None. Roof trusses are an engineered assembly of pieces of lumber and metal connector plates, the sum of which is much stronger than the individual parts alone. The top sloped lumber piece on which the roof sheathing plywood gets nailed is called the top chord, and the bottom horizontal piece is the bottom chord. The connecting lumber pieces between them are named webs.

    A truss is carefully designed so that the loads are transferred efficiently through the chords and webs to the bearing points at each end. Some parts of the truss are in compression (pushed inward) and other adjacent parts are in tension (stretched out) as the weight above and below the truss moves through them. Removing any one pieces disrupts the intended direction of the transfer of loads and weakens the truss.

   The fact that the truss is still intact after web or two have been removed is not a verification that it’s alright. A truss must be able to withstand the wind loads of a hurricane and additional weight of workmen on the roof or working in the attic, for example, and removal or damage of even one piece of wood or metal connector in a truss can significantly reduce its structural strength. Don’t do it.

   The top photo shows an attic where the homeowner cut several webs away to create an open platform for storage around the attic ladder opening. The fix for this blunder is not simple. An engineer must specify the size lumber, connectors, and nails for replacing the missing webs, and it must be inspected to verify that the work meets the engineer’s specifications before the trusses are acceptable again. Spending $1,000 or more is the typical cost for engineering, materials and labor.

    Sometimes an HVAC contractor is responsible for removing truss webs, usually because of the relocation of a furnace or air handler to attic, which requires a clear area to place the equipment and a service platform in front of it. The photo below was taken in a one-year old luxury residence where the center webs of three trusses were removed to make room for a last-minute decision to move the air handler up into the attic.

   Even if you are willing to accept the reduced structural integrity of your roof when chopping into roof trusses for a “remodeling” project, any competent home inspector will nail you for it, causing additional expense and aggravation when you sell your home.

    Also, see our blog posts How can I tell if a broken truss web has been repaired correctly? and What are the most common problems with wood roof trusses? 

• • • • • • • • • • • • • • • • • • • • • • • • • • • •  

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

• 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?

• What causes roof shingles to curl up at corners?  

• What causes shingles to buckle along a line on the roof?

• What causes leaks at a fake roof dormer? 

• What causes a sagging roof ridge line?

• What causes bubble-like blisters in a built-up and gravel roof?  

• Why does it cost so much more to replace a steep roof than a low slope roof? 

• What is "ponding" on a flat roof?

• 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?

• Why is it a mistake to replace a roof and not replace its flashings? 

• Why is there no attic access hatch in the house?

• 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? 

• What are the dark lines running parallel to shingles on my roof?

• Can metal roofing be used on a low slope/pitch roof? 

• How can I make my roof last longer?  

• What are the warning signs of a dangerous attic pull-down ladder?

• How can I find out the age of a roof? 

• Should I buy a house that needs a new roof?

• 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?

• Should I put gutters on the house?  

• 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.