Energy efficiency and home insulation

[anniej]

I live in a very hot climate. I have upgraded my windows to double pane thermal with some some success in cooling my home. I have been considering both additional fiberglass insulation and a radiant heat barrier for my attic as the air conditioning bill is still horrific and rates keep rising. I am getting conflicting opinions regarding the need to combat radiant vs conductive vs convective heat in this situation. Any suggestions on how to retrofit for a cooler house. Thanks

 

[russ_watters]

Well, it depends a little on what you have now, but generally, radiant heat barriers (ie, white roofs) and conductive heat barriers (ie, insulation in a concrete slab) only exist on the outside of the building. If you are insulating the ceiling of an attic, you need fiberglass for a convective barrier. Note, though that this will also help block radiant heat from the roof above.

 

[Crosson]

I live in a hot climate, and I think you should use a insulated barrier for the attic and also cut holes in the attic to increase airflow (consider adding an industrial fan up there that is on a timer to run at a certain time each day).

From a physics point of view, the most efficient solution depends on the humidity where you are. If the humidity is low, then focus on radiative transfer and conduction (insulation), and if the humidity is high focus on convective transfer (fans)

 

[anniej]

Thank you for your comments. I live in So. California and the humidity is generally very low in the summer. Because there is no R-value available for reflective foil barriers as there is for fiberglass batting and the like, it is hard to evaluate the return on investment. I am leaning toward a fiberglass batting with a foil sheet on one side to place on the underside of the roof between the rafters.

 

[adambeazley]

If you live in a hot region and the home is already built and you have less than a R39 insulation, a radiant barrier is your best option. It will give you your biggest bang for your buck.

I highly recommend a double sided radiant barrier so you can save energy in both the sumer and winter months. In your particular climate, you would just staple the radiant barrier to the bottom of the rafters in your attic.

The way they work, is they are highly reflective but they have a really low emissivity. So about 97% of the radiant heat is reflected while the remaining 3% is absorbed. If an air gap is left on either side of the radiant barrier then only about .03% of that heat will re-radiate to the opposite side of the radiant barrier. So this give you increased cooling efficiency in the summer and increased heating efficiency in the winter.

Check out Ra-flect, they make a good http://www.raflect.com" which I used in my own attic and it works.

 

[crayh]

I live in south Tx. Installed radiant barrier reflective foil in our 2500 sq ft home last October. I am watching our electric bills, for past 9 months we have saved $1,287.90 over previous years bills. IT WORKS! I used ENVIRONMENTAL ENERGY IMPROVEMENTS to install my product.

 

[anniej]

Many thanks to adambeazley and crayh. You gave me just the info that I needed and I will certainly use your advice.