Hi Curt:
I am not a fan of indoor temperature swings so I don’t have much use for internal thermal capacitance. This is just personal comfort preference.

Since I can’t stop outdoor temperatures swings, I am OK with thermal capacitance in the outdoor building layers, especially brick exteriors. Flattening the diurnal heating or cooling load on a building is generally a good thing. Keep in mind that this load dampening is not only a function of the thermal capacitance of the building material. When you do the detailed transient heat conduction analysis, the dampening effect is a function of the thermal resistance times the thermal capacitance. This becomes evident when you look at the units of thermal RxC which is F-h/Btu multiplied by Btu/F which gives units of time (hours). So increasing the thermal resistance of the building envelope also helps it dampen diurnal load profiles. In addition, increased thermal resistance also reduces overall (average) heat loads whereas thermal capacitance does not. So I am making the case that increased thermal resistance always helps with thermal loads whereas increased thermal capacitance only has limited benefits.

The real reason that I like brick exteriors is that I don’t have to paint it in the future, although for some strange reason around here, people are painting brick, even on new homes. I don’t get it.

Actually, I think what you get in the NFRC label for windows and doors are in fact “Assembly” figures – they incorporate the frame, mullions, muntins, etc.

1) In a heating dominated climate, it can be acceptable, even desirable for a thermal mass within the envelope be intermittently heated, such as by sun or a woodstove or similar, and then release its heat late at night when outdoor temps are at their lowest. Proponents of this approach may be satisfied by the central core / daytime use rooms of a home being kept warmer by thermal mass while outlying bedrooms are allowed to get a bit cooler – curl up with each other or extra blamkets.

2) In a cooling dominated climate, I personally enjoyed an ICF (Insulated Concrete Forms) home – that variant puts the thermal mass in the middle – split between two layers of insulation. The benefit of thermal mass in a hot humid climate is in the delay of solar gain – the hot afternoon peak is reduced. There is also benefit in the thermal mass releasing some heat into the home well after dark – that delayed sensible gain “gives the HVAC system something to do” well after dark; indeed all night long. In other words, the slow release of some stored heat into the home all night long causes the HVAC to operate, at least intermittently, all night long. This improves comfort by reducing humidity since conventional HVAC systems manage latent gain only indirectly, in other words only when there is some sensible heat gain to activate the system thermostat.

A conventional light frame home won’t carry enough sensible heat long enough into the dead of a hot muggy night to create enough load for the HVAC to manage humidity.

Thanks. I have only seen U-factors for Windows, but not assemblies. Have you found such a thing? For example, if I have R-48 SIP walls (no transfer) and Pella triple pane windows, can I get close to an assembly U-factor? I suppose you have to add in raised floor, underfloor insulation and a number of other things, but at this point I am so far away I can’t find much use for it.

Some say that you want high thermal capacitance on the indoor air side of the envelope. I disagree. To get enough indoor air temperature variation for this capacitance to have an impact, you would probably be uncomfortable. It should be on the outdoor air side of the envelope (e.g., brick or concrete block) to dampen the impact of outdoor air temperature and solar heat gain fluctuations.

If anyone can point me to the math on this I would appreciate it. Otherwise I might cover my house inside and out in tin foil with a 2 inch air gap.