Q: What is the best option for replacing a low-slope roof over an addition? We have a low-slope shed roof that was repaired with roll roofing as an emergency patch in 2014. We had ice damage which forced the roof repair, but because it was in the winter, only the lower half of the 23×12′ area was repaired.
The top half of the addition roof has asphalt shingles where it meets the wall of the main house. Now we are seeing bubbling at the adhesive line (where the roll roofing meets the shingles) and are looking to replace the roof. We live in NH where the weather is cold, icy and often miserably snowy. What would be our best option for replacing the roof? How long does roll roofing last, and are these signs real for needing a new roof? – Linda
A: The roll roofing manufactured today is a very low-quality product that I would not recommend for anything other than a utility shed. The useful life of roll roofing is 5 to 15 years, but it will probably not last 10 years in your climate.
For a low-slope residential roof, there are two main options:
1) Cover the entire surface with a self-adhesive flashing membrane such as Grace Ice & Water Shield (there are many equivalent products). Then apply standard asphalt shingles over the membrane. The membrane will outlast the shingles and seal around all nail penetrations.
Follow the manufacturer’s recommendations for end laps and horizontal laps, typically 3 inches at ends and 6 inches at horizontal laps. The membrane should go up the house wall 12 to 18 inches and be covered by an appropriate counter-flashing on the wall.
2) Where the roof is not visible, consider upgrading to a single-ply roofing intended for low-slope roofs. The most commonly used product on residential roofs is EPDM, which should last for 24 to 40 years or more if applied properly.
In either case, find a professional roofing contractor experienced with low-slope roofs and these specific products. As in all construction work, paying attention to the little details can make all the difference between a long-lasting, trouble-free project and one that results in callbacks and early failure – never a good option with a New England roof. – Steve Bliss, Editor, BuildingAdvisor.com
Kathy Morrison says
Can I Use Asphalt Shingles on a Low-Slope Roof?
Hi, my home has a 2/12 low-slope roof that needs to be replaced. I’ve gotten some conflicting info from the roofing companies that have given me estimates.
One roofer said he could use a DiamondDeck underlayment and then apply asphalt shingles (I like this option because asphalt shingles look more like a typical roof). Another roofer said roof needs to be at least 4/12 to use asphalt shingles. What is your opinion? Also, I’d like to get solar panels at some point. Is one type of roof better than another for that? Thanks for any info you can provide!
buildingadvisor says
Most asphalt shingle manufacturers will warranty their shingles for slopes as low as 2:12, but most recommend or require that you use special underlayment details for roofs between 2:12 and 4:12. Most recommend either as double coverage with roofing cement at all lapped seams or self-adhesive membrane . Roofing associations also recommend against asphalt shingles on roofs with slopes less than 4:12 without special precautions.
Many contractors recommend against asphalt shingles for roofs lower than 4:12 due to bad experiences in the past. This is especially true in cold climates where snow buildup on roofs is expected. Even if the roof does not leak when first installed, as materials wear out over time you are asking for trouble – especially around skylights, chimneys, or other flashed openings or step flashing.
If you really want to use asphalt shingles, I would strongly recommend using a self-adhesive underlayment. In addition to sticking aggressively to the roof sheathing and at lap joints, the asphalt membranes seal well around any nail penetrations.
Other options for low-slope roofs include EPDM (my first choice), as well as TPO and PVC.
Also be aware that roofing product warranties are typically prorated and are often for materials only and have many loopholes. Bottom line is that they are not worth a lot in practice. So choose a system you can trust and a contractor who will stand behind his work.
Peter says
Can I Rehab Tar & Gravel Roof With Peel-and-Stick?
I have a low-slope roof –1/12 pitch. It has several layers of older cold mopped tar which has “alligator” marks on its surface. What would be the best and perhaps least expensive option for repairing such damage? Can I install #30 roofing felt over a base of non-cured cold mopped tar and wait till it cures? Last step would be to install a peel-and-stick roofing compound. Thank you.
buildingadvisor says
My experience trying to repair old hot-mop roofs has been mixed, so I leave these things to professional roofers. I am not familiar with cold-applied roofing systems like yours, but significant alligatoring is generally a sign that a built-up roof is shot.
Not sure if this roof is over living space or utility space, what your budget is, or how many years you hope to get out of this repair. If the roof has been leaking and is saturated, you would probably be best tearing off and replacing the roof. Also consider the condition of flashings, penetrations, and edge treatments, which are hard to repair when re-coating an existing roof. Some high-quality aluminized coatings with added fibers can add 3-5 years to a worn-out built-up roof that is not yet leaking.
