Catnic lintel has bent at front

[Loz]

 

Hi,

Just having two storey extension done and on ground floor having some 2.5m bifolds, the structural engineer specified a CG110/100 catnic lintel I guess went for that so no flex above doors. What is strange is builders have put first couple of layers of blocks on and when looking at it tonight the front edge looks bent, have put couple of pictures below, no idea how that has happened as have the same lintel for upstairs laying in garden and feels absolutely solid, was this a manufacturing defect ? But guess main question is does it matter, is there a gap above where the frame of the doors will go, with a metal lintel like that was expecting it to be dead flat especially as second storey still to go:

 

 

Easier to see in this picture, if I put a long level over at front then rocks on the bend although quite hard to see in picture:

 

 

Any thoughts greatly appreciated,

Lawrence

 

 

[nod]

For that reason I would never use a lintel over bifolds Or any other large opening 

A steel with a hit and mis welded plate is a better option 

It will be a pain to swap it 

But worse later with the bifolds and render done 

[Marvin]

I do not know if this is the case but if I remember correctly, the strength in the lintel is within the cavity space part which supports the leafs holding up the outside and inside wall skins. I believe it is possible that, if you load one leaf too much before the other leaf it can distort the lintel.  Anyway I'm sure someone will correct me if I'm wrong ?. 

 

Marvin

[Marvin]

Hi Loz.

Can you confirm the opening size and also take a picture looking up at the underside of the lintel?

[epsilonGreedy]

Not much weight on that lintel yet, I wonder if you are seeing some transport damage in a short section of the lintel or is it a progressive bend across the whole length? A photo of a taught length of string end-to-end would help.

 

Is your lintel from the standard or heavy duty range?

Edited June 18, 2021 by epsilonGreedy

[Declan52]

All metal lintels bend slightly when you build across them that's why you prop it until the work above it sets. 

In normal circumstances it wouldn't really matter but with your bi folds it will depend on how much deflection has occurred. It doesn't look that much from the pics.

[Marvin]

Also the outside leaf of the lintel doesn't look like the plain edge of a catnic CG110/100. Again, I may be wrong.

[epsilonGreedy]

20 minutes ago, Marvin said:

Also the outside leaf of the lintel doesn't look like the plain edge of a catnic CG110/100. Again, I may be wrong.

 

 

I thought Catnics were black, could that be a KeyStone?

[Loz]

Wow, thanks for all quick replies, much appreciated as pretty stressed out over it all at moment, and apologies an ensuite picture seemed to creep in on original post !

 

Ran a string along to see how much it is bent, what makes it looks worse from a distance is that because there were no small bricks to be had at any merchant for a week or more they chopped blocks down and the uneven edge is at bottom so the cement varies all along, wander if the heaver blocks rather than 2 layers of small bricks contributed, wasn't propped while course was laid, here are the pictures:

 

First one is the bend - couple of mm:

 

Appears to go up at one point !

 

 

 

Here is underside:

 

Many thanks,

 

Lawrence

[Gus Potter]

11 minutes ago, epsilonGreedy said:

 

I thought Catnics were black, could that be a KeyStone?

Me too!

 

Loz.. don't panic, could well be a bit of site / delivery damage.. however something like that will not look sweet over you doors if it's more than a couple of mm. It looks like the roof joists are not spanning onto the lintel? If so the loading could just primarily be from the few courses of block above. If you are rough casting the block you could bring a bellcast bead down just below the edge of the lintel and this would hide the bit that is bent and improve the drip over the doors.

 

Just have a quick check to make sure that if the builder has swapped the lintel type it is still ok to use for the load.

 

 

[epsilonGreedy]

3 minutes ago, Loz said:

Wow, thanks for all quick replies, much appreciated as pretty stressed out over it all at moment

 

 

Given the photos and string line I reckon you are just seeing a dints and dings along the edge of the flange. As @Marvinmentioned above the strength is in the box section in the middle cavity section.

 

I fitted KeyStone lintels and yours look very similar.

 

In your situation I would be more interested to know if a heavy lintel variant was fitted over wide opening. Also if you can measure the clear span of the opening the experts here can work out if you have a decent amount of lintel seated on the blockwork.

 

How heavy are your blocks?

 

[Loz]

4 minutes ago, epsilonGreedy said:

 

Given the photos and string line I reckon you are just seeing a dints and dings along the edge of the flange. As @Marvinmentioned above the strength is in the box section in the middle cavity section.

 

I fitted KeyStone lintels and yours look very similar.

 

In your situation I would be more interested to know if a heavy lintel variant was fitted over wide opening. Also if you can measure the clear span of the opening the experts here can work out if you have a decent amount of lintel seated on the blockwork.

