Internet Know How Posted January 12, 2021 Share Posted January 12, 2021 Hey, would really appreciate your views on this one! Looking for thoughts on structural support for block and beam on a new build with basement and the various preferences from my designers Basement: 300mm concrete walls, internal cavity with insulation, inner leaf block, plasterboard Ground floor upwards: outer leaf brickwork, cavity with insulation, inner leaf blockwork My Architect wants an unbroken insulation zone from the basement to the roof, and to make this happen the block and beam to ground floor will sit on the inner leaf blockwork built up from the basement 300mm slab. We will also have block and beam on the 1st floor, so again the block and beam will sit to the inner leaf blockwork. Architect's request: My SE instead wants to shift over the block and beam so that the inner section of the 300mm basement walls provide structural support for the floors, rather than the blockwork as shown above. This is going to introduce a bridge to the insulation layer. The SE said if we use the above approach he wants to install steel posts and beams to support the floors above. SE Preference: If we didnt have a basement, and still planned to use block and beam, the beams for the floor would sit on the inner leaf of the block wall anyway. Just because we place a basement wall in does not mean it then has to be used to support the beam/hollow core floor? When we get to the 1st floor we have another block and beam, and for this we have no option but to sit the beams on the inner leaf block work. Which option should we go with? Thank you Link to comment Share on other sites More sharing options...
mvincentd Posted January 13, 2021 Share Posted January 13, 2021 With 300mm of concrete in the basement i'm wondering why you need to build a blockwork inner leaf at all..just plasterboard the internal face of the concrete, put the insulation outside...start the upper cavity wall outer leaf on a marmox block to enable the insulation to achieve continuation across to the cavity. Sit your floor on the concrete. 1 Link to comment Share on other sites More sharing options...
George Posted January 13, 2021 Share Posted January 13, 2021 (edited) The innerleaf is a good idea, there are systems which rely in on wibbly plastic lining which create a small cavity for any penetrating water to go through - but with the floor above to be supported, it's a decent solution*. I assume you are also tanking the outside of the concrete, but it is essential to have 2 waterproofing system and the internal lining is the most robust (especially for smaller builders/contractors). There are a few structural reasons why the SE may wish the floor to be supported off the concrete: - to keep a waterproof lining, there are no wall ties back to the concrete so that the blockwork alone is too slender to support the floor (a normal beam and block support on blockwork is only 2 courses high, not ~7 or 8 courses) - the blockwork specified is not strong enough - floor is providing restraint to the top of the concrete wall - doesn't want a line load on the retaining wall foundation as it will require increasing the size of the wall If those are not problems for the SE then I cannot see a reason for it not be supported on the blockwork as per the architect. I would suggest offering more fee for them to adapt the design but avoid steelwork, as this may need to be galvanised. *If you end up not using the blockwork, you get rid of it and look for a cheaper lining system Edit - you cannot disregard the SE opinion, by the way. You must use the SE option at the moment! Edited January 13, 2021 by George 2 Link to comment Share on other sites More sharing options...
Temp Posted January 13, 2021 Share Posted January 13, 2021 We have a beam and block ground and first floor. Also needed steels to reduce the span of the beams. SE was happy for the steel to rest on the block inner leaf but in one or two spots specified denser blocks and piers due to the loading. Mostly where steels bear on areas between two windows. 1 Link to comment Share on other sites More sharing options...
Internet Know How Posted January 13, 2021 Author Share Posted January 13, 2021 12 hours ago, mvincentd said: With 300mm of concrete in the basement i'm wondering why you need to build a blockwork inner leaf at all..just plasterboard the internal face of the concrete, put the insulation outside...start the upper cavity wall outer leaf on a marmox block to enable the insulation to achieve continuation across to the cavity. Sit your floor on the concrete. My architect said its a better idea to have the insulation internally. If we have insulation externally we have to bring the tanking further up the wall so the termination detail of the tanking would not be as good. He said we need the insulation to meet the SAP calcs. So, it either has to go inside or out and the preference was inside and then to run that void basement to 2nd floor as per the images. I get your point though as thats what I said to him as I wanted to avoid all the internal perimeter blockwork Link to comment Share on other sites More sharing options...
