Foundation - Ground Beams

[lstevensuk]

Due to the drains running directly under my new extension and crossing the corner my structural engineer has advised to use ground beams (something I've not heard of before). So much for the DIY dig and pour I was hoping for. Any advise on an alternative plan, or even if it's suitable for a DIY'er. I really don't think I have enough room to move the drains over as I'm right up to the boundary, around 1m at pinch points and very odd shaped driveway! The pads look easy enough but the beams look heavy, expensive and complicated

Spec for the beams:

Span: 2.6 m
Use 203 x 203 x 46 UC S275

Span: 4.5 m
Use 203 x 203 x 60 UC S275

Span: 1.4 m x 3
Use 203 x 203 x 46 UC S275

 

NP142208-S1-rotated.pdf

Edited April 25, 2022 by lstevensuk
Forgot upload

[Temp]

The only think I can suggest is moving the pipe further under the extension so you don't need the longest of the ground beams. If the pipe passes under walls at 90 degrees that minimises the length of the beams needed.

 

If the pipe could be moved under windows or doors it might be possible to use concrete lintels to bridge over it as there won't be so much weight above. The weight will be carried by the lintels above the window/door as normal. Would need to discuss wit the SE.

 

[Russell griffiths]

I did one just liked this and moved the drain so it ran dead centre from front to back through the building. 
brickwork and lintels over the top. 

[Conor]

We had to do a ground beam over an old well. But was done using rebar. As far as a I can remember it was 450mm deep, 600mm wide and a good 4m long (under the planned 200mm slab) with a rather large rebar cage and then poured with the same C35 concrete as the foundation slab. Think it was an extra £450 in labour and materials. Ask your engineer if this is an option... Not sure it'll be any cheaper though as rebar is way up in price.

Edited April 25, 2022 by Conor

[lstevensuk]

Thanks for the feedback. I'm not sure if I have the room to move it to the right but possibly can rotate it around a bit so it cuts through the middle. Would mean digging up a fairly new tarmac driveway though

 

 

[Russell griffiths]

That’s an easy fix and will save you loads on foundations, just move it to under the centre of both windows. 

Trench fill to 150mm below pipe, box around pipe and bring concrete up either side then concrete lintels over the top. 

You will probably need a new inspection chamber in the front garden. 

[lstevensuk]

That's  an excellent idea @Russell griffiths have just re-drawn and sent that idea to the SE! The drains are only about 700mm deep, don't know if that causes any issues. I wonder why they didn't come up with this idea anyway 😟

[lstevensuk]

Could I do something like this? Not sure on the bend at the front. The back man hole cover would be very close too footings (390mm at closest point).   My SE is being of no help what so ever! Thanks

 

[Temp]

6 minutes ago, lstevensuk said:

Could I do something like this? Not sure on the bend at the front. The back man hole cover would be very close too footings (390mm at closest point).   My SE is being of no help what so ever! Thanks

 

 

That's exactly what I meant in my post above. You may only need one home made beam in the middle wall and that will be shorter.

 

You wouldn't use a curve at the front. Probably a 45 degree section into another inspection chamber on the original route.

 

 

 

 

[Temp]

This describes the ground beam approach..

 

https://www.diyfixit.co.uk/building/bridging-a-drain-run/

[ETC]

I can’t believe that you don’t have the space for the drainage down the side of the extension. Speak to your BC about placing a drain less than 1m from the foundations and what the BR recommend.

 

Alternatively if you are using strip foundations speak to your BCO about stopping the foundation each side of the proposed drainage pipe and using simple pc lintels over each pipe in the sub-floor blockwork. The drawings you posted look like you are building over a culvert. I presume the pipe you need to go from the top to the bottom is 110mm diameter?

[lstevensuk]

1 hour ago, Temp said:

This describes the ground beam approach..

 

https://www.diyfixit.co.uk/building/bridging-a-drain-run/

 

Really helpful thank you, looks a lot less scary than I thought!

