Three-in-one: No Padstone Under RSJ, RSJ vs Steel Lintel, and Slabs Inside Webbing

[Gaf]

Couple queries on this. Forgive the terrible drawing.

 

Along one wall of a new build there are two separate spans (3.4m and 3.2m). Construction drawings and concrete hollow core floor slab design specified:

> 3.2m span as RSJ on 450x225 padstones

> Concrete floors bearing on top of RSJ

> 3.4m span as Steel Lintel

 

First query is whether there should be a padstone at the illuminous yellow spot? The yellow spot is a cavity wall (100 block, 150 cavity, 100block). And if so, whether that one 'middle' block in photo could be the 450x225 specified? Our building certifier's view is 'there should be a padstone there' but it 'should be ok assuming the blockwork was well done'. I personally hate the word 'assuming' for anything structural - but interested in others views on whether I'm being OTT. Above those two spans (and that illuminous yellow wall) is the majority of the second floor wall of the house.

 

Second query is just on whether there's any issue with the hollow core floor slabs having been placed inside the webbing of the RSJ and on top as specified. I'm waiting on a call back from the hollow core crew who specified the bearing as being on top. Certifier says it's normal to put them into the webbing - nothing to worry about.

 

Third query relates to the builder's decision to change the make up of the specified steel lintel over the 3.4m span to RSJ. Construction drawings specified a thermally broken steel lintel. Our building certifier said the builder didn't run the change to RSJ past him and it wasn't mentioned to us. Certifier's view is the 'builder shouldn't have made that change without telling us' but that it's nothing to worry about, no structural concerns in his opinion, and the builder used his 'experience' to make that decision i.e. no SE has had eyes on the change. This entire wall is 8.7m long and two storey high. Length wise it's made up of 1.7m block wall - 3.4m span - 250mm cavity block wall - 3.2m span - 250mm cavity block wall. Conscious of how much of this entire side of the house is held up at this location.

[Temp]

22 minutes ago, Gaf said:

First query is whether there should be a padstone at the illuminous yellow spot? The yellow spot is a cavity wall (100 block, 150 cavity, 100block). And if so, whether that one 'middle' block in photo could be the 450x225 specified? Our building certifier's view is 'there should be a padstone there' but it 'should be ok assuming the blockwork was well done'.

 

I think you need to check with the person that did the construction drawings and structural calculations. I would expect there to be a padstone there but it depends on things like the load and crush strength of the blocks used. We have beam and block first floors and in a similar areas we had to use 14N blocks and even a pier to make the wall wider.

 

37 minutes ago, Gaf said:

Second query is just on whether there's any issue with the hollow core floor slabs having been placed inside the webbing of the RSJ and on top as specified. I'm waiting on a call back from the hollow core crew who specified the bearing as being on top. Certifier says it's normal to put them into the webbing - nothing to worry about.

 

The beams for our B&B floor are done like that. Not sure about hollow core but my guess would be its ok. Some straps might be needed to tie the beam into the concrete floor?

 

40 minutes ago, Gaf said:

Third query relates to the builder's decision to change the make up of the specified steel lintel over the 3.4m span to RSJ. Construction drawings specified a thermally broken steel lintel. Our building certifier said the builder didn't run the change to RSJ past him and it wasn't mentioned to us. Certifier's view is the 'builder shouldn't have made that change without telling us' but that it's nothing to worry about, no structural concerns in his opinion, and the builder used his 'experience' to make that decision i.e. no SE has had eyes on the change. This entire wall is 8.7m long and two storey high. Length wise it's made up of 1.7m block wall - 3.4m span - 250mm cavity block wall - 3.2m span - 250mm cavity block wall. Conscious of how much of this entire side of the house is held up at this location

 

I'd get it checked out by the original specifier. The fact it was specified as a thermally broken steel lintel suggests its an opening in an outside wall? Were two separate RSJ/UB used instead ? Cavity tray above ? 

[ETC]

Padstones are needed under all structural steel.

All elements of structure need FR.

Any changes made by a contractor need to be approved by your SE.

