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Question DetailsAsked on 7/9/2012

What causes ripples/bumps on a recently replaced shingle roof and how does it happen?

I had my shingle roof replaced a couple of weeks ago, using 25-year shingles and 30 lb. felt. One can see clearly lots of ripples/bumps all over the roof, but one section is much worse than the rest. Those ripples/bumps can be pressed down easily which suggests that there is space between the shingle and decking, i.e., shingles are not properly supported by the decking where there are ripples. The contractor insisted that it is upto code and it is caused by the framing and the felt (30 lb.). But the explanation makes no good sense since it would imply that the bumps should be firm, i.e., cant be pressed down. So what is the cause and how this could happen?

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14 Answers

Voted Best Answer

Sounds like wet felt to me. What process did the roofers use when replacing the roof? Did they tear it off and felt it in on day one and then shingle it on day two? This method is frowned upon with organic felt paper because it leaves the felt exposed to morning dew. Moisture such as dew will cause the felt to wrinkle. Or if the roofers got caught in a rain and didn't protect the felt from the rain but kept on shingling this can also happen.

The wrinkles will lay down flat if allowed to dry before first installing the shingles. However this is a waste of time. This is why I live by two 1 rule, never tear off more than you can put back in the same day, and if by some chance you opened more than you can shingle, tarp it. Felt is not water tight.

I really am only speculating. Without seeing it I really can't give an accurate answer.

There are a few other possible reasons, and framing (actually sheathing) is another possible reason. If the plywood is fastened improperly or if the plywood was installed without a gap between the boards for expansion and contraction, ripples can also occur. The difference is you will see the ripples spaced very evenly 4' or 8' to match the spacing of the plywood. If it is the case of improper fastening of the plywood, meaning the fasteners missed the framing so nothing is holding the plywood and it warps, you could easily depress the warped plywood with your foot. If the plywood actually buckled due to lack of expansion gap, you would not easily be able to depress with your foot. If the roofer didn't install the plywood, it wouldn't really be his fault, though if he or his crew saw it when working and didn't fix it then they probably should have. But I am not going to play the blame game unless I know exactly what the cause is.

A storm ripped through the area two years ago. The storm chasers use the cheapest possible shingles, and I am seeing something I haven't seen before. I am only guessing but what it looks like to me is like the shingles are expanding too much and causing the ripple effect I mentioned above in regards to plywood and the lack of expansion gap. The difference is there is no expansion gap required with shingles. This affect is something I never saw before and is only related to one cheap commodity dog house shingle which alot of cheapo roofers like to use. I've been roofing 14 years and this year is the first time I have been seeing this particular problem. It seems to come and go, which also tells me expansion is some how involved. I don't think you'd be able to depress it with your foot, though I've never tried.

Can you post some pictures?


Answered 8 years ago by ReliableAmericanRoof


Fyi If you shingle when it is close to freezing and dont leave a gap you can get a wave from the expansion and you dont need cheap shingles to get it, Have seen it with a Presidential Shingle on my own home, OUCH.

We are assuming you did complete tear off and nothing was left on the decking. My non roofer best guess expansion.

Jim Casper

Gutter Cover & Gutter Contractor

Ps If it is expansion bet only solution is remove and replace but only negative to the waving is shortened life


Answered 8 years ago by jccasper


That's a good point. We try not to shingle below 40 though. It's just not worth the risk, but a topic for another discussion. We'll talk about it in a few months I'm sure!

Answered 8 years ago by ReliableAmericanRoof


Many thanks for the replies. I would to clarify a few things.

1. First of all, all agree that theinstallation of a roof with ripples/bumps is defective.
2. This will shorten roof's life. Are there any other negative impacts?
3. The entire roof work was done within one hot-day (sunny and above 90 degrees).
4. I am pretty sure the decking was properly installed (properly fastened with proper gaps, etc.).
5. The contractor insisted that the improper use of 30 lb. felt on 25-year shinlges caused the ripples. He said 25-year shinlges should go with 15 lb. felt. Is he correct?

I would appreciate if you could pose moe answers to clarify each point. Most of all, Based on what I said above, what are the real possible causes?

Answered 8 years ago by deepsouth


1. First of all, all agree that theinstallation of a roof with ripples/bumps is defective. Yep, something is wrong.
2. This will shorten roof's life. Are there any other negative impacts? If the shingles are lifted too much preventing them for sealing or creating a space for wind to blow beneath you risk wind driven rain and or shingle uplift.
3. The entire roof work was done within one hot-day (sunny and above 90 degrees).
4. I am pretty sure the decking was properly installed (properly fastened with proper gaps, etc.). How can you be so sure? Have you inspected your attic space to see if the plywood is warped, if the nails holding the plywood are missing the rafters? Can you see if H clips were used or if gaps are present between the boards? Inspect your attic before you are really sure.
5. The contractor insisted that the improper use of 30 lb. felt on 25-year shinlges caused the ripples. He said 25-year shinlges should go with 15 lb. felt. Is he correct? What a complete load of MANURE, if you ask me. "Improper" how? I have been roofing since 1998. From 2001-2010 I used ONLY 30# felt beneath my sloped roofing sytems. Last year I began promoting the fiberglass reinforced felt paper in order that I may bundle the upgraded shingle warrantys. I have installed hundreds of 3-tab shingles, all with 30 Lb. felt, and never had this problem.