 

How heavy are your blocks?

 

 

Hi thanks again for quick replies as have been really worried since spotted it earlier just after builders left, the SE specified Catnic lintel REF CG110/100 for 125mm cavity min 200mm end bearing, the opening is 2500 for the bifolds, in terms of the blocks not really sure they are not high density or anything and just assume standard blocks if there is such a thing (very new to all of this).  Has the builder swapped catnic for keystone based on few of the questions/comments ?

 

Guess thing that is really concerning me is does this need to be re-done or can bi-folds be fitted underneath okay - not yet ordered was waiting for all opening and then manufacturer was coming to measure, guess didn't want big thick sealant to take up any deformaties or do they normal have some sort of head where beam deflection can be catered for ?

 

Many thanks again, especially on a friday night.

 

Lawrence

[epsilonGreedy]

2 hours ago, Loz said:

Has the builder swapped catnic for keystone based on few of the questions/comments ?

 

 

My local BM only keeps KeyStone lintels as a stock item, catnics are a special order. Might have been the same for your builder.

 

2 hours ago, Loz said:

guess didn't want big thick sealant to take up any deformaties or do they normal have some sort of head where beam deflection can be catered for ?

 

 

What is the render edge detail along the lower edge of the blocks?

[Gus Potter]

Hello Laurence.

 

I would start by asking the builder to confirm what lintel they put in. Next step, if different from spec just drop the SE a note to say.. for example.. due to supply constraints the builder swapped the lintel for a xyz type... as said builder was trying to help out.. is this OK? and include a few photos. Many SE's are sympathetic and will go the extra mile to review.

 

As a word of encouragement. It looks like from the photos that the lintel is carrying mostly the dead weight of the blocks rather than the weight of the blocks plus a variable load (live / imposed load.. say a snow load on the roof) so most of the deflection could already have taken place. Thus when you measure for the doors you'll take the smallest dimension off a datum.. usually in the middle if the lintel has been installed level.

 

I'm being cautious here as there could be a load on the inside leaf we can't see from the photos.. if this differs a lot from the outer leaf load then you'll find in the detailed manufacturer's notes a reference to what is call the "load ratio". This is the difference between the inner and outer leaf loads. If the two say go beyond a 3:1 ratio it can make the declared load capacity invalid. Hence my suggestion to contact the SE just in case.

 

Folk on BH have different views on support beams over bifolds / large span sliding doors. Cold formed steel lintels such as Catnic / Keystone and others are absolutely fine in the right circumstances so long as you know how to design them and also very importantly make sure they are installed correctly as per the instructions. With a 2.5m bifold you should be well within the region where a Catnic or similar will be fine.

 

Yes, cold formed steel lintels are attractive as they can be cheeper and help with thermal bridging, but they a more complex beast..

 

Laurence the standard of workmanship on the blockwork could be better.. but I would like to see the whole wall inside and out before making further comment. Let your SE see this as they will want to look at things in the round. The main thing is don't panic and think it has to come down! If it is an issue there are many work around solutions.

 

 

 

For the very curious.. sizing Catnic / Keystone lintels and similar products for bifolds.

 

Yes there is no doubt that folk have issues with these cold formed steel lintels. A Universal beam is a steel beam that is rolled into shape when the steel is still hot. It starts off as a big lump of hot metal and is rolled in it's "hot" state. Roughly, a cold formed steel section starts as a big lump of hot metal that is rolled into a big toilet roll, a standard roll weighs about 6-7 tonnes from memory. This roll goes to say Catnic, they unroll it and shape it using a series of rollers into their lintel section when the steel is cold. But these two different processes result in the steel behaving in a different way. Cold formed lintels can be more complex to install depending on their shape and if they are supporting just the outer leaf of masonry or both.

 

if you are say a designer and want to use a Catnic type lintel over bifolds you can do a back calculation. Lets say you have a span as in Laurence's case of 2500mm. Now deep in the technical spec may be something that says "deflection limit is based on span / 360"  This means that one of the criteria is that the total deflection should not exceed 2500/360 = 6.9mm.. Often ok for bifolds particularly if you have more "dead" load that bends the lintel before you get the doors measured up.

 

But say you have a span of 3600 mm. Now here you take 3600 / 360 = 10mm.. This is a recognised deflection limit in the codes.. but for bifolds in particular you may be starting to push your luck. Remember that in general DIY / self builders have less control over the standard of workmanship. What an SE/ Designer can do is to say.. we are not happy with manufacture's deflection limits. We know that this lintel is certified for X amount of load at a deflection limit of span/360 = 10mm .. lets make sure that we size the lintel based on 80% of the declared load and all other things being equal (lintel bearing etc) we are now on the ball park to getting a deflection of roughly 80% of 10mm = 8mm and this we can live with in terms of door design.

