Installation FAQ

Coverage & Exposure

Can I use number four grade shingles for a starter course on my roof?

Number four grade shingles are a utility grade for undercoursing of double coursed sidewalls only. They are not a roofing material and they are not to be used as a starter course on roofs.

Is there a method of applying three or four rows (sections) before moving across the roof?

Cut a board the same width as your shingle exposure and a length where you can lay out shingles. Tack it in place being careful not to damage the underlying roof shingles, then lay out and nail a course. Move it up and tack it in place again. Lay out and nail into shingles and repeat five to six courses. Move along, and chalk line every five or six courses, being careful not to damage the underlying roof shingles.

What amount of waste factor should I count on in the product I purchase?

Waste factor will vary, depending upon quality of product, roofing contractor’s experience, and aesthetic look desired. Contact your Member Contractor/Installer for more details about your particular job; unfortunately this is not a question that the CSSB can answer for you as it is project-specific.

Is it ok to use spray foam directly to plywood roof sheeting for cedar installation?

CSSB does not recommend using spray foam underneath the plywood before installing cedar shakes or shingles on top of it. Spray foam tends to create an air barrier and a non-ventilated base. This can lead to premature deterioration of the internal side of cedar shakes and shingles which can cause cup and curling issues. An adequately ventilated base is required to ensure the long life of the cedar roof.

Decking & Sheathing

Can I use solid decking for my shake or shingle application?

Shakes and shingles may be applied over spaced sheathing. Spaced sheathing is usually 1 x 4 or 1 x 6 softwood boards and shall not be less than 1 x 4 boards. Solid sheathing is recommended for shakes and may be required in seismic regions or under treated shakes and shingles. Solid sheathing is used in areas with wind-driven snow. Please note that the only solid sheet sheathing tested with shakes and shingles is plywood. Check with your local building official for plywood thickness/ dimensions. See the CSSB’s New Roof Construction Manual.

What is the difference between "decking" and "sheathing"?

The two words are used interchangeably in the roofing industry.

What is strapping?

“Strapping” is another term for nailing strips. It is also called “open lathe application”, “spaced sheathing” or “skip sheathing”. See the CSSB’s New Roof Construction Manual.


What type of felt interlayment do you recommend for shake application?

The CSSB recommends using an 18″ wide strip of No.30 ASTM D226 Type ll or ASTM D4869 Type lV roofing felt laid over the top portion of the shakes and extending on to the sheathing. Check with your local Building Official for exact specifications in your area. The bottom edge of the felt should be positioned above the butt of the shake at a distance equal to twice the weather exposure. Note: Building officials MAY approve eliminating felt interlayment between shake courses when tapersawn or tapersplit shakes are applied in snow-free areas at weather exposures of less than one-third the total shake length (3-ply roof). ALWAYS check with your local Building Official for project approval PRIOR to deviating from standard application guidelines.

Why do I need felt interlayment between my deck and my shakes?

The felt interlay acts as a baffle that prevents wind driven snow or other foreign material from entering the attic cavity during extreme weather conditions. The felt interlay also increases the roof’s insulating value. The felt interlay system forces water to the surface, thus assisting the proper water shedding in your roof.

Are "interwoven felt", "interlayment", and "interlaid felt" the same thing?

Yes. Different regions of the country use different words to describe the same thing.

Is felt interlayment required when shakes are installed on strapping?

Yes. Cedar shake application is a system of shakes with interwoven felt.

Is felt interlayment required when shakes are installed on solid sheathing?

Yes. Cedar shake application is a system of shakes with interwoven felt.

Would you recommend house wrap or felt for shingle sidewall application?

The CSSB recommends ASTM D226 Type II or ASTM D4869 Type IV roofing felt. House wrap typically allows moisture to flow behind the shingles, where these ASTM standard roofing felts will not.

What are your requirements for felt installation on hip and ridge?

A strip of felt, metal and/or rubber flashing should be laid under the hip and ridge product. See the CSSB’s New Roof Construction Manual for more details.

