Napolitian style 106cm build inside a hobbit house

[crisp]

Hi All

I'm new to this forum, but have been reading posts on this forum for a while now. I've been so impressed with everyones different projects, ideas and Ive learned from you all. So I'd like to thank everyone for inspiring my build. There are lots of you out there that have built some fantastic ovens both indoors and outside and have experienced how the oven functions. I have a few questions which some of you have experienced. I am much obliged if any of you can answer some of my questions below.

Im building a Hobbit house in my garden, it's round building with a semicircular dome, basically the same as a huge pizza oven. The inside is a brick facade and the outside is in granite. Inside the domed walls of the Hobbit house i'm constructing a Napolatian style oven with 106 cm diameter.

I decided to build Napolation oven with a lower flatter dome. This required two radius's for the dome; a steeper first five courses on top of the soldier course; thereafter a flatter radius to the centre. There is more outward thrust for this type of dome shape, however, in my opinion a circular dome is also not stable without some form of buttressing, so I have incorporated a buttress harness. A catenary shaped dome or arch is actually most stable but wouldn't suit a pizza ovens design, read more here https://en.wikipedia.org/wiki/Catenary. Basically an inverted hanging chain which is the same length as the centre line of an arch/dome cross section, represents the line of thrust upside down. This invisible upturned line of thrust should lie in the middle third of the brick or voussoir, if it does not, then the arch/dome will be unstable without buttressing. This is why the gothic arch revolutionised spanning wider openings with less stone. Before this the Roman half circular aches and domes required higher/larger voussoirs to bridge wider openings, which meant that there was a certain limitation spanning wide openings.

I started the build on the 6th August and set the last keystone on the 16th August, so it's taken 10 long days of work to get this far. The first five courses where all cut to a steeper radius, however i only tapered the correct radius of the bed joint, not the perpendicular joints of these first five courses. After the first five courses, with the flatter arced dome, all the four sides of the brick voussoirs were cut to a different trapezoid for each course for tight fitting.
I have mixed my own mortar which is from clay / hydraulic lime / sand. There is no cement, both the hydraulic lime and clay is the binder with the sand. The hydraulic lime helps to harden the mix. Since cement was first patented in 1824 all ovens before this had no cement in the mortar. Hydraulic lime is a more flexible binder than cement and allows for for movement through thermal expansion. The joints inside the dome are 2-3 mm.

Now that the dome is completed, the next job is to build the vent and construct the chimney etc. There will be a heat break between the entrance to the dome which will be 10mm air gap sealed will fire rope. The hearth entrance to the inside of the dome entry arch is 60 cm. The pizza oven is built into the wall of a 9m² room.

Questions;

1. If the oven does not have a door, how will the radiating heat effect this small room when the oven is in full operation, will the room become unbearable to sit in without a door which can be closed? The door would have to be on the room side of the vent/chimney. I will have an insulated door for heat retention and longer cooking but this cannot be used to stop radiating heat into the room because it also blocks the vent. I'm wondering whether it's worth designing a door which can be closed within the rooms facade? If anyone advises to have a door then I need to incorporate this in my design, otherwise i might regret it later. Has anyone else built an interior oven who can tell me how hot it can get within the room?

2. Another question is insulating the dome. I thought that i would parge the dome first with clay / hydraulic lime / sand mix 2-3 cm thick to seal the dome (perhaps some chicken wire too). Thereafter, covering with 7cm of insulating concrete made with Leca / Hydraulic lime / clay. This will be a loose fairly dry mix with air voids. The rest of the enclosure will be Rockwool masonry insulation, this is slightly harder than normal rockwool. These materials are readily available to me.
Basically the clay parging firstly seals the dome; the Leca insulating concrete separates the Rockwool from the direct heat. Any thoughts on this?

I will post some more of the build at a later date

[UtahBeehiver]

Very nice brick work.

[staestc]

That is just excellent work! Very well done! Look forward to seeing further progress photos.

