Frequently Asked Questions
Why do I need a Structural Engineer?
So… you have Planning permission, and you have organised a builder. But, just before your builder starts on site you get told: “You need a ‘Structural Engineer’”.
“A what?”, you say. “Design of steel beams and foundations? Haven’t the architect and builder already done that? Isn’t that what I paid for?”
Sit back, relax, and let us explain…
The architect designs the building in terms of general aesthetics, the spaces created, and how they work for the proposed building users - be they a family or a business. This is in order to meet the clients needs, and obtain Planning permission, if necessary. After which, the architect may be employed to specify the building materials and construction details of the project - including the fire, acoustic and thermal properties of the proposed buildings - to meet the appropriate Building Regulations.
“And, then the builder then builds from the architects drawings…?” you say.
Well, not always. The architects’ drawings cover most parts of the Building Regulations and construction, but do not cover ‘Building Regulations: Part A - Structures’, which is: how the building will stand up. Part A is concerned with how the building will resist the wind loads, live loads and snow loads acting on it, as well as the self-weight of the building materials selected.
We, the structural engineers, produce the design of the structure that holds the building up. The architect and builder, who may have years of experience, do not hold insurances to cover ‘design responsibility’ for any structural items. Any structural designs or advice on structural items will need to be carried out by a suitably insured structural engineer.
Any deviation from an architects or engineering drawings and specifications will invalidate the insurance of the design, and will leave you with no recourse back to the original designer.
Why do I need a site investigation?
You are about to spend an awful lot of money on a new extension or house, the last thing you want to do is to shell out more money on a site investigation, right?
As engineers, we have available the basic geological data for the UK (through online viewers) to give us an overview of the ground conditions of the sites we work on. However, the data is generalised and the reality of a specific building site maybe very different to this large-scale information. We need to see what’s in the ground to ascertain what the potential loading capacity is, how it might behave over the course of the seaons, and how any vegetation on or around the site might affect the building.
Take clay as an example: it’s a material we are all familiar with and looks quite innocuous. However, it has seasonal variations and is impacted by trees and planting, which give it potential to damage new and existing buidlings. This impacts the design of the foundations in clays. If we have sufficient data on the clay type, we can advise on how to deal with the impact of seasonal variations and trees, and this data comes from a geotechnical site investigation. (PS: even if you cut the tree down you are not resolving the issue. Clays can take over 20 years to recover from excessive water removal.)
Another example of information to come from a geotechnical invesitgation is ground contaminants: as the population of the UK increases, so does the demand for housing, which has lead to an increasing use of brown field sites. We need to understand the previous use of the site to understand the consequences on the ground. Ground contamination can pose a significant risk to human health and child development. Common contaminants are radon, methan and CO2, but some sites have other dangerous contamination such as asbestos and petrol.
All of these things, and other critical information, can be obtained from a geotechnical site investigation. Knowing these risks early on in the design process mitigates the risk of unforseen costs during the construction of the foundations and drainage, helping you to have more surity that the costs you get back from tender will be what you actually end up paying for your project.
What is Building Control for?
What’s the difference between Building Control and a Structural Engineer?
Structural Engineers carry out the structural design and carry ‘design responsibility’ and insurances for the information in the drawings and calculations; essentially taking on the risk for the structural design solution.
Building Control Officers ensure that the building is constructed as precise the drawings and specifciations provided by the building design team. They have no authority or insurances to change or modify the design without the authority of the Structural Engineer (or other designers). They are there to assure the project is built to the design standards.