Please post questions about anything having to do with roofing

Please post questions on this thread on the following subjects:

  1. roof sheathing
  2. underlayment
  3. flashing
  4. comp shingles, roll roofing, concrete & clay tiles, slate and metal roofing.

Should there be underlayment for wood shingles or shakes

Wood shingles should have underlayment.
Wood *shakes *require an interlayment of 18-inch wide felt. “Interlayment” differs from “underlayment” in that a layer of interlayment is installed with each new course of shakes.

Have you heard about the roof sheathing that requires no underlayment for roof coverings?

Built-up roofing? :mrgreen::mrgreen::mrgreen:

No really… what is it?

That was funny;)

The Zip System

It is starting to be used in this area a little. I have seen it twice.
Also the same system for wall sheathing, but cannot be interchanged.
I have not found out the price yet. But will next week.

Marcel :slight_smile:

Thanks Marcel!

Please explain what you look for in the way of flashing for a deck when modified bitumen and also with EPDM.

What type precautions are needed?

Robert, I’m working on the ashpalt shingle section right now. I should be able to answer this when I start the flat roof section.

Are plywood clips still in use and under what conditions?
Does the back stamp go facing up or down?
Is the maximum allowable O.C. spacing the same for OSB as it is for plywood?
Why is it necessary to stagger sheets?
What is the nailing pattern when utilizing 8d nails on 1/2" CDX?
How far should sheathing be kept from a ‘B’ vent flue for a hot water heater?
How many courses of ice & water shield are needed at the starter course?
Is the ice shield applied over or under the drip edge? Rake edge?
Do I have to use step flashing where a roof meets a sidewall? Can’t it be a continuous strip?
Can I install shingles in the rain?
How many inches should roof sheathing be cut back at the ridge when utilizing continuous ridge vent?

I’m assuming you are preparing a roofing tutorial. Hope these questions help. I’ve got more.

Yes, they are still used, but whether or not they’re required is a call for the engineer or architect.

The stamp goes up or down depending on which side on will be visible after construction is complete (if that’s possible). Both sides are the same as far as their durability. Building inspectors used to like the stamp installed up so they could see the stamp as they walked the roof to inspect nailing.
If sheathing is installed stamp down at homes with attic spaces, the stamp will always be visible for inspectors wanting to confirm that the sheathing installed had the proper rating. Building inspectors don’t fail roofs because the stamp faced the wrong direction and the IRC doesn’t specify which direction the stamp must face (R803).

Both products are manufactured to standards designed to ensure similar performance when used in applications for which they were designed.
For a detailed paper by the APA on this subject, search their “Publications” page for tt-047

Aligning sheathing butt joints from the bottom of the roof to the top creates an overall roof sheathing membrane that is weaker than one in which the butt joints are bridged every other course by a full sheet of sheathing.

Typically, 6 inches on the ends/edges and 12" in the field (middle of the sheet.) With certain designs, the engineer may call for decreased nail spacing along the edges, but decreasing nail spacing in the field makes little difference in the performance of the sheathing.

1-inch minimum from any combustible material.

one, except in climates in which homes are vulnerable to ice damming. When an ice barrier is required, two (R905.2.7.1) If felt is used, the two layers must be cemented together.

Over on the eve, under on the rake.

Absolutely must use step-flashing. Continuous flashing should be called as a defective installation. (R905.2.8.4)

Bad idea. Wet underlayment can cause eventual blistering of asphalt shingles. Asphalt shingles are both nailed to the sheathing and bonded to each other by the adhesive strip, so installing in the rain may create problems with differential expansion/contraction as materials gain and lose moisture. Moisture will cause underlayment to wrinkle. If wrinkling is extreme enough it may cause deformation of the shingles.

6 inches total is common but it’s more important to follow the manufacturer’s recommendations.

Great questions Keith, ask away!

Can asphalt shingles be installed over wood shakes/shingles or should they be removed.

Unless it’s forbidden by local building codes, they can be installed over shakes or shingles if shakes or shingles are listed as an approved substrate by the manufacturer of the shingles being installed. The manufacturer’s recommendations are really the determining factor.

Due to many areas of poor support of the new shingles, it will shorten their lifespan and make them more vulnerable to impact damage from things like hail, or abrasion from foot traffic.


I’ve come to learn that re-roofing over an existing layer of composition shingles, while generally permitted by code, reduces the ability of the newer shingles to resist impact damage from hail. Therefore, in hail-prone regions the insurance industry recommends and local code may require that re-roofing should include removal of the existing layer(s) of old composition shingle roofing.


Here’s one:
What’s the difference between using 15# or 30# felt, where each one should be used and why?

What is sheathing?

Kidding, this is a good thread you started though Kenton. keep up the good work.

I dug a little deeper and edited my last post. I’m not sure about code, but shingle manufacturer’s will be worried about having to back up their warranties, so they will typically limit the substrates to those that provide good support.

GSF/ELK limits their substrates to pretty much wood decks which comply with their requirements and to asphalt shingles in good condition.

Here’s a link to their tech page in this subject.

By the way, they have a great set of tech papers available online.

“I’m not sure about code, but shingle manufacturer’s will be worried about having to back up their warranties, so they will typically limit the substrates to those that provide good support.”
Nailed to spec, at the exposure, the shingle get cracks when nailing them. The nail forces the shingle into a sharp bend/crease there. Tends to leak and void warranty.
Nailed higher than 1" above the exposure causes the shingles to slide down the roof, which creates leaks. And the high nailing also voids warranty.
Other than that, no issues I can see.

what is the # 1 cause for shingle failure

I’ve asked a GAF/ELK tech guy and a lead field adjuster for a big insurance company. If one of them doesn’t know… I don’t know who would.

Some kinds of things manufacturers don’t like to discuss much. I’ve been unable to get time lapse photos showing how shingles change as they age.