Home & Garden Columns

If you stop and think about it, the notion that old houses are better is just as silly as the notion that new houses are better. The truth is that both things are true. Older houses are better in some way and newer houses are better in others. Construction is fraught with misconceptions. Another one is that the framing or “bones” of old houses is better than that of newer ones.  

While it’s certainly true that our older housing stock has, within its walls, some of the best timber ever permitted cut dried for these purposes, the manner in which they are conjoined is inferior to current methods and come the next earthquake, I’d rather be in a house that had been built last year than one built in 1920. Of course, one can take the older house and add the hardware that the newer house has and also withstand the big one when it arrives (which is my idea of the perfect house). 

In recent years, the housing industry has gotten itself in some deep you-know-what as a result of one of its greatest successes, the perfection of the tight house. Houses in the last 20 years have been pushed to such low porosities (the rate at which moisture or gases pass through them) that they lose nary a Therm (a unit of heat measurement). While the goal of making houses energy efficient is a brave and worthy one, the consequences of living in these wooden vacuum bottles are growing more apparent every day. Too many of them are rotting away and sometimes in a matter of months. O.K., I’m being a bit hyperbolic but it IS true that massive fungal infestations are being found in many of this new class of house all across the country but particularly in those areas where humidities run high.  

Understanding how ventilation works and how moisture moves with air is becoming an important aspect of architecture, building inspection and construction as we all try to respond to this nasty bit of news.  

So, why is this happening and what changed. In short, older houses evaded these moisture related problems by leaking. They leaked air, they leaked moisture, they leaked heat. Apparently, this was not so much of a problem as we had formerly thought! Leaking, it turns out, is a good thing, but as with our initial premise, it’s also bad. It depends on what you’re testing for and what you want.  

If you want a house that has a good “drying potential” (the ability to dry out quickly after leaks occur) you get a big thumbs-up. If you want a house that’s going to hold onto a given amount of heat for any length of time, it’s thumbs down. 

A large number of mold-related cases in the recent past have involved newer, tighter houses. Like huge colonies of Stachybotrys chartarum (the favorite of the legal community), these cases having been growing exponentially and are flooding the courts in increasing numbers and all because people, including those in the construction community, fail to understand some basic (and not-so-basic) things about how buildings work. 

If you create a tightly sealed environment, one that does not dry out quickly, and you allow a little water to leak into it through a shoddily built wall, you can end up with water sitting for an extended time inside something not all that different from a cardboard box. Get the picture. 

Actually, this whole problem is even worse with newer houses because the wood products used in most newer homes are so much more digestible than those in older homes that the rate at which they get consumed by fungi can be impressive. 

So all around, it’s a bad scene and if you own a relatively new house the word is simple, keep the water out, period. If you see any sign of leakage, have it fixed properly and quickly. 

Now, let’s get back to our older home. If an older house, with its high porosity, leaks at a window, a roof or right though a wall, the water hangs around for a much shorter period and the likelihood of a mold or other fungal problem (molds ARE funguses) is greatly reduced. 

Older homes and most newer ones as well, were, and are, designed to allow air to pass under them as well as through attic spaces. This does a range of good things for us but none so good as the removal of damp air and replacement with dryer air. In places where Radon is of concern (and this is generally low in our area), the exchange of air also helps to remove this potent carcinogen (second only to cigarettes in lung cancer deaths at around 20,000 per year). 

If it’s wet under your house, some of that water is going to evaporate and find it’s way into the structure. In houses where crawlspace ventilation is poor, there is consistently more fungal growth (molds included). In houses where enough ventilation is provided, the presence of destructive fungi is much lower and usually the result of a leak from plumbing or from rain entry. 

Ventilation is also something that’s easy and cheap to provide. Crawlspace vents are really nothing more than a series of holes though the sides of the house below floor level that allow air to flow through the crawlspace.  

These vents require screening for the sole reason that critters of various sizes and nastinesses favor the space below your house for their dinner parties (“another grub, Madam?”), romantic liaisons (“You smell like rat, my darling. Come to me now”) and infant deliveries (“Look honey, Octuplets!”). The ideal screening is heavily galvanized steel mesh. This is available a range of pre-cut and framed shapes that can be installed quite easily. If you’re adding ventilation because you are aware of the moisture in the crawlspace, I would also recommend adding a plastic barrier laid directly upon the soil. This helps control moisture and requires no sophisticated installation. 

Ventilation requirements in new construction vary but are generally around 1 square foot for every 150 square feet of crawlspace. This means that most houses I see required around eight square feet or around 16 vents distributed around the house (they’re typically a square foot each). Vents do the most good when the wind can get to them so vents that are close to fence or blocked by bushes should be considered to have less value. If you’re adding them, try to place them where they’re more likely to create cross-ventilation. 

It’s worth noting that very few houses meet this requirement and many would clearly benefit from their introduction. Recent codes have allowed a radical reduction in the ventilation requirement for houses (one square foot per 1500 square feet) when vapor barriers are properly installed and where the vents are placed near the corners for improved draft.  

My personal take is that this is short-sighted and that when moisture is present, all the big guns should be brought out and used. If a house is essentially dry underneath, I’m fine to see this radical reduction in ventilation but in crawlspaces where we know it’s been getting wet, adding loads of ventilation as well as vapor barriers is cheap and sensible and there’s really no good reason to avoid it, unless, of course, you happen to like things wet and slimy, but hey, knock your amphibian-like self out.