Metal over Shingles Plan

John Baczek
3/5/2014
I have a 35 year old ranch style house that I added a large addition to 18 years ago, and with that addition, striped and re-shingled the entire house, breezeway, and garage. The front of the house (the original part of house) is North facing, and here in NE CT, has sustained ice and snow damage over the last couple of years, where ice dams have lifted shingles and gotten underneath. This has happened a couple of times over the last several years. Using a snow roof rake, I try to pull off a 4 feet section of snow off the eaves, but thaws and freezes over the Winter, the ice can build up. I’ve pulled off the ice and snow, and resealed some of the shingle edges to get through this winter. With this recurring ice damage, it’s time to reroof. There’s a 2 x 6 foot section of underlayment that’s water damaged and buckled, and I’ll remove those shingles to cutout and replace that section of ½” plywood sheathing. The trusses on the original house are 2 x 8 and 2 x 4 engineered trusses 24” OC, 5.25 / 12 pitch, with ½” CDX plywood sheathing. All sections of the roof are properly vented, with vented eave overhangs, gable ends, full ridge venting, and a thermostatic controlled roof mounted fan on the South side. There’s 12” of insulation in the ceiling joists. With the recurring ice problems, shingles are out, and I’m planning on covering the front (North) section of the house with metal roofing. The remaining roof sections have weathered the New England winters better. The addition roof has engineered trusses 16” OC for vaulted ceilings. The breezeway and garage has a greater pitch and I used 5/8” sheathing on 16” centers. I would probably continue on with metal as time goes on. For planning and pricing, I’m using Metal Sales roofing available at the local Home Depot. Here’s my plans to cover the 48 x 16 foot roof: 1. Repair buckled underlayment section. Leave roof shingled. 2. Install 1x4 perimeter and horizontal purlins 2 feet centers up the roof. 3. Install proper metal eave and gable edging. 4. Lay down ¾” foam panels between purlins. Not so much for insulation but to provide support to walk on metal roofing. 5. Cover roof with some synthetic membrane, only because I’ve read some comments about eliminating moisture under the metal. 6. Install rib steel metal (exposed screws) per manufacturer’s instructions. With slightly less than a 16 foot run from eave to ridge, and since I’ll be doing this myself, I’m thinking of ordering 8 foot panels, with a sealed overlap midway up the roof. 7. Cap the ridge with metal cap. So my questions are: 1. Does this plan seem reasonable? 2. Are purlins 2 feet apart OK? Could I use 1 x 3 furring strips? 3. Is the ¾” foam panel for walk on support really needed, or should I screw purlins closer, say 1 foot centers. I want to be able to walk on the roof without worrying about bending, denting, or popping a panel. 4. With a one-man install, does an 8 foot metal panel, with a sealed overlap, make sense?
Eric Novotny
An informed customer is the Best Customer!
3/10/2014
1. Yes 2. Seems okay but you should check with the panel maker and confirm what you are intending and if that span works. With the foam, I suspect it will be okay. 3. Either or should work. 4. Definitely more manageable Only other point I would mention would be to get that fan on a humidstat as well.
John Baczek
3/12/2014
Thanks Eric. I'll check with panel manufacturer on purlin spacing. My attic fan motor crapped out last year. I'll replace with a thermo/humidistat combination controller.
Eric Novotny
An informed customer is the Best Customer!
3/13/2014
Sounds good John. Good luck with the project. Eric
Guest User
3/19/2014
Can steel roofing be placed directly over one layer of shingles without a barrier. The shingles are in good shape with no cracking, curling, etc.
Todd Miller
Isaiah Industries, Inc.
3/19/2014
Marilyn, In my opinion, there should be an underlayment over the old shingles. It helps guard against abrasion on the back of the metal panels. Additionally, I interpret the International Building Code as requiring it.
Eric Novotny
An informed customer is the Best Customer!
3/19/2014
Marily, Underlayment is cheap and I would always opt for it as easy insurance and for the reasons that Todd mentions. Eric
gary torrence
4/27/2014
i am putting a metal roof over a shingle roof I started with a 1.5''overhang and now I went from a 1.5'' overhang to a 3'' overhang and I have a bow in the roof how would I fix this problem
Todd Miller
Isaiah Industries, Inc.
4/27/2014
Gary, I am not sure I understand what's going on but is there a chance that your first panel was not installed perpendicular to the eave?

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