For Professionals | Member Login
Find a Professional
Sign Up Log In Add New Topic

TOPIC: Roofing over existing roof

INSTALLING METAL ROOF OVER SHINGLES

Return to Roofing over existing roof

Return to Archive

Return to Forum

Your Husband Knows Best, Let Him Make the Descisions
Guest User

8/2/2010
Jill, Technically speaking, you are both right. You will need to check with the metal roof manufacturer to confirm that it is okay to their product over the top of existing, but most will say it okay. That is just the procedural part of the equation. The prudent thing to do in this case is to remove the degraded shingles and get them off of the roof. If they are already coming loose, there is the potential for them to continue to break down and break loose. While that poses no threat of a leak because your metal roof and underlayment will provide the weather barrier, it is unwise to have that roof shedding its contents under the underlayment/slip layer. There are other considerations besides the installation compliance side of things too. Asphalt is a pretty miserably roofing substrate and adds weight and thermal mass to the home. You mention that your roof is cedar planks (I suspect tongue and groove). Is your roof and insulated design (i.e. exposed rafters) or do you have an attic space? Where is the home located (climate region)? There are some other items to consider prior to deciding on an installation protocol. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

8/4/2010
Must you always use an underlayment with a metal roof?
Guest User

8/31/2010
Depends on the manufacturers recommendations. The second question would be why not? It is cheap insurance and giving the metal roof a slip layer is also important. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

9/1/2010
For all the metal roofs we put on over the 10 years, we never had any problems with leaving the old shingles on. In fact, leaving them on will actually help with sound barrier AND insulation. We use 1 x 3 furring strips or some times 2x4s. Using 2x4s you can take out the dips and sways of an old roof by using shims. As for the flashing around chimneys; it always pays to do it right the first time, then there is no worries.
Guest User

9/2/2010
If the roof is not the insulation layer, leaving them as insulation is pointless. If the roof deck is an insulated design, using them as insulation is even more foolish. They do work as a sound deaden-er but there are far better options for that if you are concerned about it. The added weight and thermal mass in most of the construction applications that we deal with is enough to warrant pulling them off. Combine that with the ability to access the roof deck and correct any decking issues, it is all the reason that I need to warrant removing them. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

9/2/2010
Thanks to the idea Hombre.. Could you suggest me someone or something that will help me about roofing estimates for my roofing replacement? I gathered some details at http://www.viddler.com/explore/pflugervillehow/videos/1/ before. But I'll consider second opinions.. Thanks in advance :)
Guest User

9/8/2010
Existing roof composition or wood shakes ? The condition of the existing roof sounds pretty bad, you may have damage to the existing substrate. Tearing off the existing roof will allow you to see the condition of the existing cedar deck you mentioned. If it were my home i would tear off. Tearing off gives me peice of mind even if the existing decking turns out to be fine. No point putting a metal roof on only to have to remove it to replace dryrot or termite damage later. Going over the existing would also be dependant upon what product your going over it with. You may also have too many existing layers of roofing, the building dept may not allow another which will require you to tear off reguardless. Roof vents leak if not done correctly, the product is irrelavent. Andy
Guest User

9/8/2010
Oops, sorry i didnt see the additional 4 pages of posts...i replied to a very old post.
Guest User

9/8/2010
I have the same questions as Alexibrad & would like for you to send me the article on step by step installation of a metal roof over asphalt shingles or stripping the shingles & putting down 1x4's
Guest User

11/7/2010
I have the same questions as Alexibrad & would like for you to send me the article on step by step installation of a metal roof over asphalt shingles or stripping the shingles & putting down 1x4's
Guest User

11/7/2010
Panels on Roof Sheet or Shingles Metal Roof Panels can be installed over existing shingled roofs or roof sheeting of plywood or OSB. Place 1x4 or 2x4 purlins on top of shingles or sheeting - the same as shown in the roof purlin section. Securely screw the purlins to the rafters not the sheeting. If roofing over an existing shingle roof, pull the drip edge from underneath the shingle and / or cut flush to the roof sheeting. After purlins are fastened, install a gutter apron #29 on top of the purlins running along the eaves to cover the wood purlins. After roof sheeting is in place, finish the rake with a residential rake trim # 18. Laying roof panels directly on top of a shingle roof has been done with success, but is not recommended due to screws not being in solid wood. Ridge vents in metal roofing are common and not known to leak.
Guest User

12/10/2010
Panels On Roof Purlins Roof Purlin Spacing should be 18 to 24 inches. If trusses or rafters are spaced up to 24 inches apart, 1x 4 rough cut is sufficient or if spacing is 24 inches to 48 inches apart, use 2x4 SPF or the equivalent. They should be replaced if purlins are not solid or split etc. on a re-roof job. Since shingle prices increased if makes economical sense to reroof over shingles with Metal Roofing
Guest User

12/10/2010