roofing construction

[bobnnorm]

I am buiding a barrel shaped oven surrounded by 4 inches or so of perlite between the oven and the exterior walls. For the roof I would like to use wood, not steel, for the rafters and plywood for the roof decking with some sort of roofing media on top. With all the firebrick, cladding , and perlite, is there really a danger of the rafters and plywood catching fire? Has anyone done their roof in this manner?

Thanks

bob


bobnnorm@ptd.net

[RTflorida]

Re: roofing construction

Theres always a danger,you just never know whats going on in there once it is sealed up.
Steel studs are actually very inexpensive and cement board (HardiBacker, Durock) is no more than plywood and both install as easily as the wood products. Don't let inexperience deter you. Really, its not that difficult working with either.

RT

[brickie in oz]

Re: roofing construction

Plywood and asphalt tiles on mine, I dont see a problem as there is ceramic blanket and looooooots of loose vermiculite..

[Mike D]

Re: roofing construction

Why risk it? I wouldn't mess around with anything flammable. You never know what is going on inside.

Mike

[brickie in oz]

Re: roofing construction

The only way it could catch fire is if the roof of the oven collapsed while in use, I think Id notice that..

[Neil2]

Re: roofing construction

Have some hot dogs and sticks handy for when the roof catches fire.

[brickie in oz]

Re: roofing construction

How can it catch fire?
There is 300mm of loose vermiculite on top of the oven over the top of 50mm of ceramic blanket, plus around 600mm of air space to the nearest part of the roof.

Ive checked the inside roof temp and it gets 20c above ambient, which means it should catch fire on one of our hot summer days that hit 50c.

I have built many fireplaces and chimneys and am very confident with this build being totally safe and enclosed.

If ever it catches fire Ill post some pics of the roof and the humble pie it cooked.

[dmun]

Re: roofing construction

I have a fifteen foot high timber structure built on top of my oven. I also have a four inch reinforced concrete barrier between the masonry and the wood, which supports the masonry chimney. There's nothing wrong with timber rafters and sheathing if they're done right. They build houses that way, after all.

[splatgirl]

Re: roofing construction

FWIW, my enclosure is wood framed. I'm not worried about it in the least.

Cement board is not intended to be load bearing or used structurally like plywood. It's also not any much more fireproof.

[RTflorida]

Re: roofing construction

I can't seem to find it, but I distinctly remember a forum member posting a photo of his timber built oven structure catching on fire. Its been a couple of years and I don't remember the details. Obviously it comes down to following fire code recommendations and the use of non combustible materials and having proper separation. If in doubt, consult with your local fire dept.
Personally, I am not a fire inspector, fire chief, or tester of fire retardant products and neither are most backyard oven builders. Why not error on the side of caution?
Last time I checked, standard plywood was not rated as a non-combustible as are all of the major brands of cement backer board. As for load bearing, not much load to be carried in enclosing an oven and can easily be compensated for in the rafters. That said, roof sheathing would not be my biggest concern, I would most likely use plywood for the roof sheathing, knowing I had done everything else properly I would be worried about framing and sheathing around the entry and or course around whatever chimney is used.

Just my opinions, far from an expert at anything. I have used all of the materials mentioned many times and my comfort level is the same working with all of them. I just think it makes the most sense to use non-combustibles wherever possible for our application, and as I mentioned, cost really isn't a factor.

RT