Sub Slab Advice

[John Gayewski]

So on underslab work, running drains under bearing walls is obviously to be avoided, as they'd be in the footing, but for non-bearing walls, there's no reason not to do it?

That would make dry venting the shower and WC easy, just put a san-tee under the wall, and the drain drops down into a combo on the building drain. The shower san-tee can be in a corner so that the vent avoids the valve area. The WC could still be wet vented if preferred.

Or if the building drain can't be under the wall for some reason, the shower could be dry-vented via a san-tee under the wall next to the entry to the shower.

Cheers, Wayne

Agreed

 

[John Gayewski]

So on underslab work, running drains under bearing walls is obviously to be avoided, as they'd be in the footing, but for non-bearing walls, there's no reason not to do it?

That would make dry venting the shower and WC easy, just put a san-tee under the wall, and the drain drops down into a combo on the building drain. The shower san-tee can be in a corner so that the vent avoids the valve area. The WC could still be wet vented if preferred.

Or if the building drain can't be under the wall for some reason, the shower could be dry-vented via a san-tee under the wall next to the entry to the shower.

Cheers, Wayne

Agreed. There is a very low likelyhood that this wall has or needs a footing.

When making a drawing from scratch don't draw the piping as if it needs to fit neatly inside of a hallway or run through the center of a room. This is actually more wrong than right. The limiting factor in designing drainage is not drainage, it's fresh air venting. Walls are generally the only path to atmosphere. So follow then and stay near them. Footings we need to avoid. These aren't hard and fast rules just some guides. Elevation would be a limiting factor for drainage.

 

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[Jayjayla]

Oh? : - )



I don't follow that comment. If you stick with the single building exit, then you still have 90' of 3" building drain under the building, so it has to fall 90/4 = 22.5" along its length, and the upper end will need to be under the slab, so the top of the pipe will still exit at least 27" below top of slab.

If you switch to two separate exits like John suggested, then your main run is reduced by 30-40', so that could exit 8" - 10" higher. You'd want a different layout for the right hand bath depending on where you want to exit (under the toilet would be easy with little change). I think the building drain under the two left baths would be still be low enough to use two different levels as I drew.

A couple more comments on the left bath--you have flexibility on where to run the building drain, it doesn't have to pass directly under that toilet. I'm not sure if it would be better to keep it unaligned, e.g. for ease of future access for some reason. And I think that there may be a better layout for the bottom shower, I don't care for the extra bends (as John just commented).

Cheers, Wayne

Sorry to disappear, was on the road yesterday. I suppose it would barely be higher if at all, you're right.

So if I did things as John suggested with two different exits, I still need to get the 3" pipe the same distance to the septic tank ultimately. How are you dealing with the two different elevations at that point?

I kinda just drew the drain in the walkways so I can see it on the plan but I would agree that it might be best to run it directly under walls to come straight up with the vents.

For the bottom shower I could still just do a dry vent and if I run the 3" directly under the wall that will make it easier.

 

[Jayjayla]

Move the main to below the framed wall with the valve. Then it's the easiest simplest design.

Thanks John, I like this idea. I assume you're just talking for the left bath. What do you think about the wet vent design on the right bath?

 

[Jayjayla]

So on underslab work, running drains under bearing walls is obviously to be avoided, as they'd be in the footing, but for non-bearing walls, there's no reason not to do it?

That would make dry venting the shower and WC easy, just put a san-tee under the wall, and the drain drops down into a combo on the building drain. The shower san-tee can be in a corner so that the vent avoids the valve area. The WC could still be wet vented if preferred.

Or if the building drain can't be under the wall for some reason, the shower could be dry-vented via a san-tee under the wall next to the entry to the shower.

Cheers, Wayne

None of the walls where the plumbing will be are bearing. The bearing walls generally have a thickened slab with steel but you could still run under them as long as you were pretty deep.

I think for the left bath, wet venting the WC and sink and dry venting the shower is probably the way to go. I can't vent the shower in any other walls than where the valve will be. To the right of the entry will be glass, that little wall with the door is just a curb.

 

[Jayjayla]

Agreed. There is a very low likelyhood that this wall has or needs a footing.

When making a drawing from scratch don't draw the piping as if it needs to fit neatly inside of a hallway or run through the center of a room. This is actually more wrong than right. The limiting factor in designing drainage is not drainage, it's fresh air venting. Walls are generally the only path to atmosphere. So follow then and stay near them. Footings we need to avoid. These aren't hard and fast rules just some guides. Elevation would be a limiting factor for drainage.

I think this is great advice John, I appreciate it. Should save even more materials this way. I'll re draw and upload to see if I got it right.

 

[John Gayewski]

Thanks John, I like this idea. I assume you're just talking for the left bath. What do you think about the wet vent design on the right bath?

Thre other bath room looks good. If you go with the two exits it would just be another version of that.

