In the UK you will need to comply with building regulations and they will require calculations from a structural engineer. The costs are not too bad mine for the roof structure on the garage workshop extension were £400.00 and that was using 270 x 90 glulam beams. Although you may well be able to build an extension under permitted development it still needs to be signed off by the local building inspector failure to do so will present problems if you try to sell the property. Calculations are quite complex as it is not just a case of knowing the beam will support the loads and that assumes you know how to calculate the load but also the bending moment. The beam will have a limit to how much it is allowed to bend under the load applied. Throw in wind and snow loads………………

Bob

Brian

Some info that may be of help … ref… Newnes Mechanical Engineers pocket manual.

.

George.

The other area that is often overlooked is the bearing conditions – normally engineering grade bricks in buildings. You need to m match your total loading to the bearing material and size. Building control will threaten to check the calculations but in reality, they probably have neither manpower or skilled people to do it – your certificate of compliance really means nothing if anything gets to litigation. They make a big point of ensuring that they do not provide any guarantee…..

Mark

When i built my extension i used a fair bit of steelwork including columns to support the main load bearing beam (rather than building brick piers) my architect used a friendly certified structural engineer who for about £80 did the necessary calcs. These came hand written on three sheets of plain A4 and were duly submitted to building control.

There was no covering letter or anything to suggest the bloke who produced them had any qualifications or idea of what he was doing, but they looked mightily impressive, i doubt anyone at building control would have had the knowledge to decipher if in fact they were beam calculations or moon landing trajectory calcs.

Being a good lad I did however follow them to the letter, and it cost me a small fortune in steel, the main span beam was only 16ft long and weighed a shade over a tonne as specced. Flipping ridiculous for what it was holding up. I reckon something half the size would have been adequate. Luckily i managed to borrow a tractor to lift it into place.

Calcs must have been ok though as its not fallen down yet……

As I said mine was for the roof structure which included 5 glulam beams and all the rafters which is more than a single beam is likely to cost in terms of calculations which should be around £100 to £150. Not forgetting if the structural engineer gets it wrong you can claim and a good one will have professional indemnity insurance.

Although it is probably true that the council have no liability they can stop work and make you make changes if they think it does not meet the standards.

Indemnity insurance is normally taken out buy the seller, a buyer will have to wait 12months after completion before they can take it out.

Bob

If you opt for the approved inspector route and they are not happy with what you are doing as they can only advise and withdraw,they have no powers, then unless you appoint another the council will take over automatically and can force changes if they do not comply even to the point of doing the work them selves and present you with the bill.

When I have been down this route and this included both extending sideways a built-in garage and also whole house construction including a double width garage, I did the full calculations of loads and steels required. The Building Regs Departments on both cases approved the actual calculations. When a friend and neighbour who happened to be a Lecturer in Building Technology submitted plans for his garage with an insitue cast roof, they threw the book at him and made him produce test cubes of the mix as well!!