Claylite sizing and excessive trench depth help?

[Bob a job]

Hi,

I have been recommended this forum by a friend who mentions the the amount of good knowledge on here, would someone be so kind to help with the below.

I am digging foundations in a high changeability clay with a tree 12 metres away. The building inspector has mentioned to use Claylite in the build, however no one seems to be able to tell me how thick a claylite board should be.

I have noticed most places stock 75mm (I am guessing I can use this?) however do building control have any guides they go by for this stuff or can someone guide me on what to get?

Lastly, I have been told the trench will have to be 2.3m deep due to the Oak could potentially be 20 metres high one day. Does anyone feel that this is excessive considering he hasn't even seen if any roots are where we are building yet?

Many thanks in advance

 

[Bob a job]

I have just had a call from the manufacturer who mentioned 75mm will be fine!

However with regards building control and 2.3 metres being set before even looking at the ground could this be argued if no roots are present?

Thanks,

Kevin

 

[DIYTom]

How big is the tree Kevin? I think it's a case of there are no roots YET. For some trees their roots can extend further than their branches, and as deep as the tree is tall. Also in a hot summer an oak will suck the ground dry of any water, and with a heavy clay soil that would cause cracking and shifting.

Personally I'd suck it up now and do the deep foundations. It might save some very bad problems down the line. Don't want your house assuming an alarming slant as the oak grows.

 

[Bob a job]

Hi,

The tree is about 9 metres at the moment but could grow to 20m. I will just have to go with what BC say.

I do have a question regards using 75mm claylite, I am guessing the trench instead of being 600mm will have to be 675mm?

I am digging tomorrow and if anyone can help that would be appreciated.

Thanks,

Kevin

 

[CambridgeBrummie]

Hi Kevin,

An oak tree is a high water demand tree.
For Highly shrinkable soils
Foundation depth for a tree 12m away is 2.3m

Yes, you need to add the width of the claytite to the foundation width.

Take a look at NHBC Guidance Chapter 4.2, for more information.

Regards

Nick,
Structural Engineer

 

[Bob a job]

Awesome, thanks for the prompt responses on this, I just hope we can get the claylite to stay where it should whilst the concrete is poured!