Do you recommend laying the untreated shingles directly over No.30 ASTM Type ll or No.30 ASTM Type lV roofing felt on the solid sheathing (plywood)?

The untreated shingles will last longer and the roof system will work better if you have an airspace directly below the shingles to allow them to breathe and dry out. It will also allow summer condensation to run out from under the shingles. Shingles directly on eave protection will not dry out very readily and will not last as long as the rest of the roof shingles. A continuous ventilation product may be installed only over the eave protection, under the shingles, to maximize ventilation.

Can I put fastener-sealing eave protection over the decking (sheathing) before applying the shingles?

Fastener-sealing eave protection is very helpful at the eaves and the valleys. If No.30 ASTM Type ll or No.30 ASTM Type lV roofing felt is installed on the remainder of the roof with a continuous ventilation product on top of the felt and eave protection you will have a great roof. If using a Certi-Last® or shake felt system product you only need the felt and eave protection.

What is the CSSB recommended procedure for base or sheathing protection?

No. 30 ASTM D226 Type ll or ASTM D4869 Type lV roofing felt.


Can I use copper flashing with my cedar roof?

Copper flashing can be used with a cedar roof in most areas, with the exception of areas that are exposed to acid rain areas east of the great lakes.

How much spacing should be left between the vertical wall or skylight flashing and the cedar shakes or shingles?

Heating stacks require 1″ space. Walls, skylights and windows that are flashed with metal should be closed. Check with your local Building Official regarding this particular application question.

Do some cedar shingles cause premature deterioration of un-painted roof flashings?

It is unlikely that the cedar is causing the deterioration of the flashings: any metal will rust if exposed to certain elements in the air. Many tropical areas do not allow any kind of galvanized sheet metal on any type of construction.

Can I nail through copper step flashing?

Yes, you can nail through the copper.

Keyways/Joints Between Shakes & Shingles

What is the joint or keyway spacing between cedar shakes and shingles?

Please refer to the CSSB’s New Roof Construction Manual and Exterior and Interior Wall Manual for specific details.

I have a buckling effect happening with my sidewall product. What went wrong?

Your project is experiencing what is called “fishmouthing”. The bowing or curving of the shingles is due to inadequate joint or keyway spacing. When the shingles naturally expand and contract with moisture content due to weather conditions, proper joint or keyway spacing provides the room that allows them to remain flat. Contact your Member Contractor/Installer for more assistance.

Nails & Staples

Is it okay to use a nail gun?

You can use a nail gun to install cedar shingles and shakes. However, the nail heads must not be overdriven into the surface of the shingles. See the CSSB’s New Roof Construction Manual for more details.

Is it normal to see a fastener here and there, between installed product, or should you never see one?

You should never see staples or nails in the joints or keyways between shakes or shingles. If you do, it means that fastener was installed incorrectly. It could also indicate other unseen incorrect installation. Contact your local Member Contractor/Installer for details.

Should the woven sidewall corner applications be nailed together?

You can nail the woven corners together, but the CSSB suggests using hot-dipped galvanized nails and pre-drilling the holes to prevent splitting.

What size or type of fastener should I use when putting on my cedar sidewall?

What kind of fastener should be used in a salt water zone?

Nails and staples MUST be stainless steel Type 316 in locations within fifteen (15) miles of salt water. Please refer to the CSSB’s New Roof Construction Manual and Exterior and Interior Wall Manual for specific details.

Oriented Strand Board (OSB)

Can you install cedar shakes over OSB?

Certi-label shakes and shingles have only been tested on plywood decking. Make sure you use a very good quality hot dipped galvanized or stainless nails that are ring shanked to hold the roof to the OSB and check with your local Building Official to see if this type of application is permitted.

Can OSB be used on walls under cedar sidewall?

Check with your local Building Official for requirements in your area.

Over Roofing

Can new ridge caps be installed over the existing caps?

No. You should remove all existing ridge caps, then apply a water proof strip of felt, metal, fastener-sealing eave protection to ensure that the ridges or hips are water tight. Finally, install the new ridge caps.

What is the appropriate fastener length to use for over roofing applications?

