What I would do first is take off a couple of receptacle plates and try and see/measure what is already in the walls. I am assuming that the builder installed fiberglass batt in the exterior walls. If you have an attic then measure the average of insulation in several areas to determine your R-Value. Batt is about R-3 per inch. Blown cellulose is about R-3.2-3.7 per inch. You want a minimum of R-19 but R-30 is the norm now. If you have a vaulted ceiling then you might be able to see what is installed from a soffit area outside. Do you have any floor insulation? Do you have a crawlspace or basement? Let me know I can help further. I will be a BPI, RESNET certified energy management consultant/auditor by March. I just have some field work left to finish or I would come take a look. But this is the extent of help I can give at this point. Let me know if you have more questions.