How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

Why is a popped nail in a shingle roof a problem? How do I fix it?

Thursday, July 19, 2018

A popped nail looks like a wrinkle in a line of shingles when you look up the roof, as in the photo above that has them at multiple locations. The wrinkles typically occur somewhere in the middle of the front edge of a shingle. Some roofers call the defect a “fish mouth.” It differs from curling shingles (shown below), which turn up at the  corners of the shingle and means that a roof is at—or very near— the end of its lifespan. Nails lifting and eventually popping through a shingle roof covering can cause small leaks in several different areas and lead to rotted roof sheathing and even damaged roof framing over time if they are not repaired.

    The reason nails back themselves out of roof sheathing has to do with how well the nail is set in the wood, as well as expansion and contraction of the decking and framing. Nail guns have adjustable pressure settings and it is important that the tool be adjusted properly so that the fasteners are not compressing the shingle too flat, and also are not setting the heads above the surface of the shingle.  

    A nail that is not anchored well in the wood sheathing can be vulnerable to movement with the daily and seasonal expansion and contraction of the wood. Changing moisture levels also have an effect on fasteners.

    Repairing a lifted nail, like the one pictured below, can be accomplished by prying the edge of the shingle loose enough to slip a small piece of wood (like a paint stirring stick) between the head of the nail and the underside of the shingle above it. Another piece of wood on the top side of the shingle will protect it while striking lightly with a mallet to set the nail back in place. If the fastener has already forced itself through the face of the shingle, replacement of the entire shingle is required. A dab of mastic at the hole is only a temporary repair.    Once in a while we come across a roof where the nails have pushed up through the shingles instead of pushing them upward. Dimensional shingle roofs with excellent tab adhesion may have this problem. The small damaged spots will runs in lines. Here’s an example below.

  Most of the time when we see a few popped nails on a roof, they are called out for repair; but, occasionally, a roof has large areas of popped fasteners and requires partial replacement. 

    Any roofing repair beyond setting a few popped nails should only be performed by a licensed professional. Also, if you are uncomfortable with heights or not used to working on an inclined surface, we recommend letting a roofer do your nail pop repairs. 

    Also see our blog posts Why is my roof leaking? and What causes a lump or dip in the roof?

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  To learn more about roofs and attics, see these other blog posts:

• What are common problems of asphalt shingle roofs?

Why is my roof sheathing sagging between the trusses?

Why is granule loss a problem for an asphalt shingle roof? 

What are the mistakes to avoid when doing attic improvements?

• Can one missing or damaged shingle cause a roof leak? 

Is an attic required to have a light by the building code? 

How can I inspect my roof for hurricane damage?

Why is premature curl of roof shingles a problem?

How can I tell if a roof has more than one layer of shingles? 

What are the common problems with attic insulation? 

What is the life expectancy of an asbestos cement shingle roof? 

What's the average lifespan of a roof?

What can I do to prevent roof leaks?

Are roof trusses better than roof rafters (stick framing)? 

What are the most common problems with wood roof trusses?

 If my roof is not leaking, why does it need to be replaced?

How can I be sure my roofing contractor got a permit?

How many layers of roofing are allowed on a home? 

Should I buy a house with an old roof? 

What are those metal boxes on the roof?

What does "lack of tab adhesion" in an asphalt shingle roof mean?

Why do roof edges start leaking?

Why do my dormer windows leak? 

Do home inspectors go on the roof? Do they get in the attic?

Should I put gutters on the house? 

How much of a roof truss can I cut out to make a storage platform in the attic? 

What's the difference between an "architectural" and a regular shingle roof? 

What does a home inspector look for when examining a roof? 

Do stains on the ceiling mean the roof is leaking?

How can I tell if the house needs a new roof?  

 Why does my homeowner's insurance want a roof inspection?

What are the hazards to avoid when going into an attic? 

     Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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