Structural design

24hr turnaround guarantee

Foundation design

Beam design

Beam design

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Beam designs include simple lintel specification to major cantilevering steel structures. We offer a 24hr guaranteed turnaround for straightforward designs while major structural designs can take considerably longer.

For simple designs it is common for us to work to information supplied to us without having to visit site to measure up. This means that most beam designs are covered by our minimum charge.

What information is needed?

The information below is provided to enable our Clients to provide us with sufficient information to design beams without coming to site to measure up. If the information seems unclear, ambiguous or does not apply to your building please ring us and we will discuss it with and, if necessary, come to site. If you have not supplied us with sufficient information we will just contact you to ask for it. We will also state any assumptions we have made in the calculations. However we cannot be held responsible if there is a load on the beam that we have not been informed of and would not have been obvious from the information we have been supplied.

To calculate the size of a beam we need the span (or width) of the opening and the width of the wall. We also need to know the loads on a beam which consist of:

  • roof loads
  • floor loads
  • wall loads
  • point loads

Roof loads

There are two common types of roof construction; trussed rafters and traditional construction. Trussed rafters are large A shaped timber frames that span across the whole house. Traditional construction uses large timber beams (purlins) running horizontally that support timber rafters that span from the ridge the eaves. We will make assumptions about the weight of the roof based upon our experience and relevant codes of practice but we would need to know if there is anything particularly unusual about the roof that might make it excessively heavy.

Trussed rafters
If trussed rafters are used and they sit over the wall being removed we need to know the length of the trusses (dimension A). We also need confirmation that they are not attic trusses (trusses that are designed to allow for some living space within them) as these sometimes take support from internal walls.

Traditional roof
If traditional construction we need to know where the purlins are and if either the purlins or rafters take support from the wall being removed.

In this case the rafters are supported by the new beam and the amount of the load depends on dimension B.

If an internal wall is being removed and it supports a purlin we will need dimensions C, D and E to calculate the weight of roof being supported by the beam.

Wall loads

We need to know what height of wall is supported on the beam (dimension F). We ignore any openings although if we are trying to prove that an existing beam will be OK we might take them into account. We need to know the construction of the wall. For example, it could be a 300mm wide cavity wall (100mm inner and outer leaf with 100mm cavity) or it could be a 450mm wide solid stone or any number of other possibilities. If we are not told otherwise we would normally assume a floor to ceiling height of 2.4m.

If it is a cavity wall we need to know what material is used in each leaf as there is a big difference in weight between brick and block.

Floor loads

There will usually be a floor on at least one side of the beam. The floor joists will either run parallel to the opening in which case they do not put any load on the beam or else they sit over the beam running at right angles to it. For each floor where this is the case we need to know the length of the joists (dimension G). There may be floor joists on both sides of the wall and there may be a second or third floors and we need this information for each one of them.

Point loads

There may already be a beam sitting on the wall. If this is the case we need to calculate the load on this beam and where it sits on the new beam. To calculate the loads on it we need to know what loads sit on this beam (in other words all the above information as it relates to this beam) and we need to know where abouts it sits over the new beam (dimensions H and J). Also let us know if these 2 beams are in the same plane as each other as we will need to provide a connection detail.

Other information

We need to know the width of the wall so as we specify a size of beam that will fit within the width of the wall but will also provide support for the full width.

We need to know about the support for the new beam. For instance, if an internal wall is being removed it is usual to leave a small part of it (possibly 300mm) to sit the beam on and, more importantly, to provide stiffness to the remaining wall. If it is necessary to completely remove the wall it may be necessary to introduce some additional stiffness to the wall to compensate. A plan of the building that shows lengths of affected walls will usually be all we need.

If the beam has to sit within the depth of the floor joists we need to know this. It is common where beams are being installed in place of internal walls that a clean ceiling line is required and the beam is therefore hidden within the depth of the floor joists. If this is the case we need to know the depth of the floor joists to try to ensure that the beam is no deeper than they are.

By removing a wall and replacing it with a beam we are taking all the load off the existing foundations and putting it though the wall at either end which increase the load on the existing foundations at these points. Where we think this may be an issue we will put a note in the calculations for the Building Control Officer.

How to provide the information

Sketches, drawings, photographs etc are all useful. If we are provided with sketches of the ground floor, first floor and roof layout plans that show where the new opening is, the floor spans and what the wall construction is, is often all we need.

Typically we need:

  1. Ground floor plan with main dimensions and size of opening
  2. First floor plan showing direction of floor joists
  3. Roof layout plan indicating either direction of trusses or supports for purlins
  4. Construction and width of wall being removed

The example below is all we would need to design a beam for the opening.

The above sketch tells us that:

  • the roof is trussed rafters and that they sit over the wall to be removed and they are 7.5m long
  • there are no floor loads on the beam
  • there is a 250mm wide cavity wall above the beam (we will assume the height of this wall)
  • there is a point load from the ridge beam of the new roof and it provides us with the area of the roof
  • the opening is 4.1m wide
  • the wall is 250mm wide with a 50mm cavity

The only information we would still need would be the material in each leaf of the cavity. Is it brick and brick, or, more likely, brick and block?

Site visits, drawings and additional costs

The above information may seem complicated and difficult so if you need to speak to us just give us a ring and we'll discuss it with you. Although we can often get all the information we need without coming to site we are quite happy to do so if required.

For simple beam calculations where it is easy to explain in the calculations what is required we wouldn't usually produce a drawing. However where there are several beams, possibly some connection details and maybe a 'goal post' frame required we would also have to produce a drawing. In such cases there would be an additional cost but we would discuss this with you before starting work.

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