Trench vs strip foundation for conservatory

[GoferBlue1947]

I have to make a choice regarding foundations for a conservatory. If I go with a trench foundation I will need 2 cu.m. readymix. Access is very poor, so either a wheelbarrow job (with a heck of a lot of trips) or a pump (£££££’s). If I go with a strip foundation I would need only 0.7 cu.m. – maybe make on site with a mixer or certainly far less wheelbarrow trips with readymix!

As I understand it, the former is preferred in the trade because of the time saving and less messing about building below-ground block walls in a confined space. Is this the case? I am a DIY-er so my time/effort is free hence the strip foundation is the more appealing option in my case.

As an aside, can I use rebar in my strip foundations? Are there any technical objections to this (other than the usual ones of being OTT or adding unnecessary additional cost)?

Thanks.
Gofer

 

[jeds]

Trench fill is only necessary if the trench is too deep or too loose to work in. Do you know the depth your foundation will be?

 

[^woody^]

It's a lot of trips with a barrow of concrete, or even more trips with barrows of concrete and barrows of blocks - plus the loading out and messing about laying blocks in a trench.

Rebar is for bridges, not foundations. In any case, if needed it will be designed by an engineer not randomly thrown into the trench.

 

[GoferBlue1947]

Trench fill is only necessary if the trench is too deep or too loose to work in. Do you know the depth your foundation will be?

Jeds - thanks for your response. I am aiming for 600mm and 400mm wide.

 

[GoferBlue1947]

It's a lot of trips with a barrow of concrete, or even more trips with barrows of concrete and barrows of blocks - plus the loading out and messing about laying blocks in a trench.

Rebar is for bridges, not foundations. In any case, if needed it will be designed by an engineer not randomly thrown into the trench.

Woody -thanks for your response. Since I started this thread I see there is one early today which discusses the use of foundation blocks. Hadn't considered these - they would greatly simplify the process. Lightweight and eliminate need for double skin blockwork and concrete infill below DPC.

I thought using rebar could be useful if I was unable to mix sufficient concrete before the first batch started to harden?

 

[cjard]

Can you get a mini 1 ton dumper truck through your access? Can get a lot of concrete in one of those and they're a cinch to drive. If you're driving it, check that the concrete co don't charge a waiting time if you're too slow unloading the wagon, or practice with it first

Trench blocks are fab, easy and quick to lay even for a novice and you don't need to be hugely accurate but your brick layer will thank you for at least making some effort to keep them level along the run

 

[jeds]

600 deep is no depth. Aim for a 200...ish thick strip and lay a couple of courses of blocks to come above ground. Barrowing blocks is a lot easier than concrete. We did one a while ago with access through the house only so we carried bagged material through and mixed on site. It was a lot easier than trying to barrow through difficult spaces and down a short flight of steps.

 

[GoferBlue1947]

Can you get a mini 1 ton dumper truck through your access? Can get a lot of concrete in one of those and they're a cinch to drive. If you're driving it, check that the concrete co don't charge a waiting time if you're too slow unloading the wagon, or practice with it first

Trench blocks are fab, easy and quick to lay even for a novice and you don't need to be hugely accurate but your brick layer will thank you for at least making some effort to keep them level along the run

Cjard - thanks for your input. No, I wouldn't be able to get a mini dumper truck in. These trench blocks look to be the answer. I can't believe that a lightweight aerated concrete block can support a two storey building yet that is what is claimed! I will be the bricklayer in this case so I will be sure to get them level.

Any thoughts re rebars in the strip foundation or indeed size of the foundation for a conservatory please?

 

[GoferBlue1947]

600 deep is no depth. Aim for a 200...ish thick strip and lay a couple of courses of blocks to come above ground. Barrowing blocks is a lot easier than concrete. We did one a while ago with access through the house only so we carried bagged material through and mixed on site. It was a lot easier than trying to barrow through difficult spaces and down a short flight of steps.

Jeds - thanks for your input. When you say "600 is no depth", this implies that this is way too shallow but wouldn't a 200 thick strip plus two courses of blocks come to only about 650 anyway? I agree about barrowing blocks - a lot easier certainly and I won't have a readymix lorry driver breathing down my neck!

This is also why I was thinking of using rebar in the foundation because if I'm mixing by myself on-site I wouldn't be able to pour the footings in all in one go; by the time I get to the end the first lot of concrete will have started to set. Adding it in a section at a time with the rebar in place I'm guessing would hold the whole foundation together (if that makes sense?).

 

[^woody^]

If concreting is an issue, then just do a traditional footing of blocks straight off the ground.

 

[GoferBlue1947]

If concreting is an issue, then just do a traditional footing of blocks straight off the ground.

Woody - no, concreting per se is not the issue, but rather the amount of concrete required. A 200mm deep x 300 or 400 wide strip foundation is ok. BTW I didn't know that I could build directly off the ground - being an amateur I think I would prefer a nice solid, flat concrete base to start from!

Thanks,
Gofer

 

[jeds]

I meant it's no depth to make trench fill a necessity. Surely you can get three quarters of a cube of concrete done in one hit. If not you maybe ought to think about getting some help in. If you must have a joint sticking a couple of bars in the end as a daywork joint won't do any harm but I wouldn't bar the whole foundation.

 

[GoferBlue1947]

I meant it's no depth to make trench fill a necessity. Surely you can get three quarters of a cube of concrete done in one hit. If not you maybe ought to think about getting some help in. If you must have a joint sticking a couple of bars in the end as a daywork joint won't do any harm but I wouldn't bar the whole foundation.

Not in one mix I couldn't obviously but I was concerned about the time gap between the first mix and the last. Any particular reason why you wouldn't bar the entire foundation?

 

[theprinceofdarkness]

You could bar the whole foundation strip but a, its waste of money and b, its a faff suspending the bars at the correct position and filling with concrete. Use a porters trolley for moving blocks and bricks. Put a piece of wood on it to make it a bit wider if required. Once moved 4000 bricks with one when I was younger and fitter.
Frank

 

[themiddleagedun]

If concreting is an issue, then just do a traditional footing of blocks straight off the ground.

Blimey, I thought I was "old School"