Assuming local Building Official approval for this type of installation is obtained, you should use the length of nail recommended for that specific material. Add the thickness of the existing roof and this gives you the nail length required for the fastener to penetrate ¾” or more into the sheathing. Refer to the CSSB’s New Roof Construction Manual.


What is the appropriate fastener length to use for installing cedar shingle siding over insulation?

Assuming local Building Official approval for this type of installation is obtained, you should use the length of nail recommended for that specific material. Add the thickness of the existing insulation and this gives you the nail length required for the fastener to penetrate ¾” or more into the sheathing. Refer to the CSSB’s Exterior and Interior Wall Manual.

Do you recommend staining #1 red cedar shingles on all 4 sides before applying as sidewall?

As long as the shingles are dry when stained it doesn’t seem to matter whether they are painted on all 4 sides or just on the front side. A local, professional painting expert may be able to provide you with further guidance.

Can I put new cedar shingle siding over my existing cedar shingle siding?

Yes, but most times you need to install additional window and door trim to ensure that the product lies flush with windows and doors. Sometimes this additional trim requirement makes it less expensive to tear off the old siding and start from scratch. Look at the diagram in the CSSB’s Exterior and Interior Wall Manual for more details.

How do I create a roof wall drip line intersection?

Put the bottom step flashing on the starter course, then bend the bottom of the step flashing out about 1″ to 1 ½” away from the wall. The top of the step flashing is still under the siding or plaster. You do have to trim the top starter course shingle with a triangle shaped cut to allow this. This does leave a triangular shaped void between the bottom of the step flashing, the wall, and the shingle, that can be filled with caulk. This will divert the water away from the lower wall so the water does not run down the wall.

Can I install grooved shingles with the smooth side exposed?

You can install grooved shingles this way, but it is a rather expensive installation. You have paid more for the grooves put on the face of the shingle, and they are manufactured with the intent of having the grooves facing out, to the weather.

Slope (or Pitch)

What is slope?

Slope is defined as the change in height (rise) as compared to the distance up the roof area (run) and is measured in inches. For example, a slope of 4:12 means 4 inches of rise for every 12 inches in run. Some people call slope “pitch”, but the technically correct term is “slope”.

What is the lowest slope that I can apply cedar shingles to?

Any slope of 3:12 or more is fine for cedar shingle application.


If I use pressure-impregnated treated shingles do they require ventilation or special spaced sheathing?

No they do not. Standard shingles tend not to last as long on unvented sheathing; ventilation should be provided on solid sheathing for the best results. Please consult the CSSB’s New Roof Construction Manual for more information.

Is it necessary to have ridge vents on a cedar roof?

If you have an area between the roof and the sheathing ridge and no other ventilation had been provided, ridge vents are a good idea.

Do I need to use a ventilation product under my Certi-label® shingles?

Good ventilation is essential and can be achieved in a variety of ways; check with your Member Contractor/Installer to see if nailing strips (spaced sheathing) or a continuous ventilation product is the best choice for your roofing project. Both choices are effective, however the nailing strips (spaced sheathing) are typically ¾” thick and the ventilation product is usually ¼” thick: if the rafters are very long the nailing strips (spaced sheathing) will provide more air circulation.

How do I ventilate a steep slope ridge area?

On steep slope roofs, the correct ridge vent products can actually facilitate the ease of installation of Certi-label® ridge units. Always follow the manufacturer’s installation instructions. The predominant ridge material manufactured today is for a medium slope roof. However, by using a ridge vent that is pliable and at least 8 ½” wide, the material can be installed across the minimum 3″ of air space at the ridge to create a shallowing of the slope at the ridge. Care must be taken to caulk the ridge vent material to the Certi-label® shakes or shingles. Proper nailing of the ridge units will create a serviceable application.

Is the ventilation product warranted?

Please contact the manufacturer of the ventilation product for warranty details. The CSSB does not administer warranties for any type of ventilation product.

Weight of Products

Is there a specific moisture content level that will yield the best cedar shake or shingle application?

Your installer should take care to ensure a high enough moisture content to avoid splitting the product due to brittleness.