Debating the value of an expensive roof
In explaining his decision to use clay tile for his roof (FHB #139, pp. 96-101), David D. Quillin asserts that the wind where he lives can “peel regular asphalt shingles off a roof as if they are paper.” My brothers and I built our parents’ house about 5 miles east of his in 1980. My mother still lives in that house on Fenwick Island, a sliver of land a half-mile wide that separates the Assawoman Bay from the Atlantic Ocean. Contrary to Mr. Quillin’s assertion, the asphalt shingles we used have held fast. In the 21 years since we installed that roof, my mother has fled inland several times as dangerous storms have approached. But she hasn’t lost a shingle; nor has any one of her neighbors.
Mr. Quillin also maintains that the price of his tile roof—$750 per square—“will be a bargain … if the material does last a lifetime.” How long does he expect to live? The materials for a 25-year shingle roof are about $30 per square. If you add $50 per square for installation (a figure that is too high for most asphalt roofs and far too low for a tile roof), the 25-year shingle roof would cost $80 per square as opposed to $800 per square for the tile roof. Because Mr. Quillin’s roof cost 10 times as much as an asphalt roof, his tile roof would have to last 10 times as long—250 years—to begin to be a bargain.
If Mr. Quillin’s 2800-sq. ft. house required about 32 squares of shingles, the cost of his roof would be in the neighborhood of $25,600. Had he used asphalt shingles, it would have been about $2,560. Like many other contributors to FHB, Mr. Quillin attempts to justify the steep price of his handsome roof by denigrating the performance of asphalt shingles. The truth is that asphalt shingles perform extremely well on the Eastern Shore of Maryland, and they are the overwhelming choice of material for builders and homeowners in that area (and just about every other area in the country). Some people, including David Quillin, don’t like the way asphalt shingles look, and they are willing to pay a premium for a more attractive material. That’s fine, but they should just say so.
—John Carroll, Durham, NC
David D. Quillin replies: Mr. Carroll states that he built his mother’s home in the same area as my home 21 years ago and that the roof has withstood the forces of nature just fine. I don’t dispute this fact, but I would point out that this area has had no severe northeasters or hurricanes in that time period. Although the mid-Atlantic area historically was hit by a severe hurricane every ten years or so, we have gone nearly 40 years now without a direct hit. This does not mean the big storms aren’t coming, and when they do come, the flimsier, lighter materials currently popular will come in for re-evaluation.
Second, Mr. Carroll states that the shingles that I used will be a bargain only if I live to be 250 years old. Well, maybe I’m planning on it. Actually, the numbers he uses to make that argument are a little high, but not too far off. I would respond in two ways. First, if a hurricane rips off the roof of his mother’s house, it would be difficult to see what kind of a bargain he considered the asphalt shingles. Second, part of the value of the clay shingles that I used is not just their own structural integrity but also the strength that they add to the entire house as part of an overall strategy of weighting the house down to resist wind uplift.
Finally, Mr. Carroll says that I am using the shingles because they are attractive, and I ought just to say so. I did say so, quite clearly, in the article. I was looking for a shingle to satisfy a number of requirements, top of the list being attractiveness. Also on the list was structural soundness in the face of hurricane-force winds.
I think that asphalt shingles are a good choice for roofing in many situations, and I have specified them on several projects that I have worked on. Their chief virtue is their low cost. I do not think that they are especially attractive, and I doubt many people would use them if they were not so inexpensive. What I like the least about asphalt shingles is that they are not especially durable (40-year and 50-year warranties notwithstanding), and so consequently they become just another “disposable” consumer item that will be taking up space in landfills.
For now, homeowners don’t have many choices when looking for affordable roofing materials, so asphalt shingles play a significant role in the housing market. That doesn’t mean that we should consider them ideal and be blind to their limitations.
