In moist or cold climates, avoid closets on outside walls. Winter humidity combined with typical spotty insulation can result in mildew growth, even frost on the walls or ceilings. Unconditioned (open) crawlspaces are a source, too, of high humidity.

In a 1948 home with a walk-in closet on an outside wall and over an unheated garage, I had to run a baseboard heater all winter to avoid frost on the walls. I've seen the problem on new homes too.

Here is a link that might be useful: Homes Moisture Problems

I live in NW Oklahoma. DEFINITELY not moist and not usually that cold either. In the winter it can get coldish but usually isn't prolonged.

okpokesfan --- I have a (very) large master with 2 walls to the outside.... It is the coldest room in the house (two windows on one wall, sliding glass door on another. I'm sure the slider is the biggest culprit for heat-stealing. The room was insulated very well on all walls, otherwise.)

That doesn't answer your question exactly, but I would suspect that a 3-sided room would be worse. You would have windows/doors on every wall, right??

No. I like my master dark. That says cozy to me and encourages sleepiness! :^) I know that's going against what a lot of people on here say. There would be only one wall with windows. The other 2 would not have any.

Hey, I support that! We have windows/door because it was what we were supposed to do. If I designed it for us, it wouldn't have had a single window or door. :) I've tried my best to blackout everything completely with blackout curtains. ;)

If you only have one wall of windows and you aren't in a very cold climate, I imagine you'll be fine. You could make the exterior walls extra thick in this room (2x6) with thicker insulation... just in case.

Is this an addition? (Otherwise, why would you have a room like this?)

No, we're building a house and are trying to decide how to place the master. Placing it to where it would stick off the back of the house and give us more bath/closet space would also put it to where it would have 3 walls facing outside.

We are going to have 2x6 exterior walls and spray foam insulation so I might be fine. I am more worried about the summer because temps here are routinely in the 90's with usually several weeks (or in the case of last summer, several months) in the 100's.

Our master has 3 outside walls and so far we haven't had any issues with heating/cooling. 1 wall is a bank of 3 windows 3'W x 6'H each topped by 14"H transoms--this was to take advantage of the mountain view. The window wall faces due north. The other 2 walls are windowless. The walls are insulated with a 'green' insulation (R-15, I think). The windows are Low-E Argon filled with an upper-midrange solar heat gain coefficient (SHGC). Someone above asked why you would do this (3 exterior walls)--in our case it had to with taking advantage of the view + privacy from the back porch & driveway. On a side note--our HVAC guy said he could put a sensor in the master which would communicate with the main thermostat to automatically raise or lower the temp at specified times of day or night based on the master bedroom temp. We had them put the wiring in place, but we opted to wait & see if we needed the sensor & everything--so far it's been money well saved. Hope this helps!

2x6 sprayed with foam in almost every climate is a waste of money. In your climate, 2x4s with rigid foam would be as far as I would go. Your main issue would be the direction of your windows - in cooling climates that dictates warm rooms more than any other factor.

You would likely have a better payback with solar panels on your roof than spray foam in your walls. You would surely have a better payback with solar hot water.

The most important thing for cooling climates is to design your windows and overhangs right. Next is air sealing. Then comes ductwork location (ie not in the attic or if you do, foam the rafters). Then comes high Seer a/c. Only then comes wall insulation. I have very conventional 2x4 with batts and the energy audit says my walls "cost" $50 a year in heat gain. This is NC and it is fair to say you have double the a/c needs so you might be $100 if you chose the cheapest wall system. This is for 5000 sqft. Try to make 2x6 with spray foam pay off with those numbers and you can't do it.

Doing it for noise of another issue may be a benefit.

Back to original question, the wall heat gain is so low that a 3 exterior wall room should not be a problem. You can always run another duct to the room just in case.

Our windows will face north so we are good there. Our builder recommended 2x6for the exterior walls because of the extreme wind we tend to get here. It's pretty standard in our area. We' re still playing with the layout and I appreciate all the feedback.

We have this....the wall behind the bed, the window wall, and the wall opposite the bed are outside walls. While it makes the master very private and quiet...I do feel it is a bit colder in there. Our house is also very well insulated with thick walls...so it might be because of the really big expanse of windows or more likely, the fact that the ceiling peaks to 20 ft (I wouldn't do that again if I were doing over....it also makes for a echo-y bedroom!) We now have plantation shutters on the windows which helps with the cold. We moved in at the end of summer, so haven't experienced the dog days yet...i'll tell you in July! We are in NC.

Love your bedroom!

I don't really buy the high wind argument. Not that there is a problem with 2x6s but you can build for high winds without them. In fact, the only thing that 2x6s allow you to do is build with 24 O.C. instead of 16 O.C.

The link for the American Wood Council 130 mph wind guide.

http://www.awc.org/pdf/WFCM_130-B-Guide.pdf

Our MBR/WIC/bath has 3 outside walls, and a 4th shared with the garage which is very well insulated and doesn't get lower than 50-60 degrees in most nights of our Michigan winters. Our lower level, first floor, and garage are built of ICFs, so for this and other reasons are very energy efficient, but the bedroom was cooler than the rest of the house for several reasons:

--all of the outside walls, and a large window (7.5' x 5' ) in the MBR plus a very small window; all 9' ceilings.
--we keep the ducts of the workshop underneath the MBR etc. closed year round, so no heat rising from there to warm the underside of the MBR suite.
--we only had them run one HVAC duct into the bedroom (SW corner of the house), one into the WIC (NW corner) which also has a small window, and one into the bath (NE corner next to the garage) which has a 4' x 3' window.
--the HVAC ducts have 3 elbows each and are at the end of the run.

We like having a cool bedroom to sleep in, but the coldness of the bathroom really bothered me, so we added a duct connected to the 2nd floor zone which comes on much more often and more forcefully than the 1st floor/LL zone, since it's 2x6 construction with 1" of XPS, and there are fewer ducts on the 2nd floor to dissipate the heat. I love the warmth in there now, and some of it spills into the WIC and bedroom.

Anne

I also have a Master Bedroom with 3 walls but only the northwest side has windows. My bedroom stays warm in winter and cool in the summer. Our bathroom which also houses our 9x7 WIC has been problematic with the cool/heat issue. When we close the closet door, there are no issues. Most of the time, it's open. There is no HVAC vent in it which I think explains why it doesn't keep the same temp as everywhere else.

If you prefer a dark bedroom, then it is a fundamental design flaw that you are not designing a home with a mostly interior bedroom in order to produce a darker room. That's basic home design 101.

a home with a mostly interior bedroom in order to produce a darker room.

Or, like Sarah Bernhardt, you can always sleep in a coffin.

Well luckily it's my house and my money so I guess I'll just have to live with a flawed house. ;^)