Ferdinand Posted January 19, 2017 Share Posted January 19, 2017 Heave: Ground heave is the upward movement of the ground usually associated with the expansion of clay soils which swell when wet. As the soil generally cannot expand downwards or sideways, the result is that the exposed upper surface of the soil rises up. .. The most common cause of ground heave is associated with trees which have died or been removed. As the root network no longer draws water from the subsoil, water accumulates in the ground, resulting in swelling that can move building structures upwards. https://www.designingbuildings.co.uk/wiki/Ground_heave 2 Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 19, 2017 Share Posted January 19, 2017 Learn something new every day . Link to comment Share on other sites More sharing options...
Temp Posted January 19, 2017 Share Posted January 19, 2017 Could be worse - he might have insisted on piled foundations. Link to comment Share on other sites More sharing options...
Ferdinand Posted January 19, 2017 Share Posted January 19, 2017 Worth costing piled foundations? https://www.homebuilding.co.uk/foundations-cost-guide/ Link to comment Share on other sites More sharing options...
Temp Posted January 19, 2017 Share Posted January 19, 2017 When we compared the cost 10 years ago the break even point occurred when trench foundations would have to be 2.5-3m deep. Ended up with a mix of strip foundations under our house and piles under the garage. The latter being needed to protect a tree. Link to comment Share on other sites More sharing options...
ProDave Posted January 19, 2017 Share Posted January 19, 2017 As I have said we are building close to trees but not THAT close. One of the things stated about trees is they remvce water and dry out the ground. Well that is not a problem we have, our water table is always very high (bottom of the valley with a burn running through the garden), so with or without trees I can't see the ground ever drying the depth our foundations are. In a recent "worlds most amazing houses" was one built amongst trees, with some tree trunks left just inches from the house walls. That was built on screw piles iirc. Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 19, 2017 Author Share Posted January 19, 2017 1 hour ago, Temp said: Could be worse - he might have insisted on piled foundations. @Temp yea, he did say it...IF there was a pine tree or a coniferous plant, that would have been the option.... 1 hour ago, Ferdinand said: Worth costing piled foundations? https://www.homebuilding.co.uk/foundations-cost-guide/ contractor is pouring concrete today @13pm, I think it wouldnt be viable now, it would only mean more delays. As I am renting, an extra month is worth 1.1k Link to comment Share on other sites More sharing options...
MrP Posted January 19, 2017 Share Posted January 19, 2017 11 hours ago, PeterW said: No - trees are referenced for up to 3 years assuming they are "known about"... I've got both the LABC tech note and the NHBC one and both refer to compressible foam or a source of a heave protection down the inside of any foundation below 1.2m. I don't see how your BCO can ignore that as it has the potential to cause movement and it's against most of the guidance I've seen. You can use EPS40 as the foam - not expensive and easily installed but it needs doing before the founds are poured. I would also ask the BCO for his foundation design in writing - if he is private than god forbid if something goes wrong you have some sort of recourse..! As Peter says, do not remove the tree, it is now known about and removing it will not alter heave/depth requirements and a crafty move like that would not bode well for your relationship going forward. Don't forget google earth images which can now be backdated are a regularly used source for site investigations by approved inspectors. The BCO will not issue a foundation design however, we do not hold the relevant qualifications or insurances to issue designs. You need to get your SE to issue a design taking the tree in to account using NHBC standard guidance which he should be well versed in. If i was you i would hold fire on pouring concrete until you have a suitably agreed design, trust me its a lot more expensive to put right than to put off. However having done the cost excersise for my build i didnt find block and beam to be particularly more expensive if you use a product like cellecta tetris to negate the need for the concrete blocks. Link to comment Share on other sites More sharing options...
PeterW Posted January 19, 2017 Share Posted January 19, 2017 35 minutes ago, hmpmarketing said: @Temp yea, he did say it...IF there was a pine tree or a coniferous plant, that would have been the option.... Your BCO worries me..!!! He has no comprehension of the guidance in the British Standards or the technical manuals that define the depths and distances for building near trees..! This is the table from the LABC Technical guidance that shows the water requirements of various trees. When you have the plasticity index (or High/Med/Low if its an easily recognised soil type) you can calculate the foundation depth from knowing the tree and its proximity. As a broad guideline, most coniferous trees with the exception of Leylandi and other Cypress are low or moderate demand. This then dictates your depth and distance, which is not as onerous as you may think. I am building on a sandy soil with low clay - the result is that a Sweet Chestnut 2.3m from the foundation only requires a 1.3m depth with 50mm compressible material - in a heavy clay that would be entirely different ! This is the link to the calculator LABC Foundations near Trees Link to comment Share on other sites More sharing options...