[Gaf]

3 hours ago, Temp said:

 

I think you need to check with the person that did the construction drawings and structural calculations. I would expect there to be a padstone there but it depends on things like the load and crush strength of the blocks used. We have beam and block first floors and in a similar areas we had to use 14N blocks and even a pier to make the wall wider.

 

 

The beams for our B&B floor are done like that. Not sure about hollow core but my guess would be its ok. Some straps might be needed to tie the beam into the concrete floor?

 

 

I'd get it checked out by the original specifier. The fact it was specified as a thermally broken steel lintel suggests its an opening in an outside wall? Were two separate RSJ/UB used instead ? Cavity tray above ? 

 

Yeah a padstone was specified on the drawings and certifier saying it ‘should’ have a padstone but is likely OK. 

 

In gathering info at the minute as builder didn’t take it well when a previous deviation from drawings was spotted. Waiting on hollowcore crew to come back on it. From what I can tell there’s no straps used and only a 90mm bearing specified.

 

Its an outside wall yeah, two RSJs used for each opening so they are thermally broken in fairness. Not sure on cavity tray but assume one is there as cavity has been pumped with beads.

 

3 hours ago, ETC said:

Padstones are needed under all structural steel.

All elements of structure need FR.

Any changes made by a contractor need to be approved by your SE.

 

Cheers. Sums up my thinking. Certifier isn’t exactly backing me up on this point so was really seeking a sense of confirmation that I’m not being unfair in asking for this change to have proper oversight. We’re not confrontational (at least as best we can tell) but the builder didn’t take it well when we flagged all dormer windows weren’t built to the plans, so want to approach this with pure facts and no emotion to reduce fallout.

 

Meant to ask, does “FR” mean fire rated?

Edited February 28 by Gaf

[ETC]

FR=Fire Resistance - you’ll need 30 minutes FR for all beams supporting floors or other elements of structure.

[Gus Potter]

On 28/02/2025 at 14:56, Gaf said:

Couple queries on this. Forgive the terrible drawing.

 

Along one wall of a new build there are two separate spans (3.4m and 3.2m). Construction drawings and concrete hollow core floor slab design specified:

> 3.2m span as RSJ on 450x225 padstones

> Concrete floors bearing on top of RSJ

> 3.4m span as Steel Lintel

 

First query is whether there should be a padstone at the illuminous yellow spot? The yellow spot is a cavity wall (100 block, 150 cavity, 100block). And if so, whether that one 'middle' block in photo could be the 450x225 specified? Our building certifier's view is 'there should be a padstone there' but it 'should be ok assuming the blockwork was well done'. I personally hate the word 'assuming' for anything structural - but interested in others views on whether I'm being OTT. Above those two spans (and that illuminous yellow wall) is the majority of the second floor wall of the house.

 

Second query is just on whether there's any issue with the hollow core floor slabs having been placed inside the webbing of the RSJ and on top as specified. I'm waiting on a call back from the hollow core crew who specified the bearing as being on top. Certifier says it's normal to put them into the webbing - nothing to worry about.

 

Third query relates to the builder's decision to change the make up of the specified steel lintel over the 3.4m span to RSJ. Construction drawings specified a thermally broken steel lintel. Our building certifier said the builder didn't run the change to RSJ past him and it wasn't mentioned to us. Certifier's view is the 'builder shouldn't have made that change without telling us' but that it's nothing to worry about, no structural concerns in his opinion, and the builder used his 'experience' to make that decision i.e. no SE has had eyes on the change. This entire wall is 8.7m long and two storey high. Length wise it's made up of 1.7m block wall - 3.4m span - 250mm cavity block wall - 3.2m span - 250mm cavity block wall. Conscious of how much of this entire side of the house is held up at this location.

Hello Gaf.

 

Firstly, nothing wrong with your drawing, it's quite informative, well done! Also the photos help back up and provide a bit of context and other info.

 

I've written at some length here as concrete slab floors are heavy. Often in a timber frame the floor dead ( Permenant) loads are modestl and thus a bit more forgiving in terms of safety if something goes wrong.

