epsilonGreedy

Yes per block. I got an estimate for my house from damp to wall plate, 50p per facing brick and £1.30 per block. In the foundation calc I discounted the per block rate to reflect no wall ties and the lower quality if finish below ground. Conversely there is leveling out and laying 18kg blocks at ankle height cannot be fun after the first 20. A search here indicates 200 to 300 blocks a day for a 1+1 team.

Post Deleted - The forum software did something strange and copied an earlier post of mine.

I am coming around to your thinking here but double checking the maths... 3 x £0.87 + 3 x £1.10 (labour) + mortar for three blocks = About the same as a fancy Celcon trench block. Is my costing correct?

Not yet, I was first trying to ascertain what the technical options are. From other posts above I get the impression that the Stowel foundation blocks arrive at a painful cost. The manufacturer has probably identified a market niche for those who want trench block convenience but none of that bubble filled rubbish and priced accordingly. I am coming to the conclusion I may as well get a large drop of regular dense concrete blocks on site because whatever the final detail of the footing blockwork they will end up in the beam & block floor.

From my reading up on Celcon thin-joint I understand that aerated blocks are known for settling and causing plastering problems. Are you saying the hairline cracks develop into true failures? I also checked out their web site earlier, a Britstol based family business. Are their blocks in the general BM supply chain?

Re. the "edge of block" bit, yes I agree which is why I am proposing just aerated foundation blocks with two courses of dense above. The upper dense blocks would carry the immediate point/edge loads of the beam & block floor. Since starting this thread I found the following claim on a product page at H&H. https://www.hhcelcon.co.uk/solutions/by-product/celcon-foundation-blocks Surely one of the major manufacturers of blocks in the UK would not risk litigation over a foundation component with such an unsubstantiated statement.

This seems to be a common grassroots perception but I cannot find any science to back up the claim. A 2-story masonry house is not that heavy per sq mm so I doubt the overall weight of a house is enough to stress the lowest course of aerated trenchfill foundation blocks to the point of fracture and crumble. I can comprehend that once a beam & block floor is loaded with blocks and 80mm of screed it is heavy and there could be concerns about point loading at the seat points where a beam is supported by an aerated block. However I am not proposing such a layup of the courses, with my original plan the point loads of the b&b floor would be taken by two courses of dense blocks which will transmit tolerable loads onto the lowest course of aerated trench blocks. Maybe the issue is differential thermal expansion where footing block courses are made from a mixture of dense and aerated blocks? What irks me is that everyone is indicating that there is something dubious about lightweight trench fill blocks but the online BM sites are oozing with such examples whereas no one sells dense blocks of the same size probably because if such a beast was manufactured it would be as heavy as three suitcases on the verge of attracting a Ryan Air excess weight surcharge. I think the greatest risk to my selfbuild right now is that I will put my footings brickie team in hospital and end up dealing with their injury solicitor.

There is a mass of specification text scattered over the diagrams, not had time to read it all yet. No, private building control covered that function. My building control chap returned some positive comments on the quality of the diagrams and just raised a point of clarification with me over sash windows and fire egress regs.

Nope ? Reckon I am doing ok so far, will post an accounting blog entry soon.

Small Update: The chap who created my building control diagrams advised this morning one of the drivers for lightweight trench fill blocks is the weight issue under the CDM regulations, particularly when 300mm wide.

My concern is that the market signals you are giving might thwart even that modest expectation. The modern estate newbuilds nearby are not a concern, they will attract a very different buyer. As to the logic of banded price searches, people will expand their search price band to factor in a typical negotiation margin. Your pricing logic re. carpets is no very logical. New carpets only have value with newbuild move-in packages. The likelihood that newish carpets match the interior design requirements of a viewer is small, the most likely result is that the viewer will think "hmm smells like a new carpet, why did they fit something so hideous just before selling... now they will expect me to pay for their clueless interior design decision".

The fear of future employment on the shelf stacking night shift at Tesco can be persuasive. This is the true problem, lack of political will. Some of the worst IT projects I have worked on are where the management use subtle hints they want to be deceived.

I am worried that you could loose possibly £20k on this sale. If your house was valued at £260k 5 years ago when the market was struggling to rebound from the financial crash then it should be worth +10% by now. Your home lies within a healthy economic region bounded by Bath, Bristol, Reading, the M4 and Bournmouth/Southampton to the south. I doubt very much property prices have been flat for the past 5 years. Another concern is this "offers over" nonsense. This is the language of deluded fools and people working around the poorly designed search algorithms of internet property sites. There are long term figures available that show the typical difference between advertised prices and sold prices, I think the national figure is -7%. Your present sales method is going to confuse the market. People will think, "wow that's cheap so what defect is lurking". Some will scroll on because they want a trouble free transaction whereas others with an appetite for risk will start pitching in at -5% and -10% of the asking price. Others will automatically resist the "offers over" barrier and mentally pigeon hole your property as one to watch & wait until the seller accepts market reality.

True but what is best for planet earth? 100 selfbuilders delivering a high spec passive house. Or 100 wayward EPC assessor rogues getting disbarred on grounds of gross negligence or fraud which then causes 5,000 of their colleagues to smarten up their act.