[lstevensuk]

@ETC Really helpful, thank you for taking the time out to draw that - makes a lot of sense and by far the easiest option. I'm trying to get the drawings completed for the build over agreement, assume I need them even though I'm technically not building over them anymore.

 

And yes 110mm

Edited April 26, 2022 by lstevensuk

[lstevensuk]

2 hours ago, Temp said:

 

That's exactly what I meant in my post above. You may only need one home made beam in the middle wall and that will be shorter.

 

You wouldn't use a curve at the front. Probably a 45 degree section into another inspection chamber on the original route.

 

 

 

 

 

Thanks for that, also helpful and definitely much easier/cheaper than the SE proposal. I can sleep much easier now  

[ETC]

Don’t forget that where you have to pass the drainage pipe through the extension:

The foundations for your new extension will most likely need to be at the same level as the house foundations.

You will only have to stop the foundations each side of the drainage pipe and use lintels across the foundation where the drainage pipe is at the same level as the foundations.

 

However:

The drainage pipe will more than likely be above the level of the foundations and if this is the case all you need to do is pass the pipe through the sub-floor walls with lintels over the top.

[lstevensuk]

Thanks again @ETC So basically I just need to decide if to go around or through! I'll have a quick look in that back inspection chamber and see what it looks like. However I really like the go around idea more and more

[lstevensuk]

Sorry to ask yet another question. I lifted the drain again to gather distance from footings, it's going to be within 400mm - am I right in thinking it has to be more than 500mm?
Also I have absolutely no idea what drain 1 is and 2 goes off in random direction - I assume to my neighbours somewhere. Would it be easy to relocate further away from footings? Or move over to the right as mentioned.
I forgot I need to get an ensuite connected into the pipe somewhere and will need to cross the foundations if on the right hand side.

 

 

 

[lstevensuk]

Ok scrap the above I've decided to go for it with Anglia water. Probably in the wrong forum section now!
Is this enough detail? You can see how helpful my structural engineer has been with the sectional drawing 

Drains v2.pdf

[ETC]

1. Where’s the en-suite?

2. Coming through the building is no big deal but can be avoided by going around. I don’t see the problem in doing this and would be my preferred route.

3. Is the pipe shown going through the extension a combined drain, a storm drain or a foul drain? And I presume it’s a drain that collects waste from your neighbours - a good reason not to go through the extension if at all possible.

4. Ask your BCO for advice and what he/she will accept. I suspect that as long as you can comply with Approved Document H you should be fine. Lintels in sub-floor blockwork where the pipe passes through should be acceptable to BC.

5. I suspect the plan needs another IC where the new drainage pipe changes direction before connecting to the new MH on the existing drainage line.

[lstevensuk]

12 hours ago, ETC said:

1. Where’s the en-suite?

2. Coming through the building is no big deal but can be avoided by going around. I don’t see the problem in doing this and would be my preferred route.

3. Is the pipe shown going through the extension a combined drain, a storm drain or a foul drain? And I presume it’s a drain that collects waste from your neighbours - a good reason not to go through the extension if at all possible.

4. Ask your BCO for advice and what he/she will accept. I suspect that as long as you can comply with Approved Document H you should be fine. Lintels in sub-floor blockwork where the pipe passes through should be acceptable to BC.

5. I suspect the plan needs another IC where the new drainage pipe changes direction before connecting to the new MH on the existing drainage line.

 

Thanks @ETC I'll have a chat with BCO with the different options.
The ensuite is on 1st floor. I was going to run the pipe down the new hallway as show in red below.

It's a combined drain and yes also coming from neighbours on the left

 

 

Edited April 28, 2022 by lstevensuk

[lstevensuk]

Ok some great news. BC are more then  happy for it to go around the side as the foundations will be lower then the pipe. And as an added bonus turns out it's not connected to my neighbours and is private so no need to worry about build over agreement.
Thanks for the help everyone! Quite a few pennies saved