 

For all, if you are asking question and posting say photos it's of massive help if you can provide enough info so we can see the whole picture. Imagine you are looking at this for the first time! We need to see some panoramic photos and then close up detail. The more you make BH members guess the less targeted info and non specific advice / suggestions you'll get.

 

@GafHope this helps a bit and lets you see how I look at stuff like this, given the info you have posted. I note you mention a certifier, I take it this is maybe a private BC or the like? Also note that "no SE has had eyes on the change." Now there are plenty experienced folk that understand a lot of this but some maybe don't fully grasp some of the nuances. 

 

The following is a kind of breakdown and what I can see from your info, what I am thinking initially in structural design terms and  why I think this way based on what I see. I won't go into great detail but hope the following helps you identify some of the things you need to check.

 

I look at your drawing and see there are two beams framing in at different levels, thus the loads on the masonry are additive. The beams appear to be simply supported.. individual beams. I can't see how much load is coming from above. The method of support to the beams is important (appear simply supported in this case) and how they are prevented from twisting.. and how they load the supports. Building foundations move about a bit and over time walls get out of plumb., this can reduce the bearing area of some floors for example. What I'm say is that you should not look at each individual element in isolation unless you have an overall idea of what you are designing. An oak framed building is much more forgiving than say a masonry building.

 

The second photo is puzzling! I can see the hollo slabs seem to be loading the L shaped masonry column via a beam between the window and door?

 

To go back a bit.  One primary strategy as SE's deploy is to look at the whole building first in a qualitative manner and ask ourselves two questions.

 

1/ Can the design cope with the veritcal loads and equally important..

 

2/ Can it resist the horizontal loads, wind and say heavy floors loading the walls off their centre of gravity.. called an eccentric load.

 

3/ We then work our way through the design, do further qualitative design, then detailed checks and go back and check everything again. In fairness to say a BC certifier they maybe don't have access or time to really lift the bonnet. But the bonnet must be lifted and any changes understood.. as if not this can be dangerous.

 

Jumping quickly ahead to the element you are asking about. I had a quick intial scan at your info, could see some of the beam supports but I first focused on the masonry column. Is is stable? It looks like a cavity construction? Can it cope with the the possible ecentric loads from the beams and also the potential sideways loading from the glazing when the wind blows. For all, many masonry columns can carry lots of load until you introduce lateral wind load loads and /or eccentric loads from beams..suddenly they can lose 50% or more of their vertical load bearing capacity.

 

@Gaf looks like you have some eccentric loads that you original SE never accounted for... as your builder has gone off and done their thing. Mind you that makes them the latest designer so probably have to carry the can for their design changes.

 

I would want to first make sure that the masonry below the beams is stable as a failure here could be sudden and unpredictable. If you get you bit of local crushing at a beam ends or rotational deflection (torsional twisting) in the beams over the glass it may crack the glass say but no one tends trends to get hurt. But twisting of the beams is bad when you have say Hollow core slabs!

 

Your builder may have significantly compromised the beam strength in terms of lateral buckling capacity. Placing the Hollo slabs with a full bearing on the top flange often allows you to treat the steel beam as being fully laterally restrained. Moving the Hollo beam rest postion to the bottom flange may have compromised the beam performance. I don't know enough about the loads from above but this is something I would want to know more about.

 

The Hollow Core slabs. The bearing may be ok if the the beam flange is wide enough. Go and check if you have enough bearing.. and remember that the walls may be moving about on their founds. The steel beams must be checked again for lateral torsional buckling not least and the twisting effect needs a look at to see if it impacts on the padstone (missing) and the masonry column stability below. You builder is unlikely to be able to do this..

 

Now as the Hollow core slabs have been sat inside and on the bottom flange then they will introduce a twisting effect in the beam which will add local stress to the inside face of the masonry column.. which will tend to bend it outwards.. add the wind to that.. it needs checked.

 

Lastly the padstones. Chances are you'll need them or maybe Engineering brick. But first I would want to make sure the Hollo slabs have adequate bearing and go from there.

 

If I was you i would get an SE to check this and make sure it is all safe. It maybe will require some tweeks if it turns out all is not as it should be so doon't panic!

