Adamantium

Stumbling at first hurdle?

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If you have a 300mm cavity, stainless ties will cost an extra £2.50 per metre and insulated ones an extra £7.50.  Have a looks at http://tonyshouse.readinguk.org/ as he has done a conventional construction with concrete intermediate floors, which would help towards the solid feeling you are looking for.

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we're going with 350mm jji wall, internal 50mm service void 50mm external void, with cladding on both it's a similar size wall. blown cellulose insulation giving a u value of 0.1.

admittedly with a large amount of insulation it will be heavy, however, not as heavy as solid block and better u values.

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This company supply screw piles and have a fair bit of information on their website if you are interested. 

 

https://www.hubbell.com/chancefoundationsolutions/en/about-us/chance-products/helical-piles

 

I have no affiliation to them but I have used their screw piles for anchoring a mast. Smaller piles  can be installed using a hydraulic motor attached to the end of a long lever running of a small hydraulic power pack, so installation might be easy. 

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Hello Adam,

I have recently obtained planning permission for a 3 bed house which will be directly over a main trunk sewer owned by Thames Water. I have structural engineering plans for cfa piling and a reinforced raft to allow us to build over the sewer. It was a long and complicated process to get the build over agreement. I have not had any quotes yet but anticipate that it will be very expensive. I would love to know what route you go down and if you have any advice.

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Adam,  I am not sure these comments will apply but might be of use to others - and are just my experience with Wessex Water who may have different rules. 

 

I have a plot with a shared 150mm sewer and Wessex Water required me to have a build over license if I went closer than 3m to the sewer. Early designs had the sewer diverted which was expensive as its pretty deep (over 3m in places). The reasons I was given (I have no idea if this is correct) for the 3m exclusion were two-fold: firstly if you are closer then there is potential for the foundation load to transfer to the sewer - so if you go closer then you need to have the foundations below the invert level (in my case over 3m) and Wessex wanted to have a say in the foundation design. Secondly they wanted to be able to maintain their sewer and get a digger in if needed - 3m makes their life easy! So by avoiding the 3m exclusion and a build-over license I can pretty much do what I want which makes life simple.

 

The design we have PP for is outside the 3m exclusion (just) and leaves the sewer alone and doesn't divert it - it does constrain the design but it should work.

 

If you really do have an 850mm sewer I am amazed they will let you get that close - but I would go with that and not argue! You may have some leeway / discussion about the depth of the foundations if you can go below invert level but Wessex went a bit wobbly when I mentioned piles as they were very nervous about the vibration of any form of driven pile. Also with that size of sewer I cant see diversion being an option - probably cost more than your build budget!

 

Another fundamental tip is to make sure the sewer actually runs where everyone thinks it does (not as daft as it seems) - Wessex were unable to tell me where their sewer was so I had to have it surveyed with a sonde :- a radio probe down the sewer and then sort of dowsing above to detect where it was! This gave me a pretty reasonable clue but I have a feeling I will need to do a cctv survey before I am done which will be more cost.

 

I used a civils consultancy not specifically an SE for a drainage design for PP - turns out they didn't want my SE work - its their bread and butter (so to speak) so they knew all the ins and outs of Wessex policy. I used PFA Consulting based in Swindon - they are consultants so surprise surprise they are not cheap but did enough to get me PP which was worth it!

 

The other extra I got out of Wessex was an agreement to put a reduced flow of storm water (1l/s) into their sewer - not normal but if you dont ask you wont get - makes my storm water solution possible as soakaways in my clay soil dont work at all.

 

Hope that helps - but my experience is that dealing with sewers is a pretty sh*** job!

 

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you want thick walls and less weight and good insulation .

ICF  is your way 

you can get all the strength you need with a 120-150 mm concrete core and have insulation up to 250mm thick on outside  with some systems 

.which will be 50%  better than  minimum passiv house wall spec ,even better by the time you add internal plaster or drywall

example 

izodom 2000 super kingblock  spec

https://econekt.co.uk/wp-content/uploads/2016/02/ECONEKT.-ICF-Elements-Brochure2.pdf

see page 10 

and with your ground problems  maybe slab is made with rebar sticking out which ICF bonds onto --making it  more monolithic can still be done on top of screw piles 

 

Edited by scottishjohn

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ICF and less weight should not go in the same sentence! 120-150mm of concrete is a heavy method to build a wall!! 

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25 minutes ago, Alexphd1 said:

ICF and less weight should not go in the same sentence! 120-150mm of concrete is a heavy method to build a wall!! 

not compared to what he was saying   2 rows of blocks. @100 mm minimum each block ,makes ICF  25% less at 150mm or  40% if you go for 120mm core 

roughly.

does not sound like a TF or sips man --so in solid construction it is lighter

Edited by scottishjohn

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10 minutes ago, scottishjohn said:

not compared to what he was saying   2 rows of blocks. @100 mm minimum each block ,makes ICF  25% less at 150mm or  40% if you go for 120mm core 

roughly.

does not sound like a TF or sips man --so in solid construction it is lighter

 

You're missing two things -the outer skin or finish on the ICF, and that mass concrete weighs a lot more than blockwork. 

 

C25 is around 230Kg/m2 at 100mm, medium block is 110kg/m2 and lightweight block is 60-70kg/m2. 

 

So if you had a 150mm core it would be 345kg/m2, where a pair of medium weight block walls would be 220kg/m2, or around 36% lighter than the equivalent ICF. 

 

Also  worth bearing in mind that ICF has to be around 80% thicker for insulation purposes than PIR - again, this is cost vs  thickness decision. 

 

If the outer finish has to be brick then the argument for ICF is pretty much lost unless you go with a slip system that will be even more expensive than brickwork. 

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Have you ever worked with concrete, it's bloody heavy!! 120mm of concrete is almost the same weight as 2x 100mm 7nm blocks (standard build block not fancy lite weight ones) so 150mm of concrete is a lot heavier! 

 

I don't know anyone who has built a external wall in 120mm ICF, it's not a good idea!

 

For the record I am a big fan of ICF but there is many ways to build a house not all but one are wrong!

Edited by Alexphd1
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13 minutes ago, Alexphd1 said:

Have you ever worked with concrete, it's bloody heavy!! 120mm of concrete is almost the same weight as 2x 100mm 7nm blocks (standard build block not fancy lite weight ones) so 150mm of concrete is a lot heavier! 

 

I don't know anyone who has built a external wall in 120mm ICF, it's not a good idea!

 

For the record I am a big fan of ICF but there is many ways to build a house not all but one are wrong!

never said other methods were wrong

never have done  --the man stated he wanted SOLID thick  walls that all.

which is why i did not suggest TF or sips to start with 

 

 thank you for the info on  block weight verus concrete -- I stand corrected--i don,t know difference in wights of dif spec concrete mixs 

never weighed  one --all heavy to me  --

120mm concrete core is what durisol +isotex UK spec  use --never seen any durisol then ?

25 minutes ago, PeterW said:

Also  worth bearing in mind that ICF has to be around 80% thicker for insulation purposes than PIR - again, this is cost vs  thickness decision. 

 

If the outer finish has to be brick then the argument for ICF is pretty much lost unless you go with a slip system that will be even more expensive than brickwork. 

that is a non argument as the ICf  I pointed him too has a 0.10 value at size stated with no internal or external finish . and it is thick like he wants .

not even going into all the other arguments of TF /sips verus solid or ICF 

no one mentioned brick slip  finish --he stated 2 block wall + void which he could render or  clad or what ever ,same as you can with any other system 

just more choices for him if he wishes to look at them 

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