Felt

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 ll or ASTM D4869 Type lV 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.