Moisture on walls

[Inspector 102]

New home less than 1 1/2 years old. R-19 exterior wall insulation assembly with house wrap, vinyl siding. High effeciency furnace and vinyl clad windows. The problem is the exterior walls and windows seem to have excessive moisture causing frost on receptacle cover plates. No reason for excessive moisture inside house but test was 42% humidity. Located in Northern Indiana where temperatures currently are about 10 degrees. I have told the homeowner to run furnace fan continuously and see if this changes anything. He is also going to do a check with a thermal imaging camera from the local fire department to see if anything is obvious. Looking for suggestions on other possible causes for this occurance.

 

[Frank]

Likely the house is too tight overall starving vent fans that are trying to remove people house plants pets bathroom and cooking moisture with the outside makeup air being admitted through the electrical coverplates--an outside air inlet into the return on the furnace can help. 2012 IMC will require. Most current homes depend on openable windows for ventilation.

Quick fix is to crack open a window and run kitchen or bathroom vent fans--assuming they have real fans to the outdoors not just recirc kitchen fan. IF with the fans running there is a good draft coming in through the window cracked open lack of makeup air is proved.

Need to look for moisture sources inside and seal any air leaks in the envelope--if getting frost on receptacle cover plates air is leaking in there to provide that cold at inside of wall--Using the foam seals under the cover plates might help there but still need to help overall air exchange preferably with the exhuast at moisture sources.

 

[cda]

Is this in a subdivision or on its own?

If subdivision, maybe knock on houses built by same company to see if they have similar problem

 

[tmurray]

Is there an HRV installed? If so make sure it is set to turn on. 42% isn't excessively high for a dwelling.

I would be interested to see what the thermal imaging camera comes back with. The frost on the receptacle covers seems odd to me, unless insulation is not continuous around the boxes.

Might be two separate issues; not enough ventilation and a continuity of insulation problem.

 

[mjesse]

I agree with tmurray that 42% isn't excessively high, however in the sub-zero temps we (here and NE Indiana) have experienced lately, 42% is way above the dew point for cold windows and walls.

My windows (also vinyl) were iced up last week with +/- 20% humidity indoors and -10ºf outside.

Frost on receptacle plates indicates poor or no insulation behind the box. This is not uncommon for sloppy installers. Back-to-back indoor/outdoor outlets may also frost up in sub-0's

mj

p.s. It's currently 15% rel. hum. at my desk. much better than last weeks 5%

 

[conarb]

--an outside air inlet into the return on the furnace can help. 2012 IMC will require. Most current homes depend on openable windows for ventilation.

Frank:

Do you have a cite to the 2012 IMC to get the section number? As was reported before ASHRAE 62.2 is going way up, on average tripling the amount of ventilation required, you may want to get a blower door test and see if the home complies with the minimum ventilation requirements of today not even taking into consideration the future requirements.

 

[Gregg Harris]

Franko you have a cite to the 2012 IMC to get the section number? As was reported before ASHRAE 62.2 is going way up, on average tripling the amount of ventilation required, you may want to get a blower door test and see if the home complies with the minimum ventilation requirements of today not even taking into consideration the future requirements.

This

2012 IMC

401.2 Ventilation required.

Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403. Where the air infiltration rate in a dwelling unit is less than 5 air changes per hour when tested with a blower door at a pressure of 0.2-inch water column (50 Pa) in accordance with Section 402.4.1.2 of the International Energy Conservation Code, the dwelling unit shall be ventilated by mechanical means in accordance with Section 403.

 

[jeffc]

The house is not too tight. We have houses that are built to 1 ACH at 50 PA and they don’t have these problems. I think the problem is likely a lack of insulation behind the boxes on the exterior walls. The inside surface of the outlet box is cold allowing moisture to condense on the colder surface. A leaky house could contribute. As the air passes through the house outlet on its way to the outside, it would condense on the colder surface.

 

[JBI]

Sounds like the vapor barrier may not be continuous also. Assuming (yes, I know...) they cut the kraft paper around the boxes, did they then seal the paper around the boxes? Many installers don't. That would certainly allow cold air in around the boxes and with 42% humidity inside would certainly cause the frost build-up.

 

[Gregg Harris]

The house is not too tight. We have houses that are built to 1 ACH at 50 PA and they don’t have these problems. I think the problem is likely a lack of insulation behind the boxes on the exterior walls. The inside surface of the outlet box is cold allowing moisture to condense on the colder surface. A leaky house could contribute. As the air passes through the house outlet on its way to the outside, it would condense on the colder surface.

I would agree it is an insulation issue.

The moisture in the house is attracted to the wall surface that is bellow freezing through conduction. This has popped up allot across the US in the last few weeks with low ambient temperatures showing poor building performance due to poor construction practices.

A leaky structure would allow outside dry air inside and lower humidity.

 

[north star]

= % =



Let's assume it's a lack of thermal insulation & [ possibly ] the vapor

barrier was not sealed properly around any cut-outs.

How would this be fixed properly without opening up the walls ?

= & =

 

[Gregg Harris]

= % =

Let's assume it's a lack of thermal insulation & [ possibly ] the vapor

barrier was not sealed properly around any cut-outs.

How would this be fixed properly without opening up the walls ?

= & =

Short of drilling hole in wall after using thermal imaging and injecting low expanding foam, cutting open wall or remove siding