Are we Building \"Sick\", Rot-Prone Homes?

Mike T., Swampeast MO

Both--sickness (especially chronic respiratory problems) and rot seem to be increasing greatly in the last few decades. Such seems to correspond with a general "tightening" of structures.

Tried to make some sense out of air change per hour recommendations. The "original" of about 0.25 minimum comes from a study based on reducing objections from body odor of all things! "New and revised" absolute minimum seems to be 0.35 ACH.

In "plain" patient rooms in hospitals the recommended minimum used to be 2 ACH, yet such has been found to produce "high values of 'Local Mean Age of Air' LMAA resulting in 'stuffy' conditions" and 6 ACH is now recommended (reduced to 4 ACH if "baseboard heating is used"). I [think] they're talking about "real" air changes here--from the outside--not just recirculation-induced changes...

Where reduction of airborne illness is desired, around 10 ACH seems the "magic" number...

Older homes were often assumed to have around 1.25-1.5 ACH--with GOOD AND TIGHT construction--and in fact older texts often state that ACH should stay in this range MINIMUM lest there be problems--both health and humidity-wise...

Are we asking for some terrible problems down the road by building homes so tight--and even when taking means to intentionally increase infiltration doing it at a quite low level?

Fred Robinson

Sick buildings

Fred Robinson

Sick buildings

Boilerpro_3

This is something I've been harping on

The problem of rot I belive is largely associsated with the practice of installing insulating sheathing on the outside of a home in cold climates. This prevents water vapor that invariable gets into walls from the interior from escaping, allowing it to condense on cold wall surfaces. Its sort of sad that this insulated cheathing is usually an extra cost option for those that are looking to keep energy costs down. Now putting this sheathing on the inside under the drywall or plaster is just fine in Northern climates. You got allow some air change in the walls to remove the moisture. Too much, however, (like when using perforated house wraps on old homes with t&G sheathing) will allow so much air to move through the insulation that it losses its effectiveness.

Boilerpro

john_27

air change

Mike...we have to be...the short run benefit of lower heat bills has to be offset by something...in this case.....more tsp in the air...an electronic filter helps a lot...but viruses...not sure...I have an old indirect broomell...and may well reattach the outside for the very reason you suggest...john

Fred Robinson

Sick buildings

Miket- I could not agree more regarding your thoughts on ACH.Even hospitals have gone from 100% o.a. for patient rooms to return air.min o.a.,even so far as to dump relief air in the mech room along with all of the "stuff" from the patient rooms. And we are exposed to this when servicing the airhandlers. I know there are masks that can be worn but my point is money is saved with arrangement to,I believe the detriment of the maint men. The supply has HEPA filters. I assume this allows for this to be installed. My hope is that this arrangement may revert to the use of more o.a.

Randy_7

Moisture in homes

Good morning: As a renovation contractor and home inspector (member of American Society of Home Inspectors) I often see the results of homes that have been tightened without thinking about and addressing the significant amount of moisture that will build up.

In this area (northern Michigan) we have many older homes and installing vinyl or aluminum siding and new windows are typical updates. The following winter it is then common to see water dripping down the side of the home, and icicles forming, especially in moisture prone areas like kitchens and bathrooms - due to moisture condensing on the backside of the vinyl or metal. It is also common to find moisture build-up in attics, and frost on the underside of roof sheathing if the attic is not properly vented. Of course all this moisture (that can't escape) leads to mold, mildew and rot.

Older homes may have been drafty and certainly less energy efficient but the numerous air exchanges resulted in the necessary venting of moisture and other air-borne products of everyday living. New home construction and tightening of older homes requires we become much more conscious of the results of the tight boxes we are creating.

Exhaust fans in kitchens and baths as well as air exchangers, all help to rid homes of excess moisture. It is a vicious circle - we tighten for comfort and energy savings but then must vent to preserve health and building materials.

One of the excellent references I own (along with several written by Dan Holohan) is: Builder's Guide to Cold Climates by Joseph Lstiburek. He makes sense of insulating and tightening homes in the north country. Just some thoughts.

