39 inch Corner Build

[Larry P]

I basically did what he did, but it took me about 3 hours. 4 bags of 50lb surface bonding cement. The acrylic admix made it set really fast, so I was only mixing 1 bag at a time, which really slowed things down.

[JRPizza]

I had my third firing since putting on two layers of stucco, and noticed some hairline cracking, mostly running parallel to the ground. We have not decided between doing a final top coat of stucco or trying to put on some kind of tile/veneer, but would like to see how the stucco will look completed. Is there a top coat mixture/formulation/product that I can put on as my finish coat that would have a good chance of not telegraphing the cracks and not cracking further, or am I better off using a dark finish so the cracks aren't visible?

[JRPizza]

Forgot to post pic of the cracks.

[david s]

Those cracks don't look too severe. Give it a few more firings to ensure all moisture is gone then fill the cracks and paint the whole dome with an acrylic render or bathroom waterproof sealer that's used prior to tiling. This will also make the outer dome waterproof.

[JRPizza]

Thanks David. I'm working on several projects that have priority over the final finish, primarily the roof over the oven. When I get ready to coat the dome and pick some products I'll PM you or make a post if I get confused

[JRPizza]

Are there any roof experts on the forum? I designed my shelter with a low slope roof 1/12 and am in a little quandary on how to proceed. Originally wanted to do something transparent but hadn't thought about having to penetrate the roof with my chimney and how to flash it (heat and aesthetics problems with plastic roof). The next plan was using metal, but the manufacturers don't warranty low slope roofs, and the low side of my flashing will be windward, making the sealing of the flashing problematic. Most all the panels have some sort of ridges/corrugations and I am not sure how to get the flashing tied down sufficiently to prevent leaking. It is pretty straight forward if you have an appreciable slope, but with the low slope I think I might have designed myself into a corner. I am now considering a membrane roof, which are recommended for low slopes and would make adhering/sealing the flashing relatively risk free. Does anyone have roofing experiences they could share?

[SableSprings]

Hey JR, I'm no expert in roofing...but I am in S. Oregon, have lots or winter rains, and built a low slope roof for the Dragonfly Den. I used metal roofing and have a couple things that seem to help.

1) Use exterior plywood 1/2" thick or better

2) Put down heavy/thick roofing paper (use a wide overlap between paper courses, making sure you are starting at the low side of the roof so the overlays always "drain" over onto the next sheet down not under). Also leave yourself paper margins around the edges so the flashing can press down and over the "flaps".

3) Use the flashing that's 2" or 3" on each side and apply it so the paper is wrapped down over the plywood edges.

4) Because you don't have a major slope, the overlapping metal sheets can have capillary action wicking water back up under the sheets. Either overlap them more than normal 6" or more or plan on running a thin bead of silicon seal between sheets at the overlap joint.

5) Those little foam pieces they sell for every style of metal roofing fit between the flashing and into each of the raised areas of the roofing sheets. You put them in place on top of the flashing and under the roofing metal. When you screw down the metal sheets, the foam is compressed and makes a pretty effective seal again water moving up under the roofing materials.

6) Plastic gutters are easy to install, but expand quite a bit when the temps rise (especially if they are in the sun). Do plan for some sort of gutter system, when it rains hard, it's amazing how much water will come off that roof!

7) Yes, flashing the chimney was a bit of a pain...but then it was primarily because I wanted to do it myself instead of getting some professional help

Hope that helps a bit...or at least gives you some additional info.

[JRPizza]

Thanks Mike, that helps a bunch. I am sweating the chimney flashing leaking, but your explanation about the foam fillers turned on the light for me. I was picturing having to try to hammer ridges flat or pump in pints of sealant ;-) I forgot the 'Den had a low slope roof - should have asked you sooner. I'm getting a couple of bids for membrane roofing, and if they are too high I'll try the metal myself. We were hoping to try to use purlins if we went metal, but you confirmed what is recommended for low slope - using plywood. How did you handle the fastening? Short screws, thicker plywood, or just have some exposed threads here and there? Also, do you remember how low your slope was?

[SableSprings]

Yes, as I said before, the flashing around the chimney was the biggest pain. I tried to the cut the metal too close to the chimney and then I put pieces underneath that metal that shingled out to the metal sheet below or adjacent. If I was to do it again, I would make a wider gap between the metal and the chimney. With a wider gap I'd be able to use flat flashing that was commercially available to skirt the chimney. As it is, my flashed gap is so small that a couple leaves or pine needles and it can (and has) backed up and dripped down my chimney stack inside. Fortunately the brick dries quickly and I've not had anything laying around that was ever damaged.

We made our own joists and the DDen's roof slope is 7"/10' or 1/17. I figured your slope as 8.3% while ours is 5.8% My brother in law that helped with the project is from Minnesota so our joists are 16" centers ... lots of roof attachment points and plenty of snow load (if we ever have any).

The nice thing about the metal roofing is that it can be pretty tightly secured with relatively few screws. I used long screws and attached the roofing into my joists directly...I actually don't think I missed any...although I do have a few misses with the plywood roofing...go figure

Again, good overlaps really help and I know there are some metal roof styles that are better than the one I got from Home Depot. Mine were 10' x 3' sheets if I remember correctly. I've attached a side shot of our roof line...hope this helps a bit.

[JRPizza]

Do you have any pictures of your flashing around the chimney you could share? You can pm them to me if you want. We got our first bid back for a membrane roof, and at 3K for a 14X16 roof I'm thinking about going the DIY route

[SableSprings]

Sorry but I don't have any pics of the flashing. I do know that the local sheet metal shop makes custom flashings for chimneys and there are some pretty good generic ones available. Check with some of the roofing folks and see who they use to make 'em or if they've got some options that might work for you. My chimney came pretty close to the end of the top sheet of metal roofing. (Two sheets covered distance from front to back.) I just cut the top metal sheet to parallel the sides of the chimney. I then took some flat flashing and shoved it up under the top sheet and brought it out below over the bottom. I put quite a bit of flashing sealant in those joints. I also jammed some flashing on the chimney downside to it provided a little rain shelter for the lower part where it was difficult to effectively flash.

Although my job has worked pretty well for the past 5 years, it is pretty ugly. I will go up later this week and take some pics for you...if you promise not to laugh...

I do wish my chimney came through the roof a little more squarely, it certainly would have made my roof sheet cutting easier. On retrospect, I would be spending more time talking to people that made custom flashing for just such situations or looked around more for "standard" chimney flashing options.

[Gulf]

JR,

Here are some pics that I took during my build. I'm not sure if it is the same type application as you will be doing.

Roof Flashing

[JRPizza]

Joe, thanks for showing me how a roof and penetration should be designed . Putting a penetration at the peak is the preferred way to go (I believe) and looks like you have plenty of slope. Your pictures might help when I start cutting metal.
I have considered reframing my roof to get the chimney at a peak or at least to increase the roof angle, but with oven placement, prevailing winds etc, I am probably stuck with my low slope design. Mike has giving me hope however that I can do something that will keep the oven and guests dry.

[JRPizza]

I have a question for all the folks with IR guns and double wall chimney pipe. I have 8" supervent pipe and I can get a flashing good for 250F for less than $50, but a 450F flashing runs about 117 in the same style. Barring a chimney fire, anybody have any heat readings on their pipes?

[UtahBeehiver]

JR,

My build is not covered but I did use Serkirk's UltraTemp double wall SS chimney pipe. Supervent is a Selkirk product and the literature that I have shows flashing with safety vents around collar on the roof penetration required for UltraTemp and a min. of 2" clearance from any combustibles.