Best way to frame a thin partition wall.

December 20, 2016 10:57 AM

I'm planning a renovation in our century home. The plan only works if I can construct a partition (non load bearing) wall less than 3" thick total. I have an idea how to build this wall. Tell me if this design would work...

I'd like to add a small bathroom to our first floor. The challenge is that the corner where the washroom needs to go has only 36" between the wall and the rear exterior door. The building code minimum bathroom width is 30", so that leaves me just 6" to fit door trim and a dividing wall.

Normally wood-frame interior walls are 5.5" thick (3.5" thick studs + 2x 0.5" drywall). I was thinking I could save 2.5" by turning the studs on the flat so they are only 1.5" thick. To make up for the lost strength, I would clad the walls in 0.5" plywood, and then finish with 0.25" drywall, for a total thickness of only 3" - just enough for everything to fit. I've done up a sketch in glorious powerpoint cad (tm) here.

Are there any carpenters here with experience framing a wall like this? Is there any reason I should not pursue the idea? Are there any other techniques (metal studs maybe) that would work better to make a < 3" thick interior wall? Thanks in advance.

posted by Popular Ethics to Home & Garden (24 answers total)

The issue is that this is not likely to pass inspection and will be a total liability (read:rip out and replace) when you sell the house.
posted by saradarlin at 11:23 AM on December 20, 2016 [1 favorite]

That works for me. Not sure on building codes, but does 15" o.c. of the toilet conform?
posted by humboldt32 at 11:24 AM on December 20, 2016

I was just dealing with a thin dividing wall. It was painted 3/4 ply wood on one side, and flat 1x3 every 16" OC, and 5/8" dry wall on the other side. This adds up to 3/4" + 3/4" + 5/8" = 2 1/8". This wall is in a rental apartment and isn't high class.

A couple of years ago I dealt with a wall between a bathroom and a closet that was what you describe with the 2x4s flat but without the ply wood. This wall looked like any other wall. It seemed sturdy enough.
posted by bdc34 at 11:31 AM on December 20, 2016 [2 favorites]

Not a carpenter, but I've done a lot of home renovation.

I see no reason that wouldn't work from a structural / practical point of view. (Local codes, etc. are a different matter.) I would put insulation (maybe the foam board kind) in the walls, just for sound muffling. I've lived in mobile homes that definitely had thinner interior walls than that, just paneling nailed over 2x2s.

If you're willing to deal with the worst-case scenario of possibly having to undo it all if you sell the house, then why not?
posted by The Deej at 11:33 AM on December 20, 2016 [2 favorites]

Will there be any utilities in the partition? Where are you going to mount the light switch?
posted by Think_Long at 11:35 AM on December 20, 2016

I don't see anything structurally wrong with that, but don't know what your local codes would say about it. Given the dimensions in your drawing, though, I would probably err on the side of standardization over aesthetics; just build a traditional 4.5" thick wall and adapt the door trim on the exterior door by 1) choosing a narrower (1.5" or less) casement molding for that door or 2) trimming down the molding that goes against the new wall.
posted by contraption at 11:36 AM on December 20, 2016

This sounds perfectly reasonable. I design a ton of multi-family housing and we often turn the studs when we are out of space and required clearances aren't an issue. There is no reason why this wouldn't work.
posted by Benway at 11:38 AM on December 20, 2016 [4 favorites]

I believe walls have to be framed with the long sides of the studs perpendicular to the surface of the wall. So turning 'em sideways might not be up to code. But if it's not a load-bearing wall, and the ceiling is no more than 10 feet high, you can use 2"x3" studs (which are 2.5" real width) spaced 16" on center then mount up to 0.5"-thick drywall on each side.

references: http://www2.iccsafe.org/states/newjersey/nj_residential/pdfs/nj_res_chapter6.pdf (search that pdf for "R602.3(5)") and http://codes.iccsafe.org/index.html. Please check your local building codes before beginning work.
posted by Old Kentucky Shark at 11:39 AM on December 20, 2016

Response by poster: I didn't read anything in the Ontario building code that forbade this design, especially since the wall is not structural, but I could have missed something. (Please tell me if I have.) The 15" o/c spacing between wall and toilet is the code minimum. I don't plan to run any piping in the walls, though I might put some outlets there. The basement below is unfinished, so most utilities will come up through the floor. Insulation (for noise) is a good idea.

