My brother recently bought a single story 1380 sq ft house in Las Vegas, built in 1987.

It is primarily a cooling environment, in a dry hot climate, and he is trying to improve the energy efficiency of the house.  There are several unknowns, one of which is what kind of insulation is in the cathedral ceiling over the living room part of the house - guessing fiberglass batts. 

The rest of the house
roof structure:
Roof covering Spanish Clay Tile
Gable end roof vents
R30 12" fiberglass batts on floor of attic/ceiling of house

Wall structure
Stucco over wood frame, not sure as to wall depth or insulation in walls, but guessing fiberglass batts in 2X4 walls.

Concrete slab:
no clue on slab insulation or depth of slab

Natural gas, Central heat, not sure as to age type or brand
Electric, Central air, not sure as to age type or brand

All duct work is in attic, no idea as to insualtion or where they are located within the attic ie. in or above the insulation.

He is getting an energy audit done including blower door, and the company doing it wants to blow in 12 more inches of fibreglass, and spray the inside of the roof deck and gable ends with Heat Bloc Ultra.

I was under the impression that the spray stuff, such as Heat Bloc Ultra, was not effective.  It costs in the range of $1100. to spray his attic.  Would a staple on reflective barrier be a better option? Or is the Heat Bloc Ultra a useful product in his climate?  any other suggestions?

He is also considering the use of a gable end fan  - possibly solar powered.  Would that be of any use, running during the day when the outside air temps are high, but maybe cooler than those in the attic space?

Any suggestions would be welcome.  I know the knowledge base at this point is limited.

Thanks,
Rosalinda

Air sealing upgrades, some attic cellulose and a new AC unit would be somewhere near the top of my list.

Unless there's a weight loading issue he'd do better with a foot of (1.5lb nominal) standard density cellulose than with a foot of fiberglass under a hot roof.  Low density fiberglass is somewhat translucent to infra red, and the temp 2" below the top surface ends up being significantly hotter than the top surface, an much hotter than the attic air.  This means you're insulating against a higher temp with less insulation. With denser goods like cellulose the hottest part of the insulation is the upper surface, and runs about the same temp as the attic air.  A foot of cellulose also has as much thermal mass as a half-inch of gypsum, which helps dampen the daily swings in load, and defers & lower the peak cooling load by a bit just by thermal mass (measurable in a lab, not a biggie in the bill.)

Low-E coatings like Heat Bloc Ultra would help the heat gain at ducts and air handler, but not as much as a foil-type radiant barrier.  CRCC rated cool roof coatings on the tile may be available.  (Not sure- I'd have to look it up.)  If so, that would usually be more effective at rejecting the heat from the roof deck than any interior low-E solution (radiant barrier foil or paint.)  If it's not rated by the CRCC, don't buy it- there's a lot of real scam junk out there in the "insulating coatings" market.

Gable fans create pressure differences between the indoors & outdoors, which drives air infiltration partially or totally defeating it's intended purpose. In Florida Solar Energy Center studies solar powered fans yielded mid-single-digit reductions in overall cooling power, but numerous studies have demonstrated an INCREASE in overall power with grid-powered fans. This is largely due to the excessive air infiltration.

Blower-door testing and remediation of all air leaks you can find/reach is the single-most cost effective energy improvement you can do, followed by duct sealing to keep duct leakage from driving air infiltration. (AeroSeal is the slickest, but if the ducts are all accessable mastic and FSK tape can do the job well enough.)

The key is to identify these areas during the design process, assign responsibility for sealing holes, and check to ensure that the air sealing was done effectively. Usually, seal all the big holes first, then the large cracks and penetrations, and finally the smaller cracks and seams.

Gable fans ... drives air infiltration

Not this again. Not true where you have one fan blowing in and one fan blowing out. Properly balanced, they will almost completely eliminate pressure differences between the attic and the interior.