 

[wwhitney]

So if I did things as John suggested with two different exits, I still need to get the 3" pipe the same distance to the septic tank ultimately. How are you dealing with the two different elevations at that point?

I don't know anything about septic tanks, but I imagine you'd join the two sewers before the tank.

Your original drawing had 90' of 3" building drain. But 10' of that is running away from the septic tank, the part at the end in the right bathroom. If you end up splitting the building drain, then that bathroom would only need ~80' of drain to reach the point where the building drain currently exits. Less if you run some of it on a diagonal outside the building.

The rest of the building drain, starting at the kitchen looks to be about 50'. So it could exit the building about 1' higher than the 80' line would be at that point, if desired, and then drop a foot to join the other sewer.

Cheers, Wayne

 

[Jayjayla]

Thre other bath room looks good. If you go with the two exits it would just be another version of that.

Ok thanks. I'm working on a redraw now. Appreciate your help.

 

[Jayjayla]

I don't know anything about septic tanks, but I imagine you'd join the two sewers before the tank.

Your original drawing had 90' of 3" building drain. But 10' of that is running away from the septic tank, the part at the end in the right bathroom. If you end up splitting the building drain, then that bathroom would only need ~80' of drain to reach the point where the building drain currently exits. Less if you run some of it on a diagonal outside the building.

The rest of the building drain, starting at the kitchen looks to be about 50'. So it could exit the building about 1' higher than the 80' line would be at that point, if desired, and then drop a foot to join the other sewer.

Cheers, Wayne

Ok, thanks Wayne. I guess I need to draw it and do some math. To be clear, UPC has no issue running exterior pipes in cold climates? I realize its not pressurized and consistently has warm water running through it but codes don't always make sense. I'm sure John wouldn't have suggested it if it was a code issue.

 

[Jayjayla]

Alright guys, what do you think of this? I ran the main directly under the washer so I could come straight up. Hard to draw it in but figured do this for washer/sink setup:

https://terrylove.com/forums/index.php?threads/best-way-to-wet-vent-a-washing-maching-and-utility-sink.83470/

For the half bath to the left of the laundry, I assume I can still wet vent it if I step the 3" down to 2" then I can just come straight up with a wye for the toilet?

With the 3" directly under the lower bathroom wall now, seemed easiest to just tie all the vents together in the wall and pop a single out the roof?

Thanks guys.

The wife is calling for breakfast with the inlaws then I'll come back and play with the multiple exit layout joining outside.

 

[John Gayewski]

I haven't looked at the drawing yet but tying the vents together in the wall isnt always that easy. You'd have to do a lot of drilling in the wall studs and then run the pipe through the holes. It's either easier to wet vent as much as you can or go up to the attic and then tie them together.

 

[Jayjayla]

I haven't looked at the drawing yet but tying the vents together in the wall isnt always that easy. You'd have to do a lot of drilling in the wall studs and then run the pipe through the holes. It's either easier to wet vent as much as you can or go up to the attic and then tie them together.

That's what I meant. Its a sealed cathedral roof, single pitch. I'd drill holes in the TJI's and join them in the roof and pop out one 3" vent.

 

[Jayjayla]

I haven't looked at the drawing yet but tying the vents together in the wall isnt always that easy. You'd have to do a lot of drilling in the wall studs and then run the pipe through the holes. It's either easier to wet vent as much as you can or go up to the attic and then tie them together.

Also if you see a way to get vent what I drew I'm all for it

 

[John Gayewski]

The upc required pipe on the exterior of a building to be below the frost line. Here that's 42".

If you wye off of thre main, earlier than your drawing shows, for the toilet you can wet vent thr toilet with the lav. Then just the shower would get vented individually.

The shower drain and vent need to be offset with thr valve and water supplies cir thr shower, it looks like you hadn't that pretty close.

I'm typing this on the move.

 

[Jayjayla]

The upc required pipe on the exterior of a building to be below the frost line. Here that's 42".

If you wye off of thre main, earlier than your drawing shows, for the toilet you can wet vent thr toilet with the lav. Then just the shower would get vented individually.

The shower drain and vent need to be offset with thr valve and water supplies cir thr shower, it looks like you hadn't that pretty close.

I'm typing this on the move.

Sorry John, I'm not sure what you mean by wye off the main earlier. I would like to wet vent the toilet for sure.

I agree on the shower drain being offset, I plan to just get it as close to the exterior wall as possible still having room for nailing plate. I just didn't draw it well, I'll adjust thanks.

For the exterior pipe being below frost line, I feel like that becomes a pretty big issue as far as not putting too much fill above my septic field. I've got an irrigation ditch right behind the house that I need to be 50' from, so once I leave the building, hit my tank, I've gotta go another 50' of 3" PVC to D-box then chamber runs.

