October 2021 – Burton Family Adventures

October 24, 2021

Understanding slab / foundation insulation

This post is a bit more for the folks interested in the science and details behind the what and why of our insulation decisions for our foundation. In the spirit of keeping things short and sweet, I plan to cover the following:

Purpose of foundation insulation
Discuss why we chose Expanded Polystyrene (EPS)

Let’s jump right in…

Purpose of foundation insulation

There is a lot of science behind the energy transference between surfaces that are in contact, namely dirt and concrete. When concrete is placed directly on dirt, there is both moisture and thermal exchange taking place. There is a large debate in the building science community around how much insulation in needed due to complex thermal calculations, weather conditions and soil types, but the thermal models from the Passive House Institute helped us settle on 8 inches. The amount of insulation helps keep the inside building temperature more stable, thus reducing the cold floor feeling, which makes my wife happy. There is insulation around the footers and stem wall as well. This all works together to prevent / limit thermal transfer between these materials. One of the key concepts of a Passive House is to eliminate “thermal bridges”, which can be thought of as solid materials that transfer thermal energy between touching surfaces. So, we have eliminated the thermal bridging between the slab and ground, the ground and footer/stem wall, and the slab and stem wall. Below is a diagram showing the slab design.

BPH slab to stem wall to exterior wall details

Further reading in the PHIUS 2021 Guidebook.

Why did we chose EPS?

There aren’t many insulation types that are well suited for ground contact. The primary types for below grade insulation are expanded polystyrene (EPS) and extruded polystyrene (XPS). Key reasons for choosing EPS over XPS:

Consistent R-values over time
Reduced moisture absorption with higher drying potential
Lower cost by 10% – 30%

Finding a local EPS supplier was a bit more challenging as XPS is more readily available, but we settled on Insulation Company of America, https://insulationcorp.com/. They custom cut our molded U-shaped footer insulation , which made pouring the footer much easier.

References:

October 20, 2021

The stem walls are done

The stem wall is the portion that transfers the house wall weight down to the footers and eventually to the ground. Our stem wall isn’t very large as the footers are only 32 inches deep to get under the frost line. The footers are 8 inches thick, thus the stem wall is 24 inches high. All that could likely be summed up with a nice picture.

It’s hard to see in that picture, but the lower 2 blocks are standard 8 x 8 inch, while the top block is 8 x 4 inched. This is to accommodate a 2 inches of insulation between the slab and the stem wall while still allowing for a 2 inch overlap from the slab to the lower stem wall for load transfer (not needed as the primary load is supported by the foam, but it’s another example of a good “belt and suspenders” approach). I’ll get into more in depth details on the wall structure and insulation in a future post.

October 14, 2021October 24, 2021

Starting off with a good foundation of insulation

The digging continues with the footers. These are 24” wide and are poured into an EPS footer mold that both insulates them from the ground , preventing thermal bridging, as well as creates a mold for the concrete to be poured into. With the cost of lumber, this was a slick idea to have the foam shaped and permitted rapid install of the footers.

Doesn’t that just look beautiful!

The footers are now all completed and on to the stem wall. Here is aerial footage of the completed footers.

October 13, 2021

What is a Passive House anyway?

This is a question we get asked often. While I do enjoy explaining it to others, I often times find myself rambling. So I thought I would try to be a bit more concise here with references for those interested in reading more about it.

Passive House (in common language)
A home designed to meet the highest levels of efficiency through the elimination of energy waste.

The technical Passive House Principals can be found on the Passive House Institutes page (PHIUS). The design principals do not dictate what materials a home uses, nor alternative energy sources. When I explain it, I usually start by says “It’s a normal house, with lots of insulation.” If folks are more interested, I dive deeper into the other keys areas of environmental management (in order of priority):

Water
Air
Vapor
Thermal

The “Perfect Wall” as described by Joe Lstiburek in a great Youtube playlist walking through some of the building science behind a Passive House.

Here is a picture from the PHIUS site which visually describes a Passive House fairly well (minus the subsoil heat exchanger).

October 13, 2021May 28, 2022

Building has begun!!!

There are many changes occurring on this project, so to help keep me motivated, I’m going to try and provide more frequent updates, but try to keep them shorter.

So, to kick things off on the project, we had electric and data lines run from our shipping containers in the front yard to the build site, ~475ft away. This power will provide electricity to the construction site during build to avoid the need for generators. The power is being provided by our whole house battery array that is setup in our shipping containers.

Will update again soon.