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plumbing in outside walls

MtnBoy's picture

I'm gonna have to "discuss" this with the archy, who's placed plumbing fixtures on the outside walls ('cause the bath is prettier that way, I guess). Down in Georgia we use 2 x 4 exterior walls. This house is getting Icynene insulation, and I especially don't want to interrupt that good insulation with plumbing.

I don't have the education to argue with the archy, but I want the plumbing fixtures moved to interior walls.

Am I just going on outdated notions? Am I all wet?! If I have a valid point, how do I present my case?

(post #77530, reply #1 of 32)

I'm not an architect or a plumber, but I agree with you. In any case, it is your house, not the architect's!

I guess it could be argued that Georgia doesn't get that cold, and I've been in many houses even in Michigan that have plumbing in the exterior walls, butI agree that it is better not to. I was called to a house a couple years ago where there were water lines running in a wall between the bathroom and the garage and they froze one day! Silly, in my opinion, to take that risk when it's not that hard to make some design changes to put them elsewhere. How pretty will that bathroom be when a pipe bursts and leaks all over?

I used to work at a HUD senior housing complex and came in one morning to hear what sounded like someone taking a shower in the public rest room--but there wasn't supposed to be a shower in that room! Turns out the builder had put the insulation on the inside and the pipes, between them and the outside of the exterior wall! Sort of complimented the waterfall we got every time it rained, where the roofer ran short of roofing membrane, so just covered the area with gravel so no one would notice.

(post #77530, reply #2 of 32)

IDEALLY, I try and avoid running plumbing in exterior walls up here in NY.

But there are instances where that is just not possible. Its also been done for many instances without any insulation in the walls.

I don't know that it would be a major concern in your climate....especially with the insulation you have planned. But it is your house....and you get to make the final decision.

J. D. Reynolds
Home Improvements






(post #77530, reply #3 of 32)

the "Icy..." insulation in the walls will probably be less than 3.5" anyway (usually 2").  I'd guess you'd be ok, especially since there will be no air leaks with "icy...".  Having said that, in my house (also spray foam), I kept plumbing out of exterior walls (even to the extent of creating plumbing chases and knee walls for toilet plumbing.


(post #77530, reply #4 of 32)

A toilet on the exterior wall can be plumbed and vented to a perpendicular wall if it is within 6'. The same goes for a tub that's in a corner.
Archititects generally know locations of plumbing of fixtures, but have no clue on how to run waste and vent.

(post #77530, reply #5 of 32)

In your situation I think it is irrelevant.

"Doubt is not a pleasant condition, but certainty is absurd."

~ Voltaire

"Doubt is not a pleasant condition, but certainty is absurd."

~ Voltaire

(post #77530, reply #6 of 32)

also on slab with plumbing on outside, they are easier to finish

(post #77530, reply #7 of 32)

Why not just build an extra wall infront of the outside wall after it has been spray foamed. You'll have to account for the extra width in any window casing but you can have your plumbing in that wall and it will no longer be an outside wall.

(post #77530, reply #8 of 32)

We do it all the time, and we're in Canada. There is an R-value criteria that must be met for insulation behind piping. It usually exceeds the rating for FG insulation, but can be achieved with closed cell foam. I'm pretty sure you could do the same. I wouldn't let this issue stand in the way of your design ideas.


Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”

(post #77530, reply #13 of 32)

Well, this is sorta like the time my knee blew out and I went to 3 different doctors for advice. All of them gave me good advice, just different.

As much as I'm worrying about pipes freezing, I also don't want to interrupt the Icynene. It's costing an arm and a leg and with only 2 x 4 walls I want it to have all the space it wants to do its thing. Also, installations aren't always perfect; pipes are just another chance to fail to fill that wall cavity. Maybe I just need to get over it.

(post #77530, reply #9 of 32)

Insulation does not provide heat; it just slows the transfer of heat from your pipes to the outside world. Here in New Jersey, I've made quite a bit of money over the years repairing damage done by frozen pipes in exterior walls. The last job was caused by several days in which the temps were in the 20s.

I spent my 20s in Atlanta. I well remember a week when the temps were down to 5 degrees in the daytime. Tell your archy to take a hike.