One thing to keep in mind is that most peel-and-stick membranes are not designed for UV exposure or for use as roofing surface. There are a few options on the market and some require a primer. I can’t comment on their long-term performance.
I would compare the cost and lifespan of your roofing rehab with the cost and performance of tearing it off and starting fresh.
If you’re replacing the roof, my personal preference for low-slope roofs is single-ply, usually EPDM, which has served me well. If done right, it’s a 40-year-plus solution. TPO is also an good product, but has not been around long enough to predict its longevity. Also, there are a variety of different formulations and manufacturers continue to fine-tune the product. Skilled and experienced installers are critical for success with both TPO and EPDM.
Peter says
Thank you for your expert advise Steve and I appreciate your response. With EPDM, since they are normally only 60 mil thick, once there is a “surface break” caused by gravel through foot traffic, are these easily repaired?
Also and my main concern is the rolled 10 foot width of the EPDM. They have been quoted me for a 400+ lb rolled sheet. Does the manufacturer make these in 200lb rolls as well? I am concerned about its weight and that of rolling it out on the ground , cutting individual lengths and re-rolling and hauling the the roof.
What are your thoughts?
This may be a DIY job with a friend to help out.
buildingadvisor says
EPDM roofs are usually not installed as a DIY project. But it’s possible to do a decent job if you carefully follow the manufacturer’s instructions about substrates, seams, flashings, and other details.
Most residential EPDM roofs used mechanical fasteners in the field and glue at seams and metal edges. Some systems now use double-faced tape at seams, which simplifies the process. Also, special self-adhesive moldable flashings can be used for for tricky spots.
The weak link in these systems is the seams. If not properly cleaned and primed, neither site-applied adhesive or taped seams will hold up over time.
If you’re planning to have a lot of foot traffic, I’d recommend a walkway built like a rooftop deck. Use 2×4 sleepers with EPDM strips glued to the bottom surface. This will protect the roofing surface from damage. EPDM is not hard to repair with a patch, but it’s best to avoid them.
Regarding roll size, different manufacturers and distributors have different offerings. Most residential jobs use 45 or 60 mil material – the thicker the better, especially if you are expecting foot traffic.
Dan Schrader says
Can You Put Ice & Water Shield Over Rubber Roof?
The contractor wants to put one layer of Ice & Watershield over the existing rubber roof with shingles to cover. I live in Indiana. I appreciate all the information.
Thanks Dan
buildingadvisor says
Sounds like a workable plan. Some contractors put new peel-and-stick membrane such as Ice & Water Sheild over an older layer when re-roofing. This is easier than attempting to strip the old membrane, which may require replacing the roof sheathing. Installing membrane over rubber roofing is a similar detail.
In your case, I’m not sure why the contractor wants to leave the rubber roofing in place. Rubber roofing is relatively easy to strip, but still takes work. The level of difficulty depends in part on the type of adhesive used. If the rubber roofing is in good condition, you should be able to get a good bond to the membrane. If it is badly deteriorated, you would be better off stripping it.
Rubber roofing is often installed over an inch or so of special insulation, so you will have to use long enough nails to fully penetrate the roof sheathing.
Finally, I’m assuming this is a low-slope roof. For roof slopes less than 2:12, you would be better off replacing the rubber roof with a new rubber roof.
Dan Schrader says
Should I Use Two Layers of Ice & Watershield?
Is there any advantage using two applications of ice and watershield on a 8′ wide X 28′ length 2:12 roof?
buildingadvisor says
I don’t see any harm in using two layers of Ice & Water Shield or other peel-and-stick membranes. But I’ve never seen it done and most roofers would consider it overkill.
A double layer might be justified if the membrane does not bond well to the substrate for any reason. Of if the first layer was exposed to sunlight for longer than was recommended by the manufacturer. Also, if the roof is exposed to extreme weather, it might give you some extra protection or increase the lifespan of the membrane.
If you feel you need the extra protection, you might want to consider using peel-and-stick membrane for your bottom layer of underlayment and then cover it with a modified-asphalt or synthetic underlayment. In this approach, the top layer of underlayment does most of the work, but if any water gets through, the membrane provides a secure backup.
Assuming you’ve used durable and non-corrosive flashing materials and installed them properly, you roof should be leak-free for many years.