Tree Loss and Slab-on-Grade Foundations: A Poor Fit with the Sustainable Northampton Plan

Kohl Construction claims its North Street condo proposal deserves deference as “infill”, but its proposal is in fact at odds with many recommendations of the Sustainable Northampton Plan. In our last article, we discussed how Kohl’s latest concept now includes two cul-de-sacs. These are disfavored by the Sustainable Northampton Plan and in this case for good reason.

In this article, we focus on the prospect of tree loss and the drawbacks of slab-on-grade foundations. Kohl proposes slab foundations for its condos due to the high water table. Seasonal groundwater is as high as 14-16″ below the surface in places (PDF report, 735KB), and might rise higher if many existing large trees are cut down as proposed. (A single large tree can remove as much as 150 gallons of water from the soil each day. They also intercept a portion of rainfall before it reaches the ground.)

First, let’s review some of the goals of the Sustainable Northampton Plan:

Facilitate the increased energy efficiency
and use of renewable energy in public
and private buildings (page 17)

Encourage development that maximizes
building orientation and landscaping to
increase energy savings (page 17)

Add standards in City’s street tree and open space programs to help reduce fossil fuel use
(e.g. provide summer shade to reduce use of
air conditioning) (page 22)

Minimize the loss of tree canopy throughout
the City and increase tree canopy in
urbanized areas to maintain a higher
quality environment in all areas… Target: 2% increase in area or number per year (page 23)

[Glossary:] Sustainability: “Meet[ing] the needs of the
present without compromising the ability of
future generations to meet their own needs”
– former Norwegian Prime Minister Gro Harlem
Brundtland. A sustainable community
manages with a balanced set of integrated
principles: Social Equity, Environmental Respect,
and Economic Strength, that preserve
a high quality of life for future generations.

A Northampton Schools Strategic Planning document (PDF, 803KB)  suggests that the Planning Department views durability as part of its Sustainable Northampton vision:

Although most of the actual policy, regulatory, and investment changes to implement Sustainable Northampton have yet to be initiated, the first changes are already underway:

  • All new subdivisions now require concrete sidewalks, granite curbs, and sufficient water pressure or sprinkler systems to fight fires. These expensive features will both lower future city costs and make it far more likely that development will occur closer to downtown and Florence, where street lengths per unit are shorter, and not in outlying areas…

At a March 26 hearing, Conservation Commission member Paul Wetzel also raised the issue of durability and longevity of materials. He questioned Smith College’s commitment to sustainability in light of its proposal to replace turf with a synthetic field that would need to be torn up, discarded and replaced every 15 years.

Durability is an important value in Envisioning Sustainable Northampton, the book recently produced by the Notre Dame School of Architecture:

The Notre Dame School of Architecture’s guiding ideal is a built environment that is convenient, durable and beautiful;
and we contend that by being convenient, durable and beautiful, the built environment will necessarily also be sustainable. (page 1)

Durable Construction: In promoting sustainable building construction in Northampton, rewarding builders for
using a limited palette of low-embodied energy building materials–e.g., integral masonry bearing walls, heavy
timber frames, slate or clay tile pitched roofs; no steel reinforced concrete or steel lintels–will result in an
environment of beautiful buildings that will last for hundreds of years, an essential component of a sustainable
human settlement. (page 7)

proposal to cut down numerous large trees in an urban neighborhood clearly contradicts several goals of the Sustainable Northampton Plan. About an acre of impervious surface would be added. We have
previously discussed the role of trees in air quality, stormwater management and reducing the urban heat island effect.

Let’s now explore how slab-on-grade construction raises questions about the durability and longevity of the condos themselves, not to mention energy loss.

First up, Bruce Maki, editor of, issues a Quasi-Rant on the matter of “Crawl Space vs. Slab Foundation”:

…Quite frankly, you couldn’t give me a house built on a slab foundation. With no easy access to any of the “environmental systems” (electrical, plumbing, HVAC) maintaining these structures is a nuisance at best, and a nightmare at worst…

Builders will say that slab foundations are cheaper. Around here some builders say that building a house on a crawl space saves money. I don’t buy into that argument. It only saves money up front, and almost certainly adds costs later, costs in maintenance and repair.

With a crawl space many maintenance and repair issues are much simpler than a slab foundation. Even more important, making changes is much easier. If the homeowner wants to build an addition, connecting to existing supply pipes, drain pipes, HVAC ducting, and wiring is much simpler. I don’t know about most people, but I prefer a house that allows for some future changes. When it comes to remodeling, I can’t imagine trying to work on a slab house. I can imagine charging a lot extra, though.

