The Cedar Guild

Frequently Asked Questions

Roofing and Wood Preserving FAQ

Why should I do anything to my roof?
Although wood is a renewable resource, cedar and redwood, in particular, do not grow rapidly. It takes 200 - 400 years for a tree to reach the diameter and height necessary to have long sections of clear knot-free wood. For this reason, cedar has become a diminishing resource that cannot be readily replaced. Cedar will be increasingly difficult to find and more expensive to buy as it becomes scarce.

Why can't I just replace the roof when it starts to fail?
You will have to, if it cannot be repaired. Chances are you will not be able to replace it with another wood roof, however. Wood is becoming scarce and more expensive each year.

Why do the shingles cup and curl on my roof?
Cupping and curling are caused when sun and rain stress the wood, (usually not vertical grain).

If I don't do anything, how long should my roof last?
Most roofs, if applied properly, will last 7 to 15+ years.

What is the insulating factor of a wood roof?
A roof of 16” long red cedar shingles, which are approximately 3/8" on the butt end, has an insulating R factor of .95. As a comparison, three-tab asphalt shingles have an R factor of only .44.

Does a wood roof add any value to my property?
Yes, your house's value usually increases $2,000.00 to $4,000.00. (According to real estate agents)

How soon should I start putting a preservative on my roof?
We recommend having the first light pigmented coating put on while the new roof scaffolding is still in place. Don't let decay and UV get started!

How does the wood get cracks?
Cracks occur from the wood being stressed with moisture/sun over and over. The wood expands and contracts, creating tiny hairline cracks, which, over time, get larger.

What causes moss and algae to grow only on one side of my roof?
Moss and algae are usually found on roofs when there is not enough airflow across the roof to keep it dry. The north side is vulnerable, as is any portion that is shaded most of the time.

Do I need to clean my roof before treatment?
Yes you do need to clean off the dirt, debris and other matter on the wood so it is clean enough to absorb the treatment. You would not put wax on a dirty car, would you?

Can power washing hurt my roof?
See Appendix V in the roof manual for complete details. Briefly, power washing, if done correctly with a cleaning solution, will do the very best job of cleaning.

What do I do about stains that do not clean off with a regular cleaning solution?
See troubleshooting guide in Roof Manual. In some cases, by using a darker pigment in your preservative treatment, the stains will not show. It is a good idea to fix the problem so it won't continue to stain the wood.

How do I know if my roof is too old to treat?
If it is no more than 0-10 years old and has no leaks, is perfect for a preservation treatment. A rule of thumb is that, shingle roofs older than 30 years, which has had no care, will be difficult to repair with any success.

How much of the roof should I consider repairing?
Given the economics on the cost of a completely new wood roof, it usually makes good "dollars and sense" to look at repairing up to 50% of the roof, before starting all over with a new roof.  In some cases repairing the roof in sections makes it possible to classify the work as repairs. This may be important as many towns will not allow complete re-roofing to be done with wood.

What parts of the roof wear out first?
The first part to wear out is the ridge cap. Ridge cap is usually replaced 2-3 times during the life of the roof. Second to wear: the flashing areas around the chimneys, roof jacks and valleys. The south and southeastern exposures will get the most sun. If you live where dirt and sand blow a lot, that side of the roof will show wear and damage first. The north side, or any area that is constantly shaded, would be an area to watch, as well.

How much ventilation does the area under my roof need to have to keep the undersides of the wood dry?
We recommend keeping the ratio of net-free ventilation area to attic area less than 1:150. We also recommend that you install a thermostatically controlled attic fan. There are very attractive ridge venting systems available, as well.

Do I need to do any yearly maintenance?
Yes. Use a trigger spray car-washing nozzle and rinse off your roof every fall after the leaves have fallen. Clean out the gutters so that water can't back up and wick up under the roofing at the eave line to cause leaks.

Can I repair the roof myself?
Yes, BUT if you are afraid of heights, are older, or have any concerns about falling, it is better to hire a professional to do the work. Details on repairing individual shakes or shingle, or small sections of the roofing are covered in the Roof manual.

Can you buy preservatives treated shingles at the lumberyard?
Yes. The label would read Certi-Last™ Pressure Treated Shakes (or shingles). The roofing material is pressure treated with CCA (copper chromated arsenate also known as copper chromium arsenate), according the Cedar Shake and Shingle Bureau guidelines.

Is CCA treatment recommended for all parts of the USA?
It can be used anywhere, but it is very important to do so if you live in an area of high moisture and humidity. We recommend that you consider doing this if you live along the Pacific Northwest Coast, the Atlantic Seaboard, or in any part of the Midwest that has wet or humid conditions.

