Window lintel - builder's rule-of-thumb or job for SE?

Hi there,

Right, I'm replacing an 800mm wide floor length window with a conventional height (1000mm), but wider (1200mm) one, so this will have to include widening the lintel. Existing lintel is a 250mm thick by 100mm concrete beast bridging the cavity. I'm proposing to replace with standard 100x70 lintels in each leaf 1500mm long to give 150mm bearing either side of the new window. Basically I want to know if this is OK, as of course BC will be having a look. My question is, is this builder's rule-of-thumb territory, or a job for a SE?

If some details would help, the wall in question is the rear elevation of my Bungalow. It's part of an extension to the rear of the original build which was initially flat-roofed, so a few courses above the window are timber joists in hangers supporting ply and felt. At some stage a shallow pitched roof has been plopped on top of the old flat roof (which remains) so a gable (about 5-6 blocks high at the centre) has been added to this wall. Whole lot - the extension and later pitched roof addon is leightweight block rendered to the outside. I'll have to re-render where the lintel is altered, hence I dont mind a concrete lintel showing. Window is about a third along this wall so is not under the full ridge height of the gable wall.

Any advice on whether my proposed lintel spec is OK would be much appreciated, or whether this really needs to be backed up by SE calcs (BC haven't suggested they'll be asking for any). Oh and one last thing - I was looking in Wickes as they're local. Is it true their 100x70 lintels 'snap like carrots' as I read on here whilst searching?! I have a Travvy-P and a Jewsons local, too. Better bet?

Cheers,

Liam

Your lintel proposal is fine. No need for an SE.

Wickes lintels don't snap any more than any other concrete lintel. They are all the same concrete

Wickes is Trav P...

Errrrr.. is it? Is that a bit like how I bought a shed from Homebase and it was delivered by Argos, then?

Cheers guys.

Liam

TP = Wickes = Keyline = CCF = City Plumbing Supplies = Benchmarx

^woody^ said:

Your lintel proposal is fine. No need for an SE.

Wickes lintels don't snap any more than any other concrete lintel. They are all the same concrete

Click to expand...

Woody, how can you be so certain that a structural engineer is not required. Does the roof span on to the lintel or parallel to the lintel? Given the description of the alteration, it does not sound like masonry arching can be relied on. You should be aware that the majority of DIY shops only stock standard lintels with low load capacity. (i.e. in cases where arching is achieved.)

It is this type of advice that has led to so many lintel failures in the UK. By failure, this does not only mean collapse, but also excessive deflection causing cracks to the masonry.

As for the concrete lintels that appear to break easily, I suspect this is not down to faulty materials but incorrect specification.

For all of the hasel and worry, is not worth spending the £50 to £100 for peace of mind.

Re-read the OP's description and you'll see it's an opening in the gable, offset to the ridge, which itself is only six courses high.

So, arching or not, the load over this lintel - with parallel rafter span and taking the load of the originsl flat roof joists - is no great shakes and within the capability of one of those precast lintels.

Hence the Woodster's comments about an SE not being required.

JS123 said:

It is this type of advice that has led to so many lintel failures in the UK.

For all of the hasel and worry, is not worth spending the £50 to £100 for peace of mind.

Click to expand...

I totally agree.

On our last extension we had 8 air-bricks, 6 window openings, 4 doors, 3 extract fans, and a flue outlet, and 2 corbels and some oversailing. Then we had to trim the floor around soil stacks and around the stairs.

Just for piece of mind I asked and SE to calculated these for me.

Cost me £5000 in all, and I am still saving up to finish the extension.

But I know it is safe

Then I asked a building surveyor and he told me that any suitable standard lintel, in a domestic property in a typical opening with no unusual point loading will do fine. Could have saved me £5k

I thought you were one o' them flavours Woods?

As an update - since they'll be inspecting I decided to run my proposal by the LABC in an email. He suggested the inner leaf lintel might want to be 140mm deep due to the floor load above. I then reminded him it was a bungalow, and what the load conditions were but he didn't seem to want to u-turn and suggested it might still want to be 140mm deep as there may be some additional roof loading (his wording just as full of mights and maybes as my paraphrasing). I get the strong impression that if I insist on ignoring his suggestion, I'll be asked to provide calcs anyway . So I think I'll just fit 140mm deep lintels both leaves and be done with it - no great extra hassle for me really.

Thanks anyway, guys .

Liam

Ah, the good ol' LABC belt and braces approach...

Good luck anyhoo.

The only time a standard lintel should require calcs, is if it was used in a non-standard situation.

Otherwise, tell the BCO to do one

A 65mm lintel will be fine

^woody^ said:

The only time a standard lintel should require calcs, is if it was used in a non-standard situation.

Otherwise, tell the BCO to do one

A 65mm lintel will be fine

Click to expand...

Thanks Woody.

A few comments about your replies:

1. Do BCO's do free calculations for builders now?
2. Regarding your comment: "Then I asked a building surveyor and he told me that any suitable standard lintel, in a domestic property in a typical opening with no unusual point loading will do fine. Could have saved me £5k." If you feel that you have been led astray, then I suggest you make a formal complaint to the Institute of Structural Engineers. I suspect that either there is more to the story or you appointed a cowboy. If he was only providing standard SE services for a normal extension then you were ripped off. Was this a chartered SE? As for your surveyor's advice, I think you would be wise to take his advice with a pinch of salt.

By the way can you ask your building surveyor to provide the conditions required to confirm whether or not a lintel is non-standard versus standard?