# how to avoid condensation in exterior wall when enclosing washer/dryer



## Michael Thomas (Jan 27, 2008)

The potential problem is not "heat emitted by the machines", it's hot _moist_ air exhausted from the dryer - as long as the dryer is properly vented, and the vent system is regularly cleaned and otherwise kept in good mechanical condition, this exhaust is vented to the exterior and there should not be a problem.


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## pemn (Nov 29, 2010)

Thank you so very much! We're going to have Sears do the actual stacking. Hopefully, our contractor will know how to properly vent the dryer. I will have to review the manual to try to understand it myself.


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## Gary in WA (Mar 11, 2009)

Sounds like they are electric units? The Inspector will look for the required exhaust fan for the laundry room because of water use there. If gas unit, the louvered doors may give enough combustion air, again the Inspector will know. The dryer hood termination should be 3' minimum away from openings to building. The insulation should have a vapor retarder to stop any moisture created from the washer from entering the wall cavity. Oil based paint or multiple coats of latex will also work. May require a pan under, if the condensing type of appliance. If the brick was constructed with an air space at the sheathing junction, no worry. He should at least insulate the wall with a v.r. for your local area, again the Inspector will check. What type of sheathing is on the outside, behind the brick?
http://www.hcpdc.com/pdf/Dryer Vent Requirements.pdf

Gary


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## pemn (Nov 29, 2010)

*thanks*

Thanks for responding! I'm not even sure what composes that wall. From what I do understand, this is not the most solidly constructed house (circa 1965). We know from punching holes in our kitchen soffits that the adjacent exterior wall has two courses of brick and NO studs. And there's no insulation to be found anywhere in this house (except for what we had installed in the attic shortly after we bought it 25 years ago).


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## Michael Thomas (Jan 27, 2008)

Depends a bit on which version of the IRC is in force in your community, the 2009 IRC has some significant changes as regards dryer installations (underline mine):

Section Number: M1502 Section Title: Clothes dryer exhaust Change Type: Modification _Change Summary: _Dryer exhaust duct installation under the 2009 IRC focuses primarily on the dryer manufacturer’s installation instructions. The code clarifies the provisions for duct materials and installation to reflect current industry practices. Except where determined by the manufacturer’s installation instructions, the maximum prescribed length for dryer exhaust duct has increased from 25 feet to 35 feet. Equivalent lengths for fittings appear in a new table and are based on the radius and type of fitting. When a concealed exhaust system with a length greater than 35 feet is installed in accordance with the dryer manufacturer’s installation instructions, the developed length must be identified with a permanent marker. New provisions require protection of the dryer duct against penetration by drywall fasteners. 

_Change Significance: __The modification to Section M1502.3 emphasizes that the manufacturer’s installation instructions are the first source for dryer exhaust termination requirements, which are related to the design and testing of the specific model of dryer._ For example, the manufacturer may permit a clearance to openings less than 3 feet or may require a termination point greater than 3 feet from openings. The prescriptive requirement for the minimum 3-foot distance between dryer exhaust terminations and openings into buildings applies only when the clearance is not specified by the manufacturer or is not known. The dryer manufacturer’s installation instructions also govern the maximum developed length of the exhaust duct including provisions for fittings, but only if the model of dryer is known and the installation instructions are submitted to the building official. Modern dryers are increasingly efficient and are generally designed to exhaust greater distances than otherwise allowed by the code, with some models permitting duct lengths up to 90 feet and many models reaching 60 feet. When dryer exhaust duct is installed in accordance with the manufacturer’s specifications, exceeds the length prescribed in Section M1502.7 and is concealed, the code now requires a permanent sign, label or tag identifying the developed length of the exhaust duct. This new requirement intends to alert homeowners installing replacement dryers to match the specifications for the make and model to the existing exhaust duct installation. Often the dryer make and model is not known at the time of construction and installation of the exhaust duct must meet the prescriptive requirements of the code. Recognizing that distances permitted by the manufacturers typically exceed the distances permitted by the code, the maximum length of dryer exhaust duct has been increased from 25 to 35 feet. By permitting the longer lengths, greater flexibility is achieved in laundry room placement within the building. Elbow fittings increase the resistance to air flow and reduce the allowable length of exhaust duct. Previously, the code required a reduction of 2 feet 6 inches for 45 degree elbows and 5 feet for 90 degree elbows. These deductions were based on 4-inch radius fittings. An exception referenced the _ASHRAE Fundamentals Handbook _for large radius fittings, but this required calculations based on air friction resistance. To consolidate the information in the code for ease of use, the 2009 IRC places the reductions for fittings in a new table that includes both 4-inch radius fittings and 10-inch radius long-sweep fittings. The equivalent lengths of 10-inch radius fittings are based on values published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA). Testing at Underwriters Laboratories (UL) verified that the 10-inch radius elbows perform significantly better than 4-inch radius elbows. Other changes to this section clarify the duct construction and gage criteria and correlate the fastening requirements to the _SMACNA Duct Construction Manual_. The SMACNA standard requires a minimum of three fasteners for ducts 14 inches and smaller and does not recognize tape as a means of joining duct. Accordingly, the new text permits sheet metal screws, pop rivets or other fasteners to penetrate the duct sufficiently to provide an adequate joint connection but requires that the penetration length be limited so as not to obstruct the flow of dryer exhaust and thereby causing lint build-up. The new Section M1502.8 duplicates the language in Section G2439.5.2 for gas dryers. Most dwellings have a space for a dryer installation and the intent of this language is to require installation of a clothes dryer exhaust system at the time of construction so it may be inspected for compliance with the code. Adding Section M1502.8 applies the requirement to electric dryers. The 2009 IRC also adds provisions for protecting dryer duct from penetration by fasteners. The new requirements are similar to protection requirements for piping and gas vents. In the case of dryer duct, the concern of fastener penetration is related to the buildup of lint catching on the penetrating fasteners over time and increasing the fire hazard.


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## pemn (Nov 29, 2010)

I went to our Township's website (that's who will do the electrical inspection), but unfortunately, there are no documents posted to check regulations. Your document is helpful, however. I do appreciate it!


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