[crisp]

Thanks guys,

Anyone got some answers about my radiating heat and insulation questions?
Ive got lots more picture from the start but I'm unsure of the best way to post them on this thread. Do you have to create an album first? it says that I can only post 6 pictures per post. When I pick the first six, the uploaded pictures come up in the wrong order.

[SableSprings]

That's one beautiful oven and demonstration of serious masonry skills!

I have two oven doors. One is my fire door and the second is a lightweight cooking door that I put on the front of my landing (actually just in front of the vent arch) or just outside the reveal to reduce the heat coming out of the oven into the room. Having a lightweight door and a slightly extended landing gives you some pretty valuable options. (Pictures below show the landing extension, cooking door in place with pizza fire, and cooking door and fire door together on landing of my oven for comparison.)

Our winters in Oregon are generally mild and I've noticed that we do get some radiant heat out of the oven opening with a good fire. Usually the draft up the chimney is bringing room air in and combining it with the oven's heated air to keep the room heating effect low. I'm not sure what the insulation value of the rock wool is, but making sure the entire outside of the oven doesn't get warm from the pizza fire will be important (insulate, insulate, insulate...) Most of the forum recommends at least 3" of ceramic batting or at least double that if using a 10:1 (perlite/vermiculite:cement) insulating concrete...so I'm not sure how your 7 cm of Leca/Lime/Clay + rockwool masonry insulation compares. I'm also not sure if the first parge layer is going to be of any value...it would seem to me that it will only increase the heating mass of the oven.

...and yes, the order in which you pick pictures to upload is not the order in which they are posted. I have resorted to uploading 1 picture, then clicking on the camera button again to load the next and so on if the order is important to me.

[crisp]

Hi Mike,

Thank you for your comments, and spending the time to answer.
Your oven looks fantastic, and adding the extra landing door give the advantage of closing down the heat into the room while the oven is burning. I'm thinking of a sliding door which lifts up into the vent room under the chimney. This means the door will not be seen when hoisted over the the entry arch. This means the door will be hidden up in the vent and invisible when raised above the entry arch. I will have to make a channel for the door to slide though and also some sort of mechanism to hoist up and down.

i agree that the parge layer is perhaps unnecessary increasing the mass of the oven walls. The Leca concrete insulates well, but perhaps not as well as a ceramic blanket, but this layer separates the direct heat to the Rockwool. Rockwell has good Insulation values but I've read that it should not perhaps be used in direct contact.

Much obliged with you your comments, I'll try your picture upload advise, love your oven and build thanks for your help

Chris

[SableSprings]

Chris, be aware that you will have soot and/or creosote build-up to some extent in all vent areas over time (and depending on your wood of course). That might cause your sliding door to jam in a slotted system or get your hands very sooty (or worse...) when you dropped the door into place. Have you considered two 1/2 doors hinged on the left and right sides of the oven opening. That way you could close either half or all of the oven from direct heat radiation into the room. Make them so they opened fully (parallel) to the oven face and they'd be totally out of your way if you didn't need them.

In my opinion, the main thing you should consider adding to any fixed door(s) would be either some low vent holes or to make the door(s) with a bottom gap--allowing enough airflow from the room, through the oven and out the vent/chimney to keep smoke to a minimum. I've seen a pizza oven door on the forum with several holes drilled along the bottom of the door and then a slider piece with matching holes that could be used like a damper for the fire (...hope that made sense ). I prop my doors at an angle to achieve variable dampening for the fire as needed.

Based on what I've seen of your build so far, the finished exterior of the oven and doors will be fabulous. (Frankly, it's too bad that the fantastic brickwork you did inside the oven's arch will be hidden from your guests...it is really inspiring!) You could even do some metal sculpture/application or cutouts in some heritage Norsk designs on the outer doors...anyway, looking forward to your progress!

Thanks for the positive comments on the Dragonfly Den...

[crisp]

Hi Mike,

Thank you for your kind comments and support, it is sometimes hard to figure out alternatives alone.

