Lintel advice

[Backhit79]

So here is our story.
We are having a lot of renovations done to our home. We have had planning approval for a lot of modifications, some of which were to the external roof that we are now not going to do.
We are having changes to the lounge and kitchen which includes a set of bifold doors. When I spoke to the structural engineer re the beam for this 3.7 metre opening he said that the builder would know what size etc to put in! When we came to that part of the job the builder asked what were the details for the beam and I said that the SE said you would know what to put in.
The builder inserted a 4 metre 178 x 102 UB with an 8mm steel plate welded on the bottom. It looked enormous to me and I was sure it would do the job. However when eventually the SE came to look at it and he did his calculations, although he said it would undoubtedly work it would not pass building regs! Shock, horror! The builder is really annoyed as he feels he has been set up and my wife and I feel we have been let down by our architect and the SE for not ensuring that we understood that the beam had to be calculated. In addition, the SE has said that the lintel should overhang by 300mm and our builder has it overhanging by 150mm - is this enough?
Should we accept the beam and just live with it as it will probably be perfectly ok? Our builder has done masses of work for us and it all has been superb but we are really worried about the potential problems, not least if we sell the house. Helpful comments for a new member to this forum gratefully received.

 

[freddiemercurystwin]

Firstly you need to get this into the Building section of the forum. Will ‘alert the mods’.

This bifold is going in an external cavity wall? What is above the lintel? Single storey/two storey? Is the bifold sitting on the floor or hanging off the beam?

Anyway taking your thread at face value the unless he’s really wet behind the ears the builder should have been older and wiser and should not have used his imagination so cannot remain blameless. The SE and the Arch were also a bit to blame for expecting the builder to know what size, yes they would have known that BC would have expected calcs, 150mm is a standard bearing, 300mm is pretty much unheard of in domestic. If you want that certificate from Building Control then the calcs will need to demonstrate it works, can’t your SE get imaginative with his calculator? He should be bending over backwards to help out!

 

[tony1851]

As above and barring unusually high loads, a 150 bearing should be fine.
Your SE must be a bit wet behind the ears if he can't provide the figures for the bearing.

 

[terrypin]

As above and barring unusually high loads, a 150 bearing should be fine.
Your SE must be a bit wet behind the ears if he can't provide the figures for the bearing.

Or a lazy git.

Why the builder has taken responsibility for fitting the correct lintel is beyond me.

Just echoing previous posters really.

Did the architect mix the cement?

 

[themiddleagedun]

If the SE said it will "undoubtedly work" and does the calcs to prove it, end of story, BC will accept it.
Though why he didn't give a spec for the lintel in the first place, and left it for the builder to choose what to use. Who knows?...

 

[tony1851]

FWIW, my guess is that the SE has checked the beam in terms of the applied bending stress, and maximum allowable deflection; to that extent, the beam itself could well be OK.

However, it's possible that the SE believes that the bearing of the beam is short enough to overstress the blockwork immediately below each end of the beam (the shorter the bearing length, the higher the stress on the blocks).

Assuming your loads are not too great (is it supporting just a roof?) then unless your wall is built of Weetabix, a 150 bearing should not be an issue. Perhaps your SE was away when they studied bearings?

 

[Rabmac1]

I would put the blame on the SE as you pay them to calculate the dimensions of the beam for you, otherwise what did he do?

 

[Backhit79]

Thank you everyone for your invaluable advice. I have now contacted another SE who is not so wet behind the ears and he is working on the problem. I am hopeful that it will all work out ok without the need for a new beam.