Randy

Greg Swob

Top Ten Stupid Things

Joe Lstiburek has several lists and excellent common sense explanations backing them up. His Top Ten Stupid Things to do in the North (or similar title) and the accompanying list for those in the South. We could all heed and get the point out. Problem is- too many conflicting opinions, especially when those with the opinions also hold purse strings. Few builders want to devote the time necessary to build with astute correctness, and many buyers will be willing to pay for the extra work. It is probably not that more costly, but some strategies would require getting builders out of their mold- that learning curve slows progress and drives costs up. Not blaming the builders - too many other involved parties know better but are unwilling to step up to the plate. Greg

heretic

rot

In terms of 'rot', a leaky structure in a heating climate is going to be worse than a tight structure.

For example, dumping warm moist air into a wall cavity with fiberglass insulation is going to cause trouble because it will condense in the insulation, which will hold the water like a sponge. If there were no insulation at all, water would still condense (and probably freeze) on backside of the cold sheathing, but it would dry out quickly on the next warm day. Fine and good if energy were free, but what you really want is a sealed and insulated wall cavity with no convective currents.

The idea that a house can be built 'too tight' is silly. Random air leakage in the building envelope is not a desirable means to obtain fresh air. Get it tight, then take control of the air exchanges.

Mark Hunt

Excellent post


Build it tight, and vent it right.

Mark H

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Contractor"

Mike T., Swampeast MO

Great Corey

If that "two-person concensus" in current post titled "Another Humidty Question" is correct such is what really got me started thinking about the quantity of water vapor.

In a really tight home WITHOUT concern for ventilation it would seem that there's still quite a bit of water vapor flowing through all those random leaks...

What kind of exchange rate is targeted when HRV or ERV is used?

Steve McCarthy

exterior sheathing

If sheathing is placed on the exterior of a frame, it is important to install a thick enough layer so that there is no condensation on the interior foil surface. The amount (thickness) varies with the severity of the cold on the outside of the foam and the amount of insulation, usually fiberglass, on the interior of the foam. The last variable is the humidity levels in the home. Where I live (7500DD) 1.5" of foil faced foam or 2" of extruded polystyrene is needed if the Interior RH is kept at or below 50%. All foam joints MUST be tight and sealed. NO BREATHING or there will be condensing at the joints. Steve / Starbright Energy Services

Mike T., Swampeast MO

That's why...

...I've long thought that EIFS systems would make a great ice chest but not a good house--awfully hard to seal around those doors & windows... Not to say it can't be done but even roofers nowadays seem to have problems with detailing flashing properly. Around here I usually just see caulk used. Have been watching a number of homes with EIFS for a few years (there for non heat-related work), see the cracks opening and KNOW that bulk water is intruding. I point this out to the homeowners but they usually don't seem to care...

Boilerpro_3

Unfortunately the norm is only 3/4 inch

with 2x6 walls in my parts...Not very smart when you look at the thermal gradient in the wall.

Boilerpro

Steve Ebels

My humble opinion

I strongly feel that every new home built today should have an ERV or HRV system incorporated into the HVAC system, whatever form that may take. The customers that have purchased those from me in the last few years have almost unanimously mentioned something to the effect that the house "feels better" than other homes they have lived in. The basement isn't stuffy, smells don't stay in the house, the windows don't sweat in the winter and the kids don't get sick as much are all comments I've had made from various HO's.

All new homes should have one, in fact it should be code required.

Steve McCarthy

Code

I Don't think we should hold our breath waiting for that code change. NAHB is kicking and screaming about having to put an exhaust fan in the bathroom.

John R. Hall

I agree

I've had the chance to see Joe Lstiburek speak twice in the last couple of years. He is one of the best speakers I've heard and most knowledgable on the subject. If you see his name on a meeting agenda, go listen to him. He is a "Dan Holohan" type speaker -- keeps the audience loose and entertained. I wrote a couple of articles on his talks, one link is below. Here is one of his standard quotes:

“Isn’t it strange that we have less water in our buildings but we have more water problems? Water hangs around longer in building materials today.”

LINK:

http://www.achrnews.com/CDA/ArticleInformation/features/BNP__Features__Item/0,1338,89034,00.html