Adobe Interior Walls

I watched a DVD called Building With Awareness where it showed the entire process of a guy in New Mexico building his straw bale home. One thing he did was use thick adobe walls for several of his interior walls. He said that they help hold heat during the winter (thermal mass which makes sense) and also remove heat during the summer. Now this removal of heat sounds nice but is it really that effective? I live in Texas and keeping the house cool is a much bigger concern for us than is keeping the house warm. The thick adobe walls take quite a bit of the interior living space away, but if it's really effective and keeping the interior cool then it's totally worth it. Does anyone know if adobe interior walls are worth the effort and loss of space?

It has to get really hot before it is a negative in the summer. I mean like Death Valley hot, where it only cools down into the 90s on hot summer nights. If that is the case and the temperature averaged over the course of the day is over 100, then yes, thermal mass is a negative because your air conditioning will be working double duty to cool all that thermal mass down.

How many cooling degree days do you run in the summer where you are?

John Elliott wrote:It has to get really hot before it is a negative in the summer. I mean like Death Valley hot, where it only cools down into the 90s on hot summer nights. If that is the case and the temperature averaged over the course of the day is over 100, then yes, thermal mass is a negative because your air conditioning will be working double duty to cool all that thermal mass down.

How many cooling degree days do you run in the summer where you are?

I don't quite understand what cooling degree days means but I generated a report for our area:

As for lows, in June, July and August, the average lows are 73, 77, 77, respectively.

Did you generate that from the BizEE degree days page? Degree days are (degrees over the set point)x(number of days). For instance, that 608 for August tells me that since August has 31 days, the monthly average temperature is about 20 degrees higher than the set point you picked. That is a load on the A/C system, but it doesn't sound too bad.

My experience has been with concrete block buildings, a high thermal mass, but not nearly as much as adobe. In the low desert of California and Arizona, daytime summer temps are always over 100F, sometimes over 110, but they seem to radiate the heat away at night and are comfortable without the air conditioning running all night. It's only when the temps start hitting 120F that the A/C seems to get overwhelmed and runs all night.

John Elliott wrote:Did you generate that from the BizEE degree days page? Degree days are (degrees over the set point)x(number of days). For instance, that 608 for August tells me that since August has 31 days, the monthly average temperature is about 20 degrees higher than the set point you picked. That is a load on the A/C system, but it doesn't sound too bad.

My experience has been with concrete block buildings, a high thermal mass, but not nearly as much as adobe. In the low desert of California and Arizona, daytime summer temps are always over 100F, sometimes over 110, but they seem to radiate the heat away at night and are comfortable without the air conditioning running all night. It's only when the temps start hitting 120F that the A/C seems to get overwhelmed and runs all night.

Yes, BizEE was the website. So do you believe my house would benefit from the adobe interior walls?

It's worth considering. A lot of other factors could come into play, such as how shaded it is by trees, do you have a high ceiling where all the heat can rise to, is there any natural evaporative cooling like ivy covered walls or pergolas, is your roof a reflective white, etc.

I plan to shade the house somewhat. All of my windows will be under porch (front and back porches) and so will have a 6 foot overhang. I will make my ceilings 8 ft and I don't expect to have ivy covered walls.

Then you should consider it. One place where thick walls work is in Tucson at the San Javier del Bac mission. The white color also helps keep it cool in the blazing Arizona sun.

I think interior mass walls would help reduce your cooling costs by a measurable amount.. but probably barely. I doubt that the saved energy would payback the increased costs to do so and the walls will be more difficult to clean compared to a more traditional smoother wall. Subtract the lost interior floor space from your costs per square foot and it seems like a pretty tough deal to me.

Brian Knight wrote:I think interior mass walls would help reduce your cooling costs by a measurable amount.. but probably barely. I doubt that the saved energy would payback the increased costs to do so and the walls will be more difficult to clean compared to a more traditional smoother wall. Subtract the lost interior floor space from your costs per square foot and it seems like a pretty tough deal to me.

If, for example, we did not run an air conditioner (not likely but just theoretically speaking), how much do you expect the adobe walls would help? I was hoping maybe run the air conditioner during the day (off solar) and turn it off at night. The video I watched the guy said he never turns on his air conditioner.

He might be tougher than you! No I think it takes a little comfort sacrifice to pull off saving energy with thermal mass. I love the idea of charging the mass with PV during the day though. Thats one of the more profound ideas Ive heard today.

Think of interior thermal mass as a thermal flywheel. So whatever inputs you put into it will be carried at a more moderate level over more time in a more consistent way. So thermal mass doesn't have much direct effect on energy input levels but it is vital for passive moderation temperature.

You can do cool things like run heating/cooling lines through TM and use it as an awesome radiant heat source as well as heat sink.