You are right about the soot and/or creosote. Maybe I could fabricate a steel envelope which the door slides up into, and build it between the chimney and the rooms facade? it would be sort of like a portcullis. I would have to design a simple hoist system. The advantages of having a sliding door is that when it is up, it is not seen or in the way. Another advantage with a sliding door is that by regulating the height of the door from top to bottom, you can effectively lower the arch slightly when lighting a cold oven; hence stop smoke escaping into the room.

Two hinged doors are also an alternative, but they are permanent and perhaps be in the way when baking? They can also be a feature so I can't rule that out. I found this site in Norway who sell oven doors http://auronimport.mamutweb.com/Shop...erovnsdør/19/1 The only thing which could be a problem is that the doors are mounted in a frame, this means there will be a threshold under the door/doors. My landing is a piece of soapstone which goes all the way in to the heat break. I guess I could cut the threshold off?

The arched entrance to the dome measures 48cm wide and 27.5cm (top underside of arch)
The vent/chimney area can be 60cm wide and 24cm deep. This gives me a reveal of 6cm either side for the insulated door. Thus, the second arch 60cm wide and 34cm (top underside of arch)

I was thinking of building in two air vents, on the bottom of each side of the vent/chimney area with ducts taking the air supply from the outside of the building. This will help the draw of the chimney and not steal air from inside the room. This means the door can be fully closed without vents.

Decisions, decisions.....I kind of like the sliding door idea, checker plate/steel door which I can fabricate myself, I can even cut out for a window. But its not going to be as pretty as buying one of those doors. However, those doors are expensive and some of the measurements don't really match exactly.

Help, What would you do?

[david s]

I've used rock wool on a couple of ovens and it is placed directly against the inner dome. I can't remember the rating of the stuff but pretty sure it was not much less than ceramic blanket, so I'm sure it's ok to lay it directly over the brick.Remember that the outside temperature of your inner bricks will be considerably lower than the inner face. I found however the stuff was a bitch to cut compared to ceramic fibre blanket, was far less dense so hard to vermicrete up to and it is also way more water absorbent than ceramic fibre blanket, so I now don't use it although it's a little cheaper.

I hope you have a decent flue diameter planned for the oven because front flued ovens are notorious for smoke out the front at start up unless the flue cross sectional area is adequate and the flue gallery designed like an inverted funnel. Being in a small hobbit house full of smoke could be unpleasant. When in Pompeii I noticed quite a few small central flued ovens in private homes (unlike the larger front flued ones in the bakeries). I presumed this was because people didn't want their houses full of smoke, while the bakers oven probably never cooled down.

If you're interested in catenary arches you may be interested in this. It is an elaborate although I think elegant shelter for my kiln.
#32

[crisp]

Here are some pictures of the Hobbit house from the start

[crisp]

Here are some pictures of the hobbit house build. It is a round building with brick interior and a granite facade outside. Inside it is 7 square meters. There will be a domed brick ceiling which I intend to build without supports, basically the same as a massive pizza oven. The Pizza oven will be built into the wall at one meter high where the domed ceiling springs from. So lots of arch and dome transitions both with the Hobbit house and the Pizza oven. I have finished the pizza oven and will post more pictures eventually. The oven is built without supports or indispensable tool, I only used a template from the centre point/ floor of the oven.

[crisp]

I've used rock wool on a couple of ovens and it is placed directly against the inner dome. I can't remember the rating of the stuff but pretty sure it was not much less than ceramic blanket, so I'm sure it's ok to lay it directly over the brick.Remember that the outside temperature of your inner bricks will be considerably lower than the inner face. I found however the stuff was a bitch to cut compared to ceramic fibre blanket, was far less dense so hard to vermicrete up to and it is also way more water absorbent than ceramic fibre blanket, so I now don't use it although it's a little cheaper.

I hope you have a decent flue diameter planned for the oven because front fluid ovens are notorious for smoke out the front at start up. Being in a small hobbit house full of smoke could be unpleasant. When in Pompeii I noticed quite a few small central flued ovens in private homes (unlike the larger front flued ones in the bakeries). I presumed this was because people didn't want their houses full of smoke, while the bakers oven probably never cooled down.

