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Pipe Chase Beneath Slab?

CloudHidden's picture

Design clients often are concerned about plumbing beneath the slab. They're thinking about future maintenance/replacement. Anyone ever build a pipe chase beneath the slab? What's the good, the bad, and the ugly of that?

(post #104440, reply #1 of 22)

Cloud,

Not a chase but a tunnel.

Slab on grade solar home, slab had 4" diam. ADS pipes bedded into the gravel beneath the slab and above the insulation.
Pipes all dumped into the tunnel which connected to a high air return fan . Fan pulled air from the highest point in the house, forced it down thru the tunnel and out the pipes to near the exterior walls.

Since we had the tunnel we used it as a chase for as much of the piping as possible . Made sense for future work if any.

"Poor is not the person who has too little, but the person who craves more."...Seneca


Life is Good

(post #104440, reply #11 of 22)

I am designing my own home in Iowa. Always lived near the ocean till now so learning a lot about climatic extremes. I want to do a 'solar slab' as you described, but not dumping the air outside as we need heating as much as we need cooling so I figure to loop it back into the house. Providing of course we deal with mold/dampness/radon issues in the tubes adequately. Any tips on where to go for information about Solar slabs. I am modifying the "concrete blocks under slab" approach of the Passive Solar House book -forget the author's name. But tubes seem so much cheaper and easier. But is this healthy and effective?

(post #104440, reply #12 of 22)

For solid storage you need to expose the maximum possible surface area to the moving air. Simple tubes may not be the most effective way to do this, plus plastic is a moderately good insulator, and you want effective heat transfer to the concrete.


So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #104440, reply #13 of 22)

Our local earth tube installer uses 8" corrugated drain pipe. 4 pipes 100' long and buries in a 10' wide trench, 8' deep and has 4' drain rock on bottom leading down to a daylight drain. The pipes are 2-3' spacing. I figure they should work also in a solar slab. I saw some info on plastic here: http://www.mb-soft.com/solar/saving.html which suggests that PVC conducts almost as quickly as other mediums. The corrugated pipe is so thin it should conduct heat very fast. So I want to have a large amount of mass under the slab, but over insulation - maybe 24" of sand? Not sure if this will be too much weight on 2' foam board. There is a spray insulating concrete called Airkrete www.airkrete.com which sets up very hard. But I have much to learn about this whole business. I have never built with earth tubes or solar slab before.

(post #104440, reply #14 of 22)

Brian,
I am located in western Ore.
We do have a heating season although not as bad as yours.

I built according to the owners specs when doing this project (1979) and as far as I know there have been no ill effects from what we did. Owner was a doctor. We used 4" ADS laid 4' o.c. in what we call "bedding gravel" which is crushed rock fines , gravel was 18" thick placed on top of 2" EXPS insulation and 6 ,mil. black plastic.

Do not worry about the crush strength of the EXPS , you will be fine.

WE were well above any water table so the only moisture we had to contend with was condensation.

What I know of solar slabs isn't much , only what we used to do which was insulate them from ground contact , both under and at the perimeter.

This house used aprox. 1 -1/2 cords of fire wood and no other heat for a heating season, 2000 sq.ft. house. Well below what others used in this area.

"Poor is not the person who has too little, but the person who craves more."...Seneca


Life is Good

(post #104440, reply #15 of 22)

Thanks, Did your pipes exhaust into the house or outside? Inside is my preference, hence my concern for mold. Did you have any provision to drain the condensate from gravel layer?

(post #104440, reply #18 of 22)

Pipes originated inside and terminated inside the house.

To my knowledge there never was any condensation .
I would guess that there was never more than 4-5 deg. temp. difference between the hottest air and the coolest. Everything was contained within the insulation envelope including the tunnel, which was concrete on all four sides.

Fans forced air through the pipes and were activated using a temp. differential thermostat.

"Poor is not the person who has too little, but the person who craves more."...Seneca


Life is Good

(post #104440, reply #19 of 22)

That's what I am intending to do- begin and end pipes inside and use an ERV for fresh air. How deep was the gravel under your slab? There was a great article in Fine Homebuilding in March 2004 in which a house in Vermont earned the title as the most energy efficient house in Vermont. They used 18" of sand under the basement slab and had 2" foam insulation under that. It was heated with the excess hot water from a solar panel. I am thinking to use something similar but use a corn stove for heat and circulate the air under the slab to help even out daily and seasonal temperature changes. Not sure how much mass I'll need, but I figure the corn stove will make up the difference for heating, and for cooling maybe I will add exterior earth tubes around the foundation walls and maybe under the yard if the internal system is not enough.

(post #104440, reply #2 of 22)

Hard to do for drains.

But you could do that for water and gas (pex and CSST).

And from a discussion I saw in another forum gas needs to be sleaved and vented anyway so that any leaks don't build up.

And I don't see anything wrong with.

When I built my house I would not allow any water line under the slab. But, while "standard" construction, th arragement is not standard.

The water feed comes in the side of the basement wall and the runs between the first and 2nd floor.

