Overlapping tin roof?

MushCreek · November 16, 2012, 06:51:02 AM

The front roof of my house has a shed roof porch across 2/3's of it. There is a pitch change 8' up the main roof. I'm wondering if I should make all of the upper tin panels the same length, so that the area without the porch has an overlap. It occurred to me that it would be easier installing the shorter panels rather than dealing with 20 footers. I could do the same on the back just for ease of installation.

Driving around the back woods here in SC, most older tin roofs are lapped. It's only the newer installs that are one piece. Maybe the old 5V roofing wasn't available in long lengths many years ago. Since I want my house to look like it's been here since the 1920's, I kinda LIKE the funky roofs (without the rust!).

Can I make a lapped roof good and water-proof? I have a 5/12 pitch, and we don't get a lot of wind-driven rain here. I can take my time and put sealer in the lap area. How much overlap? A foot? Or is it just a bad idea?

As an aside- I should have made the porch full width after dealing with the transition area!

Redoverfarm · November 16, 2012, 07:44:41 AM

They make transition metal for this type of application. It gives you more protection than just a lap joint. It will also eliminate the need for sealers which over time will eventually fail. The overlap with transition piece will determine what that overlap is. You may be limited in the amount of lower steel you can push up under the top portion before it "bottoms out" against the sheeting or rafters.

Since your porch does not extend the full width of the house roof then most likely you will need to build a small wall from the porch roof to the house roof depending on the pitch difference . Don't forget the flashing along this joint.

I would not use shorter sheets for the area outside the porch roof on the main part of the house. The more joints in the metal roof the more of a chance later for leaks. I think it will give you a better roof allowing those pieces to be full length from the ridge to soffit.

November 16, 2012, 10:14:09 AM

I currently use BestBuyMetals for roofing metal. Given the dimensions of the roof, they can e-mail back layouts showing all views of the assembled metal roof, based on your input ....and a complete materials list. The dwgs they supply are a good reference, if nothing else. I'm sure they could easily show both cases ... overlapped or not... and will have some recommendations.

Beware that the materials list may include some items that you do not want or need ... such as butyl strips, and edge metal trim for the entire perimeter ...but they will adjust the list to suit you.

In the old days, all roof metal was galvanized and corrugated, and you could just pick it up from the local building supplier. But now, roofing is made to order and shipped. No matter who you source the metal from, make sure the final quote is for what you really want ... style, color, gauge, quantities, shipping destination, etc, etc, .... anyone can make a typo. You don't want to pay for a bad key stroke. I also would not hesitate to do a partial order ... if that will help your schedule. You don't want roofing laying stacked around too long at the work site, waiting on the installation.

MountainDon · November 16, 2012, 10:26:35 AM

The butyl rubber strips make a great seal where one panel overlaps the one adjacent to it. helps with wind driven rain. Our home roof has then wherever one panel laps another.

JRR · November 16, 2012, 10:30:10 AM

Oh, I'm not saying; "don't use butyl tape" ... its just that one may already have some on hand or have another supplier. The usual materials list will include everything .... as though you have nothing, and have no other sources! Butyl tape is one of those things easily damaged in shipping.

November 16, 2012, 11:09:35 AM

There are lots of rolling mills in the area, so getting the tin made to order is no problem. I've already been through this with the barn, and everything came out perfect. As a toolmaker, I measure stuff for a living, so I trust my abilities. Oddly enough, not all the mills roll 5V anymore, and it costs more than the regular 'barn' pattern. I like the vintage look of the 5V, though, and the more modern profiles look clunky on a small roof.

I know I need a transition piece for the pitch break. You give them the angles, and they roll a piece to suit. I think those are usually 10 footers. Since the transition piece is flat, and the tin, is, well, not, there are closure strips for all that. I'm talking about the rest of the roof, including the back. My thought was that the shorter pieces would be a lot easier to deal with. I doubt I could safely get 20 footers up on the roof by myself, and helpers have been hard to come by. I prefer a lap for penetrations, such as vents and metal chimneys, since you can then overlap the upper half of the weather boot, rather than trying to seal a boot that is completely top-mounted. It would seem to me that corrugated tin on top of corrugated tin should fit pretty well. If the edge is screwed down, I wouldn't think that wind-driven rain could travel uphill more than a couple inches. If you think about it, regular shingles are ALL lapped, as are tiles and metal shingles. I'd love metal shingles, but they are WAY out of my budget!