If you're interested in catenary arches you may be interested in this. It is an elaborate although I think elegant shelter for my kiln.
#32

Hi David,

Thanks for your advise, and nice to know Rockwool can be used and is efficient. I've already got lots of Rockwool so I'd be daft not to use it, and ceramic blanket is really expensive here in Norway.
I was thinking of building in two air vents, on the bottom of each side of the vent/chimney area with ducts taking the air supply from the outside of the building. This will help the draw of the chimney and not steal air from inside the room. I thought of an 8 inch (20cm) flue which I might just build with bricks and no liner. Years ago masons parged the chimneys with clay mortar mix as they built, reaching in and rendering the sides.

Love the shelter, what a fantastic Idea. A friend of mine built a large cabin cruiser boat out of concrete similar to this. Your structure is totally stable as it is a catenary. Gaudi built many thin walled arched structures which can only be achieved using a catenary arch. Most people seem to have the idea that all arches and domes are self supporting. Not all of them are without additional buttressing and loads. This is why I used a harness.

Chris

[david s]

Thanks for the compliments Chris.
Because heat is involved, which tends to compromise joints, bracing or buttressing is more of an issue for a kiln or oven. However it also applies to a lesser extent for buildings. Have you considered the need for either for your hobbit structure because straight walls support the domed roof.

[crisp]

Hi David,

Thanks for your interest, I have alway been interested in arches and domes. I have visited Gaudi's architecture in Barcelona, it's inspiring, just like your shelter/canopy, thats so cool.

Masonry is only stable when all the units are in compression; any tensile forces result in instability. That is why modern concrete buildings have reinforced steel within; concrete has little tensile strength without it. Before cement/concrete was invented (1824) all masonry buildings had to be built in compression. I'm babbling on a bit here sorry.

I have built in a steel bracing around where the dome springs from. Also because the outer facade continues plumb and the interior brickwork arches inwards, the gap between increases with height, this is called "the haunch". By loading the haunch with masonry, the invisible line of thrust is bent downwards and through the wall. Most vaulted cathedrals have loaded haunches to bend the line of thrust down a pillar The haunch is basically a ballast. I'm not very good at explaining this but this does http://www.earth-auroville.com/stability_notions_en.php

The whole Hobbit house is built with lime mortar, I slake quicklime with the aggregate, a "hot mix". There is also a quicklime concrete between the interior brickwork and the granite facade. The stainless steel bracing is within this concrete. Both walls are also tied together with stainless steel ties. Nearly the whole project, including the oven is built without cement; there is only a cement/concrete foundation both under the Hobbit house and under the oven.

Chris

[SableSprings]

Yes Chris, the more I think about it, the more I like the drop-down door. If the groove is in the outside vent area it won't get much soot or creosote and since you're thinking of a counter weighted, chain lift/lock system, you certainly aren't going to get lots of black on your hands moving the door up/down, What would be fun to do is check with your local schools and see if there are some art students that like to work with metal,,,I bet they could really make your drop down door quite the show piece for the oven (as I bet you could--based on the pictures we've seen of your work!).

I really like that you are planning to have adequate air venting from the outside so the fire will not pull air (much) in from the room. Make sure that you cover these vents with hardware cloth/screen to make sure you don't have unwanted guests or have live coals drop down under your structure . Would these vents be built with some sort of closure? So they could actually be used control/dampen the fire as needed.

I'm going to be out of Internet service (or have very limited connections) for the next three or four weeks...I'm really looking forward to what you come up with, so don't think I'm ignoring you. We were in Barcelona last year and I agree that Gaudi's work in Barcelona is amazing (as is David's ). Since I've joined this forum, I find myself more and more fascinated with any architecture that has features of an arch or dome...I don't know if I should admit that since I got my Masters degree (40 years ago!) as a fisheries biologist.