Another issue that nobody talks about is structural longevity. Long ago I heard a rule-of-thumb for carpentry: keep all wood at least 6 inches above the soil so the splashing water doesn’t get on the house and cause decay of the wood. Around here most houses are plenty high off the ground, but many garages and sheds are built low. And I’ve seen many of these buildings get structural damage, typically rot but also termite infestations, from rain dripping off the roof, onto the ground, and splashing onto the building. The houses around here with basements usually have 18″ to 24″ of masonry directly above the soil, and no problem with rotting sill plates. Crawl spaces tend to be lower to the ground, but (from my experience) a lot higher than slab foundations. I have absolutely no confidence in the long-term structural integrity of slab-foundation houses. I have to wonder what all these fancy slab houses will be like in 30 or 40 years. I won’t be doing repairs on them, that’s for sure. Maybe they’ll be knocked down to return the land to farming…

[Maki goes on to describe how low-slung slab buildings are more likely to have animals burrow into them, such as a squirrel that became trapped inside his slab garage and did considerable damage.]

Monster Constructors reiterates some of these concerns and adds that heat loss might also be a problem without “special precautions”:

The slab-on-grade choice is very attractive to builders because of its relatively low cost. Excavation is kept to a minimum and the construction schedule can often be accelerated. The day after the slab is poured, wall framing can often begin.

But slabs come with some baggage. Frequently, plumbing drainage and water supply lines are buried beneath the slab. If something goes wrong or a leak develops, repairs can be costly. Heating or cooling ductwork buried underneath the slab can sometimes fill with water during wet seasons. Should this happen, mold can form and spores might be blasted into the home each time the air conditioner fires up. Thermal conduction issues are always present. Slabs poured in colder climates can conduct cold back into the house unless special precautions are taken. Homes built on slabs often offer little protection during tornadoes or hurricanes, unless a special masonry or concrete safe room is built within the house.

Tasha Lucas, also from Monster Constructors, adds:

Slab-on-grade foundations are constructed with reinforced concrete and are usually shallow, quickly built, and inexpensive. For a builder that doesn’t have to live in the homes that he builds, slab foundations are a dream. Slab foundations are used with homes that do not have basements. A major disadvantage to slab-on-grade foundations is that they are not resistant to seasonal movement changes and moisture disbursement due to root growth. In other words, slab foundations are not a long-term option for homes in North Texas…

Wikipedia notes that slab foundations are less common in cold climates:

Slab-on-grade foundations are…most often seen in warmer climates, where ground freezing and thawing is less of a concern and where there is no need for heat ducting underneath the floor…

The disadvantages are the lack of access from below for utility lines, the potential for large heat losses where ground temperatures fall significantly below the interior temperature, and a very low elevation that may expose the building to flood damage in even moderate rains. Remodeling or extending such a structure may also be more difficult. Over the long term, ground settling (or subsidence) may be a problem, as a slab foundation cannot be readily jacked up to compensate…

We’ve previously noted how the area at the end of View Avenue, at a relatively high point on Kohl’s land, reported flood damage from Tropical Storm Floyd in 1999. It’s also still an open question whether some of the condos would be built on filled wetlands, which is disfavored by the 2004 Flood and Natural Hazard Mitigation Plan (PDF, 1.5MB):

Many areas of the City were developed before the passage of the
Massachusetts Wetlands Protection Act of 1972. Historically filled
wetlands are commonly related to problems with wet basements, flooding,
shifting foundations and failed septic systems. Development in
historically filled wetlands should be discouraged through zoning in
order to protect health and safety. (page 24)

Combined with the high water table, there is ample reason to be concerned about water intrusion damaging the condos, reinforcing the overall concern about the durability of the proposed structures. The condos would likely face several tests over their lifetime. The latest Hazards Mitigation Plan estimates that tropical systems hit the Massachusetts coastline every six years on average. Since Floyd struck in 1999, the next one is overdue.

See also:

Mike Kirby: “The Meadowbrook Chronicles Part One”
The developers built 255 units
of affordable apartments there. They crammed them in everywhere they
could, pushing them up into the bluffs, and close to the creek and
wetlands. No backyards to speak of. One third of the buildings were
built within 50 feet of the wetlands, 63% of the buildings are within
the customary 100 feet of wetlands.

None of the buildings have
cellars under their apartments. If they have cellars, there are people
living in them. The cellar floors in the basement apartments in
Buildings #4 and #2 are lower than the surrounding swamp. Some slabs
have cracks in them. People have been flooded out. No moisture-proof
barriers between the surrounding earth and the foundations. Moisture
and mold percolate up into people’s apartments via the chases that hold

Cellars are a wonderful thing;
you’re away from the groundwater and dampness. Our first big purchase
after we bought our house in 1983 was a top-of-line Sears submersible
pump. For twenty-five years it has been working without human
supervision. The float goes up, it goes on, the float falls, it shuts
off. Whoosh-whoosh in the cellar, all is right with the world.

Gazette: “Council adopts wetlands ordinance”
City Councilor James M. Dostal proposed an amendment Thursday that
called for increasing the 10 feet no-encroachment zones in urban
residential districts to 50 feet because of serious concerns about
homes flooding, saying “We shouldn’t be building there…”

Good Cul-De-Sacs and Bad Ones

Gazette: “Developer to submit revised North Street plans”

Video: Conservation Commission Meeting of 3/12/09; Deadlock on Kohl Condo Proposal; Kohl Seeks to Withdraw Application

Tropical Storm Floyd Flood Damage Report (1999)