Preventing black marks on exterior molding

Q. I have been reading your column for some time and find it full of useful building science information. I have a question for you regarding some unsightly black marks on the exterior molding of our home.

We built a house 12 years ago with an asphalt roof and AZEK crown molding installed with a metal drip edge. Over the years, where the roof pitch is not very steep, we don't have a problem, but where the pitch is 12 inches per foot, we have noticed black streaks on the molding. Is this caused by the roof material or the metal drip edge?

How do we prevent this discoloration in the future? We will likely need to replace our roof in the next five years and would like to avoid this happening again. Perhaps you can recommend a specific drip edge material or roofing type that will prevent this from happening again.

A. From your description and the photos you sent, it looks as if the metal drip edge on the shallower roof is not compressed onto the molding, thus allowing the water draining from the roof to fall clear of it, while the drip edge on the steeper roof is forced tightly against the molding, causing water to run over it.

The dark stains are pollutants from the atmosphere and dirt from the roof that stick to the molding.

When you replace the roof, consider using a different kind of molding similar to Lamb & Ritchie's Positive Rite Flow. You could actually insert it now over the existing drip edge, as it is designed to do just that.

You will have to attempt to get it from a building supply firm, which may be a challenge, as the firm would have to buy it in a certain minimum quantity while you will only need a few 10-foot pieces.

If you cannot find a supply house carrying it or willing to get it for you, look for a small metal shop willing to make as much of a similar drip edge as you need. This may also be a challenge nowadays where everything is so compartmentalized. In my earlier construction days, it was easy to find small specialty subcontractors to do customized work.

You didn't mention where you live, but it is often easier to find independent small shops eager to customize work in small villages than in big cities.

Q. I really enjoy your column in the Daily Herald. I wonder if you could give me your opinion on something. I'm a board member in a townhouse community. About 10 years ago our development completed a major renovation - new roofs, gutters and siding. During multiple revisions of the contract, the siding contractor changed the house wrap description from "Tyvek" to "Tyvek or similar product" on the final (signed) contract and our homes ended up with Barricade house wrap rather than Tyvek. I was wondering if you have an opinion regarding Tyvek vs. Barricade. I think in all the years since the renovation project I've only seen Barricade on one building.

A. Tyvek was, as far as I know, the original housewrap, which was actually developed for another use that proved impractical.

Since its inception and with the growing building science knowledge that made us aware of the importance of air barriers, it was inevitable that competition to Tyvek housewrap would proliferate. There are now quite a number of proprietary names.

Barricade is one of the many Barricade Building Products you will find at www.barricadebp.com.

I am not aware of any industry comparison of one brand over another, and I really don't think there is much difference between any of them. It may be that the contractor who did your project dealt with a building-supply house carrying Barricade for whatever reason.

Q. I recall once you mentioning the name of a particular kind of asphalt roofing you had good luck with but cannot recall the name. My roofer estimate calls for Owens Corning, IKO, BP shingles, with a 30-year life expectancy. Have people had good luck with these?

A. The asphalt/fiberglass roofing industry has suffered a number of class action suits over the years because of the widespread failure of these products. IKO is a manufacturer that has had a sad record of such failures and a history of fighting claims to collect against their stated warranty. But so have other brands.

Most shingle warranties are almost worthless; it is too difficult to file a claim and get compensated, so many people simply give up.

Some manufacturers have eventually reached settlements and made some improvements in the quality of their products.

Contractors have reported to me that they have had some success with BP, Certainteed and Owens Corning. I do not recommend one over the other, as I really do not know which brand will perform best over the claimed life of the products.

Q. I have a roof thermostat fan for the attic. I changed my water heater, and everything else remained the same. But now I get downdraft negative pressure when the heater and fan are on at the same time.

Now I don't use fan and attic. I am not getting any ventilation. Any suggestions?

A. Attic fans are notorious for robbing conditioned air from the living area because it is very difficult to provide them with the amount of makeup air they require in the attic itself. So the fan gets that makeup air from any source it can - in your case, the flue of your water heater, which is obviously not electric.

I suggest you consider no longer using the roofing fan; these fans have more negative effects than positive ones.

Attic ventilation is best provided with a combination of full-length soffit vents and an externally baffled ridge vent, combined with an unobstructed air flow between them.

Q. I read your article where you suggested a person use WD-40 to "lubricate" a metal drawer. WD-40 is not a lubricant and should not be used as such. Damage can result if it is used in mechanical mechanisms instead of a proper lubricant.

A. WD-40 is widely used in homes and in the industry as a way to "lubricate," clean and protect squeaky hinges, all types of locks, leather furniture, bicycle moving parts, guitar strings, as a bug killer and in many other ways. It is also used to clean greasy hands, remove blood stains, etc. There are too many uses to list here, but you can find more than 50 of them by checking out Consumer Reports. Googling WD-40 will also give you much information about it.

I am not aware of any damage it can cause, but since you are, I'd appreciate your providing me with the information.

• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.