Older homes were designed to breath.[1] I live in San Francisco and unfortunately contractors often forget this (or don't care or never think to consider it). For example, painters will often use a non-porous latex on the outside with a common consequence that you'll quickly begin to see mold grow on the internal walls where in bygone years this wouldn't have been a problem. Or the paint may be much more prone to blistering as humidity tries to escape.
Most old homes in SF originally had (or at least were modified 100+ years ago to have) gravity fed heaters--no forced air, and no return registers in each room; just a single giant return register at a low point on a bottom floor. I've spoken with A/C contractors who say that there shouldn't be any serious problems rigging up a forced air system to the output registers, even without proper return registers. And plenty of homes do this. But I guess maybe the real problems come if you then being insulating the home--can the forced-air heating system circulate air quick enough without return registers to compensate for the fact the building no longer naturally ventilates? I imagine in most cases it works well enough, but you're still moderately more likely to see mold problems.
[1] To varying extents. My house was built in 1926, and it seems they used a relatively thin tar paper to wrap the house, or at least part of the house. (Unless that was somehow added much later, but I doubt it as the wall facing an adjacent house a few inches away is papered, and the siding is original on that wall.)
Heat recovery ventilation is more energy efficient than an old breathable house. But unfortunately it is not common even in new buildings. If you own a home you probably can install one but renters are out of luck.
Heat recovery ventilation is still a technology in its infancy.
Typically only around 90% of the energy is recovered, even in ideal conditions.
That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. That means after ~1.5 hours, you've lost nearly all the heat in your home.
Combine that with the fact the 90% is an ideal figure - in more typical installations it might be more like 50% because the incoming and outgoing airflows are not balanced, the heat exchanger is full of fluff and dust, and the humidity of the air is such that lots of energy is lost to the latent heat of vaporization.
Is it worth having one if you want a well ventilated house? Yes. Will it be worth replacing it in 5-10 years when more efficient models get designed...? Probably also yes.
> Typically only around 90% of the energy is recovered, even in ideal conditions.
As opposed to the 0% of energy recovered when a house "breathes" (i.e., leaks like a sieve) and lets out all the conditioned air?
> That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes.
[citation needed]
ASHRAE 62.2 does not mandate nearly that much air exchange. A 2,000 sq. ft. (200 sq. m) home is about 20,000 cu. ft. of volume, and needs about 100 cfm of ventilation. And some folks (e.g., Lstiburek) think ASHRAE (at least the newer revisions) is too high:
> What "Replacing the air fully" equates to in terms of volume is already a factor of the size of the room/house.
Exactly. If one person lives in a castle, do we need to replace all the air every hour? Certainly not. If we are talking about a person in a 5sqm room (for sleeping) then replacing all air every hour won't be sufficient.
There are more factors besides the number of people and the air volume, but I really didn't want to go into so much detail.
> That means after ~1.5 hours, you've lost nearly all the heat in your home.
As far as I know most of the heat in my home is stored in solid objects like the walls and not the air. Replace all the air and you still have the heat
Unless you live in an adobe/stone/brick house, the thermal mass of your walls is pretty small. Traditional plaster would add a limited amount to a stud-framed house, but in most US houses, what you've said isn't true.
Sort of, yes. They knew that they had to prevent water so you tend to see homes with larger eves than post WW2 homes. You'll also see attics with windows which seems weird until you realize that was designed to prevent condensation.
Also they built homes much smaller (the average home was less than 1000 sq feet 100 years ago, today it's 2400) and they tended to have smaller, compartmentalized rooms. This allowed for the inefficient home to use less energy anyways.
Where I live there are quite a few ~120 year old homes that are about 2400 sq feet. These would have been built by fairly wealthy people of that time as evidenced by old directories which indicate a live-in servant at most addresses, rift sawn moldings and floors, and stained glass windows on landings/in dining rooms. And although inefficient, they are smaller so they use similar amounts of energy to much larger modern homes.
Somewhat both. Balloon framing existed for houses when homes were heated with fireplaces and sealing the house could have been potentially dangerous as a result.
I find the idea that balloon (rather than platform) framing was part of the heating design of a house a little hard to take. The moment we could switch to platform framing, almost everybody did (not least because shorter studs were cheaper). But a balloon framed house with a fire that escaped the fireplace is going to burn only slightly faster than a platform framed house, and the main determinant is not going to be the framing but things like fire-resistant doors and wall finishes.
