Cordyline Aspire Limited
Consulting Civil & Structural Engineers
 
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Usually forming an opening and inserting a beam to bridge the opening is relatively straight forward.  However, if your proposals include any of the situations below you may face additional design and construction costs.
 
When a wall is removed and a beam is inserted to bridge over the opening, loads are concentrated at
the edge of the remaining wall below the end of the beam.  Most beams require padstones made up from concrete or engineering brick to spread the load onto the wall below. 
 
When the opening is greater than 3.0 metres, or the beam is supported on a narrow pier between windows or doorways, it becomes necessary to check the bearing capacity of the brick or blockwork for the full height of the wall supporting the beam. 
 
In some cases it will also be necessary to check the foundations especially in older properties or when the beam exceeds, say, 4.5 metres in length or supports another heavily loaded beam.  Satisfactory supports are as important as satisfactory beams.  When they are necessary, these additional structural calculations and checks increase the cost of designing the beam.

When an entire wall is to be removed it will often be necessary to insert a full frame incorporating columns and a spreader base beam.  This will provide stability to the remaining walls and spread the loads back along the existing footing without the need to construct additional footings.  If the opening extends to a party wall (a wall shared with your neighbour) a frame of this type will normally be essential.

Consideration should also be given to the type of ground floor to be provided in an extension.  If a suspended floor is to be supported by the wall footing this will reduce the ability of the footing to carry concentrated loads resulting a new beam.  The effect of this should be considered and the design completed before your builder starts work.

 
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