California radiant heating code needs to be fixed

Sal Santamaura

Jamie Hall said:

It's not the civil engineering wizards, @Sal Santamaura -- I doubt that you'll find one within miles of a typical subdivision builder, or at least one worthy of the name...

I'm not suggesting the subdivision builders retain a civil engineer for their tracts. However, whether as a result of this state's mandatory 10-year new home warranties in combination with lots of cracked slabs in the past, or if they're now required by code (I don't know), it was definitely a civil engineer somewhere who came up the cable/post tension slab 'solution.'

I'm allowed to cast aspersions at engineers. I are one, although of the electrical variety.

Jamie Hall said:

...this whole discussion, which is very interesting and valuable, does illustrate my comment about the distinction between codes which are set up for health and safety (which would address that wavy slab problem!) and codes which are set up to enforce a fundamentally opinion oriented question, such as how efficient should a house or building be...

Much to the chagrin of those who don't accept that global warming is anthropogenic, California does, in a big way. Energy efficiency increases are a way to reduce carbon emissions, thereby slowing warming. Effects of global warming are detrimental to health and safety in many ways, the most obvious of which is sea level rise. California has quite a bit of population in low-lying areas near the Pacific. Everyone's entitled to an opinion, but the California energy code is tied to scientific facts.

Jamie Hall said:

...You can lead a horse to water, but if you force his nose into the bucket and he doesn't like it, he'll probably kick you into the next county.

Or he'll be kicked into another state, where they hate such regulations.

hot_rod

Sal Santamaura said:

jumper said:

What temperature do you think built-over ground in California is? You think it's cold?...

In parts of the state that have significant winter heating loads, yes, I do. But it varies widely, as does the climate in this geographically diverse state.

I've lived in San Clemente since 1978. If production builders who churn out 99.9% of the heaps-o-stucco around here paid any attention to solar orientation and passive design, there would be no need for supplemental heating at all. Since developers make lots narrow and deep, without respect to the compass, to cram in as many homes as possible per foot of street frontage, a minimal amount of scorched air gets used from December through March. Very minimal. I've never measured the soil temperature beneath my slab, but am aware what our "cold" water temperature is. The mains are safely below the "frost line" (the surface) at around 18 inches. After opening the tap and letting things run a while, i.e. until temperature stabilizes, it's a minimum of 68F in January/February and a maximum of 81F in August. It's safe to assume the soil under our slab matches those water temperatures within a few degrees. If one had sufficient financial resources to build a custom home with a heated slab, I'd say the intelligent approach would be to put that money into proper design, thereby eliminating heating completely. Even in such a situation, insulating the slab would still make sense to keep summer soil heat out of conditioned space during the cooling season.

In other parts of the state, where soil temperatures are significantly lower during winter, Bob's post right before this one answers your question.

Will the soil temperature get to 80 with an insulated building above it? It seems the suns energy beating down on the ground drives that summer temperature

Insulation is basically trapped air. While gravel has some air spaces, the aggregate is still the conductor that transfers heat energy from hot to cold. The wider that delta the stronger the heat transfer

Sal Santamaura

hot rod said:

...Will the soil temperature get to 80 with an insulated building above it? It seems the suns energy beating down on the ground drives that summer temperature...

As mentioned, I've never measured soil temperature under our slab. However, walking barefoot during August on the main level tile floor, I don't get anything like a "cool" sensation. It still seems safe to assume the soil reaches a relatively uniform equilibrium, both under and outside the building, that's close to steady-state "cold" water temperature.

This is consistent with lack of diurnal variation in water temperature. I've found no difference day and night; the change is slow with seasons.

rimrock

The soil under my slab is like rock. It is old densely packed sea bottom that holds so little water that the water table is essentially non-existent.

The project I am doing is an addition to my existing radiant heated workshop. The project is a retrofit over an existing slab that used to be outside. There is a topping slab whose purpose is to level the existing slab, but is thick enough to allow radiant heat tubing. I have no room for insulation due to the height differential it would introduce between the existing shop and the addition, but the code does not address or make exceptions for retrofit cases.

And it really seems strange that the code requires insulation for a radiant heated slab but not for a slab without radiant heat, even though the heat loss through the slab is essentially the same. In the case of an uninsulated slab on grade without radiant heat, it just becomes part of the energy calcs, so why not allow the same for a slab with radiant heat.

Gordy

First of all the denser the material under a slab the more conductive it is at transferring btus.

I think non radiant slabs should be inulated as well specifically the perimeter detail.

Delta t drives heat transfer. The greater the delta the faster the transfer. So even a non heated uninsulated slab will suck btus from the conditioned space. However not at a greater rate than a heated slab because of the higher delta.

It sounds to me like the code is not tailored to your renovation so the code is flawed.

Mark Eatherton

I agree with Gordy. It's your money. Waste it however you want to. And trust me, you will be wasting it... Even a thin layer of insulation will give you a thermal break.

ME

jumper

California is a funny place. There they spread granular material over polyethylene before pouring the concrete. I would think that dry gravel is not the best heat conductor.

And just about everywhere is funny that hardly anyone floats a floor over a residential slab. I also wonder how much money a slab saves when building a house.

Gordy

A slab foundation home saves lots of money in the initial build, and time. Just look back to Levittown.

Here again it's the density of the sub grade that conducts btus. Is porous dry gravel LESS CONDUCTIVE than solid rock? Sure. However it is still more conductive than a proper insulation detail.

Gordy

Here is where a slab saves money, and project time verses a full foundation.

Less excavation

Less wall forming if any depending on type of slab construction detail.Usually it is one monolithic pour so in and out for pour crew. Not pour walls then floor at a later date usually under not ideal conditions.

Less back fill

Usually no drain tile, and sump pit work.

Usually the deck has to be in place before back filling the foundation. This slows down, and makes the deck harder for the framing crew. Due to an excavation between the foundation, and the material.

If done correctly a,full foundation also requires damp proofing, and insulation on the foundation walls from top to below the frost line.

jumper

I suspect the biggest economy these days from no basement is cost of hauling fill away. I also suspect that pier and beam premium (if indeed there is one) is minor as a percentage of total construction costs.

Energy efficiency regulations should specify how much energy will be consumed. Not how to achieve target.

That seems obvious to me.

For example, if I'm heat & cooling my house with my own solar energy,who cares how efficient my equipment is or how well insulated my house is? The CaliforniaEnergyCommission should have been sunset at turn of century.