Posted By jonr on 10 May 2011 11:45 PM

Gable fans ... drives air infiltration

Not this again. Not true where you have one fan blowing in and one fan blowing out. Properly balanced, they will almost completely eliminate pressure differences between the attic and the interior.

Show me an actual readily available balanced gable ventilator/fan product and I'll concede the point.  Balancing two distinct fans is not simple, even if they're nominally identical.  Even when the impellers are mechanically locked (as in an HRV/ERV) it requires measuring & tweaking to null the pressure.

Until then I'll assume the proposed gable fan under consideration the most-commonly installed exhaust-only version (which is almost universally a losing proposition from an energy use point of view.)

These folks seem to have real tile-retrofit coatings that may be suitable (more effective than and preferable to low-E interior roof deck paints.)

http://www.americanrooftilecoatings.com/

Their independently verified CRCC performance ratings live here

Anyone know of an approx cost/sq ft for the American Roof Tile coatings? I took a quick look online and couldn't find any prices.

From all your suggestions He is going to:
energy audit, including ducts, heating and cooling systems
seal air leaks
seal ducts as needed and insulate them if needed
blow cellulose in attic
look into costs of new air conditioning system and ROI
look into costs of roof coating and ROI

Thanks again for your assistance

-Rosalinda

Looking at it from strictly an ROI or NPV for these improvement base solely on future utility costs isn't always the best approach, especially if your time horizons are sub-decade. Thinking of it as COMFORT upgrading is more appropriate, given where he's starting from. Sealed ducts are quieter, and the duty cycle of the air handlers lower. The temperature of the summer afternoon ceiling goes a few degrees eliminating the "radiant heating" sensation, making the rooms more comfortable even at higher room-air temps. (Radiant ceilings are nice in cold climates in winter, but not in a NV summer, eh?)

Replacing a functioning air-conditioning system is almost never cost effective in NPV terms over a ~15-20 year lifecycle, but if the thing is the all-original 1987 version and is becoming a maintenance headache, replacing it with a right-sized system (make sure they actually run a room by room and whole house calc) sized to the new-improved (lower, after upgrades) cooling & heating loads, with a variable or multi-speed air handler can add both comfort & efficiency. Odds are it's 2x, maybe even 3x oversized for the as-built heat loads, and will be 4-5x oversized after insulation upgrades. Typical air-leakage rates from unimproved 1980s duct work is well into double digits (even 40% isn't rare!), but is often masked by the system oversizing- the thing keeps up despite it all. Odds are good that they will need to be insulated as well. Conducted & radiated heat gain/loss from attic ductwork is also often into double-digits on systems of that vintage. Radiant barrier is often a cheap band-aid to those deficiencies, but the value/ROI of RB goes down as the R-value of the duct & attic insulation goes up. Oversized systems lead to noticeable hot/cold cycling, whereas right-sized it'll run longer per cycle, and can be run with lower T-stat hysteresis to be rid of of the cook/chill/cook/chill experience without short-cycling the equipment.

In most (but not all) cases the order of cost effectiveness on energy use breaks down as:

1. Whole house air-sealing (particularly attic floor/upper-floor ceiling, and at the foundation sill, and any flues or plumbing chases that pass from conditioned space through the attic.)

2. duct sealing

3. additional attic insulation

4. Duct insulation (assuming it's starting out with R0-R2)

5. RB or cool roof

But in terms of human comfort level, additional attic insulation probably leads the list (in this situation, anyway.)

But it's never cut & dried- the ROI of any one step changes with the implementation of the others- do it all (or at least the first three, and see where it lives.)

Dana, yes I agree that comfort and saving energy for the good of the earth are important. Items 1-4 are where he will put his initial dollars, and then go from there, depending on that most limited resource - money. At least he is now going into this with some good information and advice.

My continued thanks, admiration and respect for the folks who post on these boards.

-Rosalinda

Try going for centerlized cooling system, would be best for you.....