It's difficult enough to design new construction for high-security applications; retrofitting an existing home to withstand a possible ballistic attack is a challenge. It's easy to jump to the conclusion that bullet-proofing an existing home will involve the use of high-tech materials like Kevlar, but such materials are very expensive. What's more, in many instances they are not necessary. Traditional building materials such as brick and stone provide excellent ballistic protection at much less cost, even though they may require the complete resurfacing of the building's exterior.
Determine the nature of your possible threat. Before you remodel for bullet-resistance, it is critical to define the threat you're defending against. The materials you require to withstand an attack from a small-caliber handgun are much lower than those that will resist an M-14 rifle. Are you defending against urban intruders or a paramilitary terrorist threat? Make the determination, and then look for materials with an Underwriters Labaratories ballistic resistance level that matches the threat.
Replace wood, aluminum or vinyl siding with a full brick or stone veneer. Stone and brick will stop almost anything short of a grenade, and it's much less costly than other bullet-resistant materials. In addition, these materials will provide a measure of blast and fire resistance as well. Be sure that you are installing a full thickness of material, however, and not a thin cast veneer that looks like real stone or brick.
Remove inner drywall and install bullet-resistant fiberglass wall panels, if remodeling the exterior of the house is impractical. Choose a fiberglass panel that corresponds to your threat level; the higher the ballistic protection, the thicker (and more expensive) the panel.
Replace existing windows with bullet-resistant glazing in steel frames. Once again, the price and thickness of bullet-resistant glass rises with the level of protection, so make sure you're selecting materials that are consistent with your threat level.
Replace windows which are required only for interior lighting with bullet-resistant privacy glass. Remember that removing a target is just as important as stopping a bullet; don't provide a potential assailant with a clear view of occupants if you don't need to.