Andehh Posted January 18 Share Posted January 18 (edited) Our build was completed over the summer, following 18 months of construction. Block built bungalow by a builder who was brilliant - and especially total 'belt & braces' approach to everything. He was not cheap, but always felt worth every penny & we do trust him/his work. A couple of months ago though, i noticed some cracks in one low corner of an outside wall. It's behind the single story garage in a secluded corner, so not an area anybody would spend much time. These cracks could have been there since day 1, just never spotted. This area is, however, c11m from a mature willow tree which was designed into the build. The foundations in this area are c1.5 - 1.8m deep, 900m wide, with heave protection - because of said willow tree. The render above & round the area is fine, and has been on the wall here since last summer. It's a low profile thin coat. I raised it with the builder who couldn't explain it, but thought it could have been impact from a digger bucket or equiv (as we had some landscaping done with a JCB in this area) but he wasn't worried & offered to replace the bricks or repoint if we wished. I said not yet as I wanted to keep an eye on it. The render above this area is fine & no where else is there anything of concern. Today i decided to dig down & have a closer look, pics below! Just wanted to see peoples thoughts?? Edited January 18 by Andehh Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 (edited) Edited January 18 by Andehh Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 First of all it's a narrow crack, so for monitoring, not panic. A pound coin in the gap is a decent guide. Something has moved differentially but the absence of cracking in the render suggests it might have been shrinkage during construction of the footing. The willow is dormant so the ground, presumably clay, is expanding if anything. Was the ground dry during construction? When you say " heave protection" what do you mean? The depth is already providing that for the foundation. 1 Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 Building control asked the builder to install polystyrene sheets around the foundations in this area because of the willow tree which he did (which I believe is heave protection?), you can see some of the bits of white in the mud where I have disturbed it! Foundations poured December 2021, garage blockwork finished July 2022. Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 1 minute ago, Andehh said: polystyrene sheets around the foundations in this area I think more likely to keep roots out of the concrete pour. Or just something he's come to like. 1 Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 There were surprisingly few roots we came across actually. I remember as I actually cut a few stragglers back (tiny several mm type ones). I was slightly nervous doing it, as the builder had warned me about deep foundations & wet weather when we were visiting the site over the Christmas period (My wife was supervising as my emergency help!!). The heave protection might have been something else though, the architect told me she saw them being installing heave protection after building control had demanded it, and I never asked anything more about it. What gives me comfort is not a single person visited the site & didn't comment on the ridiculousness of the foundations, the running joke was we built the foundations for the skyscraper we were going to convert the bungalow into afterwards. Thanks for your thoughts so far though! Link to comment Share on other sites More sharing options...
Mr Punter Posted January 18 Share Posted January 18 I am not sure that the foundation is deep enough. 2.4m may be more like it. The low density polystyrene is heave protection and used on the inside of the foundation trench. It can be difficult to use as it tends to float in the new concrete. Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 Can only trust the experts here on the depth of foundations, we had tree surveys specific for this willow tree, root assessments, structural engineer spec'd it then the builder was razer sharp in preparing them. We are about 1m outside of the root ball following the assessments, and it is only for a single story, cavity double garage end of the day! I can't find the dimensions, but I remember stood nervously in it & not seeing over the top and im 6ft! Link to comment Share on other sites More sharing options...
Mr Punter Posted January 18 Share Posted January 18 LABC foundation depth calculator: Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 (edited) That's interesting to see & difficult to know what to do with that info! I've pinged the photos & suggestions on foundation details off to our architects to seek their views & confirmation on foundations in this area. The foundations could have been that deep, but its difficult to remember other then remembering 'I couldn't see out of the trench'. Edited January 18 by Andehh Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 (edited) Every now & then you get lucky & you find the nugget of gold you needed that will enable you to step back from throwing yourself off the room....... Short version is, the garage/bungalow was cut down into the ground by 3-4 feet due to the nature of us building on a hillside & the willow + garden being further up the hill from our build. This means the foundations were c1.8m deep....but they already started from a depth of 3-4 feet lower then the natural ground anyway....thus foundations being c2.5m below willow ground level! ------------------------------ Dear Building Control, As discussed this morning, we would like confirmation please that you are satisfied with the foundations of the new garage with the proximity/slight incursions into the willow roots. The arboriculturalist has confirmed this is okay from a tree perspective. Please find attached the arboricultural survey, engineering drawings and part of the architectural package including substructure, floor plans and elevations. Note that the design has changed from 140sqm extension to complete knockdown/rebuild and we are pending the updated engineering drawings for the rebuild element, although the extended element footprint remains the same and the replacement build element footprint is very similar. If there’s any further information which would help please let me know. Many thanks, Architect Good Afternoon Architect, The foundation depths do not correspond with Chapter 4.2 of the NHBC Standards and look to shallow. Have they been verified by a structural engineer? Kind Regards Building Control Hi Building Control, The structural engineer confirms that the footings are already at the right level as the garage is cut into the ground leaving the footings approximately 2.5 metres below ground level at the Willow. He will add some contours to the drawing to make that clearer. The arboriculturist confirms that he didn’t recommend a root barrier in his report. If the engineers have recommended something then they will have a spec. He’s not aware that a root barrier is necessary unless the soil is known to be shrinkable, but again this is something for the structural engineer to decide when they are specifying foundations. Best regards, Architect ****Sharing of several more drawings, contours & foundation levels*** Morning Architect, Thank you for the drawing showing the contours. I can confirm that I am happy with the foundation design. Did the Planners at West Northamptonshire Council set this as a condition? If so, they will need to be sent this info to clear the condition. Kind Regards Building Control Edited January 18 by Andehh 1 Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 2.4m depth would apply at about 2m tree distance and reducing to a minimum at 24m in clay. So yours seems appropriate. I would suggest that any other heave precautions should be on an 'as built' drawing for your records and you should insist on getting them. The proprietory heave products are expensive so I'm surprised you did not get get a big extra charge. Plus I'd like to know what it is. I've built hundreds of buildings in clay. Never used clayboard or similar. It should be the SE who advises on that not bco. I should clarify. I've seen a floor slab fail for the lack of clayboard. Not a footing though. Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 Ahhhh. But cutting into a hillside may require clayboard under a groundbearing slab. That was the issue with the problem i witnessed. If it is suspended that won't apply. All the more reason to get your drawings. Link to comment Share on other sites More sharing options...
Andehh Posted January 18 Author Share Posted January 18 Yeah, it came up in discussion with the architect when I was bemoaning some additional costs walked in by our structural engineer (who always felt expensively over zealous in everything he insisted we did....!!). Our architect brought up the fact she saw builder install heave protection (or clayboard? could have been something along those lines....) per building control and/or structural engineer and our builder was lightly grumpy about it as overkill,...and architect explained that everyone was having to take a few hits on the chin with the 'contract price' build the Builder had given us (and stuck to pretty well tbf) and also us taking on a few hits on prices walked in by third parties. Would clayboard or heave protection be 100mm thick insulation like sheets? Grey or white? or something? Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 Link to comment Share on other sites More sharing options...
saveasteading Posted January 18 Share Posted January 18 Yes it's 2 boards separated by honeycomb like a mattress., so mostly air. Link to comment Share on other sites More sharing options...
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