 

If you read this far.. thanks!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited June 18, 2021 by Gus Potter

[Loz]

10 hours ago, Gus Potter said:

Hello Laurence.

 

I would start by asking the builder to confirm what lintel they put in. Next step, if different from spec just drop the SE a note to say.. for example.. due to supply constraints the builder swapped the lintel for a xyz type... as said builder was trying to help out.. is this OK? and include a few photos. Many SE's are sympathetic and will go the extra mile to review.

 

As a word of encouragement. It looks like from the photos that the lintel is carrying mostly the dead weight of the blocks rather than the weight of the blocks plus a variable load (live / imposed load.. say a snow load on the roof) so most of the deflection could already have taken place. Thus when you measure for the doors you'll take the smallest dimension off a datum.. usually in the middle if the lintel has been installed level.

 

I'm being cautious here as there could be a load on the inside leaf we can't see from the photos.. if this differs a lot from the outer leaf load then you'll find in the detailed manufacturer's notes a reference to what is call the "load ratio". This is the difference between the inner and outer leaf loads. If the two say go beyond a 3:1 ratio it can make the declared load capacity invalid. Hence my suggestion to contact the SE just in case.

 

Folk on BH have different views on support beams over bifolds / large span sliding doors. Cold formed steel lintels such as Catnic / Keystone and others are absolutely fine in the right circumstances so long as you know how to design them and also very importantly make sure they are installed correctly as per the instructions. With a 2.5m bifold you should be well within the region where a Catnic or similar will be fine.

 

Yes, cold formed steel lintels are attractive as they can be cheeper and help with thermal bridging, but they a more complex beast..

 

Laurence the standard of workmanship on the blockwork could be better.. but I would like to see the whole wall inside and out before making further comment. Let your SE see this as they will want to look at things in the round. The main thing is don't panic and think it has to come down! If it is an issue there are many work around solutions.

 

 

 

For the very curious.. sizing Catnic / Keystone lintels and similar products for bifolds.

 

Yes there is no doubt that folk have issues with these cold formed steel lintels. A Universal beam is a steel beam that is rolled into shape when the steel is still hot. It starts off as a big lump of hot metal and is rolled in it's "hot" state. Roughly, a cold formed steel section starts as a big lump of hot metal that is rolled into a big toilet roll, a standard roll weighs about 6-7 tonnes from memory. This roll goes to say Catnic, they unroll it and shape it using a series of rollers into their lintel section when the steel is cold. But these two different processes result in the steel behaving in a different way. Cold formed lintels can be more complex to install depending on their shape and if they are supporting just the outer leaf of masonry or both.

 

if you are say a designer and want to use a Catnic type lintel over bifolds you can do a back calculation. Lets say you have a span as in Laurence's case of 2500mm. Now deep in the technical spec may be something that says "deflection limit is based on span / 360"  This means that one of the criteria is that the total deflection should not exceed 2500/360 = 6.9mm.. Often ok for bifolds particularly if you have more "dead" load that bends the lintel before you get the doors measured up.

 

But say you have a span of 3600 mm. Now here you take 3600 / 360 = 10mm.. This is a recognised deflection limit in the codes.. but for bifolds in particular you may be starting to push your luck. Remember that in general DIY / self builders have less control over the standard of workmanship. What an SE/ Designer can do is to say.. we are not happy with manufacture's deflection limits. We know that this lintel is certified for X amount of load at a deflection limit of span/360 = 10mm .. lets make sure that we size the lintel based on 80% of the declared load and all other things being equal (lintel bearing etc) we are now on the ball park to getting a deflection of roughly 80% of 10mm = 8mm and this we can live with in terms of door design.

 

If you read this far.. thanks!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Thanks for very detailed post, I have also been reading some bi-fold fitting instructions and they seem to allow for at least 5mm all round so guess could go a little bit more at top, the more I look at it the more I think it is yard/transport damage than deflection due to the irregular way it is bent and it was the beam that had bend on one corner that they flattened, guess nothing I can do now and just get door installer to take it into account, shame as everything else looking good so far,  many thanks for all the excellent input really is a great forum and now only one really using as get the best replies,

 

Lawrence 

[Dave Jones]

On 18/06/2021 at 17:37, nod said:

For that reason I would never use a lintel over bifolds Or any other large opening 

A steel with a hit and mis welded plate is a better option 

It will be a pain to swap it 

But worse later with the bifolds and render done 

 

couldn't agree more.

 

too much flex in catnics, guaranteed to pinch the doors when the building settles/drys out. steel all day long.