Replies

1. GBA Editor
   Martin Holladay | Jul 15, 2015 11:22am | #1

   Jack,
   Do you have any evidence or data to support your statement?

   For decades, U.S. builders have built new homes with little attention to airtightness. In recent years, a subset of builders have attended training sessions where building science concepts are taught. These builders have learned new methods, and have done a much better job of limiting infiltration and exfiltration.

   All training sessions for builders that I'm aware of make it clear that a tight home needs a mechanical ventilation system able to ventilate at the rate set by the ASHRAE 62.2 ventilation standard. This is what we preach here at GBA, and it is the same message shared by other green building programs.

   As a result of these trainings, tight homes have whole-house ventilation systems -- a type of ventilation system that is rarely found in an old, leaky home. These ventilation systems provide better, not worse, indoor air quality than traditional homes.

   And by the way, just because a house is leaky, doesn't mean that the indoor air is fresh. The so-called "natural" rate of ventilation in an old leaky house without a ventilation system is all over the map, ranging from a very high rate to a very low rate, and the rate of air leakage in such a home is driven by factors out of the control of the homeowner (mostly the stack effect and wind speed).

2. 
   slopecarver | Jul 15, 2015 11:56am | #2

   The only way a new sealed home will have lower air quality is if the mechanical ventilation system is shut off. Just to be clear this ventilation system Martin talks about is independent of the HVAC system in most cases, it draws in fresh air from an ideal location on the exterior of a home and through a heat exchanger to capture the heat of the balanced exhaust duct. Supplys are typically in closets for fresh smelling clothing, and exhausted from bathrooms and kitchens.

3. Expert Member
   MALCOLM TAYLOR | Jul 15, 2015 01:13pm | #3

   True or not that's canard I hear all the time from both clients and builders. The other common one is that since they stopped allowing houses to breath they rot.
   Even without mechanical ventilation I'd rather rely on the windows supplying air than the leaks in the building envelope.

4. 
   vanamber | Jul 16, 2015 11:05am | #4

   It is just my experience and observation. Who determines when to employ the use of a ventilation system? This is complicated to say the least. You have crawl spaces sealed and unsealed) with duct work passing through. You have conditioned attics and unconditioned attics, again with or without duck work. Ventilation exhaust hooked up to roof vents and a lot of cases just terminated in the attic. You have a multitude of wall, ceiling and floor insulations with and without penetrations some sealed some not. House sq. footage; small, medium, large and XL.
   We need to keep discussing or occupants will have a false sense of security about the quality of the air they are breathing.
   Jack

5. GBA Editor
   Martin Holladay | Jul 16, 2015 11:17am | #5

   Jack,
   You wrote, "It is just my experience and observation." My experience is the opposite: newly built homes by energy-conscious builders tend to have very good IAQ. The worst IAQ problems I have encountered are in old, leaky buildings with damp crawl spaces, mold, and other similar problems.

   Q. "Who determines when to employ the use of a ventilation system?"

   A. These days, the building code. If you are building in a jurisdiction where residential construction must comply with the 2012 IRC, any new home with a blower-door test result of less than 5.0 ach50 must include a whole-house ventilation system. This provision of the 2012 IRC can be found in Chapter 3, section R303.4. This section notes that the ventilation system must comply with requirements listed in 2012 IRC, Chapter 15, section M1507.3. Since the new code requires homes in all zones except zones 1 and 2 to achieve 3 ach50, the code effectively mandates a whole-house mechanical ventilation system for homes in zones 3 through 8.

   You wrote, "This is complicated, to say the least." You're right. Many aspects of residential construction are complicated, so builders need to get educated. Uneducated builders can kill people -- for example, by installing decks that are toenailed to the house. (That just happened recently.) There is no getting around the fact that education is a good thing.

   You wrote, "You have ... ventilation exhaust hooked up to roof vents and a lot of cases just terminated in the attic."

   That's true. But that's also a code violation. I don't recommend that builders violate the code.

   You wrote, "We need to keep discussing." Needless to say, I agree with you. That's why GBA is here...