Flat Roof - Chimney Flashing Question

[JRPizza]

I also used heavy felt paper between my metal roof and the plywood below, and have only had one problem. I had thought the insulating properties of the felt paper in combination with the 3/4 inch plywood would be enough to prevent condensation on the underside of my roof, but when everything is cold soaked and we get a blast of warmer wet weather here in the Northwest, we still get quite a bit of moisture on the lower surface. Over the past few years we have gotten some mildew spotting on our stained surface and will eventually need to do something to clean it up.

[SableSprings]

Dan, just checking (with your "heavy" rainfall) that you are making sure you have enough overhang in front to shelter you when working the oven. It's not fun to stand/work in the rain. Also a bummer to not have a bit of covered work space to prep a pizza or to set down a finished one. If you can do a slightly flatter roof, you can extend farther out on the sides to cover you and your prep table...just another random thought

[Danno7]

OK great! only $25/roll and I can use it on the sides when I do the stucco next year. Gonna get to framing roof this weekend!

Dan

[SableSprings]

Yes, having to buy a whole roll of the membrane was the issue I had as well. I used the roofing felt/tar paper and it works just fine. I don't see why it wouldn't work in your situation. The stuff I used seemed a bit thin and would rip/tear a little too easily (at the staples), so getting a little heavier duty felt if possible is worth it. Since the tar paper I used was from 9 years ago, I suspect what they sell now and in your area is of better quality. I still think it would be worthwhile checking with some local builders or roofers to see if they have some scrap membrane material...since you really don't need that much.

[Danno7]

Hi Mike,

Do you think I could get away with roofing felt on top of the plywood? I didn’t have much luck at the local HD with the membrane (they only have rolls for $200 ). Thanks again.

Dan

[SableSprings]

Dan, roofing plan looks doable...but...Remember that you are going to need to tie the durarock/batten "sandwich" to your metal rafters and the roofing panels will need to be attached to the sandwich. I would use exterior plywood (5/8") instead of durarock simply because you can screw the roofing panels down into the plywood. You don't need lots of roofing screws to hold down each sheet, but you do want them securely fastened to the base roof material. Durarock is a good material, but I think you might have issues getting the metal roofing attached with your #19 post idea (IMHO)...I'm also a little leary of walking/working on Durarock. I used it inside to do a shower stall and I just wouldn't be comfortable using it for a larger roofing project. Since yours is only 5' x 6', the Durarock should be fine as long as you can secure that roofing down. I just haven't worked with metal joists and don't know what kind of options you have to tie down the roofing.

Also be aware that gutters work well for most of the runoff water, but if you have ice/snow slide off the roof, it can catch the gutter and take it off. Gutter covers can help not only to keep leaves/needles out of the gutters, but help keep the "snow slide" from catching them. Again, in snow prone areas, hardware/roofing supply stores sell small "fins" that help keep the snow from sliding off so easily. Usually you install several rows of these across the lower half of your roof. Just some thoughts that you might consider...I assume you are not putting electricity out to your enclosure. If you had electricity, there are heating wires sold to melt the snow along the bottom half of roofs...keeping the snow slide minimized and keeping ice from forming along the gutter line. You might go pick the brains of somebody that has done roofing work in your area or neighbors that might have experienced some of these issues (and dealt with them ). Even though your roof area will be relatively small, possible "snow slide" still should be incorporated in your planning.

[Danno7]

So, based on these great suggestions, I am thinking that this would be ideal: Durock over steel roof rafters; waterproof roofing membrane on top of that; 1 x 4 wooden battens laid across, spaced 16 in. or so; lastly corrugated metal panels on top with . All necessary flashing, foam closure strips, roofing screws, etc. Really like the idea of gutters to divert the water. Any thoughts greatly appreciated and thanks again!

Dan

[Gulf]

Carpentry terms vary due to location. Your area may call it "metal roof battens". Metal roof panels seams run vertical. Lathing "battens" run horizontal. They tie the rafters together. In some cases they allow the room for insulation and ventilation needed to limit condensation.

