Self Build Garage with room over in Bath

[wertert]

Hi All

 

Brand new member here.  Our old garage finally decided to give up on us and partially collapsed so I've taken it down.  This picture from better days.

 

 

I've stacked the Bath stone on pallets in the driveway (the family is not amused ) and planning to reuse it on the 2 visible elevation of the new building which will be a bit larger.

Planning on a concrete raft foundation but before I can really get to that we have a few retaining walls to take care of.

 

Early days for the project but exciting stuff !

 

Thanks in advance

 

wertert

[Iceverge]

Welcome welcome. 

 

You'll be short of blocks I'd imagine, hopefully you can find some matchers for the new build. 

 

What's your planned structure? Any particular reason for the concrete raft?

 

 

[wertert]

Hi Iceverge.

The old building had very poor foundations and was ultimately damaged by a large tree which we chopped down about 3 years ago.  I think we could use the dreaded S work here.  Subsidence. Technically, the roots are still in the ground which could lead to ground movement in the future.  The site is slightly sloping and the neighbours built right up to the boundary so we want to minimise any impact and not go any deeper than we need to.  We will be about 1.2 meters from the boundary wall.  We did take advice form a structural engineer so it's really the safe option for our site I feel.

[Temp]

Welcome to the forum and good luck with the planning application. 

[wertert]

Thanks.  The good news is we have planning permission and I am looking to start in a few weeks.

 

The site is "cleared" and there are a couple of things to cover before we can start on the garage foundation.

Yellow line- retaining wall built in stepoc ( hollow block ).  Design by structural engineer.

Red line – existing retainer/planter.  This is keeping me awake at night.😴

 

It’s basically there to support the ground level on the other side of the stone boundary wall and has been there for *many* years.  about 1.2m deep and filled with soil.  Our first instinct was not to touch it and build the new garage in front of it basically hiding it.  There are a couple of issues with that idea.

1. Garage foundation – We want to maximise the amount of driveway we have so I’d like the raft foundation to be built and close as practical to the planter.  If we dig down 700mm in front of the planter I feel the planter could well collapse.
2. Planter location. – It’s not actually built square to the stone boundary wall.  The front face is actually curved.  Possibly historical movement of the right hand side.  We would therefore have to twist the garage location or move it further away from the planter losing ~1 foot of precious driveway. ( not major issue if i'm honest )
3. Once the garage is built it would be very painful to sort any issues with this planter should something happen in the future.

We can’t really replace the planter in one go as taking it all down would lead to the problems mentioned above so I am considering some kind of retaining structure built in sections or sheet piling.

 

I'll continue on next post as there's a size limit..

 

Cont...

 

 

 

 

[Iceverge]

Congratulations on planning permission. 

 

Have you considered a poured concrete retaining wall tied into the foundations and doing away with the planter. 

 

It could form the outer leaf of a cavity wall for the sections near the neighbours and at the yellow line. 

 

A block wall may well suffice instead of a poured wall I'm not a SE I'm afraid. 

 

 

 

Ok my plan.....

 

Wait for some dry weather, get a mini digger and dig out the site including the planter. 

 

Pour standard strip foundations with some rebar for the walls embedded. 

 

Build a leaf of hollow blocks filled with concrete and tied with rebar to the strip foundations for the outer leaf of what will later be a cavity wall. 

 

Apply a suitable tanking membrane to the outside of the blockwork, include a perimeter drain and backfill once all the walls are set and the roof is on. 

 

The variation in the width of the blocks could be accommodated with differing insulation widths. 

 

 

 

[wertert]

Hi Iceverge. Thanks for the response.  

I moved this discussion over the structural/foundation section and it was probably going beyond me introducing myself 😉

 

I would be very nervous taking down the whole planter in one go.  The stone wall behind is built on an angle and removing the planter would expose the foundation blocks.  Red line is approx line of bottom of foundation block ( 6 inch bath stone on it's side ) - as you can see on the left it's already fallen down below.

 

 

I was thinking in terms of hollow block but possibly built in small sections to minimise impact to the wall/neighbours.  We would take down the planter in ~650mm sections.  Checkout the details on the linked post.

BTW - the stone wall is not a party wall and we own it 100%. If it fell down it's really not the end of the world and we won't see it as it's behind the garage;-)  As you mentioned on your first post we may run out of blocks for the new garage so this would be our backup source. Boundary wall side we still need to retain the ground level next door, its a driveway.  The rendered building you can see is a garage which is not used for car parking afaik.