Tuesday, January 17, 2017

Extreme Examples In Roofing

Photos here are from the job that is the basis of this post of October 30, 2016: Mandatory Attic Access Walkways .

Where a builder failed to insulate much of the attic space in a two-year-old home, other faults were observed that express extremes of construction error.

I find much fault with this careless and dangerous cut-in of a roof high vent

This is ordinary 7/16" OSB employed as roof sheathing. Where such sheathing is of the least quality and cost that a builder is permitted to use, an awfully-excessive and careless cut for a roof high vent is a great compromise of roof integrity, as a stress riser. An opening larger than the vent perimeter is yet-worse by saw cuts that go far beyond corners. Where stress risers at adjacent vents are aligned, who would say this could not speed roof collapse in a high-wind event?

The served roof high vent is an inexpensive Famco FA50, with 50 sq in screen net free area. Where a pipe 8" diameter could efficiently feed this vent, the sheathing cut is seen as very foolish. A neat 8" hole in sheathing is not likely a stress riser at all.

This is the FA50 manufacturer illustration .

And, here is detail of dangerous vent misalignment with the sheathing cut. Perfect alignment is unlikely, and this is the worst I have seen.

At vent base I see staining from to-be-expected leakage, that must increase as a tar-only seal degrades. 

More important, someone walking the roof below this vent might break through the unsupported  shingle slot about 5” wide, with severe injury.

Now consider the installation errors in view of the prior blog post:
Roof Caps For Bath and Kitchen Exhaust Ducts 

A new-home roofer carelessly left possible tragedy for the known home buyer. The builder might ultimately be at fault, certainly failing to represent the buyers interest in this and other matters. The manufacturer and relevant building codes too, are at fault; and let us propose solutions from this direction.

Propose a better static roof vent, NFA 50
Look back in this blog: 

Land here:Slow Progress In Solar-Powered Attic Ventilation

Find that inspiration of roof vents with an intervening roof penetration adapter, came from wishes for quite-large roof cuts for powered attic fans, say 12.5" maximum diameter. 
Re-post here:

The simple adapter plate is set atop roof membrane, sealed at top to the roof membrane. All involved lower shingle courses rest on the adapter plate.

Fan electronics are serviceable/ swappable, without impact on roof sealing. A bug-blocking screen will get fouled, and may be serviced from the roof as needed. Good fan aerodynamics include smooth draw through a bellmouth. If fan blades of larger diameter than the roof cut are better, let the fan reside below the flare or bellmouth. Let us get over treatment of attics as inaccessible trash pits as treated by the Solaro crew.

For an 8" static vent, let the roof cut be 8 3/8". For a 12" duct of a large powered fan, let the roof cut be 12.5" diameter. Bring air to the roof opening via a bellmouth and an Aperture Box.

I will be back to complete this post. In my next post, create a searchable resource in the invention of "Aperture Box."

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