QUESTION FROM :  Brett from Utah

 hi my question is In my attic there is r38 fiberglass blown in insulation there is a company here that is recommending that I blow r19 cellulose on top of the fiberglass this does not make sense to me the fiberglass would compress and loose r value correct?have you heard of this practice?is it worth doing or am I loosing r value. would I be better of to blow more fiberglass thanks.


Hello Brett,
Thank you for your question. You are absolutely correct. If the situation was reversed and you were blowing fiberglass on top of cellulose you would not have a problem.

The recommended R-value today is an R-49. If your currently have an R-38, I would not recommend you going to the expense of trying to add an R-11. I think you would be better off to consider looking for another heat loss in your home. For example a storm door, a front door, a particular window, storms on your basement windows

if you have a basement, addition of a water heater jacket or just chalking your present windows. This would probably be more cost effective for you and save on your heating and cooling costs.

If you were to add the R-11 your energy savings would only affect a small portion of your heat loss. Therefore, your return on investment would be spread out over 7 to 10 years due to the fact that your already have an R-38. Hope this helps, Bruce Jones The Insulation Doctor