If you heat with open fireplaces, then you can't seal the house unless you have really really good artificial ventilation (which you don't because it's 1840 still when you're building this house), regardless of how the house is built. A sealed house with a fire burning in it is a suicide machine.
> A sealed house with a fire burning in it is a suicide machine.
Modern designs use direct vent systems, where instead of using inside air for combustion, they bring in outside air (and then exhaust externally as usual):
Correct, that is a common botched (ignorant, clueless) doing ignoring humidity aspects of highly insulated homes that was not an issue while air tightness (and consequently the energy efficiency) was on a lower level and traditional materials were being used. No excuse for those ignoring this as this is taught for many many decades now for the professionals.
Buildings don’t need to breathe, people do. Buildings need to dry out, and there are many ways to do this that don’t involve uncontrolled air flow that destroys energy efficiency.
You're sort of wrong here and the proof is the massive graveyard of homes built in the 60's, 70's, 80's and early 90's before we really understood new techniques and materials that were being used to build homes. So many of those homes rotted out and rotted out quickly. It's similar to all the moldy basements that were finished without considering that water vapor that can't escape is the real killer. Open up a 100 year old house that has been maintained and you'll see pristine lumber that has hundreds more years if allowed to not rot.
You could take an old house and bring it up to a modern standard but you would never recoup those energy savings both in terms of the cost to upgrade and the energy used to create and transport those materials.
Even just replacing the single glazed, wood windows that have an uninsulated weight box with modern windows is probably not worth it if the existing windows are weatherstripped (the most important thing) and have storm windows.
I think both of you are correct, you can have a tight building, but you need to have a way to get the moisture away from both sides of the vapor barrier. There are definitely been cases in the past 30 years were buildings were built tight without correctly considering removing moisture.
There are lots of dimensions - old building techniques, breathing materials, natural ventilation, proper maintenance etc. And there are lots of solutions and it can be done, but it requires expertise.
It's possible to mess up a very good old house made up of breathing materials with adding some plastic for example.
My parents had their rafters spray-foam insulated about a decade ago, now there's a growing awareness/hysteria about condensation getting trapped in pockets and rotting the timbers. More than likely my parents were fast-talked into it.
The important part is there is exactly one barrier that water cannot get through. Spray foam is generally good. there are different spray foams as well. Open cell and closed cell work completely different.
Water will move through the wood framing to the other side and out. It takes a little longer, but we have plenty of time. It is when the water cannot get out either side that you have a problem.
I am hopeful that the +100r old timbers haven't suffered, unfortunately it's becoming an issue for mortgage companies, who seem to be refusing to lend as a blanket policy. We have a roof guy coming tomorrow to check out the situation though so fingers crossed. We're prepared to have it removed if necessary but aren't relishing the extra cost or the upheaval of clearing the loft.
Foam on timber is a bad idea, for those talking about open cell vs closed cell foam in this thread, beware, both are bad for timber. Im renovating s Victorian property at the moment and when I run the simulations on condensation and vapour pressure etc etc… in several colder climates the system even with open foam accumulates enough moisture content in the wood to rot it. A large part of that is the cold bridging effect generating liquid water close to the wood which it soaks up much faster than it can release during the summer.
Please always run a simulator for your climate before allowing modern materials near timber and or old properties.
It depends if it's open or closed cell foam. If you're insulating the walls of your crawlspace, open cell foam is still recommended on wood because it can breathe
Not in any situation I know of. 3 sides are in foam, the 4th is attached to plywood and the other side of that is the outside. That is enough to let water out. It is slow, but we don't need it to be fast.
Most old homes in SF originally had (or at least were modified 100+ years ago to have) gravity fed heaters--no forced air, and no return registers in each room; just a single giant return register at a low point on a bottom floor. I've spoken with A/C contractors who say that there shouldn't be any serious problems rigging up a forced air system to the output registers, even without proper return registers. And plenty of homes do this. But I guess maybe the real problems come if you then being insulating the home--can the forced-air heating system circulate air quick enough without return registers to compensate for the fact the building no longer naturally ventilates? I imagine in most cases it works well enough, but you're still moderately more likely to see mold problems.
[1] To varying extents. My house was built in 1926, and it seems they used a relatively thin tar paper to wrap the house, or at least part of the house. (Unless that was somehow added much later, but I doubt it as the wall facing an adjacent house a few inches away is papered, and the siding is original on that wall.)