Ok I am getting a strong sense that aerated trench blocks are the invention of the devil. I still do not really understand what the problem is but the consensus is obvious. Some elements of the building trade and SE's must find trenchblock acceptable otherwise they would not be manufactured. I now need to rework the block course maths to get to the right beam support height using the 350 x 300 x 100 examples mentioned above. The JCB actually removed an extra 70mm of oversite so I can comfortably maintain a 200mm void clearance height should the beams sit a bit lower (10mm to 20mm) relative to DPC. Furthermore, should I opt for thin-joint and jumbo blocks for the inner wall then there is no need to maintain course height parity with the facing bricks (apart from ho hmm external door thresholds). Or Or, final thought just start the cavity footing with standard 7N concrete blocks sitting on the poured concrete because the finished level has such a small variation?

I see the OP is getting loads of quality structural advice so instead I thought I would chip in re. lifestyle. First I think the big wide Potton statement fireplaces are great and it is worth surmounting the structural challenges to achieve the end result. The 1800 sq ft Potton "cottage" demo house in Sandy is a testament to how good this can look. Where I would caution the OP is on the gas stove focus. I put a gas stove in a proper class-1 chimney and regretted that decision for 12 years. For the last three years I have lived with a proper fire and there is no comparison. This hiss of the gas delivery does not match the random sound track of a proper fire while reading the Sunday papers on a winter afternoon. I would prefer to have 10 proper fires a year than 50 gas fire click-start experiences. My now started selfbuild will have two working chimneys and a 3rd false one, which reminds me I need to start researching what block floor widget I need to draw air up from the void into a wood burner stove.

Interesting. I purchased a secondhand cement mixer last weekend from a pro brickie who was getting rid of his 240v equipment after a run-in with health & safety. We got talking about my selfbuild and he stressed this very point about not skimping on the height of pipework upstands emerging through the unfinished floor. Shame on Potton for cursing you with that team of groundworkers.

Now I am confused, I can picture the layup with alternating flat/upright courses comprised of standard block. It sounds cheap in material costs and avoids pouring a concrete mix into the below ground cavity. What I do not get is: 300mm thermalite trenchblocks = bad 300mm special concrete blocks = good

Yup. Unless persuaded otherwise in this thread I will be following the diagram posted on the OP. Ok. I thought they were an expensive labour saving solution. You mean where my concrete pour is high? I sounded the finished foundations with a borrowed rotating laser and found 50% is +/- just 2mm and 90% is +/- 3mm.

Not decided yet. If I raise an inner block wall to 10ft using Celcon thin-joint in the two months before my facing bricks arrive then blown beads would be the preferred option because the facing brickie would not then be fighting the expansive tendencies of cavity batts as he skins the structure with facing bricks. Or if my inner block wall is built with thermo blocks in step with the facing bricks then the inherently good U-value of these mean I can use the less dense version of cavity batts. My potential brickie advised that the uber efficient variety of cavity batts expand too much if taken out of the tight manufactured roll too early in the day, then the brickie has to fight the material's tendency to push apart the cavity. Would I be right in thinking this decision can be delayed until the beam & block is installed but I will need to decide before the facing engineering bricks are taken up to my elevated ( 150mm + 150mm) DPC?

Are you referring to just the course of blocks the beams sit on? Or did your SE advise not to use 300mm trenchblocks for the lowest course? My concern with any type of aerated block below ground is that they could suffer from free thaw cycles when damp.

As a minimum I want to get a course of foundation blocks laid on my trenchfill just poured last Friday. If the heavens open and finish this summer drought, muddy water can then wash into the trenches without causing too much trouble because I expect the trenchfill blocks will keep their upper face above any puddling. The trouble is I am confused by all the block types on the market. Given the following diagram specific to my house what should I order to get up to the beam & block floor? My guess... 200 x Thermalite trenchfill blocks 440 x 215 x 300 (7N). A large delivery of regular 440 x 215 x 100 dense concrete blocks. Footing lintels for service entry points. Telescopic air vents for the inner wall (need some extra reach due to the elevated main dpc). 100mm DPC roll for the beams to sit on. Coursing blocks (65mm) for that awkward 150mm part of the inner block wall (to avoid block cutting). Should I amend this order to substitute in thermal blocks to reduce cold bridging near the beam floor?

I know some of you have taken a diy approach to creating diagrams for building control submission and others have splashed out many thousands for the same. I took a middling route which involved forwarding the outline architect's house design that had planning permission to an Architectural Technology (AT). The original architect was a quill & pen operator which meant my AT had to lift the design from paper into digital format. For £1200 I got 8 diagrams with impressive detail plus some lengthy building advice telephone calls thrown in. The AT also accommodated changes such as removing a supporting wall to create an open planing sitting room, reversing the stairs and incorporating a 90 degree twist. He gave me permission to post examples of his work, here are some snippets... Snip-2. Snip-3.

Ah, as in the PM transgressing her own Brexit lines in the sand. I remember those pre selfbuild days when I had time to follow the news.

Swmbo and I are going to puzzle this one for another 12 hours before seeking an explanation for the politically simple minded. ?