use some baseboard electric in the worst months. To do this should I :

1 assumes water is likely only down the wall

2 assumes i need it to flow on the floor into the drain

the google was inconclusive other than "hire a pro to do it" which is why I am asking here for any insight. 

Edit: I am confused after writing the below statements. How does the water enter the basement from above the floor? Usually water enters from under the foundation wall and runs under the footing and then up and around the slab edge where it butts up to the concrete wall.

That's an interesting way of installing a drain tile. I would be worried about radon leaking out of that void. I would have some lite weight clad or galvanized steel or aluminum bent up and caulked to the floor and wall and attached to the wall (I don't know anything about metal to concrete electro chemical reactions). They make a latex based coating to separate the two.

Concrete walls are rarely straight or plumb so usually the furring stud wall is placed an equal distance at the ends of the wall with around 1/2" gap between the C. wall and the S. wall, or what ever it take to build a nice straight and plumb new wall. You can than shim the rigid foam tight to the concrete wall with shims between the foam and studs.

Make sure you hang your drywall with at least 1/2" to 3/4" gap off of the concrete floor for whenever your basement eventually floods. 

Is there a floor drain?

That's a Northern basement detail. We used to always do that in basement floors. 

was your house built in the 80's?

The argument was it would drain if the basement ever flooded. Gravel was also put on top of the footings so water could flow around the slab and get into the granular fill below the slab for drainage. 

Note: that also predated a good awareness of radon. 
 

I think the reality was it was a production issue. Concrete masons would save all their basement slabs for rainy days, and do them toward the end of construction. With the basement walls already in place, it was much easier to stick a 2x4 along the wall to act as a form. 
 

If your basement has been dry, I wouldn't worry about it. If you fill it, I guarantee the water will still drain somewhere in the event of flooding. 

Late 90s build iirc. I believe the theory goes if the water table is high on one side the sump can take care of it. There is additionally a lot of good external drainage and a cistern in the plans but never located it. We do have a separate radon vent and were ok when we bought. 
 

I could see a 2x in the gap for the floor pour but there definitely is drain pipe under going to the sump. 
 

Water always finds a way, hence the additional thought. Appreciate the responses!

Ok then, now that the mystery of the drain tile is cleared up... I helped build houses in the 80s and 90s in the North Central US and have never seen anything like that, lol.

Now, the question is do you need to add polystyrene insulation behind your new 2x4 furring wall? White bead board is R-4 per inch and the pink or blue extruded polystyrene is R-5 per inch. Fiberglass friction fit insulation is R-11 or R-13 in a 4" furr-out wall. After pricing out the cost per insulation value of fiberglass and polystyrene, I think that you will just want or need fiberglass.

Always thought batts sub ground was a nono. Will have to think about that. 

In reply to Paul_VR6 (Forum Supporter) :

I would avoid batts in direct contact with masonry, and in humid areas where the batts can absorb moisture

I've been out of the building loop for 20 years and building practices are constantly changing, for example, do you use a vapor barrior on attic ceilings or not?

As soon as the temperature of any surface in your basement hits the dew point, you will have a moisture problem. I suppose it depends on your heating system, forced air would be best for basement moisture. Up here in North Dakota in the winter, I used a humidifier upstairs and a de-humidifier downstairs at the same time in an old poorly insulated 1950 house with forced air which didn't have any cold air returns in the basment. Mold would grow on the drywall paint in places like behind the couch. After I cut returns in, I turn off the de-humidifier during the winter.

1" R-5 extruded polystyrene is something like $20 per sheet so I suppose that isn't such a terrible price hit. 

Yea my cuttent thought is no barrier as the moisture vapor moving would be better. 
 

The foam panels aren't too spendy even if i do just 1/2-1" on the wall, frame out a little I can still do batts in the wall if I want to keep costs down a little. Will have to do some math on which is best $/R

I don't have enough heating capacity excess to add the basement. Thats why I was thinking supplemental baseboard elect. I usually have a dehumidifier down there regardless. 

In reply to Paul_VR6 (Forum Supporter) :

Rigid insulation IS a vapor barrier. Extruded styrofoam is permeable, but can still act as a vapor retarder. 
 

At least it's on the right side of the wall. 

I was thinking more in terms of an extra layer, taped, etc. Good point about the insulation, I think I'd be best off using the permeable kind and seal the walls.