The rules are divided into the categories of notching (cutting away an area of wood at the top or bottom) and bored holes (drilling through the center).

Notching requirements:

1. Notches in the top or bottom not to exceed 1/6 of the height of the joist/rafter.
2. The length of the notch cannot exceed 1/3 of the depth of the joist/rafter.
3. No notches in the center 1/3 of the span.
4. Notches at the end of a rafter/joist cannot exceed 1/4 of the the height
5. Notches and bored holes cannot be in the same area.

Bored hole requirements:

1. Holes cannot be more than 1/3 of the height of the joist/rafter.
2. Holes must be a minimum of 2 inches from the top, bottom and other holes in the joist/rafter.

    The worst offenders who ignore these safety standards are plumbers and HVAC contractors struggling to retrofit piping, ducts, or an air handler through a space obstructed by a structural member, like in the photo at the top of the page.

    Also, see our blog post How much of a roof truss can I cut out to make a storage platform in the attic?

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To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation?

• What causes vertical cracks in fiber cement siding planks?

• What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

• What causes the surface of old bricks to erode away into sandy powder? 

• What are the pros and cons of concrete block versus wood frame construction?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• There's cracks running along the home's concrete tie beam. What's wrong? 

• What would cause long horizontal lines of brick mortar to fall out?

• How do I recognize serious structural problems in a house?

• What is engineered wood siding?

• Should I buy a house that has had foundation repair? 

• What is a "continuous load path”?

• Should I buy a house with asbestos siding?   

• How can I tell if cracks in the garage floor are a problem or not? 

• What do you look for when inspecting vinyl siding?

• Why is housewrap installed on exterior walls under the siding? 

• How do I recognize serious structural problems in a house?

• Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

• How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

• Should I buy a house with structural problems? 

• What are those powdery white areas on my brick walls?

• What causes cracks in the walls and floors of a house?

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

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