Dormer windows must have precise dimensions to fit a home's roof space appropriately. Your goal is to design dormers with roof lines that create a balanced look for the whole house design. You don't want dormers to look too small or too large from any angle. Find a ranch home similar to your own that has existing dormers you find appealing. Look in home design books and magazines.
Sketch Dormer Shapes
Draw the house on graph paper to define all dormers you will add. Typically, you will install only a couple of dormers on the front façade of a ranch house. However, you can add a dormer on the back side of the house in a different way. It's possible to construct a row of windows in a long section of roof. Envision this type of dormer as a section of roof lifting to look like a wedge sitting on the sloped roof. This dormer style is called a shed dormer.
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Design Window Space
Each standard dormer will require framework designed in a box-like shape. A ranch house can gain lots of light for a living room or dining area, for example, when you install windows in dormers. Framework will require cutting into attic space or roof rafters to accommodate the dormer shape. If the ranch house attic is tall enough for standard ceiling height, you can add dormers to construct upper bedrooms. This will likely require additional load-bearing walls on the first floor.
Dormer Roof Details
Roofing a dormer properly protects inner house space. If a dormer is covered with an A-frame roof section, you will add roofing material to match the house. But, you will need to install flashing in the valleys of the dormer roof. Otherwise, a dormer area can leak easily and cause roof or wall areas to decay.
Porch Dormer Designing
Take front porch space into consideration. A ranch house with a large front porch can cause design problems for dormers. While you can define and build dormers, the fact that dormers sit on top of an extended front roof with no actual room underneath looks odd. Consider enclosing the front porch to make the dormers look more appropriate. Build the dormers to bring direct light from windows into the porch room enclosure.
Vaulted Ceiling Options
Consider vaulting a ranch house roof before adding dormers. You will need to add angle iron in the peak of the upper roof to all roof rafters, so that no attic floor joists are needed. By opening a house roof this way, you can install dormers that allow windows bringing light to rooms below. The dormers essentially act as skylights for the home, but dormers add more architectural appeal from outside the house.