Responses (7)

Marc-Andre Roy
Marc-Andre Roy 2 years ago

Thank you. To be clear, there is no basement. This is a floating slab with a 4' frost wall (on footings) around the periphary. The contractor is suggesting that 2" insulation on interior or frost wall is all that is needed. Frankly, I have seen so many different approaches online hence my confusion. Any help clarifying would be appreciated.

Mike Reynolds 2 years ago

It will work fine, but it is a lot of excavation and a lot of concrete for no reason. Many builders and even homeowners have it in their head that you 'have' to go below the frost line, but that is just out of familiarity because it's what was always done. That contractor is factoring dirt as insulation, where if you use 'insulation' as insulation you can do it all pretty much on the surface. 1 foot of dirt insulates about the same as 1 inch of EPS foam insulation, so you only have to go down 4 inches instead of 4 feet. 

Where are you building Marc-Andre? 

Marc-Andre Roy
Marc-Andre Roy 2 years ago

Thanks. Building in area of Wakefield QC. I would have preferred monolithic slab but contractors indicated more complicated, less experience with this,  potentially more difficult for permitting, and no real cost savings. 

Mike Reynolds 2 years ago

Any type of contractor will steer their clients towards what they like and are familiar with, that's not new. These slabs are actually less complicated because they come with step by step instructions and training for installers, but it may look complicated to anyone who hasn't built one.  Permitting is never an issue either. As for cost, sometimes it is more expensive sometimes its cheaper, that's really on a case by case basis and what you are looking for. 

Stephan Prystanski
Stephan Prystanski 7 months ago
Mike Reynolds 7 months ago

If it's a moderate to mild climate that's a reasonable amount of insulation, but in colder climates you would benefit from more than just 2 inches. Building code for any region is typically insufficient in terms of a reasonable pay-back time on the investment in insulation, so if there were to be a sensible 'rule' in insulating, I'd say double whatever code says. And XPS under a slab in a very expensive option for no reason, you'd get way more R value for your buck with EPS insulation. 3 inches of EPS would be probably be cheaper and give you a higher R value.