On that note, are you saying that when my main 3" leave the building, it has to be below the frost line to meet code? I don't know how anyone could do this and not have septic crazy deep. I've never left the building below the frost line before and it never was flagged by the inspector.

 

[John Gayewski]

Sorry John, I'm not sure what you mean by wye off the main earlier. I would like to wet vent the toilet for sure.

I agree on the shower drain being offset, I plan to just get it as close to the exterior wall as possible still having room for nailing plate. I just didn't draw it well, I'll adjust thanks.

For the exterior pipe being below frost line, I feel like that becomes a pretty big issue as far as not putting too much fill above my septic field. I've got an irrigation ditch right behind the house that I need to be 50' from, so once I leave the building, hit my tank, I've gotta go another 50' of 3" PVC to D-box then chamber runs.

On that note, are you saying that when my main 3" leave the building, it has to be below the frost line to meet code? I don't know how anyone could do this and not have septic crazy deep. I've never left the building below the frost line before and it never was flagged by the inspector.

So your toilet wye would be right next to the shower wye. Then you run parallel to thre main for the toilet and laver vent branch.

Yes any piping containing water needs to be below the frost line.

Usually the septic tanks are kind of deep. The exit of the septic tank would be higher than the bottom of the septic tank and that would be the same elevation of the leach field. There's generally an access hatch or cover that extends to grade. Our leach fields are layered in lifts of 12" or so and alternate between sand and rock with filter fabric between the layers. The leech field then exists to daylight. There are times where sites need to be shaped to allow for a septic system.

We generally poor footings at 48" below grade TOF. Then the sleeves in the wall set on top of the footing.

I'm not sure how anyone could install pipe within the frost line and expect it to perform reliably?

 

[Jayjayla]

So your toilet wye would be right next to the shower wye. Then you run parallel to thre main for the toilet and laver vent branch.

Yes any piping containing water needs to be below the frost line.

Usually the septic tanks are kind of deep. The exit of the septic tank would be higher than the bottom of the septic tank and that would be the same elevation of the leach field. There's generally an access hatch or cover that extends to grade. Our leach fields are layered in lifts of 12" or so and alternate between sand and rock with filter fabric between the layers. The leech field then exists to daylight. There are times where sites need to be shaped to allow for a septic system.

We generally poor footings at 48" below grade TOF. Then the sleeves in the wall set on top of the footing.

I'm not sure how anyone could install pipe within the frost line and expect it to perform reliably?

Ok, I'll mess with the drawing later and see if I get what you're saying.

My tanks always have the inlet maybe a foot lower than the outlet. I use chambers which are maybe 18" tall or something. Sometimes they say 3' max fill over top of leach runs, sometimes 5' so I guess we'll see. Still need a 1/4" slope from tank outlet to D box which in my case is going to be 50' from the tank, maybe a little more.

I've never had to put exit line below frost and I've never had an issue. Is not pressurized and there is always hot water flowing through from showers/sinks etc. I'm not a plumber obviously but I've never been called on it and its how everyone else here does it too. Are you in Canada?

 

[John Gayewski]

Ok, I'll mess with the drawing later and see if I get what you're saying.

My tanks always have the inlet maybe a foot lower than the outlet. I use chambers which are maybe 18" tall or something. Sometimes they say 3' max fill over top of leach runs, sometimes 5' so I guess we'll see. Still need a 1/4" slope from tank outlet to D box which in my case is going to be 50' from the tank, maybe a little more.

I've never had to put exit line below frost and I've never had an issue. Is not pressurized and there is always hot water flowing through from showers/sinks etc. I'm not a plumber obviously but I've never been called on it and its how everyone else here does it too. Are you in Canada?

No. Not Canada, Iowa. Any professional design will have a below frost requirement.

What's your local frost line depth?

UPC chapter 13 covers this in a short section. Protection from frost is possible without going deeper. On one occasion we lined a ditch with foam board and ran hest trace. No matter how you do it its required. I guess I don't know why you wouldn't want to to it.

A higher flood plane can put a wrench into things, but 3 feet of cover shouldn't be a max for a leech field. Why would this be? Leech fields are below the distribution tile.

You only need a sloped pipe below the frost line. Your landscape would determine the amount of cover. In some cases elevating a home with a building pad and building up the surrounding grade is a good idea.

One thing is for sure. I've built a large number of buildings professionally. A spec book that allows no frost protection doesn't exist.

 

[wwhitney]

UPC chapter 13 covers this in a short section.

FWIW, the fact that it only comes up in UPC Chapter 13 on Healthcare Facilities means it's not generally required. Although it still may be a good idea.

Shallow frost protected foundations use a wing of insulation outside the building footprint to raise the frost line under the foundation. I wonder if a strip of buried insulation board on top of the sewer lateral would work similarly. It might need to be impractically wide to be effective, though.

Cheers, Wayne