Alan Moore
19th March 2018, 22:23
I'm considering a ground up build on a virgin site in Phoenix. For the foundation - slab on grade is the most common here - and it is beneficial in summertime as it tends to stay quite cool. In winter it's less good of course, but our winters are relatively mild.
A few thoughts on improvements to this standard practice - Like to get feedback.
Deeper foundations are cooler still in summer - at about 10 feet deep the temperature variation seasonally is quite small and the temperature is about the annual average air temperature, About 75F. However I don't really want to build a substantial basement home.
I believe insulating the foundation edge and surrounding the house with well shaded areas and/or paved areas like driveways with decent insulation underneath will make the foundation act as if it is deeper (e.g. better shield the surrounding earth from the seasonal variations). To some extent we already get this with shaded patios, trees, planting beds with mulch and even crushed rock (with air gaps). My thought is to exploit this effect much more deliberately and aggressively.
Within the insulated building envelope I'm then thinking about the possible effectiveness of dual slabs. A slab on grade - insulated at the periphery and with hydronic circulation, then a layer of high insulation and then another slab on top also with hydronic circulation.
In the summer time I'd circulate through both loops to leverage the cooling effect of the slab on grade - and also have 2x the thermal mass once everything is cool. Then in the winter I'd not circulate in the bottom slab at all and instead gently heat the upper slab.
The outside slab areas with insulation below (think large driveway areas) could be made into daytime solar collectors (via more hydronics) for indoor slab heating when there is sufficient solar heating e.g. most of the shoulder seasons here and many days even in winter.
There is some extra expense in dual slabs - but the only practical way to implement this would be to design the whole structure with it from day 1. I had hoped to find some details on this commercially but have drawn a blank... Anyone ever hear of anything like this, or have ideas?
Alan
A few thoughts on improvements to this standard practice - Like to get feedback.
Deeper foundations are cooler still in summer - at about 10 feet deep the temperature variation seasonally is quite small and the temperature is about the annual average air temperature, About 75F. However I don't really want to build a substantial basement home.
I believe insulating the foundation edge and surrounding the house with well shaded areas and/or paved areas like driveways with decent insulation underneath will make the foundation act as if it is deeper (e.g. better shield the surrounding earth from the seasonal variations). To some extent we already get this with shaded patios, trees, planting beds with mulch and even crushed rock (with air gaps). My thought is to exploit this effect much more deliberately and aggressively.
Within the insulated building envelope I'm then thinking about the possible effectiveness of dual slabs. A slab on grade - insulated at the periphery and with hydronic circulation, then a layer of high insulation and then another slab on top also with hydronic circulation.
In the summer time I'd circulate through both loops to leverage the cooling effect of the slab on grade - and also have 2x the thermal mass once everything is cool. Then in the winter I'd not circulate in the bottom slab at all and instead gently heat the upper slab.
The outside slab areas with insulation below (think large driveway areas) could be made into daytime solar collectors (via more hydronics) for indoor slab heating when there is sufficient solar heating e.g. most of the shoulder seasons here and many days even in winter.
There is some extra expense in dual slabs - but the only practical way to implement this would be to design the whole structure with it from day 1. I had hoped to find some details on this commercially but have drawn a blank... Anyone ever hear of anything like this, or have ideas?
Alan