Why do you say building on a slab is more ecological than starting with a basement?

Anonymous Dec. 11, 2017, 11:45 a.m.

I watched a presentation by Emmanuel Cosgrove of Ecohome who said that a house built on an insulated slab floor was much more ecological and more affordable than a basement. How does he arrive at this conclusion? Basement or not, you need a mechanical room, storage space, a laundry room, cold storage, etc. The way I see it is to build without basement is to decide to build bigger, meaning more materials, more external walls to heat, and a bigger ecological footprint. Please explain, thanks. 

Responses (1)

Ecohome Dec. 11, 2017, 12:05 p.m.

Your question raises pertinent points. Basements are certainly useful, but from an environmental point of view, the benefits of slab-on-grade construction over a basement are undeniable, I will explain how we come to this:

Why build on a slab?

Ecology:

From an ecological point of view, the main advantage of a slab-on-grade (or frost protected shallow foundation) over a basement is the reduced use of concrete, which produces about 1 ton of greenhouse gas emissions per cubic meter. A basement will have an 8 foot high, 8 inch thick wall of concrete plus the slab floor. So even if you build a bungalow instead and have to double the floor area, you will still end up using less concrete than you would need to use in the basement walls of a smaller footprint.

There are far more options for lower environmental impact materials for above grade walls than below, but to be fair, if you were to build for example a two story ICF house (insulated concrete forms) then there is simply no difference being above grade or below. But walls made of wood and insulated with rockwool, fiberglass, cellulose or even EPS foam will have a much lower environmental footprint than an insulated wall that uses concrete as the supporting wall. 

Another advantage: a concrete slab can easily be polished and sealed for use as a final finished floor; that saves a lot of materials such as hardwood or other flooring materials, and if done with non-toxic sealant like a concrete densifier, the result is an affordable, healthy and extremely durable floor with very low maintenance. 

At grade level, a slab floor can also act as an excellent heat sink for passive heating and cooling, if you have adopted that design strategy. Radiant heating is also an easy addition to make to a concrete slab floor, offering a reliable very comfortable heat source.

Cost savings:

A slab foundation can be a cheaper way to build because a slab requires less work in excavation (you may only need to strip the top 6 inches of organic matter), and less aggregate. Along with high GHG emissions concrete is very expensive by volume, and very expensive for the load it can carry compared to wood, so cost savings is another great advantage to slabs. And not to be overlooked, is the quality of life that comes with living space that is above grade with natural light, as apposed to being in a hole. 

Main floor mechanical rooms:

All the mechanical equipment people are used to installing in basements can easily be on the main floor. This also gives you the ability to group plumbing together and keep bathrooms and kitchens close to the mechanical room, this can lead to less plumbing cost, as well as energy (and time) savings by not having to wait as long for hot water to arrive at your faucet.

Durability:

The majority of basements you will ever go into will have some level of mold issues or water damage at some point in their lifespan if they don't already. Flooding is a growing concern as major weather events regularly destroy basements entirely, so our conclusion is only reinforced by the amount of renovations that won’t need to happen by avoiding potential flooding and humidity problems.

The disadvantages:

We would be remiss if we did not acknowledge the downsides of slab construction, and they exist:

The disadvantages we find are the same ones you mention: loss of space for storing seasonal items, water heaters, washers and dryers, etc. Basements are also used as additional living space or for guest rooms, that as well takes some forethought with a slab design in order to make up for the lost space.

Another disadvantage is that the placement of bathrooms and kitchens are limited to their original location with a slab, so there is a mark against in terms of being able to do a full home remodelling.

But from where we stand, those disadvantages are all mitigated with a careful design process, and in our opinion they don’t outweight the cost savings, environmental impact, health and durability advantages of a slab. As you set about designing a slab, it takes thought in the following departments:

  • Sufficient living space with privacy
  • Sound proofed main floor mechanical room
  • Storage space in the design or an outbuilding
  • Sensible design to ensure plumbing layout meet the needs of a family.

 Have a look at the Edelweiss House that we built a few years ago, it is a 4 bedroom home (or three and storage room). Thanks for the great question, I hope that helps!  Regards, Emmanuel

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