 

 

 

 

 

 

 

 

[saveasteading]

Yes it should have a pad stone.

Its not an expensive thing or can made on site.   so this was , lets not say laziness but expedience,  not cost

 

If a load is put on one side only of the bottom flange it puts a twist on the beam. Beams are normally designed for vertical loads OR need further  analysis.It might require the beam to be of thicker plates or need flange bracing.

 

Your certifier is probably a generalist, only does spot checks and is unlikely to know all the nuances of Structural Engineering.

The builder may well be genuine in thinking it is OK. But the fact that they have changed things unilaterally only shows how little they really understand. I anticipate them saying that Engineers overdesign.

 

You do need an SE. I reckon this can be resolved without rebuilding but do get it looked at.

Sorted at the builder's expense obviously, including any fees. It would be useful if  the builder engages with the discussion.

[Gus Potter]

1 minute ago, saveasteading said:

I reckon this can be resolved without rebuilding but do get it looked at.

I'm of like mind. So +1

 

15 minutes ago, saveasteading said:

Sorted at the builder's expense obviously, including any fees. It would be useful if  the builder engages with the discussion.

Yes.. make no mistake about this. You are a domestic Client. The builder has lead you down a path, changed the design so legally they are on the hook! Unless you have signed something that make you responsible for the changes in terms of say structural design.. which I doubt you have.

 

 

 

 

[Gaf]

@Gus Potter Cheers for taking the time to reply with such detail. Provides further validation that I am justified in getting this properly checked.

 

Im on my phone so apologies if I miss any query or clarification you had asked for. 

 

The second photo, yes it is the case that the hollo slabs are resting inside the RSJ and are loading on that single L shaped column. The column is a cavity wall (100mm blocks, 150mm cavity, 100mm blocks). The design specified by the hollo company was for the slabs to be on top of the beams, not inside them.

 

I hate even posting this next bit but how I came to notice this myself is through sheer chance of organising all of my photos from the build. Over time I came to understand some of the building regulations so when I saw this I had a “hmmmm” moment and worst bit is the internal plastering and skimming has been done… (as has the external render) so this can’t be inspected in person without pulling off the plastering. I’m in Ireland and the process is to hire Architect and/or SE who design and spec all elements, and then a Chartered Building Surveyor (CBS), Architect, and/or Engineer are recognised by Building Control (and the bank for the mortgage) as the three professionals qualified to inspect the works in stages. We hired a CBS and I am concerned about the quality of his inspections given he didn’t spot this - when I flagged the missing padstone his first reaction was “there should be” one in place but then rowed back saying he “assumes” the blockwork done is sufficient.

 

And absolutely, as you mentioned, I did not sign anything to take responsibility for any changes. So this will be on the builder.

 

@saveasteading Yea it appears our certifier is a generalist. 

 

I hope this doesn’t turn into an argy-bargy between builder and certifier, as it is very likely the certifier has already ‘certified’ the structural build

of the house.

 

Has to be looked at regardless.

 

Thank you again.

[saveasteading]

On 03/03/2025 at 13:36, Gaf said:

certifier has already ‘certified’ the structural build

 

But they do spot checks only. Easy to miss things esp when no reason to think that the builder has ignored the detailed design.

[Gus Potter]

On 03/03/2025 at 13:36, Gaf said:

Has to be looked at regardless.

Agree, get it looked at by the SE. Main thing is don't panic!

 

Things like this crop up all the time. If there is an issue, might not be, we adopt a belt and braces appoach to fix anything with minimum disruption.

 

 

[Gaf]

On 03/03/2025 at 18:38, saveasteading said:

But they do spot checks only. Easy to miss things esp when no reason to think that the bu8lder has ignored the detailed design.

 

Say an SE looks at this and says it has to be redone / remedial works completed (e.g. pad stone has to go in as per drawings). Does that land squarely on the builder or is there some shared responsibility with the certifier for signing off on the structure as meeting regs? I'm hoping it's purely on the builder because dragging both into it could get messy.

