Why do flat roofs even exist?
Flat roofs became more prevalent during Streamline Moderne (1920’s-1930’s) – a late branch of the Art Deco design style. It was somewhat a break from traditional architecture at the time, although in reality, pueblo and Mediterranean style flat roofs have been around for thousands of years. In many cases today the construction of a flat roof home simply comes down to stylistic preference – just look at the city of Santa Fe or the High Desert neighborhood in Albuquerque as quick examples. Additionally, there are some construction cost benefits (i.e. less expensive trusses). With a large commercial building in mind, a pitched roof, more often than not, would literally be out of the question.
What are the issues with owning a flat roof?
Traditional flat roofs have always presented their owners with a myriad of challenges when it comes to performance. These common problems with traditional flat roof systems can include:
- Noxious fumes during installation
- Inability to maintain protection with the inevitable water ponding/puddling
- Necessity for regular/frequent maintenance in order for the roof to be effective
- Pro-rated (limited) warranties
- Short term warranties (3-7 years)
- Lack of effective means for long term seal on/around items on roof that are highly susceptible to become sources of leaks (pipes, vents, skylights, canales/scuppers, duct penetrations, etc.)
- Failure to be able to expand and contract with temperature and weather fluctuation (especially here in the Southwest). This leads to cracking/splitting which of course leads to leaks.
- Heavy weight on structure
- If a problem arises, normally very difficult to identify the source
- Suspect methods for patching or new flash-ins if needed during remodeling (patches typically peel away and become source of problems)
What are the benefits of a flat roof?
A flat roof is the most cost-efficient roof shape as nearly all room space can be used (below and above the roof). They also provide space for outdoor recreational use such as roof gardens. Unlike a pitched roof, if designed properly, a flat roof surface can be used as real functional living space.
- If you have to be up on the roof, a flat roof is certainly safer
- Some of the most popular and beautiful architecture today includes flat roof construction (Southwestern, Pueblo, Mediterranean, Tuscan, Midcentury Modern, etc.)
Are flat roofs completely flat?
No. A well constructed flat roof will typically have 1/8”, 1/4” or even 1/2” per foot slope built in. This of course will help minimize ponding/puddling water on the roof.
What do I need to do to maintain a flat roof?
The life expectancy of a flat roof is often proportional to the maintenance done on it. All flat roofs require some form of maintenance in order to maximize their effectiveness and lifespan; however, the frequency, cost, approach, and difficulty of maintenance work varies among the different types of flat roof systems. For example, common built up roofs (tar and gravel) or spray foam roofs need yearly inspections and fairly complicated (and messy) maintenance on all roof penetrations (pipes, vents, skylights, etc.) and parapet wall flashings for any chance of lasting success.
In general, home and building owners’ lack of attention to regular inspections and maintenance on their flat roofs often lead to premature failures.
In response to homeowner demand, Lone Mountain has launched a new maintenance and inspection service.
Beyond tar and gravel (BUR), what are some of the popular re-roofing options available?
- Thermoplastic (PVC and TPO) – white (or other colors) rolled roofing. Seams are created by hot air welding. Long lasting and usually energy efficient, this type of roof addresses the common shortcomings of other types of systems and provides a real solution. This has been Lone Mountain’s specialty for about 25 years!
- A slight variation of built up roof (BUR) with gravel is a BUR with Modified Bitumen capsheet – it still involves plies of felt paper and tar, however, it is then capped with rolls of bitumen which require the seams to be flame torch welded (posing a potential fire hazard). An even cheaper version of a BUR with a Modified capsheet is simply the Modified Bitumen rolled roofing with no plies of felt paper and tar.
- Spray polyurethane foam (SPF) roofing is made up of an application of foam covered with an elastomeric coating or aggregate. The coating provides most, if not all, of the waterproofing.
- EPDM (ethylene propylene diene monomer) is black rubber rolled roofing. Seams are sealed using adhesives.
- I’ve heard that foam roofs are a good treatment for a flat roof. Is that true?
- While foam is a fantastic insulator, our experience dealing with home and building owners have shown us that foam roofs end up being the most problematic of all systems available. The necessity for frequent inspections and maintenance, and the fact that, realistically, folks simply don’t keep up with it leads to problems – sometimes unknown to the owner until they are major problems.
My roof is flat, and covered with tar and gravel. It’s about eight years old, and not leaking anywhere. Do I need to replace it?
While more information would need to be gathered for the best and most accurate answer, generally an eight year old tar and gravel is, at minimum, approaching the end of its life (possibly already there). A wise owner won’t wait for interior damage to signal that they need a new roof, so here are a few helpful tips:
- Collect as much information as possible on the existing roof (age, type of roof, previous installer, leak history, maintenance history, etc.)
- Get 1-3 (or more) evaluations on the existing roof’s condition from professional roofing contractors.
- Get 1-3 (or more) re-roofing estimates from professional roofing contractors.
Depending on the results of the evaluations, it may be best to:
- Get other estimates for maintenance/repair work to extend the life of the existing roof
- Contract for the re-roof immediately
- Wait on re-roof, but retain those estimates for future reference and to start budgeting. As always, if you don’t accept a price at that time, a future estimate may be higher but you can use those original prices as a frame of reference.
- How long does the typical flat roof last before needing re-roofing?
- Our experience, having talked and dealt with thousands of flat roof home and building owners over the last 30+ years, has shown to us that traditional tar-based flat roofs typically last 3-9 years. With considerable and careful maintenance, a tar and gravel roof may last as long as 10+ years. Simply put, there’s a reason their limited warranty is usually only around 5 years in length.
What’s the difference between flat roofs on commercial buildings and flat roofs on homes?
Aside from possible variations in construction materials (wood, steel, concrete, etc.) and obvious size disparities, there shouldn’t be much difference. We believe that the roof installed on a 2,500 sq. ft. home should be of the same quality and durability as a commercial roof on a 250,000 sq. ft. building. Unfortunately, most roofers don’t take this same approach which leads to residential roofs that fail sooner than they should.