Bearing Wall Removal
by John F Mann, PE
INTERIOR WALLS UNDER ROOF TRUSSES
DETERMINATION OF LOAD TO BE SUPPORTED
Opening up space by removing interior walls has become a popular feature in home renovation projects.
The first step is to determine whether or not the wall supports any other element of the building. If not, the wall (then termed a "partition" wall) can be removed without the need for any remedial work.
A wall (or part of wall) that supports other elements of the building is termed a "bearing" wall. Although used moreso in the past, the phrase "to bear" has essentially the same meaning as "to support" when used in the context of construction. A "bearing wall" can be most clearly understood as a "support wall".
Determination of whether or not a wall is a support (bearing) wall is not always as easy as some will have you believe, especially for older buildings.
The most frequent problem is that floor framing above is covered by ceiling finish. Although stud finders may be useful for preliminary investigation, they can also provide a false sense of security. The only sure way to determine if a wall is supporting other elements is to perform visual inspection along top of the wall to be removed. At least some ceiling finish must be cut away to allow for inspection.
Additional discussion focused on residential bearing walls is provided in the following article;
A general condition that can be difficult to evaluate is when floor or roof framing members are continuous over an interior wall and are also bearing on (in contact with) top of wall. Being continuous means there are no joints or laps in the member between ends.
If a floor joist or ceiling joist is lapped over a wall, or anywhere along the length of the joist, then the joist is not continuous. All walls supporting such joist are then bearing walls.
For continuous framing members, the issue is whether or not the interior wall is acting as a necessary support, or if the continuous framing members (floor joists, floor trusses, roof trusses) have adequate capacity to support loads without the wall.
Even if the wall was not intended to act as a bearing (support) wall, you will find that in many cases, the wall is actually providing some additional (redundant) support that prevents downward movement (deflection) of the floor or roof above. Therefore, if the wall is removed, the supported element may deflect (sag) downward or may begin to vibrate under load (such as persons walking on floor).
However, in some cases, what may at first appear to be a redundant support wall is in fact an essential support (bearing) wall.
A recent example of this type of condition was encountered at a townhouse in Montgomery Township NJ. Buyers wanted to remove a short wall on the first floor between kitchen and family room. The second floor above was framed with 16-inch deep floor trusses spanning side-to-side between side walls of the townhouse.
Inspection from underneath showed that, although floor trusses were in contact with top of wall, there was no vertical web directly over the wall. Lack of such web can reasonably be taken as evidence that the floor truss designer did not consider the interior wall to be a bearing wall. The initial conclusion therefore was that the wall was not necessary as a support and could be removed without the need for remedial work.
However, further inspection on the second floor revealed that a large whirlpool-type tub had been installed very near the wall below. When filled with water, total weight of the tub was about 2,000 pounds. The initial conclusion then had to be changed. Someone had made a mistake during the design process. The wall was in fact acting as (and was necessary as) an important support even though such support was not intended by the floor truss designer. The only way to safely remove this support wall would be to; (1) Remove the whirlpool bath on second floor, or (2) Perform extensive remedial work to reinforce the second floor framing, such as installation of a header beam.
INTERIOR WALLS UNDER ROOF TRUSSES
Roof trusses are generally designed to span between exterior walls, without support from interior walls. To be sure, it is best to obtain the roof truss design diagrams (including layout plan) from builder, architect or office of the municipal code official. Of course in many cases, especially for houses built more than 10 years ago, truss diagrams are no longer available.
For use of a roof truss diagram, it is essential to have the correct diagram. The roof truss layout plan (placement plan) shows locations of every roof truss.
The truss diagram will show the number and locations of all supports that the truss designer intended.
For roof trusses with length of 40 feet or less, it is highly likely that the truss diagram will show supports only at each end of the truss.
For long trusses, with span length greater than 50 feet, there is more likelihood that interior walls were intended to be supports.
Even without the truss diagram, it is often feasible to reach correct conclusions about support conditions and requirements based on visual observations.
If an interior wall is not directly under (or very near) web members that connect to the bottom chord, it is very likely that the wall was not intended as a bearing (support) wall.
Of course if there is a gap between bottom chord and top of wall, the wall is not providing support.
Even if an interior wall is not necessary as a support, some minor deflection of a truss could occur after a wall is removed if the truss is currently bearing on the wall.
DETERMINATION OF LOAD TO BE SUPPORTED
If the wall to be removed is a bearing wall, a new header beam must generally be installed (at the location of the wall) to maintain necessary support (for elements above) that has been provided by the wall.
For design of the header beam, the type (uniform, point) and amount of design load must be calculated. Complete description of how to calculate design load is beyond the scope of this article. However, in addition to satisfying building code provisions, the following key factors are involved;
(1) Length of framing members (floor joists, attic floor joists, roof joists) on each side of the wall that are supported by the wall.
(2) Any floorbeams or girders that must be supported. Length of framing members supported by such beams or girders.
(3) Any upper bearing walls (on the floor or floors above) that must be supported. Length of framing members (floor joists, attic floor joists, roof, joists) supported by such walls.
Bearing walls on the floor above can still apply load to the new header beam even though far away. Such load must be considered if the upper bearing wall is on floor joists that have to be supported by the new header beam.
Thorough evaluation of load requirements should start at the roof and proceed down. Roof load might be applicable if there is a structural ridge beam supported by interior posts.
The building code allows reduction of live load as total tributary area increases above a minimum amount. Also, live load can be reduced for load combinations that include snow and other live load.