The roof serves as your home’s primary barrier to rain and snow - keeping water out of your home is particularly important during construction. Water is an enemy of most construction materials and trapped moisture can encourage growth of mold.

If possible plan for any future penetrations through the roof prior to installing or repairing an existing roof. It is always more work and less effective to retrofit penetrations through an existing shingle or membrane roofing installation. Some examples of potential penetrations include chimneys, flues, roof vents, plumbing stacks, and skylights.

Roof Types

There are three primary types of roofing found on homes in Des Moines: single-ply membrane (flat), built-up (flat), and the most common being shingle/tile (sloped). Some buildings have combination roofs with a sloped roof in front and a flat roof in the back.

Built-up roofing (BUR) is a generic term for any roof that is built with multiple layers on a flat roof. A BUR system typically has layers of “felt” or other membrane alternated with layers of tar/bitumen. The top layer is usually a stone aggregate spread over the entire surface. This roofing type is more typically found on commercial buildings.

A single-ply membrane (SPM) roofing system consists of a single layer of waterproof sheeting. The SPM material comes in large rolls, and can be fastened in a number of ways to the substrate on a flat roof. Its ease of installation makes SPM systems relatively inexpensive.

Asphalt shingles are the most common roofing system on sloped roofs. Shingles are mechanically fastened (nailed) to the roof’s substrate. A layer of roofing felt between the shingles and the substrate helps provide a waterproof barrier. In general, shingles may be installed over existing shingles up to three layers deep. All layers must be removed prior to the subsequent installation - this is also a good time to make any required repairs to the roof sheathing. If your building has existing slate shingles that cannot be repaired, they should be removed before installing asphalt shingles.

Insulation

Roof rafters and trusses must be insulated to prevent heat loss in the winter and heat gain in the hot Iowa summers. In fact, the roof is one of the primary means of heat transfer to and from your home. The two most common means of insulating the roof are fiberglass batts and blown insulation. Fiberglass batts come in either large rolls or pre-cut lengths that are placed between rafters or studs. Batts are typically installed before drywall and after electric rough-in. Blown insulation consists of fibers (often recycled material) and a fire retarder. It is spread evenly using a blower that may be rented. It is important to use enough to get the required thickness for the desired insulation value.

Resistance to heat flow is indicated with an “R-value”. The higher this number, the more insulation is provided. Insulating the roof to as much as possible will result in significant energy savings.

In some cases, if the underside of the roof sheathing is exposed, it is possible to install expanding foam insulation such as Icynene. This type of insulation is very efficient (high R-value) and serves double duty as a vapor barrier but requires professional installation.