PeterW Posted January 19, 2017 Share Posted January 19, 2017 4 minutes ago, MrP said: The BCO will not issue a foundation design however, we do not hold the relevant qualifications or insurances to issue designs. Thanks - that's what concerns me though about this one, he's making a design change on the fly and I would be really concerned if this is not checked by an Engineer. And when there is 20 cubic metres of concrete in the ground then its a bit too late... 1 Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 19, 2017 Author Share Posted January 19, 2017 (edited) @PeterW I will have a word with house builder later on, their SE issued the design for the foundations, will check this out for sure Regarding being near the tree and concrete, I assume regardless of the outcome we still need to go 2m deep? Edited January 19, 2017 by hmpmarketing Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 19, 2017 Author Share Posted January 19, 2017 12 minutes ago, MrP said: As Peter says, do not remove the tree, it is now known about and removing it will not alter heave/depth requirements and a crafty move like that would not bode well for your relationship going forward. Don't forget google earth images which can now be backdated are a regularly used source for site investigations by approved inspectors. The BCO will not issue a foundation design however, we do not hold the relevant qualifications or insurances to issue designs. You need to get your SE to issue a design taking the tree in to account using NHBC standard guidance which he should be well versed in. If i was you i would hold fire on pouring concrete until you have a suitably agreed design, trust me its a lot more expensive to put right than to put off. However having done the cost excersise for my build i didnt find block and beam to be particularly more expensive if you use a product like cellecta tetris to negate the need for the concrete blocks. Thnks MrP for your input. Link to comment Share on other sites More sharing options...
AliG Posted January 19, 2017 Share Posted January 19, 2017 I had this same issue at the last minute. SE decided that with clay soil and large trees close by (5m+ away) I need "heave" protection. I had never heard of it. We put 90mm Cordex boards under the slab. This cost an extra £23 per sq metre of ground area. I don't know if he also changed the strip foundation depth, some areas may have got a little deeper. I guess you can compare costs versus a block/beam floor. I wouldn't want to mess around with foundations without getting an SE involved. Better safe than sorry. However, if the BCO signs off on it I could see why the cost might seem high for piece of mind. 1 Link to comment Share on other sites More sharing options...
TerryE Posted January 19, 2017 Share Posted January 19, 2017 Have you not just thought about finding out what a reasonable cost of the extra foundation work is, knock off the price of felling it and grinding out the root ball and offering your neighbour that as a lump sum plus you carrying the cost of removal for his agreement to let you remove it? There's nothing like a bit a cash to encourage cooperation. 1 Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 20, 2017 Author Share Posted January 20, 2017 Hi guys, update, was busy the last day! For beam and block change including heave protection + extra concrete near tree (2.1m deep), it will cost £4.2k extra, foundation area 80m2 Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 20, 2017 Author Share Posted January 20, 2017 16 hours ago, TerryE said: Have you not just thought about finding out what a reasonable cost of the extra foundation work is, knock off the price of felling it and grinding out the root ball and offering your neighbour that as a lump sum plus you carrying the cost of removal for his agreement to let you remove it? There's nothing like a bit a cash to encourage cooperation. that sounds like a good plan to eliminate any future worries with that tree around Link to comment Share on other sites More sharing options...
TerryE Posted January 20, 2017 Share Posted January 20, 2017 @hmpmarketing, this also has the advantage that the neighbour did this from the planners PoV so its outside your control Check with your BInsp that the neighbour has offered to remove the tree and grind out the stump and see if he will give you a concession on this in this light. 1 Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 20, 2017 Author Share Posted January 20, 2017 (edited) @TerryE Just went for a site visit, one of my other future neighbours popped in to say hi, I had spoken with him few days earlier regarding the tree, he had a word with the neighbour that owns it and he said I was welcomed to come have a word. Knocked on his door, had some tea together and he gave me permission to remove it (he only wanted a couple of new fence boards no biggie)....I will have a tree surgeon come around and fell it, it will avoid future maintenance with having to trim branches and all the mess with leaves. Regarding the situation with building control, I think even going 2.1m deep with concrete and no tree they will still insist on beam and block.... Edited January 20, 2017 by hmpmarketing Link to comment Share on other sites More sharing options...
