roof materials

[jlaw]

i am on the home stretch with my oven - brickwork is done, dome is insulated, and all framing is done (walls and roof). i used metal studs for all of the framing. i will make the walls out of cement board, and cover them in stucco. my question is about the roof - i have been trying to avoid combustible materials at all cost, but i am at loss for the roof - if i use cement board, there will be nothing to nail shingles into. my local lumber yard sells some type of fire-retardant plywood (i guess treated with some chemical), so i was thinking of using that, then tradition roof construction - tar paper, shingles.

i am sure the concern unnecessary - i have 2-4" of insulating blanket, and intend to fill the remainder of the chamber with vermiculite, but it is worth a slight consideration just to be safe.

any ideas for this? thanks!

[dmun]

Re: roof materials

Even what we think of as masonry roofing materials, the tiles and the slates, are nailed to wood furring strips supported by wooden rafters. With that much insulation I can't imagine it's even going to get warm, unless you do something dumb like vent with single wall stove pipe.

[christo]

Re: roof materials

I used a rubber EPDM membrane on top of cement backer board. The cement backer board was screwed to metal studs.. Used contact adhesive to glue membrane to backerboard.

Little over 1 year - So far so good!

Christo

[dlgeis]

Re: roof materials

On my Scott oven I used brick walls with conventional wood frame roof plywood deck asphalt shingles loose fill vermiculite. Cedar planks on the roof ends and eaves. I used double wall stainless 8" chimney pipe from Lowes topped with a spark arresting vent top.
The system has never showed signs of excess heat or of the flamable items trying to ignite.

The I've is 30' from my house so I am not concerned with a fire threatening a dwelling.

Doug

[cvdukes]

Re: roof materials

if i use cement board, there will be nothing to nail shingles into. my local lumber yard sells some type of fire-retardant plywood (i guess treated with some chemical), so i was thinking of using that, then tradition roof construction - tar paper, shingles.

Other option would be to forget nailing. Just use the screws designed for cement board to screw your shingles to the cement board roof. It'll take a little longer than nailing and just slightly more expensive than nails, but you won't need a whole lot for a small roof. You won't need tar paper if you use the Hardee board...its already moisture resistent.

[jlaw]

Re: roof materials

yes, but screwing INTO cement board would be very weak, as the board is very crumbly. that is very different than screwing cement board into metal studs, where the head of the screw is essentially what is holding against the cement board (NOT threads)...

[Breven]

Re: roof materials

I've had my oven up to 1,000 degress F, and I can promise you that if you inlcude an inulating blanket, along with additional vermiculite filling your enclosure to the rim- you won't feel any heat on the ouside roof or walls. It really does all stay inside. I wouldn't hesitate to tack some wood strips to the outside. No problem at all. (again, this is assuming you have insulated correctly).

[dlgeis]

Re: roof materials

Put concrete board first top with 1/2" plywood or OSB attach shingles with pro-fit or similar screws (they will self drill into the cement board nails may damage it).

The fasteners work mostly in shear to keep the shingles from sliding of the roof one of the most important parts of the system is the tar strip adhessive between the shingles themselves. I believe it is worth it to use tar paper, drip edge, chimney flashing etc. This is not the place to save $50.00 on a 1500.00+ project with who knows how many hours of labor. For performance and longevity KEEP YOUR OVEN DRY.

Lowes and HD have roofing books.

Doug

[Pop Alexandra]

Re: roof materials

I used a rubber EPDM membrane on top of cement backer board. The cement backer board was screwed to metal studs.. Used contact adhesive to glue membrane to backerboard.

Little over 1 year - So far so good!

Christo

Likewise.
And I'm quite confident that it will last quite a few years more.
_________________________________________________
Alexandra from

[Baza]

jlaw - great question that I struggled with too - I can't count the number of online and this-forum searches I did to get an answer to this question!
I did an enclosure too (just finishing the outer cladding now). I used steel studs and concrete board AROUND the oven.
I filled the enclosure with vermiculite (7 bags) over the 3" of insulating blanket.
I elected to use 1/2" plywood for the roof - screwed into steel studs.

I shingled it with normal roof shingles AFTER applying a ice/moisture barrier, drip edges and roof-cemented the edges down.
Cut vents in the soffits and made a gap for venting using a roof cap.
Sealed and sorted!

Working great and feel absolutely NO heat on the exterior anywhere. You'll be fine with wood - but ... builder's choice!

Throw in a pic to let us see your progress!
We're always keen to see a build!!

Take care
Barry

[mongota]

With the house being filled with insulation, regular CDX ply would be fine for sheathing the roof.

If you REALLY are concerned and you still wanted to use cement board, you could put cement board on the rafters, then lay plywood on top of the cement board. Screw the ply to the rafters, screwing through the cement board. Fasten your shingles to the ply.

I would not use cement board by itself as your only roof sheathing. Over time it'll sag in the unsupported spaces between the rafters.