Retaining wall for extension built into a banking

[Lounge About]

Hi, i'm having an extension built in the banking at the side of the house. The banking will be the full height of the extension and will have a green roof

1. How far into the banking should I excavate beyond the actual building line to give me room for the drains and maybe an extra damp-proofing skin?

2. How deep will the foundations need to be?

3. How thick will the retaining wall need to be?

Hope you can help, really worried about the cost, cheers

 

[Delinquent]

Hi, i'm having an extension built in the banking at the side of the house. The banking will be the full height of the extension and will have a green roof

1. How far into the banking should I excavate beyond the actual building line to give me room for the drains and maybe an extra damp-proofing skin?

2. How deep will the foundations need to be?

3. How thick will the retaining wall need to be?

Hope you can help, really worried about the cost, cheers

afraid the only "help" I can give on that one is that you are right to be worried about the cost... I've been having the plans drawn up for a buried garage, so the retaining wall is only 2.5m high... the cost however reaches much, much higher.

Width of the retaining wall for mine is 400mm, made up of 100mm block, 200mm reinforced concrete, 100mm block. Damp proof layering etc adds another 100mm or so on to that, beyond that is a fair thickness of gravel etc to allow rapid downflow of water. I enquired about a drain as I'm thinking about having a loo put in and there was comment that it could be fitted into the gravel layer?

depth wise - mine is bugger all! They've made the reinforced section form an "L" which runs under the garage, I would imagine they could do similar with yours? Maybe not but might be worth investigating.

 

[noseall]

it seems to me that the retaining wall may be as much a portion of the cost as the main extension.

the wall will need to be engineered and approved.

there is no way i would be asking a diy forum about something as structural important as you are describing.

you need the services of a local s.e.

 

[Lounge About]

This could get out of hand by the sound of it. There will be a garage, utility, toilet and lounge. Are there any links/web sites that showing the reinforced L concrete section, cheers

 

[Delinquent]

This could get out of hand by the sound of it. There will be a garage, utility, toilet and lounge. Are there any links/web sites that showing the reinforced L concrete section, cheers

not that I know of - mine were drawn up specifically for the site by a structural engineer (which another engineer disagreed with and upped the width of the wall to my above comments...)

It's a VERY long calculation on the loadings, that much I can tell you!

 

[Bowness72]

Just to give you an idea of what you should expect, the thickness of the reinforced concrete "stem" part of the wall will be somewhere in the region of one tenth of the retained height, possibly slightly less if the quantity of steel reinforcement is increased or slightly more if necessary to carry a thicker wall above. The width and thickness of the base and quantity/arrangement of the reinforcement will need to be calculated by a structural engineer and will depend on the type of soil, ground water level and how the structure is arranged if there is any built off the top of the wall etc.