Flat Roof Advantages and Disadvantages

Flat roofs aren’t just for commercial buildings. We’ve also installed lots of flat roof systems onto residential structures, such as home additions and detached garages. If you’re in the unique position of choosing a roof design, than you’re probably wondering what the advantages and disadvantages are of a flat roof. Depending upon your requirements, desires and budget, a flat roof might suit you well or it might not. If you’re considering a flat roof, review the following flat roof advantages and disadvantages.

In this article, we discuss:

Flat roof advantages:
Space (outside)
Low Profile

Flat roof disadvantages:
Space (inside)

house with flat roof next to house with sloped roof
house with flat roof next to house with sloped roof

Flat Roof Advantages

1. Price

a. Installation and Repair

a roll of EPDM roofing material
a roll of EPDM roofing material

Because flat roof material often comes in large rolls, and residential roofing material, such as asphalt shingles, come in small sheets, it takes less time to install a flat roof system.

The same applies to repairing a flat roof system. Patches are available for the various flat roof systems, so it takes less time to repair. If an asphalt shingle needs repaired, for example if a tree branch punctured it, often the surrounding shingles need to be repaired as well. You see, asphalt shingles are layered – half of one shingle is underneath half of the one above it so there’s always at least 2 layers of asphalt shingles at any point on your roof.

b. Roof Deck

Under every roof system is the roof deck. Because there’s less lumber in a flat roof than in a sloped roof, it costs less to build.

2. Space

a. Equipment

new pvc commercial roof for Panera Bread in Cheyenne, WY
new pvc commercial roof for Panera Bread in Cheyenne, WY

What happens when you put anything on a hill? It wants to roll down the hill, doesn’t it? Because a flat roof is almost flat, equipment such as air conditioning units can be installed on them.

b. Rooftop Patio or Garden

With a flat roof, you have the option of having a rooftop deck or patio. When designing your flat roof with your general contractor or structural engineer, be sure to mention you want a rooftop deck because some changes will need to be made, but at least you have the option.

3. Low Profile

Flat roofs offer a lower profile. For example, maybe you don’t want to block the view of the mountains, or maybe you want to stay below overhead utility lines.

4. Safer

It’s much safer and easier to walk on a flat roof since they’re basically flat. Because sloped roofs are often at least 3/12, or 14º, there’s a greater risk of slipping and falling.

house with flat roof next to house with sloped roof
house with flat roof next to house with sloped roof

Flat Roof Disadvantages

1. Appearance

This is a matter of opinion, but some think flat roofs are less stylish. In the mid 1900s, flat roofs were popular. Today, although they are less popular than sloped roofs, they are seeing a come-back (can I call it a come-back?)

2. Stability

Flat roofs have a tendency to be less stable, especially large flat roofs. The larger the flat roof, the less stable it is. To compensate, additional structural stability must be built-in to other areas of the building.

3. Drainage

Flat roofs do not drain as well as sloped roofs. The greater the slope, the fast water runs down it. Water tends to pool on flat roofs. Pooling water tends to break down the roofing material. Also, extra precautions need to be taken to ensure seals are made around pipes and flashing.

4. Less Space Inside

A sloped roof gives the home owner the option of an attic. With a flat roof, there is no attic option because that space simply doesn’t exist.

5. Less Insulation

Again, because there’s no sloped roof and therefore no attic, there’s less insulation space. Insulation is basically empty space between the undesirable (the outside) space and the desirable space (the inside). With a sloped roof, that insulation is your attic. With a flat roof, there is significantly less insulation. As a result, your home or building might be effected by extreme fluctuating temperatures.

The Bottom Line

If you’re building a new commercial structure or home addition, you need to consider whether you’re going to have heavy equipment on your roof, or if you’re going to have a rooftop patio or garden. You can install heavy equipment onto a sloped roof, but it is more difficult, and it can be more difficult to get to that heavy equipment. Consider the above flat roof advantages and disadvantages carefully and consult your roofing professional to make sure you get a roof that works for you.