I have seen specifications from roof consutlants, architects and engineers all specifying 30 Lb to be used in conjunction with asphalt shingles. 15 lb. is minimum, that doesn't mean 30 Lb will create roof defects or void warranties. Contact the shingle manufacturer, and ask their stance on the use of 30 Lb. Also who proposed 30 Lb, him or did you request it?

I would appreciate if you could pose moe answers to clarify each point. Most of all, Based on what I said above, what are the real possible causes? If moisture is not possible, then it leads me to belive that the sheathing may be improperly fastened. Or perhaps the felt was installed loosely.

Or perhaps the felt was wet left outside overnight in a rain perhaps and they installed it before it had a chance to dry out?

I still would like to see some pics.


Answered 8 years ago by ReliableAmericanRoof


Many thanks again for your prompt reply.

They took everything off with the bare decking left. I was on the roof and visualized the smooth decking with H-clips, no warps, nor big gaps. But cant be sure if there are any nails missing.

I requested 30 lb. felt. The contractor wanted to use 15 lb.

The contractor picked the fresh felt and shingles in the morning from Home-depot or Lowes right after they tore down the old roof.

Since you mentioned serious risks of wind driven rain and or shingle uplift, I think I better ask they redo the entire roof? What are my options and how should I handle this to make the contractor do this?

P.S. I will try to see if I can take some good pictures to show you.

Answered 8 years ago by deepsouth


hi tom from universal construction verona ohio. the good and bads about #15 and #30 felt is#30 felt tends to have more asphult. this on hot days will bond to wood decking and help to presurve wood. also#30 provides safty for roofers travling around on roof during construction. if an area of roof cant be shingled in #30 when nailed rite will take long term exposure to rain snow wind.when #30 felt is installed in cool morning it doesnt lay very flat.felt expands when it is cold.if shingles were installed over cold expanded#30felt you would see bumps all over the roof..#15 felt has none of these good or bad other cause for these bumps could be that the roofernailed the shingles wrong.when nailing a shingls you start nailing at the end butted to the last shingle laid and nail across shingle working felt bumps out from under shingles. if shingles are nailed backwards it will trap exsess felt and shingle between nails creating bumps.if bumps were traped in when shingles were fully contracted bumps will get larger when expanision acures

Answered 8 years ago by construction1


Contractor1 and ReliableAmericanRoof pretty much covered it. If you are talking gentle waves "travelling" sideways across the roof spaced the same as the roof joists (high spots over the joists, low point in the wave between) then the problem is sheathing that has gotten wet and deformed, pieces only one joist wide (no pieces should be less than 2 joists coverage), or possibly excessively thin sheathing - i.e 1/4 inch or 3/8 inch (yes, I have seen builders try this) versus what code requires in your area which could be from 15/32 to 3/4 inch thick. However, if this is the problem than the existing roof would have shown the same waves - it would be god for your case if you had recent photos of the roof proving this was not the case.

As Contractor1 said, ripples, like on a pond, can be due to improper stapling or nailing direction (always staple felt and nail shingles moving forward, i.e. in the direction you are laying).

The most common reason I have seen is rolling out wet felt or letting it get wet from rain or dew and not drying fully before shingling over it. When felt gets wet it swells quite a bit, so if it has been stapled and then gets wet it will ripple and sometimes even form folds.

The same effect can happen if the rolls of felt were stacked on their sides (particularly for a long time or in the sun) rather than upright, causing the rolls to become oblong rather than round. Then when they roll them out on the roof, if they do not stretch the felt or "squeegee" it out with a broom or roller, the loosely rolled felt will have "waves" in it - varying in spacing from maybe about 18 inches or so for the part that came off a full roll down to just 6 inches or so for the tail end of the roll. This is pretty common, particularly at box stores - most lumber yards know to stack the rolls on end, but a lot of box stores receive the rolls on their sides stacked 6-10 high on a tightly banded pallet, and leave it that way untill sold, so the rolls come out looking like an elephant walked over them.

Rolling out very cold felt and not "running it out", meaning brooming or rolling it forward to stretch it out as you staple it down can also result in ripples when the cold felt expands as it heats up. (It expands, not contracts with heat). This is not anywhere as common as wet felt or oblong roll ripples.

