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What Is A Torchdown Roofing System, Is It Best For My Home In Seattle?

What is a torchdown roofing system?

There are many choices and material types you can use on your flat roofing system in Seattle. Single-ply membranes such as PVC, EPDM, TPO or torchdown (also known modified bitumen) are the most common low slope and flat roofing materials. Depending on your roofing systems design one of these membranes might be a better choice than the other. In this consumer education article I would like to shed some light on torchdown roofing systems. Chase Construction North West has been installing torchdown as a Seattle roofing contractor for over a decade.

Torchdown is a ruberoid (rubberized) membrane modified with an APP weatherized asphalt for waterproofing. The material is strong, very durable and has a non-woven polyester mat. Torch down is light weight at less than 2 pounds per square foot. Torchdown membrane comes in smooth and granulated sheets. The granulated cap sheets come in many colors, some of which are energy star rated and qualify for the Federal tax credit. Torchdown can be used to re-roof (tear off the existing roof and install a new system) or recover (install a ply of torchdown over an existing roof).  Applying the second ply of granulated cap sheet can give you a more aesthetic finish to your roof. The cool colors also reflect the suns solar rays keeping your structure cooler and saving you money on costly energy bills.

While granulated sheets are the typical cap sheet in a modified bitumen system, smooth sheets can also function as cap sheet.  They provide a better surface for liquid-applied silicone membranes down the road.  This can result in cost savings over the long run since the smooth torch down sheet can be used as substrate for a new roofing system when it’s near end of life; whereas a granulated sheet is more likely to be torn off and replaced when it nears end of life.

Why use torchdown instead of other roofing options?

As torchdown is a rubberized material it allows for excellent expansion and contraction in the extreme heat and cold a roof can endure. It also adheres very well to metal roof flashings and as they expand and contract the torchdown is in melody with the movement. This flexibility keeps roofs from cracking and makes it a very effective low slope or flat roofing material.

Low slope or flat roofs

Torchdown is considered a low slope or flat roofing system application. Low slope roofs are qualified by having a roof pitch of less than 4:12 or 4” of rise per foot. It is not recommended by the NRCA or roofing manufacturers to install asphalt shingles on roofs with a pitch less than 4:12.  With advanced applications, asphalt composite shingles like GAF Timberline HD can be installed down to 2:12 pitch. Torchdown is most commonly seen on commercial roofs, but is also very popular and appropriate for low slope residential applications.

If you live in an area with risk of puncture from falling objects, torchdown can be the best choice for your roof because the plies are significantly thicker than competitors.  One torchdown sheet can be over 3 times thicker than the typical waterproofing membrane in a TPO or PVC flat roofing system.

Torchdown can be a solution to condensation damage

Condensation can be a make or break issue with some non-ventilated flat roofs.  Since the roof is one part of the building envelope, as heat tries to move from inside to outside (or vice versa) condensation can happen at one point inside the systems.  Insulation and vapor barriers (and vapor retarders) play an important role in protecting from condensation concerns, and recently roofers and engineers have rediscovered the value of a the dark torchdown roofing membrane.

Because of focus on climate in the last few decades, many dark roofs of built-up tar or torchdown have been replaced with lighter colored roofs, often with TPO or PVC.  But now some of these roofs have rotted from the inside out.  A key factor for why is that the light colored roofs reflect so much solar radiation that they never get that hot.  Since flat roofing systems are often expected to get some amount of moisture inside them, the dark-colored roof usually reheats under sunlight enough to vaporize that moisture and allow it to escape.  But with white roofs, that doesn’t happen, and once moisture gets inside it often stays inside and rots.

This issue can be addressed with TPO, PVC, and liquid-applied silicone using non-white colors, like dark gray.  There is not yet adequate data to say if the black torch down color is superior to grays, but some specialists say it is.

Experience is extremely important with torchdown roofs

The typical standard material warranty for a torchdown roofing system is 10 years and up to 20 years with upgraded system specifications. “No dollar limit” warranties are available on torch down roofing systems through certified roofing contractors. No dollar limit warranties must be installed to exact upgraded commercial specifications and inspected by the manufacturer with a passing grade. The manufacturer then guarantees not only the material but also the workmanship of the contractor for an X amount of time with a 100% guarantee.

90% complete on a 160 square torchdown re-roof with silvercoat near Seattle, Washington.

Torchdown is applied by an open flame. It comes in rolls of 1 roofing square and can easy be rolled out across the roof. The entire width of the membrane is to be heated adhering the whole roll to the sub deck or existing roof in the case of a recover. An error often made is for a contractor to only heat the seams of the modified bitumen leaving the remainder of the membrane laying loose on the roof deck. This compromises the integrity of the waterproofing ability as the seams over time are the first aspect of the membrane that will fail due to weatherization.

Due to technicality of torch down roof application it should be installed by an experienced roofer. Insurance is required to install torchdown which ensures the safety of both the home owner and contractor. Before you consider utilizing torchdown please contact a local Seattle roofing contractor and get a professional  consultation to make sure its best for your roof system.  We recommend following the National Roofing Contractor’s Association  (NRCA)  regulations for applying torchdown.

We have been providing quality materials for torch down roof repair and re-roofs in the North West for over a decade. If you are interested in a fee inspection or estimate please call us at (253) 544-3651 or fill out our free estimate form.

Contact us and we will get back to you quickly with an effective and affordable solution for your torch down roofing needs.

Chase NW Roofing is factory trained and certified with GAF, IKO, Versico and Custom-Bilt Metals to install almost every roofing application. We specialize in composition shingles, torchdown, single ply, metal roofing, wood shakes, slate and concrete tile.

Don’t take our word for it! Please see what our past customers have said about us on !

4 thoughts on “What Is A Torchdown Roofing System, Is It Best For My Home In Seattle?”

  1. This post shows a very good idea for all homeowners and builders. I thought this was something that would effect harm to the environment but based on what you have posted it seems very good and will surely build a sturdy house.

  2. I personally do all of my work in the North Texas areas. When I have a low-slope project I always recomend the torch down method primarily do to the extreme weather changes that we get. It gets to be extremely hot during the summer and gets as cold as any where else during the winter months. The rubber made material IS great for the contraction and expansion reasons for my area.

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