Soffit and ridge vent combo provides best ventilation

Q. We live in the Chicago suburbs and are in need of a new roof. Our contractor recommended Owens Corning TruDefinition Duration Shingles and ridge vents. We also heard about DaVinci slate roofs and would like to know what you think about them, as well as what type of ventilation is best. I value your opinion and have trusted your advice in the past.

A. Sorry, I have no knowledge or experience with DaVinci tiles.

The best passive ventilation system consists of continuous soffit and ridge vents combined with an unobstructed air space between them of at least 1½ inches on most roofs. On long rafters and low-slope roofs, the clear space should be increased to a minimum of 2 inches.

The soffit vents should have a net free ventilation area, or NFVA, equal or greater than the NFVA of the ridge vent.

Passive ventilation is accomplished by thermal flow: warm air rises. The flow of air through the ridge vent is augmented if the ridge vent is externally baffled, such as in the Shinglevent II (www.airvent.com). An externally baffled ridge vent deflects the wind over the vent, thus increasing its exhaust - Bernoulli's principle. Otherwise, wind can stop the exhaust and even inject rain and snow into the attic.

Q. We have a hairline crack across our front stoop that makes our front porch look shabby. It has been there since the house was built seven years ago. Our builder said he doesn't repair any cracks that small. We thought of having the stoop tiled, but it was too expensive. Also we live in the north and didn't think it would hold up. Do you have any suggestions as to what we might do that would make the crack disappear and also be economical?

A. Hairline cracks are very hard to eliminate, and any attempt is likely to make the stoop look worse. A cement slurry can be washed into the crack, but it is probably going to be prominent, as the color will be hard to match.

If you decide to try it, and if the results are not satisfactory, you may want to apply a stain to the concrete. If you choose this plan, and the concrete surface is very hard-troweled, the concrete may need to be slightly etched to allow the stain to penetrate. If the concrete has a broom finish, all it should need is a thorough cleaning.

Painting the stoop is another option, which I seldom recommend because paint may start peeling from the concrete over time. The best paint to use on an exposed slab, after a thorough cleaning, is epoxy.

Q. The back of our house faces south. For some reason, the wood of the eaves - both the edge and the wood underneath - rots and appears moldy. This does not happen to the front of the house, which really doesn't get much sun on it. The back side of the roof also melts snow quickly and icicles frequently hang from the back.

We have both a ridge vent and soffit vents along with gable vents on either side of the house. We do have rolled fiberglass insulation, and there is a pull-down staircase. The center of the attic from end to end has plywood, which we use for storage. There is an insulated attic tent over the staircase when it is closed. The ridge vent was added by the roofer when our roof was replaced about 10 years ago. I have attached two pictures of the issue.

Do you have any suggestions for how to repair the existing damage and how to prevent it from recurring? Our house is a raised ranch and was built in 1968.

A. The photos you sent clearly indicate you have had ice dams at the eaves of the back side of your house. The continuing melting of the snow backed up into the wide overhangs over a number of years.

If you haven't noticed leakage inside your house at the window heads, it is because of these wide overhangs.

Since you haven't encountered the same problem on the front of the house, it sounds as if the snow melting is sun-induced, and not because of a warm attic - a positive situation for you.

When the roofer installed a ridge vent, the gable vents should have been closed up in order not to impede the airflow from soffit vents to ridge vent. You should do this now by fastening plywood painted matte black over the gable vents.

It also seems as if the roofer did not install a protective membrane to guard against the leakage you have been experiencing all these years. Such a membrane should have been put on bare sheathing from the edge of the roof and at least 6 feet up the roof since you have such a wide overhang. This should be done now to prevent further damage and before the fascia and the plywood soffit are replaced.

