The final major detail in preparing our cottage foundation for concrete is to lay PEX tubing for a radiant heating system. We don't have immediate plans to use it, but at a cost of about $100, it seems foolish to leave such an efficient heating option off the table. Our installation consists of a single 300 foot run of 1/2" tubing which enters and exits the floor in the northwest corner of the slab.
We ran the first two courses of tubing (where the circulating liquid is hottest) along the north side of our slab because that is likely where it will be the coldest. Following that, we circled around the perimeter with runs 6" on center. In the middle, we expanded to 12" on center, simply because the maximum recommended run of 300ft isn't long enough for 6" spacing throughout.
We haven't run tubing under our strawbale walls, or under the kitchen counter on the east side of the house, hence the large gaps as seen in the photo below:
Initially, we plan to heat the house with a wood stove—the Salamander "Hobbit". It can be fitted with a boiler attachment, so we might be able to use it in conjunction with a low power DC pump to circulate water in the floor? We're also laying a short section of insulated PEX piping to the exterior of the house—this gives us the option of hooking our radiant system to a solar hot water collector, someday.
With the slab details complete, all that's left to do is brace the form. Then, we'll be ready to pour concrete!