Dreamer turning to "do-er"

[Blairt]

I've been dreaming of an outdoor kitchen and pizza oven for years. We finally built our retirement home and moved in this past summer. We are on Vancouver Island in British Columbia, Canada. Starting the oven build in our cold and rainy winter isn't ideal but if I choose the times right I think I can get some good progress and be done in time to be cooking next summer.

I've attached some pictures of the base that we built. The buttresses and concrete slab were engineered to support the weight of the oven so I'm quite confident that my base is good. I do have a question on the chimney though. Our local building codes require a full masonry chimney on any wood burning stove or fireplace. I had hoped to be able to use double-wall stovepipe but it will not meet the building code.

Since I'm under the overhang of our roof, this means that I have to go two feet ABOVE the peak of the roof. This will result in a masonry chimney of about 12-13'. My concern is being able to build the door arch and the opening in the base (for wood access) strong enough that I do not have to worry about the weight of the chimney above. I've never seen pictures of anyone building such a tall chimney. How can I build to be confident of the height and support?

In the photos attached, I've tried to show the buttresses and pad. The red outline shows approximate area where the oven will go and the final photo shows how high I have to go with the chimney to clear the roof.

[MarkJerling]

That's going to be quite a bit of weight. The door arch will carry the weight, provided it's buttressed sufficiently. The problem, of course, is: What is sufficiently?
The problem you will have to contend with is "lateral thrust" which will be the mass from the top trying to flatten and push the arch below sideways. There are a few things you can do:

• You can construct your door arch much more solidly than normal.
• You can add further stress relieving arches over the door arch.
• You can have very solid buttressing to the sides of your arch.
• All of the above.

[Gulf]

You may need to make sure what the actual code for your area says.

Since I'm under the overhang of our roof, this means that I have to go two feet ABOVE the peak of the roof

You say "over hang". Is that an eave or a gable?. My local code says that I have to be two feet above any structure within 10 feet. For an eave, a level horizontal line drawn from the nearest point from the exit of the chimney to the run of the roof plus two feet above that satisfies that rule for us. Your code may be different, but it is worth double checking.

This will result in a masonry chimney of about 12-13'.

Yes, that's a lot of weight for a chimney that maintains an 8" masonry thickness. Some areas allow 4" of masonry around a flue liner. But, clay liners and 4" of brick still add a lot of weight. A stainless steel liner (single or double wall) will be much lighter. It may boil down to what your code defines as a liner. You may also be able to add a lighter weight 4" ("masonry") around that than 4" thick brick. But, lets check out your codes to see what we can safely do within what your local codes, insurance carrier, and your own peace of mind will allow. If you can post a copy, I might be able to help.

EDIT: Try to go to a larger size pic for your posts. You may need to add fewer pics and use multiple posts to satisfy the forum requirements.

[Blairt]

In searching for insulation for under my WFO, I've found a thermal ceramic insulating firebrick TC-23. It is rated to 2300F. Can I use this as the base layer between my concrete pad and my firebrick oven floor? Morgan IFB Datasheet.pdf

[Blairt]

Finally starting on the CMU base. With help from my brother, got the first two rows done on Thursday. Finished second two rows yesterday.

[Blairt]

Put blocking underneath Durock and installed rebar today. I filled several of the CMU holes with rocks to avoid having to fill ALL of them with cement. When I looked at the height of the door opening for the firewood under the dome, I thought that 3 blocks high wasn't enough for comfort. I used 2 pieces of 3/8" angle iron to span the opening. This will be filled with concrete as well.

[david s]

Yes you can, but IFB's are overkill and an expensive solution. Use the 23's as they are lower temperature rated and should be cheaper. You will get a shock at the price and probably want an alternative solution.

Do some more investigation re stainless flues. Some areas require triple walled flues for indoor applications. That would certainly get around any issues created by the extra weight of a masonry chimney.

[MarkJerling]

Put blocking underneath Durock and installed rebar today. I filled several of the CMU holes with rocks to avoid having to fill ALL of them with cement. When I looked at the height of the door opening for the firewood under the dome, I thought that 3 blocks high wasn't enough for comfort. I used 2 pieces of 3/8" angle iron to span the opening. This will be filled with concrete as well.