Internet Know How Posted January 13, 2021 Author Share Posted January 13, 2021 10 hours ago, George said: The innerleaf is a good idea, there are systems which rely in on wibbly plastic lining which create a small cavity for any penetrating water to go through - but with the floor above to be supported, it's a decent solution*. I assume you are also tanking the outside of the concrete, but it is essential to have 2 waterproofing system and the internal lining is the most robust (especially for smaller builders/contractors). There are a few structural reasons why the SE may wish the floor to be supported off the concrete: - to keep a waterproof lining, there are no wall ties back to the concrete so that the blockwork alone is too slender to support the floor (a normal beam and block support on blockwork is only 2 courses high, not ~7 or 8 courses) - the blockwork specified is not strong enough - floor is providing restraint to the top of the concrete wall - doesn't want a line load on the retaining wall foundation as it will require increasing the size of the wall If those are not problems for the SE then I cannot see a reason for it not be supported on the blockwork as per the architect. I would suggest offering more fee for them to adapt the design but avoid steelwork, as this may need to be galvanised. *If you end up not using the blockwork, you get rid of it and look for a cheaper lining system Edit - you cannot disregard the SE opinion, by the way. You must use the SE option at the moment! Yes to forms of waterproofing...sika in the concrete and then a sika membrane under the slab and on the exterior walls. I agree there is no tie back to the concrete walls from the blockwork. I think he just sees the concrete wall as useable and far superior than the block, which it is really isnt it. Its just the cold bridge it introduces by splitting the insulation. The SE has suggested we increase the concrete wall to 350mm to support the block and beam. I think we will end up going with the SE's preference and dealing with the bridge in the insulation it introduces. Link to comment Share on other sites More sharing options...
mvincentd Posted January 14, 2021 Share Posted January 14, 2021 I have as sketched below in various positions on my build....the Marmox block continues the insulation. Link to comment Share on other sites More sharing options...
George Posted January 14, 2021 Share Posted January 14, 2021 Most likely the primary reason is the lack of ties. Structural walls must have minimum thicknesses for building regulation compliance and, more importantly, a slender blockwork wall has a much reduced load bearing capacity. Another solution could be developed, I'm sure. But I wouldn't worry too much about small thermal bridges - you might be able to sit the beam and block onto foam glass blocks to minimise the thermal bridge and use 25mm PIR boards to wrap around any potential cold spots. Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 I have just been on a call with him and he feels that even with a 140mm block supporting the hollowcore, he wanted to add in steel frame support. He has gone away to look over the calculations. We could use a 140mm block and tie it into the concrete wall. Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 6 minutes ago, mvincentd said: I have as sketched below in various positions on my build....the Marmox block continues the insulation. thats great, thanks for providing this I will speak with my Architect about this design option Link to comment Share on other sites More sharing options...
PeterW Posted January 14, 2021 Share Posted January 14, 2021 17 minutes ago, Internet Know How said: I have just been on a call with him and he feels that even with a 140mm block supporting the hollowcore, he wanted to add in steel frame support. He has gone away to look over the calculations. We could use a 140mm block and tie it into the concrete wall. Why..??! Just up the strength of the blocks to 140mm 10N and you can go to 4 storey with beam and block floors anyway. 1 Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 1 minute ago, PeterW said: Why..??! Just up the strength of the blocks to 140mm 10N and you can go to 4 storey with beam and block floors anyway. I agree with you and this is what my Architect was telling him on the call too and the SE seemed more comfortable using the concrete wall so lets see what he comes back with later having done more work on the calcs. Maybe he is using software that makes is job easier and it brings out steel all times. Link to comment Share on other sites More sharing options...
ToughButterCup Posted January 14, 2021 Share Posted January 14, 2021 On 12/01/2021 at 21:45, Internet Know How said: ... Which option should we go with? ... Who is taking responsibility for the decision? Put another way, whose PPI is on the line for getting it wrong? 1 Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 1 minute ago, ToughButterCup said: Who is taking responsibility for the decision? Put another way, whose PPI is on the line for getting it wrong? Its always going to be the SE isnt it Link to comment Share on other sites More sharing options...
ToughButterCup Posted January 14, 2021 Share Posted January 14, 2021 There's your answer. Bloody interesting problem though; thanks for asking here.? Link to comment Share on other sites More sharing options...
