How much can I cut out of a floor joist?

Friday, September 28, 2018

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. 


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