Q. Thank you for your column, where I always learn something or find out about a useful product.

We have a lovely, stone-tiled, walk-in shower; it has a pebble stone floor. Our problem is the caulk line where the wall meets the shower floor. Is there any caulk that will not mold or mildew? We run the exhaust fan and use Lysol spray on the shower floor. We still get deteriorated caulk with mold and mildew. The shower is 4 years old, and we have replaced the caulk once so far. Before we do it again, we'd like to know if there is a better product to use.

A. I have tried a number of caulking products over the years and have yet to find the perfect one for tubs and showers.

Here is a reprint of my response to a similar inquiry:

"Your shower/tub was probably caulked with regular silicone, which has a tendency to mildew and separate from surfaces over time. Unfortunately, it's a product widely used in these applications.

"My favorite caulking compound is Sikaflex-1a, a polyurethane compound, which I have used in most indoor and outdoor applications since the late 1950s/early '60s.

"You are likely to have difficulty finding Sikaflex-1a in local stores. Home Depot carries Sikaflex Construction Sealant, which seems to be the same as Sikaflex-1a. You can also buy it online through A.H. Harris stores (www.ahharris.com). It ships at a reasonable cost.

"Please keep in mind that if you use a polyurethane caulking in a bathroom, you should not get it wet for a week or it will turn pink. This presents a problem if the tub/shower is the only one you have.

"An alternative is to use a caulking made for baths and kitchens that contains a mildewcide, such as DAP Kwik Seal 3.0 Advanced Caulk With Microban. It's silicone-based and advertised as mildew-proof. I have tried it on half our tub with the other half caulked with Sikaflex-1a. The DAP Kwik Seal remained a bright white, but began to peel off in about a year. It could be that I didn't thoroughly remove all remnants of the old caulk. Sikaflex-1a lasted for years, but it will turn slightly grayish as it matures.

"The most important preparation is to remove all remnants of the previous caulking, especially if it was silicone. You can remove silicone caulking by running a utility knife on each side of the caulk to peel enough to get a grip on it; it is quite easy to peel the rest of it off.

"Once you have pulled off all the caulk, you need to remove any residue from the surfaces or the new caulk may not adhere for long.

"You can do so with special caulk removers, such as McKanica 0351 Silicone Caulk Remover Gel by Neutraders LLC, which you can buy from Amazon. An 8 oz. cartridge will cost you less than $20, including shipping."

Q. A while back, our local newspaper had a column written about someone selling their walnut tree. At the time I didn't keep the column, so I don't know who wrote it. Was it you?

My mom has a huge walnut tree that we know is over 90 years old. She has decided it is time for the tree to go. Everyone says she should sell it for the lumber, but no one knows who to call to do this.

If the original column wasn't by you, do you have any ideas about who would do something like this? Thank you in advance for your help. Every week I always read what you have to say. It sure has given me a lot of helpful advice!

A. It wasn't I who wrote this column you have described. I suggest you call a certified arborist (most licensed tree experts are, or have one on staff or on call), or the forest service of your state.

Q. I've been in my home 19 years. Six months ago my kitchen cabinet doors (oak) began sticking when I try to open them. At 250 pounds, I had to pull some with both hands and they would pop open.

I have used Mr. Clean, Magic Eraser on all the cabinet doors and it works for some of the doors. A short time later (two to three weeks), some doors are back to the tough pull to open the doors.

Any suggestions on cleaning or treating them so I don't have this constant problem?

A. If the hard-to-open difficulty is not caused by the magnetic catches or other form of catches, and the stickiness is due to the doors themselves sticking to the cabinet frames, try cleaning both with Milsek (www.milsek.com).

Milsek is truly a miracle cleaning and polishing product, which I have used and recommended for years, and many readers have commented how wonderful it is and how well it has worked for them.

You can find Milsek in Ace hardware stores and other outlets. You can also find a local store on its website by clicking on Store Locator and scrolling down to your state.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. His book, "About the House," is available at www.upperaccess.com. His website is www.henridemarne.com. Email questions to henridemarne@gmavt.net, or mail First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.

© 2015, United Feature Syndicate Inc.