I've already built the wall where the porch roof ends. I'll slide the underlayment and tin up under it as far as I can, and the flash the wall well up under the overhang. Building that wall is the reason I now realize I should have gone full-width with the porch- what a PITA. But I wanted more light in the master bedroom, since the porch is 12' deep, plus a 2' overhang.

MushCreek · November 16, 2012, 03:57:47 PM

According to the instructions at BestBuyMetals, you only need to overlap the panels 6" for a pitch over 2.5/12.

Redoverfarm · November 16, 2012, 04:22:11 PM

Quote from: MushCreek on November 16, 2012, 03:57:47 PM
According to the instructions at BestBuyMetals, you only need to overlap the panels 6" for a pitch over 2.5/12.

Most that I have used and read about suggested not to use metal for roofs less than 3/12 .

MushCreek · November 17, 2012, 06:07:07 AM

I've heard that, too, but I see much flatter tin roofs all over the place. I think adhesive underlayment is used on flatter roofs. My house is 5/12, and the porch is 3/12. I though about using peel 'n stick underlayment on the whole roof, but the cost is prohibitive. Ice damming is not an issue here in SC.

November 17, 2012, 10:33:37 AM

Just a general observation...

Quote from: MushCreek on November 17, 2012, 06:07:07 AM
.... but I see much flatter tin roofs all over the place. ....

And a neighbor up in the mountains near us has a roof that is probably 2/12, if that, covered in galvanized corrugated sheets. Doesn't make it right or a good thing to emmulate.

Quote from: MushCreek on November 17, 2012, 06:07:07 AM
.... I think adhesive underlayment is used on flatter roofs....

A dangerous assumption. The above mentioned neighbor does not even have building felt under the metal.

Tifflery · December 01, 2013, 09:31:21 PM

Hello!
I actually have the same question. Did you end up using several lapped shorter pieces on your main roof? I like this look as well! Thanks!
Tifflery

MushCreek · December 03, 2013, 06:43:04 AM

I did do the overlap on the front. The supplier said that 3" overlap was enough; 6" was better. The panels I used ended up about 9" overlap. We used butyl tape, but the overlap fits so well, you can't even see it unless you are looking for it. I mostly used the tape to try to keep water from sitting in there for long periods. Time will tell if our installation will hold up. I did the back of the roof with full-length pieces. My contractor offered to do it for a very low price (and then complained about it the whole time).

Tifflery · December 03, 2013, 04:49:38 PM

LOL. Thank you, MushCreek!
I am still looking for metal, but we might have to buy used metal off of Craigslist or the like, and it will probably be easier to find shorter lengths. I have yet to check into the cost of new metal at MetalMart, (we are still working on the house wrap and roof wrap and will need to save a bit before the actual purchase of metal roofing) but Im betting it will be cheaper to buy lightly used.

At least I know it is a possibility if we happened to come into some for a great price!
Thanks for your reply!

Redoverfarm · December 03, 2013, 06:10:51 PM

Personally I would stay away from "used" roofing. You are just asking for trouble unlesss it is standing seam and then you are taking a chance. Regular V-grove will have a fastner pattern that probably will not match what you are doing. Why did they pull this off a roof if it was in good shape.

For a woodshed or storage building maybe. You might check around some of the suppliers. They sometimes will custom cut longer sheets for some jobs leaving a sizeable left over length that may work at a greatly reduced cost. Problem is that unless they have a lot in the same color you could end up with a Patchwork of colors.

The metal roof manufaturing companies say not to install on roofs of 3/12 or less pitch. Yes generally water rolls downhill but with snow & ice it will back up or not slide off leaving it stand on the roof where there is a great possibily of leaking. Same goes for shingles. With a slight pitch most will recommend a membrane or rolled roofing.