Can A House Be Sealed Too Tight?

[DBoon]

I have an older 1920's house. Short of tearing down all the plaster and starting over again, I'm not sure that there is too much you can do to stop air infiltration. I've done a lot, and it has helped a lot, but the house still "breathes" plenty well as far as I can tell - no lingering cooking odors, no excess humidity, etc.

McBride - great list, it's giving me some things to think about.

I've done the following on my older home:

1. Installed foam covers on all outside wall outlet and switch covers
2. Insulated outside walls with blown-in fiberglass (all interior walls are plaster with wallpaper over them, so there is not much moisture migration, I believe)
3. Sealed attic penetrations (there weren't many)
4. Insulated the attic hatch with foam board and sealed the edges with EPDM weatherstrip
5. Insulated the bottom edge of the double hung window with EPDM weatherstrip
6. Weatherstripped the sides of the double hung windows with sprung bronze
7. Caulked all of the floor penetrations with fire stop caulk
8. Insulated the above ground basement walls with 2" of spray on foam
9. Caulked the joint between the sill and the top plate with silicone caulk

I've probably done a few other things that don't come to mind right now.

So, to the point of the original poster, I wouldn't be too concerned about weatherizing an older house - there is not enough you can do to ever tighten it up too much without extreme renovations. For a newer house, I wouldn't be too concerned either unless you knew the builder and all contractors were trained in building a tight house. Otherwise, they will leave lots of opportunities for infiltration either through ignorance or neglect.

For commercial buildings - perhaps a different story. In that case, often there are inoperable windows and a tighter building envelope.

 

[benjamin]

Woodgeek, thanks for the info relating ACH50 to ACH nat.

I say it is theoretically possible to make an old house too tight, but in most cases it's like telling a morbidly obese man to cut back on the calories and at the same time worrying that he will die of starvation.

New houses deal with fresh air, and any house that is completely redone should be treated like new construction, but the typical old house has so much leakage that it will never get to a dangerously low level of air leakage without adding an entire new surface to the inside or outside. Even with a completely sealed building envelope, most chimney are leaking enough air past the damper to maintain air quality inside.

 

[ihookem]

Dboon, # 8 did the most but everything helps. My 1 year old home is so air tight it ain't funny. 4" foam in the walls, r 60 ceiling. Everything is sealed very tight. I even have storms on a new all brick home. I don't believe a house can be too air tight. I believe the walls and ceilings should be encapsulated so no air infilterates the walls. Make sure it's dry when building. If you have a house like this you need to do things mom and dad never had to do. You can get an air exchange for 1,000 bucks. This helps. I am cheap and don't think it's worth it. When it's cold like 30F or less I open every window and door in the house. When I'm done I shut the first opening, then go along and shut them all If it's calm I wait a few minutes then shut them. An easy way to tell is sweaty windows. This also gives fresh air daily, keeps dust down too. My RH shouldn't get more than 50% if under 35*, 45% if it's 25* and if it's cold like below 0 It should be no more than 40% or so. It varies but moisure on the windows tells me it's too damp. If it's real damp outsied I may wait a day. It seem summer builds moisture so fall is when I can open the door on a dry morning and see the moisture leave the house. It is to some degree an air tight house to open the windows but I'm sure it still saves energy. If ya got sweaty windows put on storms, it reduces moisture 50% on the inside glass. A moist house is very comfy though.

 

[midwestcoast]

I'm with the crowd that say "Yes, houses can be made too tight through renovation work" and "No, it is not likely unless the whole house is overhauled". As prev stated the biggest concern after doing very significant air-sealing in an older home is checking for any backdrafting in open-venting combustion appliances (like water heaters, low efficiency furnaces...). Getting an older home sealed-up to the point where things like moisture, off-gassing & cooking emissions are a real problem is VERY difficult. Many leaks are often hidden behind finishes & those will be very tough to seal.
As for newer homes, controlled ventilation is becoming the norm & I'd way rather have an ERV or HRV bringing in conditioned fresh air where & when needed than feel cold drafts on a windy day & have a stuffy house on a calm day. Saves energy too.