George Patterson

Edited 5/1/2007 10:33 pm ET by grpphoto

George Patterson

(post #77530, reply #11 of 32)

Indeed, we have times when it gets, and stays, as cold as the Canadian border. Not everyone knows that, but as an Atlanta native, 59 yrs. old, I remember a lot. I've had pipes freeze here, but only those where a plumbing fixture was on an outside wall. Better safe than sorry.

I do like some of the false wall and knee wall ideas here, if it turns out I want to put something on the exterior walls.

(post #77530, reply #21 of 32)

It does not matter if the plumbing is in the outside wall or not.

It depends on how they are detailed.

I remember Christmas of 1989 when MO and KY had about 2 weeks of extreme cold weather. Lowes about -20.

In a Louisville subburb there was a group of new 3 story appartment buildings. All had plumbing in interior walls. All had freezing problems.

They walls where perfect chases and allowed the cold air to circulate and freeze the pipes.

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 #77530, reply #10 of 32)

I have a SIP house and I wanted some sinks in a Jack and Jill bath to face the outside wall.  There is a mirror over each sink and a window between the sinks.

What I did was use a 24" countertop and 18" deep vanities.  This allowed me a "false wall" in the back of the vanities and below the counter top.  I ran the plumbing horizontally in that "false half wall" over to the side wall (an inside wall) and then "vent up, drain down".

The side benefit is that extra bit of counter space behind the sinks for the soap disp and other crap that DW likes to put in bathrooms.

Is this an option for you?

If this is not clear, let me know.
Adventures in Home Building
An online journal covering the preparation and construction of our new home.

(post #77530, reply #12 of 32)

Thanks, I got it. Went to your blogspot and found the bathtub under the window.

BTW, nice bathtub in the mudroom for your pooches!

(post #77530, reply #14 of 32)

Here is the picture of the sinks on the outside wall. You can sort of see that the wall behind the baskets is a bit closer than the wall behind the counter.

(you can click on the pic to make it bigger. Pay no attention to the fact that the counter top edges are not caulked yet!)

We were just talking about the dog tub in another thread.  I made some mistakes on that.  It is not high enough and I did not put in a toe kick.  However, with still no lawn in this Spring, it's been great to have for paw rinsing; and, it is still very usable as the utility sink.
Adventures in Home Building
An online journal covering the preparation and construction of our new home.

Edited 5/2/2007 6:31 am by jhausch

(post #77530, reply #15 of 32)

First, the waste pipes are not so much of a concern except if there is a trap in the wall, like for a washer box.  In that case the wall is normally framed with 2x6s for other reasons besides inulation.  Regarding the supply lines, as long as you have a decent amount of insulation between the pipe and the exterior sheathing you won't have a problem especially since you are using spray foam insulation.  Also, for vanities, both supply and drain can be run through the floor.  The DWV would likely then have to go to the exterior wall, but the supply would likely go to a central location and go down.  Also, if you are using pex piping, it is much more freeze tolerant if something did freeze.

Regarding your concern about interrupting the insulation with pipes, in that case, you need to get rid of all those pesky studs too. :-)

Edited 5/2/2007 7:11 am ET by Matt


(post #77530, reply #16 of 32)

Matt, thanks for the details. Very helpful.

I am trying to get rid of some of the studs. I asked the archy to specify 24" O.C. studs and any other suitable OVE Advanced Framing that are practical. Icynene installers suggest the 24" for more Icynene, less thermal bridging from those nuisance studs. But I still don't know if framers around here are doing that routinely. If it's something new, that's gonna cause trouble.

(post #77530, reply #17 of 32)


I've got a washer box on an outside wall and it's not been an issue in our cold snaps.  Know of several others and the same -  no problems.  With the icy you should be OK.  As a heads up re: the 24oc, check now with the building dept (probably have a web site) for the paperwork requirements from the archy for it.  My county doesn't allow 24oc unless the plans are stamped by a PE.  Maybe the archy is already aware of this? Which jurisdiction is your house being built under?

(post #77530, reply #19 of 32)

Thanks, John. City of Roswell. When we get to that point I'll "remind" the archy of that. Archy has a mechanical engineer on staff who works on all her designs. I suppose he could stamp that.

(post #77530, reply #18 of 32)

Check with your local inspections department on the 24" OC thing.  It may or may not be acceptable to them. 

Also, as far as framing details, check into energy corners, wall tees and insulated headers.  These items can cause other issues, so you have to be careful.

