The two basic types of exterior wood doors are flush doors and stile-and-rail doors. Flush doors are made by bonding face panels to solid or hollow cores. Stile-and-rail doors (also referred to as panel doors) are solid doors that consist of vertical and horizontal members (called stiles and rails, respectively) that enclose wood or glass inserts. (See FIG. 5-7.)
Most flush doors have hardwood veneer face panels, although hardboard and softwood panels are also available. Some doors are made with cutouts for windows or louvers. Flush doors are used as interior and exterior doors. As exterior doors, they should be made with waterproof adhesives rather than water-resistant adhesives. You can often tell whether the proper adhesive was used by looking at the top edge. In many quality doors, you will find a small red plastic plug in the edge. This indicates that the door was bonded with a waterproof adhesive that is suitable for exterior use. When an improper adhesive is used, the exterior face panel eventually begins to delaminate and peel.
A solid-core flush door provides greater heat and sound insulation, fire resistance, and dimensional stability than a hollow-core door. The solid core of a flush door might be made of wood blocks or a composition material that has been formed into a rigid slab. A hollow core is generally made of wood or wood derivatives (cardboard) that have been formed into a honeycomb or parallel strips. When resistance to heat, sound, and fire are not important factors, the hollow-core flush door is sometimes used as an exterior door. This is not considered quality construction. When used on the exterior, the door should be treated with a water-repellent preservative and bonded with a waterproof adhesive. Unfortunately, this is not always the case.
One variation of the flush door is the metal-clad insulated entrance door. This door is available in a selection of surface styles and is becoming more popular. Basically the door consists of metal face panels with an insulating core. Some doors are provided with a thermal break to separate the interior parts of the frame and door panel from the exterior parts, thereby minimizing condensation during the winter months. Because of the insulating characteristics of this type of door, the need for a storm door is essentially eliminated.
Although stile-and-rail doors are not used as commonly as flush doors, they are available in a greater variety of designs. Because of the number of panels and joints, the stile-and-rail door is not as effective an insulator as a flush door. Also, one or more panels might crack as a result of shrinkage. If you stand inside of the house looking at the door, cracked sections are very noticeable. Daylight is visible through the cracks.
Some exterior doors are not considered secure because of the location of the glass panes relative to the door lock. If the door lock can be reached by breaking a glass pane in the door or in side panels, an auxiliary lock is recommended. This lock should be positioned where it is not accessible from the outside. Since you normally do not know whether you were given all the keys to the exterior door locks, it is recommended that after you take possession of the house, you replace all of the door locks or at least have the locks rekeyed.
The condition of the exterior doors should be checked during your exterior inspection, and the operation of the doors should be checked during your interior inspection. On the exterior, inspect for cracked, chipped, broken, delaminating, and rotting sections. Inside, check the doors for cracks (visible daylight) and ease of operation. Does the door open and close easily, or does it bind? Also check for weatherstripping around the exterior joints.
Weatherstripping is desirable, since it minimizes air infiltration. If you find any problems with the doors, record them on your worksheet.