 

[jimbom]

I built my house very air tight from the beginning. I foamed every penetration in every location in the house interior and exterior. All fixtures. Everything. Now, I am in control of the air and vapor that enters my house. I supply a lot of outside air, but it comes in where I want. Direct to the mechanical space in the basement. Direct to the dryer. To a fireplace that we never use. Makeup for the exhaust fans comes up from the basement. All from always open exterior supply entries through insulated flex duct so I have no condensation. So far in twenty years, it has worked well. I am sure I could squeeze a few more btu out of the in/out exchange, but never enough to meet economic payback criteria.

 

[ccwhite]

If a home is sealed too tight, there must be a means of introducing fresh air into the home for healthy IAQ purposes. This must be done mechanically...either by ducting outside air through an air handler and blowing it throughout the home...or by utilizing an energy recovery ventilator (ERV) which exhausts air from inside the home to outside, while bringing outside air in to replace that which was exhausted (there is more to these machines, but not pertinent to this discussion).

I guess the question is:
Which is best...natural leakage in the home or mechanically controlled fresh air?

I cannot speak for all areas of jurisdiction but in mine at least, a HRV or ERV is a code requirement on any new constuction so it makes your debate mostly moot. It is far less likely that a renovation would make a house tight enough to require a HRV/ERV retrofit.

As for what's better, IMHO air tightness and a HRV/ERV is. Uncontrolled leakage (egress) can result in indoor humidity condensing in the structure on the way out resulting in mold and rot. It has been said that a single leaking electrical outlet can dump 5 gallons of water into the wall cavity over the course of the heating season.

Well said. You beat me to it. Seal as tight as possible and control your fresh air with an HRV/ERV. Rather than uncontrolled airflow.

 

[pyper]

I'm considering an HRV as my house has high humidity even with the stove heating my house full time. Windows sweat profusely anytime the temp goes into the 20's or below. Also my house is covered with a clear moisture barrier underneath the drywall. I'm told that can be a problem.

It definitely can be a problem, especially if it isn't done correctly.

The higher your humidity and the warmer your climate, the more likely you are to have a problem. Here in the south the backing on insulation is all the vapor retarder that you want. I don't know about Ohio.

In North Carolina 15 or so years ago they started requiring builders of apartments under a certain government program to build very tight, including a plastic vapor barrier. A few years later, they started getting massive mold problems in these units. They didn't have HRV/ERV in them, so the water vapor was just accumulating in the buildings and mold started growing on the paper on the back of the drywall.

If you have an old house you probably *can't* make it too tight -- there are just too many paths out.

I can see some real benefits to HRV/ERV, but what happens when the power goes out?

 

[woodgeek]

I'm considering an HRV as my house has high humidity even with the stove heating my house full time. Windows sweat profusely anytime the temp goes into the 20's or below. Also my house is covered with a clear moisture barrier underneath the drywall. I'm told that can be a problem.

It definitely can be a problem, especially if it isn't done correctly.

The higher your humidity and the warmer your climate, the more likely you are to have a problem. Here in the south the backing on insulation is all the vapor retarder that you want. I don't know about Ohio.

In North Carolina 15 or so years ago they started requiring builders of apartments under a certain government program to build very tight, including a plastic vapor barrier. A few years later, they started getting massive mold problems in these units. They didn't have HRV/ERV in them, so the water vapor was just accumulating in the buildings and mold started growing on the paper on the back of the drywall.

If you have an old house you probably *can't* make it too tight -- there are just too many paths out.

I can see some real benefits to HRV/ERV, but what happens when the power goes out?

you open a window

 

[ccwhite]

I'm considering an HRV as my house has high humidity even with the stove heating my house full time. Windows sweat profusely anytime the temp goes into the 20's or below. Also my house is covered with a clear moisture barrier underneath the drywall. I'm told that can be a problem.