If I use CCA treated materials, do I still have to use a preservative treatment?
Yes, you need to put on a preservative with a petroleum base after several years have past, to prevent cupping, curling and checking. There is some thought that the elemental copper in the CCA formula can eventually leach out, so a preservative treatment would help on this, as well.

What if I don't want my roof to look green like CCA treated lumber?
Ask the lumberyard to order CCA Sunwood™. This has a warm cardboard brown pigment, quite similar to natural cedar color.

How do I know if its time to re-coat the roof?
The most common sign is a bit of color or pigment fade on the south side of the house. Watch for mildew or moss on the north side. If you have strong prevailing winds that blow dirt or sand, that side of the building will show the first wear or pigment loss.

What does good roof maintenance consist of?
Keep the roof clean, trim back overhanging limbs, clean out valleys and gutters every year. Check every spring or after severe storms for visual damage. Missing ridge cap is the most common problem.

How often, on the average, does the roof need to be re-coated?
It needs to be re-done every three to seven years, depending on the chemical used, your geographical location and the application procedure used. Usually after the second time it is done, the re-coating time extends to 10+ years.

Can I spray on a fire retardant treatment?
Yes, you can. However, it must be reapplied after every rain.

Is there a fire retardant shake or shingle?
Yes, there is a pressure treatment called Certi-Guard™. The Cedar Shake and Shingle Bureau has set the standards for this process which has been accepted by the ICBO and the California Fire Marshall. Remember that there is no such thing as a "fire proof" wood treatment.

Can I get both a fire retardant and CCA treatment done at the same time?
No, You may do either one or the other as they are not compatible with each other.

Why should I use a petroleum-based product rather than a "natural oil", like linseed oil?
Natural oils do not taste bad to insects or to organic organisms. Natural oils actually encourage these various unwanted critters to grow and feed on the wood. There are also better penetrating oils among the petroleum-based products.

Can I really make the wood last longer?
Yes, it has been proven by several independent agencies. The Forest Service Products Research Lab in Madison, WI, the Forest Products Lab at Texas A&M, Oregon State University, the Forest Products Lab of the University of California at Richmond, CA, and others, have done extensive weatherization tests which show that using a good preservative will increase the life expectancy of wood for many years.

What exactly is a preservative?
By EPA guidelines, a wood preservative must have no less than 2% active copper or zinc in its formulation.

Lots of paint on the lumberyard shelves have copper or zinc listed as an ingredient. How can I tell if it meets EPA standards?
The percentage of actual metal will be listed on the label, in the ingredient section. Watch for any indication that the product had a certain percentage of active metal before dilution. Sometimes after dilution, the amount of available active metal is well below the 2% required to qualify as a true preservative.

What is a good rule of thumb for evaluating paint products before I use them?
The quickest way to see if a product might really stand up to the claims it makes in its advertising, is to look at the label and see what the percentage of solids is vs. the inert ingredients. The higher the percentage of solids, the better the chance is that you will have enough "good stuff" in the can to back up the advertising or labeling claim.

I like the natural look. Why do I need a pigmented product?
Pigment is the primary ingredient that protects the wood from ultra-violet rays. Ultra-violet rays from the sun are the ones that "gray" the wood. When you see wood starting to gray, you can be sure UV is damaging it.

How does UV damage the wood?
When UV hits the wood it starts being absorbed by the lignin, which is the material that binds the wood cells together. Once destroyed, the lignin washes out of wood, exposing the cellulose fibers, which are white. This is why the wood looks gray.

Why don't the natural oils and resins in cedar and redwood prevent this from happening?
They do, at first, but the infrared rays from the sun draws out the oils and resins. This lessens their ability to protect the wood because when the oil and resins (extractives) come to the surface, rain will wash them away.

How do preservatives help the moisture problem?
The main purpose of wood preservatives is to put oil and resins into and onto wood, which keeps out the water.

Which is better, oil based or water based preservative?
Oil based products penetrate deeper and help combat weather stress better, according to the US Service Forest Products Lab and Texas Forest Products Lab. Water based solutions work well in areas that have 13 or less inches of rain annually.

Why can't I put on preservatives in their pure form?
You can't, because they must first be dissolved in a carrier of water or oil.

What is the advantage of water based solution?
It is generally less expensive, and potentially less of an environmental problem.

Is there any disadvantage to water based preservatives?
Some treatments only stay on the roof until the first bad rains, leaving just the pigment behind. Also water-soluble chemicals leach off the roof over time.

What oils should I avoid?
Tung, linseed, palm, rosewood, and soy oils are all natural oils. These oils are all a natural food source for mold, mildew, insects and fungi.

What advantage is there to using an oil-based product?
The big advantage to an oil-based product is that it does a great deal to replenish the oils and resins in the wood and to protect it from moisture, sun and heat.

What is the best way to put on a preservative?
It can be brushed on or applied with a pump-up garden sprayer, but an airless sprayer works the best.

