Roofed enclosure - Help!!!!

[ashley_hedges]

Hi Guys and girls hoping that you can help..
I have built a Mongrel of a Wood fired oven based around an oil drum and storage heater bricks covered in vermiculite/cement and while it works well and has been up to ferocious heat, it constantly cracks due to the expansion of the drum which rules out my original plan of rendering the outside. So my next idea is to create an enclosure with a roof and fill the space inside with vermiculite.. only one problem, I'm not really sure how to go about building one, and I must admit to being really nervous about putting a hot chimney through the roof.
I had thought about using a wooden frame and cement board but I am open to better/easier suggestions.
Please bear in mind my DIY skills can at best described as minimal and more often described as a Visit to Accident and Emergency

Thanks in advance for any help you can throw my way

[cobblerdave]

Re: Roofed enclosure - Help!!!!

Great
Looks like your post has slipped behind another, as happens.
You have said you were thinking about building wood and cement sheet. Why not use steel framing instead. Hope is available in UK. If it is its easy to use. Cutting easy tin snipes will do , and fixing is as simple as metal screws and it will give you a no combustible frame.
If expansion is the problem why not a compressible layer of insulation. If you have a fair layer of insulation in the pearlite cement you might be able to use something with a lower heat rating as well. You can chicken wire and render over that. Once done you could even 1/2 brick over that as well as I have done. 2 ins render and a. 1/2 brick gives you a pretty thick skin
Anyway hope something here helps
Pherhaps post in in the chimney finish section for some more answers
Regards dave

[Greenman]

Re: Roofed enclosure - Help!!!!

To put your flue through the roof I suggest that you need an inner (flue pipe) and outer (chimney pipe) going through the roof. The outer section needs to be sealed to the roofing material and how you go about that depends on the roofing material you use.

Mine is colourbond steel and I just cut the appropriate size hole in the roof slipped it all through the hole and sealed between the roof and chimney with hi temp caulk. There are other sealing mechanisms available but I just kept it simple and given that the roof is only for the benefit of the oven a leak would not be the issue that it would going through a ceiling. It doesn't leak anyway.

The pic looking up was taken before the caulk was applied. The gap between the flue and chimney is approx 3/4" or 20mm. The chimney pipe doesn't really get hot either.

Hope this is some use.

[david s]

Re: Roofed enclosure - Help!!!!

You can get a double lipped cowl that will fit an inner and an outer pipe. Also a Decktite seal to seal around the outer flue pipe where it goes through the roof.

[ashley_hedges]

Re: Roofed enclosure - Help!!!!

Thanks for the replies guy. Much appreciated. I'm sure you can get the metal framing over here in the UK, I never actually seen it sold- so it may be a specialist item. I had set my hopes on a wooden frame as it's quick,easy and cheap to build especially as my wife has set me a "cheap or free" budget..she's no Fun at all!! I have already tried chicken wire to reinforce the cracked area but it still cracks especially so when the ovens at over 400 degrees - I get numerous cracks around 1-2mm wide. I suppose I could use a layer of ceramic insulation as an expansion joint and chicken wire/render over that, but again bang goes the budget I don't have. I am hoping that the wood frame will be OK as it will be around 6" away from the current exterior of the oven and will have vermiculite/perlite in the gap created so all being well there shouldn't be too great a heat transfer to the wood. I only have a single skin flue which does get rather hot - would I be OK to run it straight through cement board, should I go through a metal plate or go through a Terracotta chimney and back fill with vermiculite then to off with some form of capping.
I know it's a lot of questions but if you want the right answers you ask the experts.

Cheers

[david s]

Re: Roofed enclosure - Help!!!!

Your plan sounds ok, just make sure that your flue pipe is no where near any timber framing in the roof.

[stonecutter]

Re: Roofed enclosure - Help!!!!

You need a minimum of 2" clearance from combustibles when you run your flue.