What is the best flat roofing system today? Assuming a gut rehab.
 

I'm doing a gut rehab on a commerical property. What is the best (longest lasting) flat roofing system I could buy?

Longest lasting...low-slope metal

Properly installed, 50+ years

side note: You are going to get a million different responses based on each persons "preferred" system. You asked for the longest lasting system and nothing will outlast metal. More expensive up-front but always wins out in life-cycle costing.

O+B is right about long lasting on a pitched or low slope roof,But on a flat roof,PVC may be a better solution,unless you`re adding some pitch for runoff

Talking about flat roofs too TRG
PVC would be second I would say.

On a dead flat roof ?? would you waterproof everything 1st,you said low slope,not dead flat,I would want some pitch for drainage

Any flat roof should strive for minimum 1/4" slope but even in ponding water it will never wear out. No pre-waterproofing necessary, the system is watertight with a 30 yr NDL warranty. Oldest one is in Oregon, 38yrs and no sign of failure.

Is the question more properly asked, what's the best longest lasting roof I can afford?

O & B is right about the answers you'll get, here's my $.02 worth.

Old School 4 ply Built up with gravel, Minimum R20 insulation on the deck, 160 mil Mod Bit flashings.

Caveman school, 4 ply BUR with coal tar and slag. That's a 40-50 year roof dead level or not.

Single plies need not apply.

:thumbup: :thumbup: :thumbup:

There is a widespread perception that single ply PVC type of roofing is the better, modern way and that BUR built-up-roofs are the old way, becoming obsolete. This notion is FALSE.

Many experts would agree that a CTP (coal tar pitch) BUR is the best all around flat roof. CTP can resist ponding unlike other asphalt products due its unique "self healing" properties. Because its a BUR with several layers, redundancy against leaks is achieved unlike PVC where one nick, one tear in the seam and voila - instant, often torrential leaks.

The advantages of PVC are that it is lighter weight and faster for the contractor to install. Leaks may perhaps be easier to find - but only a little bit.

Problem is CTP BUR is a dying art and fewer contractors are availalble to do it - well good contractors that is.

Above all - well above all - is the quality of the installation - Is that contractor really the "right stuff.?" I would prefer a cheaper material that was installed expertly than to have expensive high end stuff installed carelessly.

I ended up with the latter unfortunately.

Foam it
 

I use a 3 pound closed cell foam which gets two coats of acrylic paint to prevent damage of the UV light. This roof is now very well insulated and will never leak in 100 years. All that is needed is to re-paint in 5-10 years.

In the northwest we have another name for those...Sponges! Unless they are religiously maintained they always suck water. And most bldg owners never think twice about their roof until they start having problems with them anyways. You may want to revise your 100yr claim on watertightness.

Gotta agree with oldnbroke

My old roof previous to the current new roof mess
was foam coated with silicon paint. Had it for 15 years, got to know that beast well.

Foam must be applied in a way that preserves its unified seamless one-piece structure. They need to be sprayed down all at one time, not in sections over several days etc.

UV damages foam very easily - new foam must be coated with a protective coating as soon as it dries, no later than the same day or even just half a day max. A cloudy day might be better than a sunny day to lay foam. Only the very best contractors with robotic sprayers should ever touch this stuff so the qualifed pool is low. Definetely not something for the average mom-n-pop outfit.

That protective coating must be maintained religiously and recoated every few years. Wherever there is a nick not patched right away, the UV rays will penetrate and kill the exposed foam. Birds love pecking this stuff. The degradation doesnt result in immediate leaks so its easy to ignore the warning signs. Eventually it became a waterlogged spongecake.

My foam roof was garbage but I still have a favorable opinion of these types of roofs if installed expertly. The thermal/vapor barrier created by its seamless structure is hard to match with any other technique and they can last 30+ years.

Not in a million years will you get 100 years out of a Spray roof. Even with coating ever 5-10 years, the birds wont show up on year 10 because they know your coming to recoat it. IMHO sprayed roofing belongs on nothing. its one step above a metal roof on a less then 1:12 slope with end laps. On the other end that metal roof is good for spraying a few layers of Top Coat or the like. If properly cleaned and installed.

Back on topic, longest lasting roof. pitch roofs, or dead level asphalt roofs, no slope, raise the drains, cant the walls, hold the water in. Thats old school. Other wise 3 or 4 ply with mod cap and gravel will last a very very long time. 90 mil epdm will also last a good long time, so will a 80 mil TPO or a PVC. Just depends how deep your pockets are.