I was thinking the plywood should make the thin wall as strong as thicker stud wall. Something like a Structural Insulated Panel. The fact that some of you have seen walls this thin without plywood gives me even more confidence, thanks.
posted by Popular Ethics at 11:48 AM on December 20, 2016 [1 favorite]

A lot of campers and mobile homes are made with 2x2s, even weaker than sideways 2x4s, and those are structural walls. You can also use 1/4" plywood and 1/4" drywall on both sides if you want to have drywall on both sides.
posted by 445supermag at 12:03 PM on December 20, 2016 [2 favorites]

You could always use something like frosted glass as the divider...
posted by fimbulvetr at 12:11 PM on December 20, 2016

Metal studs are available that are only 1.25" thick. Typically they're used in pairs with a chase between them, but you can use them for your application. Don't use hard foam for sound insulation, but fiberglass or cellulose or mineral wool.

Plywood is good, but not necessary. Standard drywall is fine provided you anchor the studs at the top and bottom (metal uses a track, wood uses a perpendicular piece).
posted by flimflam at 12:15 PM on December 20, 2016 [2 favorites]

I would call the building inspector and ask. But first - why do you feel you need to give 3" to the door trim? I'd probably try to steal some of that before I resorted to non-standard building techniques.
posted by mr vino at 12:43 PM on December 20, 2016 [1 favorite]

if your plan is just a sink and a toilet, I think some design work might be a good idea - hanging a door on a 2x2 wall, running wiring, etc, are all going to be way harder. Can the outside door be moved? Is the trim all that special? Maybe it's possible to put the toilet away from the door and put the washbasin in its place (less clearance needed) - then maybe you could bump the width of the toilet area by having a jog in the wall, or have a trapezoid shaped washroom.
posted by youchirren at 12:59 PM on December 20, 2016

Where are you planning to put the vent for the toilet?
posted by notsnot at 1:00 PM on December 20, 2016

Response by poster: Where are you planning to put the vent for the toilet?
The house stack is just to the right of the toilet in the diagram, buried in the brick wall. If stack venting won't work though, I can wet vent it using the line to the sink and an AAV / cheater vent.
posted by Popular Ethics at 1:13 PM on December 20, 2016

Response by poster: Can the outside door be moved?
Nope, not without a great deal of masonry work that would look pretty ugly

Is the trim all that special?
It's not a castle or anything, but the trim does have some nice heritage aspects. This photo isn't the door in question, but it's the same trim. The consensus seems to be that 3" is the minimum a door opening can be from a wall, and would already be pushing the trim design tight against the corner (the opening in the photo is 4" from the wall)
posted by Popular Ethics at 1:22 PM on December 20, 2016 [1 favorite]

Best answer: IRC2012 says you can use 2x4 flat studs in some cases: Interior nonbearing walls shall be permitted to be constructed with 2-inch by 3-inch (51 mm by 76 mm) studs spaced 24 inches (610 mm) on center or, when not part of a braced wall line, 2-inch by 4-inch (51 mm by 102 mm) flat studs spaced at 16 inches (406 mm) on center. Interior nonbearing walls shall be capped with at least a single top plate. Interior nonbearing walls shall be fireblocked in accordance with Section R602.8.
posted by bradf at 2:10 PM on December 20, 2016 [3 favorites]

Is there an egress window in the room? This might be code.
posted by H21 at 3:19 PM on December 20, 2016

Since you are making the walls thinner than usual, be sure to use good sound insulation to keep bathroom noises in the bathroom.
posted by NoraCharles at 4:08 PM on December 20, 2016 [1 favorite]

An egress window is often required for bedrooms and habitable spaces below grade, but I've never heard of one being required for a bathroom.
posted by contraption at 4:13 PM on December 20, 2016 [1 favorite]

Best answer: bradf probably has it. The code being cited there is based on the IBC - International Building Code - so I'm not sure if Ontario or your specific municipality has adopted it.. As long as the wall you're framing isn't structural, either as a bracing shear frame or vertical support, or fire resistant, you should be OK based on that section of code, but you should probably run it by a plan checker or something at your building department. In many jurisdictions I've worked in, this wouldn't really even be something that got inspected. When I first started reading the beginning of the question, I thought, "oh, this is easy, just flat-frame the wall".
posted by LionIndex at 5:12 PM on December 20, 2016 [1 favorite]

I bet if you used 1/4" plywood with some adhesive, it would be pretty good.
posted by bonobothegreat at 7:42 PM on December 20, 2016

My 95-year old house has the wall between the dining room and kitchen as well as the upstairs bathroom and bedroom balloon framed with (full size) 2x4 flat studs. There are no apparent structural problems and this wall supports kitchen cabinets as well as the weight of the bathroom, including a three-inch thick concrete bathroom floor. I think you'll be fine structurally.

Also, your outlets end light switches should be fine in shallow work boxes.
posted by buttercup at 8:01 PM on December 20, 2016 [1 favorite]