AliG Posted January 20, 2017 Share Posted January 20, 2017 I really wouldn't recommend asking the neighbour to cut down the tree. The whole point the BCO is making is that in the future if the tree wasn't there the soil will expand due to having more water in it. Whilst you are being asked to build foundations that will protect against this, I don't see why you would want to force the situation to happen. Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 20, 2017 Author Share Posted January 20, 2017 59 minutes ago, AliG said: I really wouldn't recommend asking the neighbour to cut down the tree. The whole point the BCO is making is that in the future if the tree wasn't there the soil will expand due to having more water in it. Whilst you are being asked to build foundations that will protect against this, I don't see why you would want to force the situation to happen. I understand your point. However if neighbour wanted to remove the tree at his own will in the future, I would not be able to stop him at all. Since he gave the permission to remove it, while I will still follow BC recommendations and SE, it will prevent me from having extra maintenance, right now tree branches re hanging over and I will have to remove them soon Link to comment Share on other sites More sharing options...
MrP Posted January 20, 2017 Share Posted January 20, 2017 Even with the tree removed you will still need a suspended floor but you will be able to reduce the foundation depths by approx 30%. Ive had a play around with the figures but cant quite get to the 2.1m though that you have been advised. If you can tell me what the tree type is and where about on the south coast you are i can calc the depths your BCO will ask for. The only other thing is your soil type - clay soils are either classified as low, medium or high volume change potential (basically it is how much it will shrink or heave due to the clay content). If you do not have this information from a soil report then the BCO has no option but to calculate based on the worst case scenario - im not sure whether you would have had a soil report done? Link to comment Share on other sites More sharing options...
hmpmarketing Posted January 20, 2017 Author Share Posted January 20, 2017 2 hours ago, MrP said: Even with the tree removed you will still need a suspended floor but you will be able to reduce the foundation depths by approx 30%. Ive had a play around with the figures but cant quite get to the 2.1m though that you have been advised. If you can tell me what the tree type is and where about on the south coast you are i can calc the depths your BCO will ask for. The only other thing is your soil type - clay soils are either classified as low, medium or high volume change potential (basically it is how much it will shrink or heave due to the clay content). If you do not have this information from a soil report then the BCO has no option but to calculate based on the worst case scenario - im not sure whether you would have had a soil report done? Yes, I have a soil report, this was done as soon as I had purchased the plot, can pull up data from it soon when Im home. According to neighbour it is a Sycamore tree, plot is located near Pagham, West Sussex. We are 1.3km straight line from sea. Link to comment Share on other sites More sharing options...
Ferdinand Posted January 21, 2017 Share Posted January 21, 2017 (edited) If it is a sycamore (check) that close and still that small I would want it out anyway - perhaps after the build having listened in above, provided the new foundations are specced to stand the potential heave, and insurance etc is in place. In due curse (deliberate typo!) it will possibly become a 60-80 ft weed which could be 50-60cm closer to your house, unless there is something severely restricting its growth. The difference in cost between removal now and in 15-20 years could be 300-500%. At the very least it will be a concern to any future purchaser, and may end up with a TPO if someone wants to put one on it. Replace with something interesting in a suitable place instead imo. Ferdinand Edited January 21, 2017 by Ferdinand Link to comment Share on other sites More sharing options...
TerryE Posted January 21, 2017 Share Posted January 21, 2017 I left some 75mm wide sycamore saplings on my boundary when clearing it just over thirty year ago. About 5 years ago I had the last one felled and the root ground out. It was about 400mm wide by then and the root ball was even bigger! 1 Link to comment Share on other sites More sharing options...
Oz07 Posted January 22, 2017 Share Posted January 22, 2017 The only way you could come unstuck with the addition of b&b is it could end up pushing ffl up if you've taken your trench fill too high. Also it could have paid to have spine walls if you'd have known beforehand. Could be the difference between needing a machine to move beams and being able to do it with few lads. Also again a longer beam may be 9" instead of 6" Link to comment Share on other sites More sharing options...
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