Is the shuttering permanent?

[Blairt]

Hi Mark. Are you referring to the angle iron? If so, yes. The final height of the pad will be about 1" higher than the iron rails.

[UtahBeehiver]

I agree with David on IFBs, they typically run in the 4-5 USD range each. CaSi or AlSi board, Thermo Gold 1200 or "equivalent" is the best current floor insulation. Min 2 inches up to about 4 optimum. PS, your CMU base is done right and has some serious metal in it. The oven is going nowhere. It is deep so play with how you place the oven opening and access with a peel. Gulf has a really deep oven so look at his build for ideas.

[Blairt]

Thanks Russell. A vote of confidence on the base is really appreciated! There's some pretty serious rebar in there (all free which was a bonus! Many of the pieces are 3/4") The corner rebar pieces are also drilled into the concrete base about 3".

I have actually found 4" CaSi board so that will be my insulation. I'm pondering still adding a couple of inches of perlite/cement to raise the oven base a bit more but, as you suggest, I'm going to play with it a bit to see where I think it will be most comfortable.

I have a roof overhead and need to clear a beam which is directly above the front of the CMU base. That pushes my opening back a few inches from the front so I will likely have a longer than typical opening.

I'm constrained by our local building code which prohibits any type of steel chimney or liner on a masonry fireplace or oven without going through a professional engineer sign-off. That would cost a lot so I don't want to go that route. I'll end up with quite a tall chimney once it clears the roof peak by 2' so there will be a LOT of weight on this base and the oven arch.

[UtahBeehiver]

Look at Gulf's build, he also has a large brick chimney under a scissor frame open roof structure. Also the CaSi should have these two critical specs

Compressive Strength of 75 PSI at 5% compression and a K value of around 0.55 BTu*in/(hr*ft2*F) at 500 F. There are some soft CaSi out there so be aware.

CaSi is very water absorbent so you need to mitigate, weep holes in the concrete hearth is easy for you to place now rather than try and drill in later with all that rebar. Place on 1/2" pvc cut just short of the top surface with the end taped over then after the pour you can take a piece of rebar or rod and knock though the top easily. Also place the CaSi on on cheap or scrap ceramic tiles to raise the insulation off the concrete hearth. With being under a pergola water ingress would be as prevalent but these are two cheap preventive measures.

[Blairt]

Thanks again Russell. The CaSi is Thermo-1200 which I've seen others use. Not cheap! Ouch!$$

I do plan on putting in a few drain holes. I've bought some cheap ceramic tile to lay under the CaSi board. Only $1 per foot - they are large tiles but I'll cut them up to allow for more drainage options for the water to find the weep holes.

The final design will have a doghouse coverage with steel roofing so hopefully once the initial moisture is baked off I don't have ongoing moisture issues. I'm in BC where we get a fair amount of rain so I definitely want good coverage to keep both the oven and myself dry in the long term.

I'm looking at Gulf's build. Very nice! And yes, that's a tall chimney! Mine will be even higher by the time I go through the roof and clear by 2'. I'm having a professional mason do that part of the build. Better safe than sorry...

[MarkJerling]

Hi Mark. Are you referring to the angle iron? If so, yes. The final height of the pad will be about 1" higher than the iron rails.

No, I'm referring to the sheet of stuff behind the angle iron, resting on the blocks.
You'll need to be quite a bit thicker than 1" above the angle iron if you don't want a crack forming above the angle iron. How thick do you plan to make your concrete slab?

[Blairt]

The sheet under the rebar is Durock - cement board. It stays in place and will be a base for the slab. Under that, I have a particle-board support which has 2x4 blocking all around it and is supported by additional 2x4s which are temporarily screwed into the CMUs to ensure that they cannot come down once we start pouring the slab.
My slab will be about 5". I know there's a risk of cracking above the angle iron but I don't think it's too much of a concern as it would be cosmetic and will eventually be hidden behind the front wall of the doghouse covering. When I go to pour the slab, I am also going to lay down a sheet of fiber mesh concrete reinforcement in that front area where the angle iron is. I used this material when I poured concrete countertops in my outdoor kitchen last fall. It seems to work very well...