The Facts on Roofing Construction

Factual Questions
1

Home Depot gave me a high-ball estimate for a new roof including removal of the old roof. The old roof is only one layer, and in relatively good condition. The current roof does not leak, and the shingles are not buckling. However, several shingles have blown off and the consensus (home inspector, etc.) agrees the roof is about that age for replacing. And, there are a modest amount of nail pops present. Does this constitute throwing out the baby with the bathwater?

Home Depot wants to remove the old roof to have control over every piece of the project so they can give me a 10 yr warranty on their craftsmanship (plus 30 years on the GAF shingles - prorated after 10 years). Oh, and cut in a roof vent across the peak. This all sounds so extreme to me.

People say you can lay a new roof over one layer of old roof, but what is NOT being said here? If this is true, there must be some qualifiers to that statement. Personally, I feel this roof does not warrant removal, but what about the nail pops? Is there some “margin” when laying a new roof to account for such little imperfections, or can they hammer down the nail pops? And, will the old shingles buckle from heat once trapped under the new layer, or is this a scare tactic?

In short, what criteria make it possible to lay a new roof over the old? What are the rules of thumbs and pitfalls about a new roof, in general…especially if I keep the old…will it come back to bite me in the butt during the lifetime of the new roof?

  • Jinx :confused:
2

Funny you should ask. I just had the house reroofed. No roofer would give me an adequate guarantee on either workmanship or shingle life on a roof installed over the old one. Ask several other roofers for estimates and guarantees both ways.

3

I’m not a roofer, but am friends with a few. I also replaced the roof on our previous house by myself.

First of all, it is my opinion that there’s nothing wrong with adding a new layer of shingles over an existing layer provided the latter meets certain “qualifications.” These would include:

The existing layer must have been installed correctly to begin with.
The existing layer must be in relatively good shape.
The existing layer should be relatively “flat” (corners are not too badly curled, etc.).
The existing layer must not leak.
The existing layer must have tarpaper under it. (This is almost always true.)

Now having said that, if the new shingles’ warranty specifies that they cannot be installed over existing shingles, then you have no choice; you’ll have to tear off the existing layer. But I would verify this firsthand, and not go by the word of the roofer.

4

Twenty-five years ago, the rule of thumb was that you could put two additional layers on–three total–before you should remove them and start over. There’s probably no reason that things should be different now. Remember to use longer nails. :slight_smile:

5

Sure there is a reason. It’s called a “building code”.

In my locality it’s illegal to put more than two layers on. (I live in Iowa…where it DOES add snow weight, maybe the south is different?

6

Jinx Where do you live? As in what geographic area. Second, How long are you planning on living there? If less than 5 years, you have a few options. If more then 10 you options change slightly.

Personally, I’d go with the lowest bidder for the roof replacement, but then again my roof has slate tiles which I am not too worried is going to go anytime soon.

Anyway, check building codes, check with other roofers, and go with what feels best. I like the idea of another layer. I soo no reason besides the afor mentioned building codes, not to go another layer.
Home Depot in my experience always has a fair however, high, bid on jobs.

7

I’d say get more opinions. We had our roof (17 yrs old) done last year and they put the new over the old. Ask around your area and see who the good roofers are- in my area every single person I asked had the same reply- so that’s who I went with. If you’re going to be in the house for a while, find a roofer that’s been around for a while.

8

Why are you using Home Depot? Does it employ fulltime roofers? I would guess not. It’s probably a middleman, and it simply maintains has a list of local roofers that do work for it. If this is the case, you should understand that this arrangement is not a guarantee the roofers will do a good job. In fact, I would predict the opposite. (This is often done in the carpet laying industry, where a big national retailer will sub-out jobs to low-bidding, no-name carpet layers. We got burned by one of these outfits. Never again. The next time we buy carpet we will deal directly with an independent company that employs its own fulltime carpet layers.)

Why not approach a reputable, independent roofing company that employs their own fulltime roofers? You’ll probably get a better product, and maybe even a better price. Plus you’ll be dealing directly with the company instead of a middleman. Just be sure to verify they’re insured, licensed, and bonded. Also check with the BBB.

9

A suggestion: Whatever you decide to do, ask for a quote to ‘hand tab’ the shingles when they are installed. Roofers don’t like to do this because it takes more time, but you will have fewer problems with the wind.

10

Ditto that. You may even wish to walk around your neighboorhood to find recent roof jobs (or jobs in progress) to see if you can find recommendations from home owners.