It definitely can be a problem, especially if it isn't done correctly.

The higher your humidity and the warmer your climate, the more likely you are to have a problem. Here in the south the backing on insulation is all the vapor retarder that you want. I don't know about Ohio.

In North Carolina 15 or so years ago they started requiring builders of apartments under a certain government program to build very tight, including a plastic vapor barrier. A few years later, they started getting massive mold problems in these units. They didn't have HRV/ERV in them, so the water vapor was just accumulating in the buildings and mold started growing on the paper on the back of the drywall.

If you have an old house you probably *can't* make it too tight -- there are just too many paths out.

I can see some real benefits to HRV/ERV, but what happens when the power goes out?

Nothing. You won't accumulate enough moisture to be a problem during a power outage. The hrv won't do anything without power it has its own fan. (no real air leak) When the power is back on the hrv will be too.

 

[SandManConservation]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

 

[ccwhite]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

Welcome to the forums sandman. I don't think this could be true. We are constantly recirculating and filtering our indoor air. I guess you could live somewhere where the outside air is exceptionally pristine. I don't know.

 

[Alan Gage]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

Sounds right to me. All the air inside your home has to come from the outside so it all starts out the same. It's not cleaned up at all, at least in most houses, before it gets inside. The longer it's in the house the more "contaminants" it's going to pick up from everything that goes on in the house from cooking in the kitchen, out gassing from some materials, to people breathing and probably lots of other things.

Alan

 

[semipro]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

I'm pretty sure this depends on what your contaminant of interest is. If its formaldehyde or some other material out-gassing from construction materials (plywood, carpet, paint) then its likely indoor air is dirtier. If you're talking pollen, soot, mercury, ozone, or airborne soil, then outside air is probably dirtier.

 

[Alan Gage]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

I'm pretty sure this depends on what your contaminant of interest is. If its formaldehyde or some other material out-gassing from construction materials (plywood, carpet, paint) then its likely indoor air is dirtier. If you're talking pollen, soot, mercury, ozone, or airborne soil, then outside air is probably dirtier.

You're right. It would also depend on the house. In my house I have no forced air heating/cooling and no filtering of any kind. So anything that's outside is inside too. Plus anything that I add to the mix. If the air is cleaner when it leaves my house than when it came in it's because it left any contaminants (pollen, dirt, dust) behind in my house.

Alan

 

[henkmeuzelaar]

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?

I'm pretty sure this depends on what your contaminant of interest is. If its formaldehyde or some other material out-gassing from construction materials (plywood, carpet, paint) then its likely indoor air is dirtier. If you're talking pollen, soot, mercury, ozone, or airborne soil, then outside air is probably dirtier.

Agree with both comments.

Two big indoor air quality problems common to many houses are:
(1) VOCs (volatile organic hydrocarbons) coming from the garage, because of gasoline containers/tanks, as well as solvent, paint and other coatings stored, used and spilled there; and

(2) fine dust stirred up by moving around, vacuum cleaning, making the beds, faulty driers and stoves, etc.

And, of course, cutting lumber (or am I the only one running his radial saw in the living room when it gets too cold on the porch?? )

Henk

 

[begreen]

I suspect you may be the only married guy that does this.

 

[marcomjl]

Sorry to bring up an old post but wanted to address some questions and ideas.

New construction planned or old home remolded planning to tighten up the home with spray insulation and preventing any air leaks is very beneficial. But like anything doing this causes sickness in the air of the home since it can't breathe you'd want to install a simple air exchanger and that solves the issue. Not only is the home super insulated but can exchange the old air for fresh clean air.

 

[begreen]

Old house or new, a heat recovery ventilator makes sense once it has been greatly tightened up. It's a necessity in modern super-tight construction.

http://www.thisoldhouse.com/toh/article/0,,212227,00.html