By Dan Kolbert

I am a numbers guy, but this column’s number is about theoretical weights. Think of it as one ounce of prevention vs. one pound of cure.

We know that certain things we do to improve the comfort, durability and performance of a home cost more than doing the bare minimum. We can often quantify those costs. But what about the savings? What problems are we avoiding or minimizing down the line?

Let’s take mold, for instance. Our colleagues at the Maine Indoor Air Quality Council (MIAQC) have done a great job looking at the cost of mold remediation (see Mold and Mildew and Fungus, Oh My!, page 56). Mold issues can occur in a home when indoor moisture isn’t properly managed. MIAQC estimates the costs as anywhere from $100 to $500 for a simple patch of surface mold, scrubbed and repainted, to $5,000 to $10,000 for an area of 30 square feet or more in an exterior wall.

A bit about mold

Different types of mold grow in different conditions, but typically they need a food source, moisture and abovefreezing temperatures. In houses, the food is often either the paper face of drywall or the cellulose in the wood fibers of the framing or exterior plywood. The moisture can come either from excessive interior humidity due to poor ventilation (especially in bathrooms) or from condensation where moist air hits a cold surface (like the plywood or framing lumber in a poorly insulated and air-sealed wall). The above-freezing temperatures can come from escaping heat in the same walls, or just the interior ambient temperature.

In addition, mold is often the precursor to rot. Both mold and rot are fungi and thrive under similar conditions. Problem areas that re-occur or are left untreated can lead to even more serious problems down the line. Poor-quality OSB sheathing turns out to be an excellent food source for fungus, thanks to the type of wood used—hardwood has more sugar than softwood and therefore tends to be quite appetizing for fungus. But any wood surface, like plywood or solid lumber, will easily support rot or mold fungi under the right conditions. In extreme circumstances, houses less than a decade old have needed to have all the exterior sheathing replaced because of rot and mold. Often some of the framing has deteriorated as well. As you can imagine, the costs here can easily be in the tens—or even hundreds—of thousands of dollars.

How do we prevent the problem and what does it cost?

Keeping water out

Although interior moisture can and does cause many problems, the biggest problem by far is water coming in from outside, either by rain getting in behind the siding or getting trapped between the siding and sheathing with no way to escape.

Since these are construction defects, the costs really should be zero since they should not be happening in the first place. Nevertheless, the costs are relatively trivial. The window and door flashing for an entire house can be bought for a few hundred dollars. A rain screen, which allows any water from the outside or inside to run down between the siding and the sheathing, can be as simple as a crinkly or bumpy housewrap (like Tyvek’s StuccoWrap or Benjamin Obdyke’s HydroGap), which is a minor upcharge from their flat counterparts, or nailing vertical sheathing before attaching siding (maybe $1,000 in labor and materials for a medium-sized house).

Other barriers to intrusion, like flashing for plumbing vents and chimneys, kick-out flashing at roof-wall intersections (special flashing designed to push rainwater away from a wall at the bottom of a roof ) and drip edges to prevent splashback (where rain bounces off the ground up into or behind the siding) are all easily and inexpensively integrated into a project if thought of beforehand.

Managing interior moisture

Preventing interior moisture from causing problems can be a little trickier. Making sure your basement or slab stays dry is step one. In new construction, sealing the foundation and providing drainage around the exterior perimeter are both easy and required by building code. For an older house, sump pumps or dehumidifiers—or both—might be needed. None of these is more than a thousand dollars.

Air sealing keeps warm air from escaping through your walls. While this helps keep your home comfortable, it also helps keep moist air from hitting a colder surface, where it condenses into water. The energy codes are finally including air-sealing requirements (see “BS 101: Does a house need to breathe?” on page 53). Maine is still operating under the woefully inadequate 2009 International Energy Conservation Code (IECC). But even the 2009 standards require a minimal level of air sealing, and the subsequent versions have tightened those standards. We will be catching up with those versions soon. So again, for new construction it’s a requirement.

For similar reasons as noted above, sufficient insulation of the right kind can also minimize problems. The IECC acknowledges the issue and requires a certain amount of what is called “continuous insulation”—a layer on or between framing to stop thermal bridging—to maximize the effectiveness of the insulation. Thermal bridging occurs when something like a stud or rafter extends from the interior to the exterior, unbroken by an insulating layer, and conducts heat. After a light snow, you can often see this effect on a roof—stripes of melted snow show where the rafters are. The continuous insulation provides a thermal break and separates the interior and exterior surfaces. In the houses that I build, I like to achieve this break by having a double-stud wall with a space in between, then dense-packing the entire assembly with cellulose. The space between the two walls (typically 3–5 inches) is thus continuous cellulose and provides a very effective thermal break. The cellulose also has the ability to absorb and disperse any moisture that does get in the walls, allowing it to escape slowly and without causing localized problems.

How much does this cost? I spoke with my insulation contractor, Jon Riley of Casco Bay Insulation. The upcharge from a 2x6 wall to a 10-inch double stud wall on a 2,000-square-foot, two-story home would be about $5,500. The increased labor and materials for the framing would be about $2,000.

What does all this tell us? Despite the slightly increased upfront costs, building with comfort, efficiency and durability is affordable insurance—and provides a qualitatively and quantitively better house with both immediate and longterm payoffs.

This article appeared in the Spring 2021 edition of Green & Healthy Maine HOMES. Subscribe today!

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