[Danno7]

Hi Joe and thanks for your message. I am planning metal framing with corrugated metal roofing panels. I am not sure I understand about the lathing. Is this the same type of lathe that we can use for stucco and scratch coats, and just lay it over the framing, under the corrugated metal? Second question, will either method (lathing or durock) work to help against the condensation under the roof? I did not know about the lathing so thanks for mentioning that.

Dan

[Gulf]

Dan,

Mike brings out some good points about metal roof condensation. We call it "sweating" down here. But first::

I had planned to lay the corrugated sheets right over the framing of the roof (rafters every foot).

I just wanted to note that there must be horizontal lathing installed to which the metal roof is attached. You probalbly knew that, but I have to be sure. The sheathing that Mike describes would take care of that.

Down here, insulation under the metal roof is installed to limit the sweating. I was wondering if you are going with metal or wood framing?

[Danno7]

Thanks, guys!! The plan is coming together. Great call re: gutter, as I will have a counter on the right side of the oven. I hope to post pics soon...

Dan

[UtahBeehiver]

I'll leave this to those who have done a roof. My build is out in the open.

[SableSprings]

Hello Dan! I put just metal roofing over my WFO in 2009 as a temporary cover during the oven's first Oregon winter. To my dismay, I noted that condensation from the underside of the roofing was dripping onto the oven every morning. I resolved the drip problem by taking the roofing off and putting plywood down with a Tyvec cover before replacing the metal sheets on top. On the permanent den rafters the next spring, we just put down tar paper on top of the plywood before the final metal roofing because I couldn't find a reasonable price/source on some type of heavier/sturdier roofing underlay or house wrap.

If it was my roof in your climate, I would use Durock or exterior plywood with a waterproof layer material under the metal roofing. There are some great materials now available as an underlay for roofing (shingles & metal)...as well as more variety of house wraps. If you have any builder friends, check to see if they have remnants from the big commercial rolls of the building wrap or check with some of your local roofers.

p.s. Glad Joe "turned" you back to a gabled roof. I'd plan as much overhang as you can to give you a bit of dry space around the structure. Also, think about putting in gutters with downspouts that direct water away from your entry/working area. With your heavy snow loads, make sure you look at installing the little roof "snow catchers" so the snow doesn't slide off and damage something on the sides of your enclosure. I've seen lots of deck railing destroyed when the house roof unloaded its snow buildup.

[Danno7]

Joe, thanks again! Very encouraging. I hope to finish the roof within the next 2 weeks. I also ordered peak roof flashing for the duravent chimney. The chimney flashing will be vented, with a storm collar. We get a ton of rain in spring and fall.

I had planned to lay the corrugated sheets right over the framing of the roof (rafters every foot). Then I was going to use molded foam srtips under the bottom edges of the panels and ridge panel to keep out bugs, etc. Then I saw pictures of the roofs being clad on top with durock or other outdoor sheathing, and then the metal roof panels on top.

If I could trouble you and Utah with one more question: Which is best, with or without the durock sheets under the roof panels? Just wondering if this (durock panels under metal roof panels) would be necessary if I put proper flashing on edges and eaves, along with the foam strips. Thanks again for your patience and advice!

Dan

[Gulf]

A 6/12 roof is a good looking pitch. You may have to lower the eaves to get it to work out with your height limitations. Russell is correct about snow loading codes. That is not an issue down here. However, shorter spans and proper bracing will increase the strength of any roof. If you can possibly do it, projecting the gable out over the front of the oven will vastly increase the number of days per year that the oven can be operated comfortably.

I am just trying to figure out what to finish the walls with, to match

I'm a very big fan of old corrugated metal. I would only seal it with a clear coat to halt the corrosiion if any is present. I have even artifically aged some new metal to match the older patina. I think that it will look good with what ever you decide.