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Small Cabin Forum / Cabin Construction / Replacing asphalt shingles with metal??
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Sustainusfarm
Member
# Posted: 15 May 2012 04:06pm
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I have a 20 yrr old asphalt shingle roof that I would like to replace with a metal roof so I can collect rainwater for showers and sinks (not drinking). Question is can I go right over the shingles with the metal or??? There is only one layer of shingles on the roof now....
Since the water I collect will only be for showers and sinks and I will filter it for that use do I really need to switch to metal at all? I am in a pine forest and there is a lot of pollen at this time of year too!

ErinsMom
Member
# Posted: 15 May 2012 04:35pm
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My mom replaced her shingle with metal last year. They just placed the metal over the shingles.

MtnDon
Member
# Posted: 15 May 2012 04:49pm
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You can, however depending on the condition of the old shingles you may see unevenness. We ripped off the old and installed new roofing underlayment. We also determined before hand that if we removed the old shingles our insurance company would give us 10% off forever.

Sustainusfarm
Member
# Posted: 16 May 2012 09:02am
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So.... I don't need to put furring strips or something on the shingles first to keep the two separate?? If that's the case I'm sold and will do it this year so I can start collecting rainwater!!

Malamute
Member
# Posted: 16 May 2012 09:58am - Edited by: Malamute
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The metal (Fabral) I use won't warrant the metal if you dont use 1x4's over the shingles. They want the 1x's screwed into the rafters, then you have soemthing solid to screw the metal into. Spacing the 1x's at 24" intervals and along the edges is how they want it.

Also, use the correct screws for your sheathing. OSB uses fatter screws, wood or plywood spec the skinnier screws, tho I've heard many are using the fatter screws for everything.

Sustainusfarm
Member
# Posted: 16 May 2012 11:14am
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Thanks MtnDon and Malamute...this sounds like an easy project...I am glad I dont have to remove the original shingles but I will call insurance to see what deal I can get...I only pay $300/year as it is for insurance though!
Do you all think this is a project for the DIY person? I did build the entire cabin... I think I need to research what tools I will need ( cant imagine I dont have them already)! I know how to flash regular shingles but metal roof ???
One other question...as you see in the pics I have a 12/12 pitch that falls onto a 4/12 pitch on the porches....what about snow load from all the snow coming off the 12/12 roof and piling up on the 4/12??? As it is I have 3-5' of snow pile up on the roof and sit all winter like that...no issues in 15 yrs....
cabinNov06_044.jpg
cabinNov06_044.jpg
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Malamute
Member
# Posted: 16 May 2012 04:38pm - Edited by: Malamute
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Do you have the T flange trim on the edges of the shingles? I'm about to do a small building that has that, I'm going to remove it. Either that, or nail on some 1x or 2x spacers along the edges to give backing to the gable and eave trim for the metal. I use the smallest gable trim, I think they call it mini-gable. I also use 1x6 instead of 1x4 along the last gable ends, in case a rib ends up being in a bad location for the last gable trim, and the screw flange ends up being farther in from the edge than it did when you started. When the rib isnt in a good spot at the end of the last panel, a wider profile trim is required to finish it right (they'll make it any width you want, but you have to order it). Sometimes I wait on the last gable trim, as I can't return any of it after I order it.

I use a cheap circular saw with a normal, non carbide blade installed backwards to cut the metal. I cut from the back. It makes a terrific racket to cut it, and throws nasty sparks and hot metal chips, but its the quickest way to cut angles. A couple pair of good tin snips helps, a right and a left. I've caulked with good quality caulk along walls. I've used Log Jam, and Log Builder with good results. It bonds well to the metal and whatever I've caulked against. Big Stretch works pretty well also. Don't even consider using cheaper caulk. Use a good quality spray bottle with a mixture of 1/2 rubbing alcohol and 1/2 water to tool the caulk if you do it that way, and a small magin trowel or log chinking tool, or even your finger, to tool it out and smooth it.

Order you metal panels the length you want, (I do about 1 1/2" of overhang on the lower ends) avoid cutting any more than you have to, it saves time and money. You have a little leeway on the length at the top, as the ridge metal covers a fair bit. When you order your metal, they should make your ridge to your roof pitch so you dont have to fight it. Pre drill the holes, separating the pile for each section so the overlap goes downwind from your strongest winds. Hold a block of wood right next to the hole when drilling it so the panels dont separate when drilling, it keeps the bit from breaking. Read the info that comes with the metal before proceeding, or get it from the company before you start, so you know what you're doing when your metal shows up.

I usually order some extra screws just for fun, I don't like running short. The ends should have two in each flat, the fields just one on the high lap side of the flat. I dont go less than 24" spacing up the run of the panel. Stitch screws go in the ribs in line with the fields screws to hold the laps tight. If you have cedar facia, I get screws long enough to hit the solid sub-facia. I use gold torx screws to screw the 1x's into the rafters, either 3" or longer as needed.

Your metal sales person should have a chart to tell how many screws you need for your square footage. They should also know what type screws you need, but some are not up to speed on what type screws for what application. Going into 1x, you should be good with the smaller diameter screws. If your sales person doesnt know much (even if they say they've sold it for years, that's no guarantee they now anything useful), call the company and talk to someone to get all the info you need.

I'd use wider 1x's up the edges of the valeys also. I generally use a wider valley flashing, and the higher grade highly compressible foam stuff to seal under the metal. It isnt cheap, but works well.

You'll need closures also, top and bottom, to fill the ribs in. Upper closures under the ridge cap, and lower closures for the bottom ends.

ErinsMom
Member
# Posted: 16 May 2012 05:23pm
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Sustainusfarm,
This is off subject but is there a thread that shows your cabin build?
I'm interested in your ground to roof windows. ? doors?

Sustainusfarm
Member
# Posted: 16 May 2012 09:40pm
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Thank You Malamute!! That was alot of great info! I really appreciate it! I can now make a plan t otackle this project. ErinsMom, I am working on it...since I started building in 1996 alot of the early oics are "real pictures" in an album! I am working te get the digital so I can post a timeline here.
The windows are pine french doors that I take out for the summer and replace with screen doors. I got for $40.00 ea long ago when I was storing materials for the cabin before I built.

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