How did the Guild get involved in wood preservation?
We became involved with preservation issues in 1989, when we started making custom roofs for log hunting lodges and other specialty buildings. The owners were aware that wood was becoming scarce and wanted to know what could be done to preserve the new wood roofs they were buying. We didn't know the answer, but knew it was a very good question.  We started researching, pulling in information from many sources. We found that a good body of research had been done on comparative product studies by Texas A&M Forest Products Lab, Oregon State University and by the US Forest Service Forest Products Lab, in Madison, Wisconsin. This included actual weatherization and accelerated weatherization tests with side-by-side comparisons of most of the standard off-the-shelf wood care products on the market. Their research is still continuing, with a recent addition of studies being done at the University of California, Richmond Campus.

What were the results?
They all found that the TWP products, made by Amteco, Inc., a small Midwest paint company, were by far, the highest rated wood preservative products in these independent studies.

What is different about the TWP products?
Several things are different. FIRST, the chemist found a way to use resin-locking formula to bind a brown-based copper compound with mildewcides and fungicides.  SECOND, several kinds of paraffinic oils, including Chevron Shake and Shingle Oil™, were used as carriers. These oils carry the active ingredients deep into the wood fibers while the resin-locking feature fastens them onto and into the wood fibers.
THIRD, the high solids content of these products, plus the oil base, assures you that the finish will remain as a "gel" coating. This gel finish, capable of softening in the heat of the sun, will re-fill any microscopic cracks, should they appear after a winter's damage cycle.

Have you used these products?
We have been recommending and using TWP products since 1990 on our working farm.

How does the Guild use the TWP products?
We have been specifying TWP products for private use on roofs, fences, decks, sidewalks. TWP is the preservative of choice for most of the National Forest and Parks Service's projects.  The Guild has been instrumental in having Amteco develop a special color, TWP318 FOREST GREEN, which replicated the green paint the CCC (Civilian Conservation Corps) buildings used in the 1930's. Modern technology adds mildewcides and other features to this well known color.

In addition, the Guild has revived the process known as shingle dipping. This process immerses the whole shingle into a specified color to apply preservative to all services. This can be used on roofing materials as well as sidewall clapboard and shingle finishes.

How do I care for Cedar siding?
Siding needs to be cleaned and treated with a preservative treatment.  After draping or otherwise protecting landscaping near the house, cedar siding can be cleaned with a solution of: 1 gallon warm water, 1/4 cup TSP [trisodium phosphate] (or dishwashing detergent used in a dishwasher), 1/4 cup household bleach, 1/4 cup laundry detergent.  Spray this on and let it remain on the wood for 20 to 30 minutes.

Power washing this solution off is recommended, if you know how to use a power washer. Otherwise, scrub the solution with a stiff bristled patio brush, or similar brush, to loosen the surface material.

The pistol type nozzle used for washing cars will also work. It is important to rinse this solution off  thoroughly, and after the protection is removed from the landscaping, it should be thoroughly hosed down, too.

If the wood is blotchy or stained, this can be removed by using a wood bleach or lightener.

When the siding looks the way you want it to, we suggest protecting it with a coat of translucent TWP. Ask us for a recommendation as to which TWP
product to use as there are some variables we should discuss.


How do I keep my wood fencing looking good?
It can be kept its original color by using either a TWP 200 series color or a TWP 500 series color that matches the wood. As mentioned before, we do not recommend using a clear product.  TWP 210 Slate Gray will give the fence and instant aged look.

My fencing lumber was treated with CCA ground contact preservative when I bought it at the lumberyard. Do I have to do anything else to keep it up?
Yes, because CCA treatment does not guarantee the wood will last forever. After a year or two, you will notice the green fading, or in the case of Sunwood Brown™, the wood starts looking "dry" and splintery. It is time to put an oil-based preservative with an ultra violet barrier, like TWP 200 or 500 series onto the wood to keep it protected.

I am going to put new cedar siding on my home. How can I keep it looking good?

We suggest treating all four sides plus the ends with a pigmented TWP 500 Series before it is installed. This keeps damage from ever starting, and makes maintenance easier. Treat any ends that are cut. After it is installed, a light coating of TWP will smooth out any "ding" marks.

What should I do about treating my deck?
FIRST, you have to determine if there is any residue of a previous product on the wood. Wait until a dry day and flick some water on the wood to see if it beads up. If it beads up, the wood will not accept another finish. Especially check the areas that have been protected from the weather. SECOND, if there is old finish on it, it must be stripped. At this point you can prepare the wood for a new preservative coating. If the wood needs to be lightened or repaired, do it now. THIRD, we recommend using one of the TWP 500 series color products on all surfaces before it is installed.

TWP for Deck Applications PDF   XPS