 

The certifier's job is only to inspect on site work to ensure it aligns with BRs, versus also being required to compare on site work against the plans? As in, it wasn't his job to cross reference the plans with the builder's work right to ensure the builder was following the plans?

 

On 04/03/2025 at 21:19, Gus Potter said:

Agree, get it looked at by the SE. Main thing is don't panic!

 

Things like this crop up all the time. If there is an issue, might not be, we adopt a belt and braces appoach to fix anything with minimum disruption.

 

 

 

Have an SE lined up to look over the plans and photos this coming week as a first step check. Have it in writing from the Architect that we didn't need a structural engineer, so be very interesting to see what SE thinks. On the phone he said we're probably OK given the architect is a 'proper' one.

[Gus Potter]

8 hours ago, Gaf said:

Have an SE lined up to look over the plans and photos this coming week as a first step check.

Well done. Here are a few of my thoughts, may or may not be applicable. I appreciate you are in Ireland but the same principles apply I think.

 

Was there SE design input to the original design or did the Architect use standard rules, say the small buildings guidance (often superceeded now) or the building regs standard details? Nothing wrong in that approach so long as the guidance is followed and the rules not bent, even inadvertantly. Does the Architect have sufficient PI cover to carry out structural design? To find this out you'll often need to know just what the Architect is declaring to their insurer and just what they are covered for.

 

I ask this as this may reflect how I make a living. I'm an SE who over time has got into the Architectural design side. I'm a one stop shop and often and provide both services. The name over the door is " Structural Engineer and architectural designer. My primary PI insurance (Professional indemnity) covers me for the SE side.. it's a lot. I have a bolt on that covers me ( a small increase in premium)  to do the architectural design and BC drawngs for example. Your Architect may have a similar sort of cover but in reverse.

 

Lets assume that the Architect designed something that not only complies with the regs but took into account the site specific behavior of the house, the hollow core slabs and the beam design, bearing and masonry column stability.

 

Now in some ways this might be a moot point. The builder may well be on the hook here as they have modified the Architect's design. Last man on the job gets the blame! But doing so (the builder) they now become liable for all of the design (including building stability) equivalent CDM regulations? It's a tough world and many builders and self builders don't know the risks the run when they deviate from the drawings, even with the best of intent.

 

 

8 hours ago, Gaf said:

The certifier's job is only to inspect on site work to ensure it aligns with BRs, versus also being required to compare on site work against the plans? As in, it wasn't his job to cross reference the plans with the builder's work right to ensure the builder was following the plans?

 

To comply with the building regs you need to comply with the design drawings as the regs also include the structural design. It absolutely is the Certifiers job to ensure (in so far as reasonably practicable) that what has been build

complies with what was consented. As soon as a certifier puts in writing that they think a structural design change "will be ok" they are taking on a massive liability.

 

8 hours ago, Gaf said:

Have it in writing from the Architect that we didn't need a structural engineer

That suggests to me that your Architect is confident they have complied with, in full, the general guidance notes for example.

 

Remember don't panic.. your are rightly seeking reasurance and all may be ok.

 

You may have already done this but a good thing to do is to knock together an "aide memoir" for your SE visit. You will no doubt be paying for this so you want to get the best out of it. Put a time line on when things happened, who roughly said what to whom and include a few photos, give the SE access to all your photos. It's a good thing to do as it also crystalises your own mind to some extent. Your SE is working for you so be entirely open in your discussion.

 

All the best.

 

 

 

 

 

 

Edited Saturday at 22:04 by Gus Potter

[Gaf]

On 08/03/2025 at 21:54, Gus Potter said:

Was there SE design input to the original design or did the Architect use standard rules, say the small buildings guidance (often superceeded now) or the building regs standard details? Nothing wrong in that approach so long as the guidance is followed and the rules not bent, even inadvertantly. Does the Architect have sufficient PI cover to carry out structural design? To find this out you'll often need to know just what the Architect is declaring to their insurer and just what they are covered for.

 

There was zero SE input to the original design. We had one lined up, but as they were adamant we didn't need one (we asked more than once), we didn't go ahead - obviously we were very green at the start of this process. From what I can decipher from the way the architect describes what they did, they worked from standard rules. They describe our house as "a simple structure" and a "standard structure". When I asked about the wall with the yellow highlighter and their calculations of the structural stability / capacity to hold what is above it, they just repeat the same line of it being "of standard structure". 

 

 

On 08/03/2025 at 21:54, Gus Potter said:

Lets assume that the Architect designed something that not only complies with the regs but took into account the site specific behavior of the house, the hollow core slabs and the beam design, bearing and masonry column stability.

 

Not sure they did anything to account for site specific behaviour. The foundation depth, for example, was specified as "Depth of foundations subject to favourable conditions". Unsure whose job it was to define and assess what accounts for 'favourable conditions'.

 

 

On 08/03/2025 at 21:54, Gus Potter said:

Now in some ways this might be a moot point. The builder may well be on the hook here as they have modified the Architect's design. Last man on the job gets the blame! But doing so (the builder) they now become liable for all of the design (including building stability) equivalent CDM regulations? It's a tough world and many builders and self builders don't know the risks the run when they deviate from the drawings, even with the best of intent.

 

To comply with the building regs you need to comply with the design drawings as the regs also include the structural design. It absolutely is the Certifiers job to ensure (in so far as reasonably practicable) that what has been build complies with what was consented. As soon as a certifier puts in writing that they think a structural design change "will be ok" they are taking on a massive liability.

 

This is the area that's causing me the biggest headache. Architect has been unequivocal that they signed off on the design drawings and want no part in any modifications made on site - and I do agree with them on this, they can't be on the hook for an onsite change that was not run past them.

 

Here's how I'm looking at this (I'm using 'flaw' as a generic term), if the SE reviews the construction drawings / on-site change and:

> Flags a structural design flaw on the original construction drawings that needs remediation, then this is on the architect.

> Flags a structural flaw in the onsite change by the builder or omission of padstone as specified, then this is on the builder. However, I predict the builder going the route of (a) over engineering and unneccessary to do remediation and/or (b) certifier signed off on it, so it's on the certifier now. 

> When I flagged the onsite change to certifier, response was the builder "shouldn't have" made the change without telling us but he believes it will be fine based on the builder's "experience". 

> When I flagged missing padstone to certifier, response was "there should be" one but again should be fine "assuming" block work done well. With a previous issue that arose, certifier said that any issues that crop up down the line then it's on the builder and not on the certifier...

 

On 08/03/2025 at 21:54, Gus Potter said:

You may have already done this but a good thing to do is to knock together an "aide memoir" for your SE visit. You will no doubt be paying for this so you want to get the best out of it. Put a time line on when things happened, who roughly said what to whom and include a few photos, give the SE access to all your photos. It's a good thing to do as it also crystalises your own mind to some extent. Your SE is working for you so be entirely open in your discussion.

 

Have a Google Drive full of categorised photos to help the SE, hopefully be enough for him to assess the situation. Have got my ducks in a row with the aide memoir alright. Cheers again for the input. 

 

 

Edited yesterday at 12:07 by Gaf

[Gus Potter]

8 hours ago, Gaf said:

Here's how I'm looking at this (I'm using 'flaw' as a generic term), if the SE reviews the construction drawings / on-site change and:

> Flags a structural design flaw on the original construction drawings that needs remediation, then this is on the architect.

> Flags a structural flaw in the onsite change by the builder or omission of padstone as specified, then this is on the builder. However, I predict the builder going the route of (a) over engineering and unneccessary to do remediation and/or (b) certifier signed off on it, so it's on the certifier now. 

> When I flagged the onsite change to certifier, response was the builder "shouldn't have" made the change without telling us but he believes it will be fine based on the builder's "experience". 

> When I flagged missing padstone to certifier, response was "there should be" one but again should be fine "assuming" block work done well. With a previous issue that arose, certifier said that any issues that crop up down the line then it's on the builder and not on the certifier...

Your train of though, analysis and identifying the key questions is good and logical. Hope it all works out ok. Keep us updated as lots of folk on BH have faced / are facing similar.