About the pressure at the bottom of a dam
Congratulations on your most excellent June/July 2001 issue. I especially enjoyed the article “A Stair in the Air” (FHB #140, pp. 70-73). Although I might occasionally lapse into this degree of compulsive infatuation with an idea, I wouldn’t have tackled this one. A stair this open would guarantee that my wife would never again visit the second floor.
In “Hang Ten” (“Great Moments in Building History,” p. 146), Paul E. Mitchell notes “… I wish I had remembered a basic physics principle I learned in college: The pressure at the bottom of a dam is proportional to the height of the dam squared.” Sorry, Paul. The pressure is proportional to the height, not the height squared. What college was that?
—Larry Sher, Naples, NY
Precautions for heavy snow
After 17 years in Tahoe, I finally had enough snow shoveling, blowing and plowing to fill my memory bank with a whiteout; I moved to a snowless part of California. Ed Trembly’s plowing ideas (FHB #139, “Commentary,” pp. 16, 18) are a good primer for medium snowfall areas. Big—I mean huge, deep and dangerous—snowfalls are a whole different story. The drawing of the New England house and garage is cute, but illegal to build in a heavy-snow area. The snow discharge from the garage roof could easily total the car and its passengers. The drop distance from the second story of the house to the front door would also kill someone entering or leaving the house. Typical snow-load designs for the Tahoe area are 185 lb. to 220 lb. per sq. ft. Many winters, the actual load has been double that. Structures collapse from the weight of the snow and ice. Pets and people are hit, trapped or killed by the “white death.” Chimneys, vent pipes, crickets, antennas, decks and rails are wiped off houses. Windows will be blocked for an entire winter, and the weight on the house may compress walls so that sliders or hinged doors won’t move until spring.
A completely different thought process is needed if you build in heavy-snow country. Outside: Do all the items that Ed suggested, and place high snow poles near fences, curbs and valued plants. When there is 4 ft. to 6 ft. or more snow from a single storm, the snow-plow driver can’t see what is there, so don’t use PVC snow poles that are the same color as the snow. Valuable shrubs and trees should be kept away from the discharge zone because they will be smashed by thousands of pounds of crashing snow and ice. Think of the snow’s discharge path, and place garage doors at the gable end of the garage so that you won’t get trapped in or out of the garage. The same is true for exterior doors; they should be at a gable end or have a well-engineered cricket over the door.
If a roof discharges its snow load onto a deck, then it will have to be designed to hold the original deck’s snow load in addition to the discharged roof load.
Add in wind (drifting snow), the sun (melting the snow unevenly from one side of the house to the other), earthquakes (with a huge weight on the roof), and you better find a good local engineer and architect who are familiar with snow problems.
—Ken Menzer, Auburn, CA
Senco’s nail gun works well on cement siding
I appreciated John La Torre’s timely article “Working With Fiber-Cement Siding” (FHB #140, pp. 104-109), but I wanted to add a comment about nailing. I have used the Senco nail gun (SN 65) quite a bit on cement siding, and this gun makes it easy to set the nail depth so that nails drive in just right (flush) every time that you pull the trigger.
The nailing system on this nail gun has what Senco calls a “restrictive trigger.” What this means is that it is a single shot and not a bounce gun. To fire it, you depress the nosepiece and then pull the trigger. It fires one nail and won’t fire again until you repeat the operation. A different trigger can be installed that allows you to use this gun as a bounce nailer. I hear that Senco’s latest version has a microchip that allows you to bounce or single-shot nail without changing triggers.
—Larry Haun, Coos Bay, OR
The housewrap debate continues
I’m glad to see that Joseph Lstiburek isn’t willing to knuckle under to the spin doctor from DuPont (FHB #140, “Letters,” p. 6). The way I see it, building paper is for waterproofing. I use 15-lb. tar paper and double it on the corners. I don’t really worry about air infiltration through the walls. We always use full plywood sheathing, and I have yet to blow air through a piece of plywood.
And how does Tyvek seal the nail holes? Tar paper leaves a residue on the nail as it passes through that helps to seal the paper to the shank of the nail.
