Mold-Free Bathroom Techniques - Cold Climate

[hank mavery]

Hello,
Have to do a new bathroom, and going back to studs on an uninsulated old home. Insulating from the outside (below siding) isn't an option.
Thinking about ways to eliminate mold and condensation/mold in the wall cavity.
:
- No Drywall (concrete board, vinyl panels, ??)
-Good bathroom fan
- Thinking about rigid xps fitted into the stud and rafter bays, and layered on the interior of walls and ceilings. Then a non-drywall finish over this.
- Permanent Dehumidifier on humidistat


Here's more on the subject of condensation in walls in cold climates by John Straube:
http://www.buildingscience.com/docum...ing-insulation

I would appreciate hearing solutions for cold-climate bathrooms.


Thanks,
Hank

[MarkMc]

Cold [water] shower.
Shower timer.
Shower squeegee.
Incorporate warmed/heated floor/receptor in overall HVAC design.
Attention to airflow patterns rather than simple mass volume when sizing/locating equipment.

[dgbldr]

I don't know why you think this requires such extraordinary steps, unless there is something else involved in this particular building we don't know. Certainly a dehumidifier seems a bit much.

I've never seen mold/humidity in bathroom wall cavities with a proper, but ordinary, job of sealing and insulating. You can certainly do rigid or spray foam. Drywall is just fine under a properly done Kerdi or Noble. Cement of fiber cement also fine under membrane. On areas outside the shower, drywall is just fine. Vapor retarder paint helps, but a couple coats of latex is much the same.

Air sealing is key. The only condensation to worry about is warm inside air escaping. The cold outside air, even if leaking into the envelope, ain't gonna condense when it hits something warm :)

[BeachBoy]

The GreenPoint Rating criteria requires "tile or other water resistant materials on walls to a minimum of 4 inches horizontally and vertically (from edges of the tub and/or shower assemblies)."

This is something that is a great idea but not commonly done, which is why the drywall rots out just past the tile, near tubs and showers.

[Dancing Dan]

Several bath fan manufacturers are making units with humidistats now - I think Panasonic and Delta Breez have some.

[hank mavery]

Is it possible to avoid condensation on windows in a cold climate when a person takes a long hot shower?

Hank

[MarkMc]

Possible, yes. Practical, maybe, maybe not. Think say car defroster or you could also make the shower enclosure much more sealed/controllable in terms of air flows so excess is largely contained in the receptacle/exhausted from it directly w/o spilling/filling the room, say with glass wall/door.

[dgbldr]

Yeah but if you make it tight enough to keep the humidity in, the bather(s) may suffocate :)

[MarkMc]

That's a [hot] water saving feature ....?

[Bill Robinson]

We just had a 2-day ASHRE 62.2 2010 train-the trainer class and used this to provide spot and continuos ventilation.
They will retail around ~$200 depending on the model.

Since we are heading toward the 62.2 model it is a good idea to look into these or similar models sooner rather than later.

I would use this or something like it in every bathroom from here on out.
They are using them in the weatherization programs with good success.

[dgbldr]

Wow, Bill. "Up to 871% more energy efficient than ENERGY STAR® standards."

Since even the lousiest AC motor has well over 70% efficiency, this one not only doesn't use any electricity, it actually pumps some back into the grid. All while doing work.

What's next, cold fusion?

[Bill Robinson]

Not next but coming soon to a theatre near you.

However you might be confusing your efficiency metrics.
The one you are tripping on is how efficient the conversion of energy to work the motor is, the one referenced here is how much energy the appliance actually uses.

Make better sense that way?

[dgbldr]

No it doesn't. How much energy the appliance uses is motor consumption x time. To get that bogus number you would have to hide some BS assumption, like running the regular fan 24/7 vs. running the "efficient" one on a timer or motion sensor or humidistat.

A more sensible assumption is that I already have my bath fan on a timer, so it already runs only as much as necessary. So the "new invention" is ....0% more "efficient"

[Bill Robinson]

whatever scooter, you run your timer and I will install better fans.

what does your 70% efficient apply to?

Energy efficiency or motor efficiency.

How many amps and what is the wattage of your mitered fan and what is the energy efficiency rating compared to Energy Star.

I have no intent to defend Panasonic's claims however your objection is better played in trade talk.

[dgbldr]

On the contrary. Note the word "Science" on the forum title. As in, science talks and BS walks. Just the opposite of Trade Talk.

It's not that complicated. It takes X kwh of electricity to exhaust 1,000 cu ft of air with an ordinary bath fan. If they say it takes their fan a lot less electricity to exhaust 1,000 cu ft of air, great. Let me see the test results by an independent.