11

For a second there, I thought you wrote “…it’s illegal to put more than two lawyers on…” :slight_smile:

  • Jinx
12

Right you are. This page says that Oregon went from 3 to 2 on April 1, 2003. It may be a nationwide trend.

13

I’ve roofed quite a few houses over the past 5-6 summers so I don’t have any professional knowledge, but I have a little bit of experience with roofing. First off I was always taught that a homeowner could put upto 3 layers of shingles on a roof, before all the layers had to be ripped off. If your nails are popping up and shingles have already blown off though, I agree in that you should have the old shingles ripped off and new laid down. Just exactly how many bundles of shingles does Home Depot say it is going to take in order to re - roof your house? If you do decide to go ahead and have them re - roof your house you can save yourself some time and money by ripping off the old shingles yourself. Simply have a dumpster delivered to your house and rip off the old shingles with a flat bar or shingle shovels (shingle shovels are good because they rip out the nails as you go). Just scrape them off and throw them over the side. if you want to save yourself even more money go get yourself some black tar paper and lay it down over the wood, keep it held in place by a fair amount of staples and put some boards over the joints so the wind doesn’t rip them up. I would be a little iffy about buying shingles from a company like home depot; if it was me personally I would buy them from this company: http://www.certainteed.com/. They are excellent shingles with a great warranty. You might have a little trouble finding somewhere around where you live to get the shingles and have them put on for you though. Sorry this is so chopped up and not very fluent, but I have to get back studying for finals. Good Luck.

14

Some decent answers above, but no straight summary. So I’ll try one.

Tear off has to be done sometime. Cost to tear off old roof depends on how many layers there are. So it’s pay them now, or pay them later. So a good part depends on whether you are going to be paying them later or the next owner. That being said:

Cons to leaving on old…
New shingles lay a little rougher and look less professional even if a new layer of tar paper is added.
Generally estimated to have shorter roof life. How much shorter is up for debate.
Less likely that the roofer will redo the flashing properly.
The longer nails hold marginally less well as they have a lot of unsupported length to go through the two layers.
Increased weight (which isn’t much of an issue on a properly designed house.)
Cannot investigate roof sheathing to see if there have been any hidden leaks that rotted the plywood.

Cons to tearing off old…
More money.

On the roofs I’ve done, the premium to tear off old was a small fraction of the total price and did locate rotten sheathing. I would NOT recommend doing your own tear off unless you have your own safety gear or a very low pitch roof. I second the advice to not go with the Home Depot installer. I caution against the advice to take low bid for a reroof. The main field of shingles is easy enough for anyone to do, and anyone often bids on the job. But the hard stuff that the low bidders do wrong (Flashing, valleys, etc) is where you get your money’s worth out of a medium bid.

Get at least 3 bids (with type of shingles specified). You will be amazed at the range of prices.

15

To avoid overinflating my qualifications… make that the roofs that I have HAD done. Much of the info comes from a decent amount of research done before bidding the jobs, general construction knowledge, and watching several jobs done by contractors of several different price ranges.

16

Heat build-up is the greatest enemy of roof shingles, so this is probably not a bad idea, assuming it isn’t going to cost a small fortune. Compare it to the cost of adding a good attic fan, and it might turn out to be a smart move. It’s certainly easier and cheaper to do it as part of a re-roofing job than at any other time (the same is true of putting in an attic fan, of course).

17

Around here you will not find a competent roofer who will roof over old shingles. For one thing, a pemit is needed and an inspector has to look at the sheathing before the new roof goes on. That sort of knocks in the head the plan of not removing the old shingles. As BoringDad said, the cost of tearing them off isn’t too high. If you do it yourself you have to dispose of them which always costs money at the dump these days, inexperienced people regularly fall off roofs, and in the summer time heat exhaustion can be a problem.

Cheap jobs are just that. Look for proper flashing in the valleys, drip edges at the eaves so that water doesn’t run back under the shingles. Make sure that you walk around with the roofer looking for high staples. Most roofers use air-driven staple guns around here and they work fast. There is an occasional misfire that doesn’t quite seat the staple all the way.

18

In addition to the good points already noted, here is my 2¢.

I do a full tearoff to afford the customer full benefit of advances in roofing technology. Among those being: self-adhering rubberized bituminous membrane for the roof perimeter, and in all valleys, areas of abutment (dormers) and other areas of questionable flow (crickets).