I haven’t had a callback for a sidewall leak in my 25 years of building, and I won’t switch to a more expensive product that is of dubious value to my clients.
— Kurt Housh, via e-mail
Joseph Lstiburek, in his letter (FHB #140, p. 6), disputes the effectiveness of Tyvek for reducing air infiltration. Although Lstiburek demonstrates that he does understand the principles of air leakage and has successfully built tighter houses, his letter demonstrates nothing about the effectiveness or lack of effectiveness of Tyvek.
The only way to do a proper controlled study of the effectiveness of Tyvek is in the manner described by Todd Apple of DuPont Tyvek Weatherization Systems in the same FHB issue. The study described by Apple employed two identical houses built in the same climate, tested in identical manners, one using Tyvek, the other not. The results of such a study are based on sound, scientific procedure.
All that Lstiburek can honestly say is that he is able to reach a certain standard of air tightness without using Tyvek housewrap. Good for him.
—Tim Murphy, Canmore, AB, Canada
Don’t rely on toenails at the rafter-to-plate connection
Mike Guertin’s response to the question from Jake O’Brien (FHB #140, “Q&A,” p. 20) on how to resist rafter thrust when the joists are perpendicular to the rafters contains at least one pitfall. He suggests building a diaphragm floor in the attic to take the tension forces induced by the rafter thrust. Although there is plenty of tension-resisting capacity in such a floor system, a weak point in this scheme could be the connection between the rafter and the plate.
Scaling your drawing (for the sake of argument), a building of about 19 ft. in width with hemlock-fir rafters 24 in. o. c. at a 12-in-12 pitch under a snow load of, say, 40 psf will develop a horizontal rafter thrust of something like 530 lb. at each rafter tail. If the carpenter uses 16d nails and toenails the seat cut of the rafter into the plate (and every nail is perfectly placed), each fastener can carry only about 70 lb. of load. At least eight nails would be needed to resist the calculated thrust. It is unlikely that such a nailed connection could be made without splitting the seat of the rafter.
It would probably be better to engineer some kind of steel-strap connection between the rafter and the floor diaphragm to resist the thrust.
—Carl Mezoff, Stamford, CT
Basement drains breed mold
Thank you for the great article by Larry Janesky, “Keeping a Basement Dry” (FHB #140, pp. 64-69). I would like to add a caution, however.
The one drawback to the interior-drainage correction practiced by many contractors is the wall/footing joint drainage flashing. Several types of plastic cove flashing are available and used with interior drain-tile replacement. Some contractors use a piece of cedar beveled siding to keep a space at the wall and then remove the siding after finishing the cement.
Concrete-block walls have holes drilled into each core at the top of the footing to allow water to leak out and down to the interior-drain tile. If the floor is not removed in cases where there are no drain tiles, a plastic cove base is glued to the floor to capture water seepage and conduct it to a new sump pit installed by the contractor.
Here’s the caution: These coves are breeding ground for mold and bacteria. People with asthma or other sensitivities to airborn allergens often have to leave the house due to the toxic reaction they experience when the spores circulate in the air in the house. The blower in the furnace or air conditioner picks up the irritant and distributes it throughout the house.
I am working with a microbiologist on several cases where the occupants of existing homes and new homes have been hospitalized for serious seizures, blackouts or swelling of the extremities.
Some of the problems originated with mold from the base cove flashing after the interior-drain tiles were replaced and others from charred wood left after fire-damage repairs. One house had a furnace installation where the filter could not be removed, and after two years, the mold and yeast buildup on the filter caused severe toxic reactions to the homeowner.
In conclusion, the cove joint flashing should not be open to the basement. The concrete should seal to the wall over the top of the flashing, or the flashing should be flush with the top of the floor and the joint sealed with a polyurethane caulk.
—Donald V. Cohen, P. E., building consultant, Thiensville, WI
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