Foundations (literally)

[Mhairi]

Hi there,

Registered today and looking for some guidance.

We are keen to start plans to build our outdoor oven but I have some concerns over our chosen spot - I have attached a picture to illustrate my concerns. Please excuse the mess in the garden - new home lots to be done!



We want to build an extension to the front using breeze (cinder?) blocks and use the height of the existing wall as our base (The depth from front to back is 35 inches - we need to build out quite a bit for the dome). I am wondering how we deal with the soil in the wall and what we can do to ensure when we concrete on top that I have secured the foundations. The wall is just above waist height and to our knowledge has soil all the way to the floor.

The wall is around 5 metres long and we intend to build in the middle section - retaining the soil at either side.

Would we have to dig out the existing soil and fill with brick or is there a way to secure it so that we could build to lay our concrete base (obviously not directly onto soil).

Any offerings of advice would be greatly received!

Many thanks in advance
Mhairi

[ATK406]

Re: Foundations (literally)

If I were you, I would decide where you wanted to put the oven and cut an openning through the wall to dig out the area underneith the oven and build your foundation front to back. You could still use part of the wall to support your slab but you would have access to the space immediately below the oven. I would use full size cinder block for the rest of your foundation (looks like your existing wall is only 1/2 thickness). It would be great if you could tie in the new walls with the old wall (using rebar to join the cores) and fill the cores at the same time that you pour your slab. Unless you plan to build a really small oven I hope you know that your slab will extend a good foot or so beyond that wall. Do you have adequate clearance in front of that wall to work the pizza peel?

One more thought. You've got quite a long planter there (5 m) don't be shy with your foundation width to give yourself some countertop space on one or both sides of your oven. You'll still have penty of room to keep your green space. I'm so glad I have space on either side of the oven to put things down (hot pans, pies, beer etc.).

Looks like you've got quite a project on your hands. Look forward to seeing your progress.

Good Luck,
Regards,
AT

[NCMan]

Re: Foundations (literally)

I'm not seeing any photos here (?)

[stonecutter]

Re: Foundations (literally)

I would recommend building in front of the retaining wall. It looks like the first three courses were deteriorating but got a new paint job, and a new course was laid on top. If you set the oven back into the wall, you will have to deal with waterproofing membranes or paint....a must given you are probably in a wet location, seeing the condition of the block and that drain pipe. It's not that doing it is bad, it's just more work.

If you don't want to build in front of the planter, then do not tie your oven structure to the wall. That needs to be a control joint, allowing each structure to be independent of each other, to prevent damage caused by different movement.

It does look like 4" cmu, but that is plenty if that's what you want to use to build your stand.

[ATK406]

Re: Foundations (literally)

Stonecutter brings up a good point about the moisture. Looks like there is already a drain pipe built in to the wall. I would look into that and possibly reengineer it (if necessary) to take
the water off of the hill side and channel it away from the oven.

[Toomulla]

Re: Foundations (literally)

If you want to build back into the bank I suggest that you excavate an area large enough to build a retaining wall that is independent to and separate from the oven base. The soil height appears about 5 feet so the footing to the wall will need to be substantial and will be sufficient for the oven separating the retaining wall from the oven base will help with moisture control 2 inches should do. Of course you will need drainage behind the retaining wall

[Gulf]

Re: Foundations (literally)

Building into a retaining wall is a Btch!. I speak from experince! It requires enough excavation to pour the foundation slab, build the oven stand, install french drains, cap the whole surround.......................the hours involved are countless..............I'm still not finished . But, I would still do it again if faced with the same area to work with as I did .

[Toomulla]

Re: Foundations (literally)

I totally agree

[NCMan]

Re: Foundations (literally)

I agree also. If there is any way you can build independent of the wall, that's the way to go. If you decide you have no other option but to build it into the wall area, be sure you know what you're doing or try to find a knowledgeable person to advise or help you. Hopefully, you can build in front of it.

[deejayoh]

Re: Foundations (literally)

My oven location is very similar to yours - I built the oven with the base on top of a retaining wall. It was a newly poured concrete wall so I was certain it was sound and had a good footing. Two years in, I haven't had any issues with settling, cracking, or moisture (knock wood!)

Assuming that wall is sound, I think you could build up the front section and put the oven on top. Dig down 8 inches or so, put in 4 inches of compacted gravel, and pour a 4 inch slab on top of that. You will need to get some waterproofing/anti-wicking additive for the concrete - otherwise you'll be dealing with water problems forever (assume your weather is probably like ours in Seattle...)

I'd also suggest thinking about having the front of your slab come out a bit over the front of the wall so you get some storage space for wood under the oven.



edit: and if there are problems with the wall, I'd knock out a section and rebuild or pour concrete. I wouldn't bother to dig back into the dirt to excavate a full foundation. The dirt at the bottom of the hole you will dig is no better suited for a foundation than the dirt at the top. All you'll be doing is ending up with a big pile of dirt you need to get rid of, while building a place for spiders and bugs to live. You're going to end up with a woodpile anyway. IMO, unless that pile is very far from your oven, the most wood storage you'll ever need under your oven is enough for one or two fires.

[Gulf]

Re: Foundations (literally)

.......... I wouldn't bother to dig back into the dirt to excavate a full foundation. The dirt at the bottom of the hole you will dig is no better suited for a foundation than the dirt at the top.....

Unless the dirt immediately behind the retaining wall was backfilled, which many times, is the case