PeterW Posted January 14, 2021 Share Posted January 14, 2021 7 minutes ago, Internet Know How said: Its always going to be the SE isnt it Not necessarily ... 9 minutes ago, ToughButterCup said: Who is taking responsibility for the decision? Put another way, whose PPI is on the line for getting it wrong? So... Architect has specified it this way for waterproofing and reduced condensation Structural Engineer has specified it this way for strength and structural integrity. Do it the SE’s way, it leaks and who pays ..?? Do it the architects way and cracking and movement occurs, who pays ..?? Only way to resolve this is a solution they both agree in writing on. Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 Architect is saying professionally he cannot disagree, and the SE is in review again, however I can echo my thoughts after consulting with the builders and from what I am hearing there are really no issues building up off the block wall as per the Architects preference, and that's using a solid floor at first and timber on 2nd floor. If we go with the SE preference it means we do not require block internally in the basement or the internal insulation, so it would save about £10k materials and labour Link to comment Share on other sites More sharing options...
George Posted January 14, 2021 Share Posted January 14, 2021 7 hours ago, PeterW said: Not necessarily ... So... Architect has specified it this way for waterproofing and reduced condensation Structural Engineer has specified it this way for strength and structural integrity. Do it the SE’s way, it leaks and who pays ..?? Do it the architects way and cracking and movement occurs, who pays ..?? Only way to resolve this is a solution they both agree in writing on. The architectural proposal minimises cold bridging, but are (or can be made to be) equivalent on waterproofing and a low risk for condensation. It is not optional to chose an architectural suggestion over a SE design as it is the structural load path in question. 1 Link to comment Share on other sites More sharing options...
PeterW Posted January 14, 2021 Share Posted January 14, 2021 16 minutes ago, George said: The architectural proposal minimises cold bridging, but are (or can be made to be) equivalent on waterproofing and a low risk for condensation. It is not optional to chose an architectural suggestion over a SE design as it is the structural load path in question. I’m not disagreeing but that wasn’t the point of my comment, it was who’s liability would pay in the event of an issue and it was outlining both the issues in question. Getting agreement in writing is vital, especially when litigation could occur. 2 Link to comment Share on other sites More sharing options...
Internet Know How Posted January 14, 2021 Author Share Posted January 14, 2021 19 minutes ago, George said: The architectural proposal minimises cold bridging, but are (or can be made to be) equivalent on waterproofing and a low risk for condensation. It is not optional to chose an architectural suggestion over a SE design as it is the structural load path in question. 100% agree and in this case we have other SE opinion who said although a steel frame will work fine, its not necessary Link to comment Share on other sites More sharing options...
Internet Know How Posted January 17, 2021 Author Share Posted January 17, 2021 My SE has said he is happy to progress using the blockwork as structural providing we use 140mm block. So I have 2 options available at this point 1.) Use blockwork internally for ground floor support, this means I have to install 210sqm or over 2000 block in the basement perimeter. unbroken insulation zone 2.) Use concrete formed walls as support, which means I do not have to use any block in the basement. Walls supported on 1st floor from internal block. Insulate basement externally I am tied between the two options because option 1 will cost me £10k more minimum in block and labour. We have standing water according to SI report at 1.5m so not sure if insulating externally is the best option either. Link to comment Share on other sites More sharing options...
PeterW Posted January 17, 2021 Share Posted January 17, 2021 £10k..?? 140 7.3N blocks come in around £30/m laid so you should be closer to the £6k, and that would be offset by a slimmer concrete wall so it should be cost neutral. Have you considered ICF for below ground ..?? 1 Link to comment Share on other sites More sharing options...
Internet Know How Posted January 17, 2021 Author Share Posted January 17, 2021 (edited) The SE wants 10n blocks he said, so I have also added on a little for the extra scaffold too. The walls are going to be 300mm at the moment but he may push them up to 350mm if we use the concrete walls. That extra 50mm increases the concrete/sika mix by £2k So the trade off is the saving on not using the internal block work compared with the external insulation termination detail....plus I gain more space internally without the block, but it is a large house so wont notice it in the basement. And....extra space means more ££ on tiling as we have a large pool area to tile ICF...I have looked into it and I prefer the poured concrete. Not priced ICF though to be honest. Edited January 17, 2021 by Internet Know How Link to comment Share on other sites More sharing options...
keith65 Posted January 17, 2021 Share Posted January 17, 2021 Hi Could you make the concrete wall wider in the basement and step it so the floor sits on the step this would save on laying blocks and wall would be stronger. Link to comment Share on other sites More sharing options...
Internet Know How Posted January 17, 2021 Author Share Posted January 17, 2021 4 minutes ago, keith65 said: Hi Could you make the concrete wall wider in the basement and step it so the floor sits on the step this would save on laying blocks and wall would be stronger. We could create this, but it is more work and the same as it sitting on the top of the wall. Maybe this below reduces any bridging..i dont really know Link to comment Share on other sites More sharing options...
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