Just out of curiosity, what plumbing fixtures are drawn in exterior walls and what type of exterior sheathing are you using?


(post #77530, reply #20 of 32)

Right now, it's washer in laundry room. And 2 sinks and toilet in master bath.

Assuming the budget doesn't kill it: brick siding.

(post #77530, reply #30 of 32)

> you need to get rid of all those pesky studs too. :-)

Next best thing, have a look around for the "Mooney Wall" thread here.  It gives you a substantial reduction in thermal bridging, and more room for insulation. 



-- J.S.


Edited 5/2/2007 2:01 pm ET by JohnSprung



-- J.S.


(post #77530, reply #31 of 32)

Very interesting. Didn't read all of the thread on Mooney. I'm looking at all that 2 x 2 installation and paying for the labor. Mucho dinero, i'm thinking. I do like pulling electrical boxes and such out of the wall cavity--one of the things I was trying to get at.

(post #77530, reply #22 of 32)

My rules of thumb for supply lines in exterior walls:

1) Aviod them, if possible.
2) If not avoidable, place them interior of well-sealed closed cell insulation and baffle them so no cold air can enter the plumbing space. Do not insulate between the plumbing and the interior wall. (I.e., don't insulate *around* the pipes -- just behind them. You want the heat from the building to keep the plumbing cavity above freezing.)
3) Vent the plumbing space to conditioned air where possible.

Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #77530, reply #23 of 32)

Mike: I'm starting to get it. But your #3, <vent the plumbing space to conditioned air> I don't get. The plumbing vents go up through the roof, but with Icynene in a "cathedralized unvented attic" application, as they say, the vent pipes would go THROUGH conditioned space (the attic). Is that what you mean??


(post #77530, reply #24 of 32)

"I'm starting to get it. But your #3, <vent the plumbing space to conditioned air> I don't get."

Different kind of vent. Not the stack vent. When plumbing in outside walls, wherever possible, I provide a path for the warm room air to enter into the insullated plumbing chase (a "vent") such as cutting a hole in the wall in an inconspicuous place and covering it with a grille. This allows warm air to get to the plumbing chase. The concept is that you want the space where the pipes are run to be more like the inside of the house than the outside. Many folks think it's a good idea to insulate pipes to keep them from freezing. I disagree with that. Insulation keeps cold IN too. (Technically, I suppose it's really keeping heat OUT.) IMHO, it's better practice to seal the chase from any cold air infiltration, insulate the space between the pipes and the cold wall, but leave the pipes uninsulated so they can be warmed by the conditioned air and warm walls of the home. Then, although the pipes are in an outside wall, they are really more like being in the warm room.

One place that often causes problems is where piping is in an exterior wall behind cabs. In this sort of situation, it is doubly important to isolate the piping from the cold and provide warmth to the chase. Every job is different, but I always try to do something to make sure pipes in outside walls are not cut off from the warmth of the room.

Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #77530, reply #25 of 32)

AHA! Got it now. Never heard anything like it before. Its similar to the idea of opening doors of the sink base cabinets to let a little warmer room air in there.


(post #77530, reply #26 of 32)

Are you all wet?  Probably not.

Now, the thing you are up against is that there's no such thing as "no plumbing in outside walls" unless you can delete all the hosebibs, and such similar finicky "bits" that wander through the walls.

Now, my preference is to always go up a framing size for "wet" walls anyway (two for toilets, sometimes).  Not only does that better allow for framing around the plumbing, but you get a better space to define the insulation in--but, that's my preference, ans others' differ.

I like hanging the hose bib off the supply to the toilet, too, if one has to be on the outside wall, if only as a "dodge" to prevent an "oops we forgot the hosebibs connection to the HW supply--BTDT <eyeroll to this day>.

Now, what might be a good way to start this discusion with the archy is to ask about how the plumbing vents will interact with the edge of the roof (especially in narrow overhang roof situations).  Sometimes it can help to "tilt" the arhy's spacial perception out of the plan view and into the section to think about these things.

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)

(post #77530, reply #27 of 32)

Big hat, big brain under it! Yeah--that's a good idea to ask about the vent/roof overhang thing. Just to aid that switchover, I think I'll ask if archy can just do me a little sketch of it.

(post #77530, reply #28 of 32)

Big hat, big brain under it!

Nope, medium hat; not so much brains as experienced in getting "locked in" on the wrong parts of plans.

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)