What is better, a slab on grade or basement?


Should I build a basement or slab on grade?

robert baker Published: March 27, 2020, 6:54 p.m.Last updated: March 31, 2020, 1:28 p.m.

Our buider tells us that building a full basement is much cheaper that a "slab on grade" with a four foot frost barrier at the perimeter.  We don't understand how this cold be true.  It would also mean that it would not make sense to use infloor heating ane geothermal heating as we had planned.  Your toughts?

Robert Baker

Responses (7)

Matthew Gioia
Matthew Gioia July 7, 2020, 11:12 p.m. Reply

Hi Robert. We are in the same exact situation. How are you folks proceeding. Everything I am reading indicates a slab on grade is a cheaper option. With the environmental impacts being less severe, I really want to go this route. As with your project we are banking on the slab being cheaper so that we can install radiant floor heating as well. The Geothermal company I spoke to practically laughed at the idea we are building on a slab.

Mike Reynolds
Mike Reynolds July 9, 2020, 2:16 p.m. Reply

Hey Matthew, Where are you building, and how big? Geothermal is a costly but noble undertaking as it extracts heat from the ground, and unless you are building a 7-10 thousand square foot house or you plan to build an extremely inefficient one, it has a terrible return on investment. It will cost you anywhere from 25-40K to cut your bills in half (this is what installers have always told me) so you're bills need to be extremely high for it to make sense. For any reasonably-sized code-built house, you could invest half that amount in extra insulation and sealing the envelope properly and probably cut your bills by 75% or more. And about slabs - they are often rejected by those that don't understand the benefits, don't know how they work, or by sales reps and contractors that can profit more by talking you out of them.

As an example - our LEED Platinum Edelweiss House is a 1450 square foot house in Quebec, Canada and is heated for under $300 a year. Yoda wouldn't live long enough to get his money out of a geothermal install on that house, we put the money into insulating instead. 

Matthew Gioia
Matthew Gioia July 9, 2020, 2:26 p.m. Reply

Thank you for the detailed response! I agree the the cost in undertaking geothermal may have a very poor ROI. With that said there are significant Grant's and tax savings that can cut the cost of geothermal by nearly 50%. We would also use the geothermal for a forced air heating and cooling system. What is the heating and cooling system installed in the Edelweiss house?

Mike Reynolds
Mike Reynolds July 10, 2020, 10:59 a.m. Reply

50% off for sure makes it more appealing! Energy modelling showed that about half of the heat load of the Edelweiss House is met with passive solar heating, so that's a huge part of it. We also have a radiant floor system, but that is usually kept very low simply to provide comfort. The house is extremely airtight, and with it being very open in concept and with good circulation, most of the remaining heat demand comes from the mini-split heat pump. The house is only powered with electricity and no gas at all (including heating, water heating, cooking, drying etc) So the whole house electrical load (heating, water heating, cooking, clothes drying - everything ) comes to under $600 a year. This is why we advocate for designing the home to use minimal power rather than look at supply options. So things like solar panels or geothermal aren't necessary as the demand is so low to begin with. Here is a more detailed page about the Edelweiss House heating systems.

And out of curiosity, I'd love to hear why the geothermal company laughed at a slab, those reasonings are always fascinating to me :)  And where are you buildling? Climate zones are important for best design. 

Matthew Gioia
Matthew Gioia July 10, 2020, 12:01 p.m. Reply

All this information is amazing. Thank you! I've heard a couple folks mention energy modeling. I'll definitely look into some consultants to see if we should have some energy modeling done.

So, it just seems like folks are not very familiar with building on slabs in New Enlgand and its associated benefits, namely the cost savings and environmental benefits. I am afraid that this lack in knowledge will result in higher costs negating one of the large reasons why we want to go with a slab. For example, the geothermal company quoted us 10k more to route the HVAC ductwork for the slab than if we were to go with the basement. If that's the true cost, then we might as well put the 10k into a basement. Our biggest hurdle right now is figuring out how to route the ductwork for a slab at a comparable cost to a basement build. 

We are in climate zone 5.

Mike Reynolds
Mike Reynolds July 11, 2020, 10:23 p.m. Reply

How big is the house you plan to build Matthew? And will it be one story?