I want to see the roof decking, and know that it hasn’t been compromised by a poorly vented bath fan, a leaking plumbing vent, or failed/poorly done flashing.

When the decking is exposed, it is easier to spot depressions owing to a knot in a rafter which has failed, or any other anomaly which spurs deeper investigation. Soft spots owing to delaminated plywood might go unobserved without tearoff.

As noted, some roofing was done with wide crown staplers. I won’t touch them without a tearoff, because they’re a blow-off waiting to happen. Every Authority around here does not recognize wide crown staples owing to their inherent degree of failure.

I use good old-fashioned round head nails with a gun mounted pressure regulator, so as the day gets warmer, I can cut pressure and not overdrive the fastener.

Ridge vents are the way to go, but are not a panacea. Air must have a way of getting in at the soffit point, or installation of a ridge vent constitutes sucking out of a paper bag.

19

New homeowner who needs a new roof checking in with more questions.

First, some background. My house is 84 years old and has three layers of roofing, including the original cedar shingles. The newest layer is asphalt shingles, and I think the middle layer is too. Underneath the shingles, there’s no solid roof decking. It’s just horizontal slats that the shingles are mounted on. So if you removed all the asphalt and cedar shingles, you’d be able to see into the attic.

So onto the questions. First, I gather that this (the slats with shingles on them) is the old way of building a roof, and it’s just not done anymore? Is that correct? Will a new roofer want to put a layer of something down to put the new shingles on? What will that layer be? Does not having this solid decking make the tearoff more expensive (seems more dangerous)? How about the roofing job itself?

What’s the “sheathing” some of you guys are referring to?

Should I worry about ventilation? The current roof is basically a very steep peak (16/12 pitch), 40 feet long, with one large vent at the top of the wall at each end. Do the ventilation requirements change since I’m using a different roofing technology than the original cedar shingles?

I’ve seen brochures for metal shingles that look like traditional shingles (i.e. they don’t make your house look like an industrial building). I like the idea of shingles that won’t rot. Is that ridiculous? I don’t mind paying more if it’s conceivable that the roof could end up being a selling point later. I know – I’ve heard the argument that you don’t get the cost of your roof back in resale value, but if your roof is a significant improvement over traditional ones (i.e. if it’s going to last 50 years), I could see that having a positive impact on resale price. In addition, I really like the idea of living in a house where I don’t expect to ever worry about the roof in my lifetime, even if I’m not going to live there forever. Is this a pipe dream?

From others’ comments here, it sounds like I should ask the following questions when I get estimates:
What kind of fasteners do you use (staples, round-headed nails, etc)?
Do you ‘hand tab’? (can someone elaborate on the meaning/benefit of this?)
Will you put a rubberized membrane around the perimeter?

After the job is done, I want to inspect the flashing and make sure there are no high staples/nails. Any more advice on that? I don’t really know what I’m looking for with respect to the flashing, and I’m not sure if I’m supposed to be able to spot high staples from the ground or what.

One more question: while I’ve got the roof ripped off this sucker, what other jobs might I look at performing while I have the opportunity? I want to put some conduit between the lower side attics and the upper attic, so it’s easier to snake data cables and whatnot, plus replace a lot of knob-and-tube wiring in the attic. Would it be smart to do this while the roof is off, or am I just giving me, the roofer, and the electrician headaches by having too much stuff going on at once? Any other ideas?

Any pointers greatly appreciated.

20

The slats that you are referring to were put in that way to allow the wooden shingles to dry out. Current design is to cover the rafters in a solid layer of plywood. This is the sheathing. When converting from the original wood shingles to asphalt shingles, roofers would often just fill in the gaps between the slats with
more boards. I found that in the hosue I had where this was done, there were many shingle nails that hit the 1/4"gap between boards and so had no holding power. I would recommend a layer of 1/2" playwood over the slats.

The gable end vents (what you have) are not very efficient because they rely on air coming in one end and blowing out the other. Modern ventilation has openings under the eaves and exausts it as high as possible on the roof (ridge vent being preferred) using the “hot air rises” prinicpal. This keeps your attic cooler in summer (lowering cooling costs) and colder in winter (preventing ice dams).

Modern “architectural grade” asphalt shingles have 30 year warrantees and really don’t look too bad. Much better than standard 3 tab flat shingles. And for resale… no, you get nothing out of having an improved roof. Most people buy a house assuming that the roof is good.