hot tar vs torch down applied membrane
oolong86
| Posted in Construction Techniques on
Does anyone out there have an opinion, positive or negative, about membrane roofing? Should it be torched down or adhered with hot tar over new plywood decking? I have opinions from roofers using one or the other & both but no explanation why.
Replies
There are advantages and disadvantages to both.
The key to both is good quality materials install by competent workers.
A modified bitumen membrane in a flood coat of asphalt (hot tar) is a good roof if the asphalt is not overheated, which it often is.
After a certain temperature, the volatile components of the asphalt are driven off, resulting in a brittle roof, greatly reducing the servicable life of the material. This is done mostly because it makes installation proces go faster and easier.
This is also a very heavy roof, and not easy to remove when you need to re-roof.
The advantage is that it's inexpensive.
A torch-down roof made of top-quality materials (like SWEPCO)applied by competent installers is an excellent low-slope roof. It is comparatively light, clean, easy to maintain, and reasonbly priced.
With inferior materials you get an inferior roof. And you have someone on top of the house with a torch. As much as I like torchdown, that really is a serious consideration.
The reputation of your roofer is probably the most important factor to consider.
DRC
See more hotmop roofs installed wrong. Especially in cold weather, the rolls lay out lumpy. Lumpy rolls and cold weather keeps the layers from bonding together. The biggest problem is no slope and dips.
Good point, I agree. I've repaired a lot of hot mop, never had to repair torchdown unless something big landed on the roof.
Aisha, slope is critical. The roof must slope to drain with no ponding, no matter what system you use.
DRC
Our condo project got together and put on sloped metal roofing over the flat membrane roof.
Flat roofs fight mother nature.
i think they are something architechs put on to save money (in the short term).
then the sun hits it, a little building say, puddles, unseen leaks, termites etc etc.
Aisha,
I prefer EPDM rubber membrane for most residential low slope roofs now over either of those you mentioned.
The hot mop roofing is the traditional three or four ply built up roofing called BUR. I've installed miles of it. I suppose it is possible to get the problems sungod mentioned, but only from a low quality outfit. If rolls are improperly stored to become "lumpy" we throwed them away. Excuse me, we threw them away!
BUR is highly dependent on the mpop man laying down a good layer of hot and the paperroller laying in a good rool and controling it, and the kettle man maintaining a good temp. It is a skilled job for each.
Then nrew technology came along with a copy of the above, calling it "modified" meaning that the hot asphalt stickum is built right into the roll of paper which is a very thick material in comparison to the older 14# rolls. It is dependet on getting that 4" lap exactly right, and as Dave said, keeping the torch on it just long enough to get it hot enough to seal without overheating it. It is easy with modified torchdown to get a lumpy lap too if the installer is not experienced with it.
Neither of these installs directly on the plywood. If the installer is trying to do that, you are screwed. Both use a base sheeet first, nailed to the plywood. The reason is that both can be brittle enough to move and break. The plywood will move at the joints and that is where either of these will develope cracks and fail if directly applied. The base sheet acts as slip sheet.
The EPDM is a rubber that is much like an inner tube rubber material. It is generally attached directly with contact glue and the seams welded. A seam is 6" and occurs only every twelve feet. Since most leaks occour at laps in any membrane roof, the elimination of most of them with the EPDM naturally reduces the likelyhood of leaks from that souirce. The rubber is extremely pliable and handles minor movement of the plywood if directly attached to it, but we oftern use a gypsum product for a slip/thermal barrier.
Perhaps you will benefit more from this conversation and get more direct advice if you describe the exact nature of the job you are considering this for - a whgole house, a deck, a condominium , a new house....
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Thanks for the detailed response! The house is 130 years old with traditional T & G covering the 2 roofs. The larger roof (approx. 1600 sq.ft) has a very low slope from the center to front & back. The smaller roof on the back wing of the house (approx 350 sq. ft.) has a gentle one sided slope.
The roofers contacted so far all plan to install a 2 ply modified bitumen membrane (Soprema). They all want to apply it on new decking as they feel the original planks will create to many imperfections. One wants to torchdown both layers. Another wants to hot tar adhere the first layer & torch the second and the other roofer wants to hot tar apply both membranes. They all are using a smooth first membrane with my choice of color & texture for the second.
What is the composition of the base sheet you refer to? Any brand/trade names? I've also heard that some roofers are suspect of the longevity of rubber membranes. Do you have any idea how they're protected from breaking down under UV rays & extreme temperature changes?
One last question. Any opinion on the "fake slate" shingles? I think they're composite recycled rubber & other bits. Only brand I know of is Authentic Roof and it's difficult to find any info on their life expectancy.
I have not specialized in the roofing trade for close to fifteen years now, so these products and methods you mention are ones I am not familiar with. But all reputable manufacturers provide installation specs. You should be able to have the roofing contractor provide you with a copy of these specs or find them on-line to study for answer to your specific questions, or somebody else here might be more familiar with the product line.
The plywood sheath is a good idea over the t7g and will act somewhat like a slip sheet, but I still am unawarte of manufacturer specs recommending direct application. Any roofing wholesaler stocks the base sheet in 43# weight. A dozen makers provide it. Maybe the whole industry has changed, but-
If the roofers are individually specing an installation different than that suggested by the manufacturer, then the warrantee is automatically void. However, with BUR roofing there were twenty some various specs in the book for various applications allowed, sometimes according to the judgement of the architect or roofing contractor.
As was suggested above, the skill of the installer is the single most important factor in the performance of a low slope roof system. Therefore, it is highly important to not only research the material product as you are doing here, but to reseach the reputation and history of the contractor(s) you are considering.
UV rays are the aging factor for most all bituminous or rubber roofing. Many require or advise re-coating with specified products every five to ten years. The torchdown modified that I am more familiar with will last nearly forever is perfectly installed and recoated every five years for protection from the sun. the EPDM rubber has a life expectancy of forty years when exposed with little maintainence other than gently washing grit and leaves off. it is possible the product you are being offered has the toplayer with colour for the purpose of UV protection.
Finally,
Everyone I have known to have fake slates has lived to regret it so far. Use the search button here for similar threads. There have been two or three about that in the past year.
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