.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #104440, reply #3 of 22)

Keep in mind that (aside from DWV) a large-diameter plastic sewer pipe would suffice -- don't need to form up this thing. Especially if water pipes will be PEX it should work out well.

The pipe can double as drain tile and radon vent, as needed.

Do run it by the BIs before you settle on anything, to make sure they won't have a calf. In general it should make the BI's job easier, and produce a more reliable and maintainable overall setup, but there are always nits to be picked.


So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #104440, reply #4 of 22)

We're going thru a major repair job at my church right now, jackhammering up the concrete to get access to the 40 y.o. rotted cast iron sewer pipes.


If someone had thought about a chase, the job would have been a lot easier.


And cheaper.

(post #104440, reply #5 of 22)

it's to late now it sounds like,but did you check on having a plastic pipe pulled thru the old one? sounds like a perfest place to do that. larry

hand me the chainsaw, i need to trim the casing just a hair.

the older i get ,

the more people tick me off

(post #104440, reply #7 of 22)

Yeah, we , and the plumber considered that, but the pipes are actually broken enough that fecal matter was leaching out, and coming up in the church parking lot.


They've also sagged from the soil eroding under the building and pipes, which has contributed to the breaking.


So we've got to jack up the concrete, add fill to support the pipes, and run new plastic.

(post #104440, reply #8 of 22)

There is a local plumber that has a radio show. Told a story about one of his client that has a house built on a slope.

Missed the first details. But apparently the lot was steep enough that there was lots of backfill in the basement. The foundation was down to good direct.

Anyway the builder did not compact it, but just dumped in dirt for fill.

2 years later the drains stoped working. Used camera and locator to find the break under the basement slab. Cut a hole.

Found that the fill has settle about 3". There where some concrete piers that was supporting the slab, but nothing to support the pipes.

Ended up taking out the whole floor.

Don't know how they repoured it. Maybe used some of the collapsable cardboard supports unit.

Anyway the hung the drain lines from the new slab. I gather that they used rebar and hung them from the rebar before the pour. But he did not give that much detail.

.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #104440, reply #9 of 22)

as mentioned before, I think the tunnel method is a good option. in a situation much too hard ot explain, I just put in a tunnel aboiut 16 iunches wide and 10 inches high under a section of slab I pouered in a mudroom between our house and barn to run electrical and plumbing out to the barn etc... All it cost me was $65 to rent a 14" concrete saw to cut through the barn foundation. I imagine that tunnel is all I'll ever need space-wise to run wahtever I need.

I formed it up with 2x material which could easily be done on site when you are douing the sub-grade for the slab (minus the concrete saw if it is in new construction) If it is a radiant slab, just be carefull to insulate around it.

not sure how it will hodl up over time but so far so good.

(post #104440, reply #10 of 22)

FWIW the tunnel I built was actually 24" h., 36" w.
Pan decking was used to support the slab above.

"Poor is not the person who has too little, but the person who craves more."...Seneca


Life is Good

(post #104440, reply #6 of 22)

Back eons ago when I worked briefly as a pipefitter in a steel mill, there were utility tunnels under most of the slabs. These were generally big enough to crawl through, although not always spacious. On occasion, there would be a utility "trough", which would be a concrete lined trench somewhat larger than the utility line and covered with a removable reinforced concrete lid. Sometimes there was angle iron reinforcement along the edge of slab that ran along the edge of the trough. The inside of the troughs I remember most were square and probably 8"-12" or so wide and deep. I have seen some in older buildings where the trough cover was just a 2x plank of appropriate width. I don't remember the bottom of these troughs being badly cracked, but it would seem to be a potential stress focal point.

(post #104440, reply #16 of 22)

That kind of utility trough covered by a plastic grate is very common in film developing labs.  As for the OP's question, how about going with a crawl space instead of a slab?  That gives you the maximum possible versatility in dealing with utilities in the future.


 


-- J.S.


 

(post #104440, reply #17 of 22)

>how about going with a crawl space instead of a slab?

Not viable in this case. It's an earth sheltered house, and the way the heat storage is being done wouldn't be a good fit with crawl space.

(post #104440, reply #20 of 22)

Corrugated plastic culvert pipe comes from 8" up. It will handle the load.


SamT


SamT
A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #104440, reply #21 of 22)

Sure seems sensible.


Always wondered why plumbing chases weren't formed when building a slab.


Use to work with a plumber down south a ways where slab homes are the norm. A lot of dollars end up getting spent by homeowners 10 or so years down the line when the plumbing starts leaking under the slab.


It seems so unnecessary to have to roll back a carpet in a living room to bring in the jackhammer while you look over your shoulder to see through the taped off plastic wall separating you from the guys sofa and computer desk 10 foot away.


Just pouring the slab over the plumbing is the norm as I think the extra dollars for a chase doesn't want to be spent by the builders when they've been 'doing it that way for years'.


 




"I would rather sit on a pumpkin and have it all to myself, than be crowded on a velvet cushion."
-Thoreau

 

(post #104440, reply #22 of 22)

Yeah, especially now that it could all be plastic preforms of one sort or another, and PEX could be snaked through.


So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville