A version of this post ran in 2018.

Roofing is one of those things you don’t usually think about until it’s a problem. With the rainy season on its way, now is a good time to think about whether your roof needs some attention, or even replacement

If you’re looking to repair or replace your roof – or build a new home – you probably have questions. Here are a few roofing basics to help you get started.

Selecting a Roofing Material

The kind of material you select for your roof will depend on several factors, including your climate zone and the slope of your roof.

Qualities to consider are:

• Durability
• Lifespan
• Installation costs
• Water resistance
• Fire resistance
• Maintenance costs
• Energy efficiency
• Appearance
• Cost

You should always talk to your architect or roofing contractor about your options, but here are some general guidelines:

Low-Slope Roof

If you have a low-slope roof, water-resistance and solar-reflectiveness are likely to be key considerations, while appearance may be less important, as your roof will not be highly visible from the street.

Materials for low-slope roofs generally include single-ply membrane, built-up (tar-and-gravel), and modified bitumen.

Marin County roofer Darren Little, of Booth and Little Roofing, notes that fully adhered roofing – a single-ply membrane – are an option for low-slope roofs where a traditional roof attached with nails (known as “mechanically attached”) is less desirable, as in many mid-century moderns where the electrical system is in the roof.

“If you’re building doing a full remodel or tear-down, a mechanically attached roof is fine, but for other jobs where nails can be a problem, fully adhered is a good choice,” he says.

High-Slope Roof

For roofs with a steep slope, aesthetic considerations might be more important to you because more of the roof is visible from the street. Your roof can add or subtract from your home’s curb appeal.

Fortunately, you have a lot of options, including asphalt shingle, tile, slate shingle, and metal.

Why I Don’t Recommend Foam Roofs

You might notice that I haven’t included foam roofs in my list above, although they have become a popular option.

A foam roof consists of a polyurethane coating sprayed onto a roof deck then coated with another water-resistant material, such as acrylic. Its popularity stems from its density, which can provide insulation, and its water resistance.

But, in my experience, there are significant drawbacks to foam roofs.

An inexperienced installer may introduce lumps and bumps in the foam, which can decrease reflectiveness and create drainage problems, and an improperly installed foam roof – or one installed when it is too cool or too humid – can blister and develop holes. Mistakes can be difficult to fix.

Moreover, installers must be very careful not to overspray, as the polyurethane foam can be carried on the wind and adhere to other structures or pose an inhalation hazard.

Foam roofs can sustain punctures or cracks, which can affect their performance.

Little also notes that foam needs to be recoated after around 10 years.

Considering Energy Efficiency

Your roof can play a significant role in keeping your home warm in winter and cool in summer.

We enjoy a moderate climate in the San Francisco Bay Area, so we don’t need to worry about snow buildup, but most of us will want to maximize solar reflectance and thermal emittance – how much light the roof reflects and how much heat it holds.

A number of factors affect reflectance and emittance.

Color

A lighter color (“cool”) roof reflects light and can significantly lower your home’s temperature on hot days. The Cool Roof Rating Council evaluates and rates roofing products for solar reflectance and thermal emittance; their directory lists the ratings for numerous roofing materials.

Some roofs can be coated with a white acrylic polymer (a “white roof”) that is highly reflective and cost-effective for homes that get a lot of sun.

Green Roof

Another idea that is gaining traction is the “green roof” (also known as “living” or “vegetated” roofs) – a layer of planted material that sits on top of an existing roof, which is water-proofed and fitted with a root-repellant and drainage system.

A green roof adds insulation, reduces water runoff, and reduces heat. It can be a beautiful and nature-friendly alternative to a traditional roof, but it isn’t for everyone. Your roof’s slope, load capacity, drainage, and local ordinances affect whether a green roof is a good fit for your home.

Insulation

Re-roofing is a good time to consider adding insulation to your roof to improve its energy efficiency.

The amount of insulation your home needs depends on your climate and how much existing insulation you have. The Energy Star site has a chart with recommended levels depending on your situation.

Types of insulation include batt-and-blanket, loose-fill/blown-in, and foam board/rigid foam. Your architect and roofing contractor can help you decide what material is best for your home.

Skylights and Energy Efficiency

Installing a new roof is a good time to think about fixing problems with skylights – degradation of seams around skylights can lead to heat loss in cooler weather, and even leaks. And replacing the glazing can offer benefits for energy efficiency. Glazing options include glass, fiberglass, acrylic, and polycarbonate, and each has its benefits and drawbacks in terms of durability, appearance, and energy efficiency.

The best time to discuss improving (or installing) a skylight with your architect or contractor is in the early stages of planning your roofing project.

Maintain Your Roof

Most roofs should last 15 to 20 years, says Little, as long as you take care of any minor repairs before they become bigger problems. He recommends a roof inspection after 10 years for most types of roofs.