Hot Mopped Roofing – a time tested solution for commercial roofs

If you’ve ever seen a hot mopped roof install you’ll be thankful your not the one doing it. This is definitely a professional only roofing category. Hot mop roofing is a very dirty and somewhat dangerous job, it’s essentially putting molten asphalt tar over a roof. This hot mop roofing application is seen almost entirely in commercial buildings. However we do occasionally see it on porch roofs on homes or other flat roofing area’s.Also referred to as; hot mopped asphalt roofing, hot tar roofing, tar roofs, multi-ply tar roofing. Or most commonly SMELLY.

How much is Hot Mopped Roofing (Cost)

Hot mopped roofing cost vary depending on the quality and layers of roofing you are having applied.  With a base sheet plus three layers you can expect from $600-$850 a square depending on installation requirements.

Hot mop roofing installation with ballastInstallation: This is where the professional commercial roofing company is at their most valuable. You can apply hot mop roofing over old hot mopped roofing or as the first roof on the deck. When applying it as the first roof a base sheet is used to protect the raw wood surface. The process involves melting blocks of asphalt in a large metal cauldron. It truly looks like a bubbling witches pot before is goes on your roof(although rectangular with an enclosed burner). Some of the more professional or “cutting edge” contractors are using enclosed tanks that limit the noxious fumes coming from tanks. It then is either pumped up to the roof surface on spread out over the roof deck and a couple of guys who don’t mind getting burned take mops and spread it out. This process is repeated with layers of felt and fiberglass in between till they get to the desired thickness. Some installs require an aggregate be placed on the finished product as seen to the right. Pea Gravel or river rock is often used.

Longevity: The average life of hot mop roofing is around 20 years but may last as little as 15 years or longer than 30 years given proper maintenance and conditions.

Advantages / Pro’s: One of the primary reasons commercial building owners or property managers decide to install hot mop roofing is price. Compared to other commercial roofing hot mop roofing usually saves quite a few dollars. It is also fast. Most installs can be completed in a day or two with the right sized crew. It also easily conforms to irregular decks or roofs with many protrusions such as HVAC units, vent stacks and chimneys.

Disadvantages / Con’s: This roofing product is MESSY. It’s a liquid when heated that can get almost anywhere. Often roofs that have been hot mopped have “splashes” of the tar like substance up on the siding, HVAC units or any other structures around the roof. It’s really not a do it yourself project although some have tried, this is a job best left to the professionals.