One other possible source would be cheating on the nail pattern - three tab shingles need 4 or 6 nails per shingle (depends on shingle manufactuer warranty requirement, and on dsign wind speed for the area). A shoddy installer will just pop a nail near each end - saves a LOT of money for the contractor in nails and labor cost. However, shingles will bulge up and tear off easier in the wind, and when they heat up can bulge up in the center. This would create a pettern of little ripples with each shingle bulging up (at least in the sun), rather than large waves. Spot checking the nailing would prove or eliminate this cause.

The end result,unless it is caused by sheathing problems, is you have a problem of defective workmanship. The ripples will provide spots for the wind to get under and teat shingles off easier, make it easier for any ice damming or wind blown rain to get up under the shingles, and make them MUCH more susceptible to cracking due to sunn exposure and to any walking on them. I hate to say it, but this job should be torn off and redone from scratch. The materials hsould NOT be reused, partly because they are now damaged, and also because shingles are almost impossible to remove without damaging them, and they will have holes in them from the original nailing.

If he does not agree to do the repair AT NO ADDITIONAL CHARGE, you may end up having to make a claim against his bond company, see if the city/state will threaten his license if he does not redo the job right, or sue the contractor. Now is the time to get GOOD documentation with camera and a written and photographic report by a qualified building inspector or architect. Your local government may have a building inspector who can document it also, and write up the job as failing to meet code, and therefore having to be redone. I would start with this route if the contractor does not agree to fix it up front.

Answered 7 years ago by LCD


WOW! First I will say that shingles normally will look a little lumpy when first installed but with in a couple of 70 degree days they should lay flat! 2nd your stating that they are not properly supported by the decking. What type of decking do you have? Plywood or Planking. I have come across several older homes that have planking. Most of the time they are improperly spaced which allows for unsupported shingles to sink into the gaps. International Building Code no more then 1/8 th of an inch gap is allowed on roof deck. So when we come across these roof we will suggest 1/4" plywood on top of the exsisting decking with a penny nail seperating them at the unions to allow for expansion and contraction. Then we install the rest of the roofing system. Some roofers like to use 30lb felt because it's thicker and should support the shingle but this is not the right way to do it. Also if the felt got wet it would ripple causing lumps which would allow for a void under the shingle as well. All I can say is either way it sounds like your new roof needs to be replaced. I hope you didn't pay the roof infull. Best of Luck - Richard Jeziorski -

Answered 7 years ago by LibertyRoofing


Not to rub salt in a wound, but if you are inclined to do so, this was a pretty well followed case and I am sure that like me the other contributors to the thread would like to hear the outcome, especially if the cause of the ripples/bumps was definitively determined during tearoff.

Thank You, and hope it all came out OK for you in the end result.

Answered 6 years ago by LCD


There are several reasons for this to occure. Was the new roofing applied over an existing shingle? Ther can also be a venilation in the attic area. these are two of the most likely causes.

Answered 6 years ago by sethbonilla


I had found this myself in both roll roofing and regular strip type shingles and in those cases it was too much moisture/humidity in the manufacturers factory in Walpole ,MA. This company is now out of business but had a very good product.

Moisture can get trapped in the felt during its' making and will appear fine until it's installed. & then the heat causes the water to boil or expand to escape. The real problem is the granules will erode off the base faster and once the bumps are hard they will break whenever stepped on.

During the last 10-15 years I did roofing in the Northeast I always used ice & water shield on the lower 3 or 6 feet but never felt on any roof with a pitch of 7 or more. All these roofs never had leaks until they were 20 years or older. Many times felts best job was to keep the property dry overnight or during stormy weather.

Most were Bird or GAF 15 year shingles.

The roofing I did was primarily between 1969 and 1995.

Answered 6 years ago by Guest_9821307


Many times until there has been some hot weather the shingles have not sealed down good. Temperature changes mainly cold weather will make them raise slightly giving them this look. Usually a summer season solves this issue.

Answered 6 years ago by jhenderson


I have the same problem, they took all the shingles off, replaced 32 sheets of plywood, then all new GAF shingles. when summer time hit, the summer came,and the roof rippled EVERYWHERE there was new plywood. NO one could beleive how bad the roof rippled. they went into the attic, and found ALL the new plywood sheets dripping ,literlally with water or some thing. When the weather cooled, the shingles started to lay flat, (NOT SO FAST) when the weather cooled the ripples came back. I went outside today, Christmas 2014, and guess what , THEY ARE BACK. I'm looking for an answer also! anybody got any idea's? Ken

Source: Ken Colletta, missouri phone 314 5784502

Answered 5 years ago by kpcolletta


3 weeks ago we had a new roof installed. We are now seeing ripples particularly on the West side. A representation of the company came by. Climbed on the roof. He said the felt was laid with wrinkles. Next week they plan to take the shingles off, cut the felt to flatten it then relay the shingles. We paid over $17,000 for this new roof with a reputable roofer even recommended by our insurance company.

Does this sound right? Will this work and will we still have the quality roof that we paid for. Should we ask them to completely relay the West side of the roof?

Answered 4 years ago by SandyR

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