Home & Garden Columns

About the House: What to Look For When Replacing a Roof By Matt Cantor

Friday February 24, 2006

Dear Matt Cantor, 

Your information has been so helpful that I’ve have a question for you. I have to get a new roof on my four-bedroom, two-story, step-roofed house. The old roof has to be completely taken off. What should I look for in the roofers’ estimates? 

Thanks so much. 

—Nancy Ward 


Dear Nancy, 

Can you tell me a little about your roof, including approximate slope, type of roofing you currently have, the approximate age of the house and anything else you thing is relevant (where it has leaked, etc.). 



Dear Matt, 

My house is 79 years old. I can’t tell you the approximate slope but the upper part is very steep. It’s all composition shingles and has had partial roofing done many times but it hasn’t had a complete reroofing in the 40 years I’ve been here. I believe that parts of it have four layers. The part that leaked was on a part that was not the steepest. That has been repaired. 




O.K., here goes. 

There are lots of issues so take notes. The first thing is that four layers is too much. Roofing weighs a lot. There are a few of you out there who have surely helped install a roof and may recall climbing that ladder over and over again with bundles of shingles that seemed to weigh 40 pounds a piece. If you multiply that by 60 or so bundles on a roof (about 33 square feet to the bundle) and then times four layers (give or take some for varying material), you get a huge amount of weight. 

If you’ve ever been in an attic, you’ll note that the framing is often quite delicate. Roof framing has gotten beefier in the last 60 years or so but much of our housing stock has roof framing that uses 2x4’s laid out at wide spacing with very long spans. In short, far wider than we would ever allow for a floor. 

The presumption was that the roofing material was going to be the only weight and that high winds, snow or multiple layers never happened. The reality is that these things all happen and one thing more that we all need to be very much aware of: earthquakes. 

Earthquake forces interplay with heavy, weak or multi-layer roofs in interesting ways. First we need to remember that when earthquakes occur, it’s the earth moving, not the house. Actually, that’s the problem, if the house moved easily with the earth, it would do well. It’s the dissonance or struggle that’s the problem. 

The less flexible the house or the heavier the house, the more resistance there is to moving easily with the earthquake. Take a house and load the very top with a huge amount of excess weight and what happens? It has more inertia, more resistance to moving with the earth. So the bottom moves rapidly and the top is dragging behind and what this does is tear up or “shear” the section in the middle. This may be the walls, the “cripple” walls below the floor or the roof framing itself. 

So having less roof weight, fewer layers for example, is one way to decrease damage to the house during an earthquake. Therefore, when you replace your roof, take everything off except for the framing itself. 

In fact, I even recommend removal of the “skip” sheathing that is used to hold the original wooden shingles to the framing prior to installing plywood. You might have these skip sheathing boards and if you do remove them, you’ll end up with a better connection between the plywood sheathing and the framing. Plywood can actually increase the cohesion of an old roof framing if it’s well nailed and decrease damage in an earthquake. 

When you’re replacing your roof, be sure to replace all of the “flashings.” These are mostly metal components and are designed to prevent leakage between surfaces of different shapes or orientations. Some are used where pipes or chimneys penetrate a surface. Some are used in valleys where two surfaces coincide. Some are also used at edges to prevent water from reaching the edge of the sheathing material. These are cheap to install when you’re doing a complete roofing job there’s no good reason to short change this portion of the roofing job. 

If you have joints between a wall and a roofing surface, it’s wise to install wall-to-roof flashings here and make sure they ascend the wall behind the wall finish (shingle, stucco or what-have-you) at least a few inches. This often means removal and replacement of some of this surface. Leave a gap at the bottom so that splashing or wind-driven water can’t get under the siding edge. A couple of inches is best. 

You mentioned that you were thinking about replacing a “part” of your roof. It’s really best to do the whole roof at the same time if you are financially able. Now, sometimes I’ll see one part of the roof that’s just fine and I’ll know that there are viable methods to integrate one part into another but roofs, in general, are not like skin. They don’t heal and the joints between portions are vulnerable to leakage. 

A good roofer, under the right circumstances may be able to replace a portion of a roof and give reasonable assurances that the interconnect won’t leak but as a rule, it’s best to replace all of the roof at once because of the methodology of roofing. 

Roofs are made up, generally, of multiple layers from the wood decking, through underlayments and flashings through finished layers. These tend to be installed in a process that involves “stepping” up the incline and overlaying all the preceding vulnerabilities. 

When you cut through this or try to replace one part, you violate the protocol that does so much to keep things dry. This is one of the reasons that skylights often leak. They are often added after the fact and the joints around them don’t integrate into the roofing system adequately. So think about doing the whole thing if you can manage it. 

Lastly, consider the right material for the job. If you have steeply sloped portions, almost any roofing type will work and composition shingle is a good choice for low cost and good longevity. Although this kind of roof can be used on relatively shallow slopes as well, it is less reliable and I recommend switching to something like a “modified bitumen” roof for lower slopes and what we call “flat” roofs. 

Built-up roofs, like “tar and gravel,” can work but have shorter lives and are harder to fix. Also, I find that many of the installers of tar and gravel don’t pay close enough attention to the details.  

Choose a roofer who seems smart. One who can write a contract and speak intelligently about the way the roof will be done. Ask lots of questions and don’t pick the cheapest guy. The best person is almost never the cheapest, although they might not be the most expensive. 

If you can replace the gutters and downspouts at the same time, that’s worthwhile as well.  

One more thing to add to your list of things to think about when you’re roofing is to add or subtract anything that penetrates the roof at the time of the roofing. 

If you have an unused chimney flue (from the 1910 coal burner or stove), consider taking it down below the roof line prior to reroofing. Remove any other flues or vents that are no longer in use. If the bath fan vents to the attic, run it through the roof during the job. This is also the best to time to add a skylight, attic ventilation or a vent opening for the bath fan you’ll add next year. 

Talk to your neighbors in advance about the noise and mess. They’ll be less upset when things go wrong and ask the roofer to keep things clean (including the attic).  

I hope these thoughts will help you and your roofer produce a better product and avoid some of the potential dilemmas. 



Got a question about home repairs and inspections? Send them to Matt Cantor, in care of East Bay Real Estate, at realestate@berkeleydailyplanet.com.ª