insulate beneath metal roofing outside and seal roof

ray tartakoff
energy saver in the catskills
8/18/2011
i want to roof my 800 sq ft cathedral ceiling house on outside with metal roofing. i converted the ceiling to cathedral in 1999. it was an old bungalow from the 30's. it has open eaves and insulation was blown into the walls. i replaced the sash windows with energy saver inserts and am concerned that snow melts off my roof quicker than id like. on the inside ceiling i installed 6" fiberglass, foam battens and a ridge vent. outside is 1 layer of shingles and tar paper. i want to put foam insulation under the metal roofing. what kind of insulation will give best r for the money? should i go thicker than a 2 by four? would it be cost effective to take off the layer of shingles (pain in the neck) and tarpaper and seal the roof surface before putting down foam? if it is, what is the best material to do this with? thank you in advance. i went onto dan perkins website and it scared me into joining this website before i get into trouble. i cant tell you how much i appreciate this website.
Todd Miller
Isaiah Industries, Inc.
8/19/2011
Thanks for your post. First of all, I think you need to choose your metal roofing product and then work out the details with the manufacturer. Not all products can / should be installed over foam. Additionally, some products can be installed over battens. In my opinion, you need ventilation beneath the new roof more than insulation. Ventilation will help avoid ice dams and also allow moisture that is generated inside the home to be vented out. I would suggest choosing your product and then working with the manufacturer to determine how to install it with ventilation and possibly with insulation as well.
Eric Novotny
An informed customer is the Best Customer!
8/19/2011
Putting foam atop the roof deck will do very little, if anything at all, in the means of insulation because your roof deck is already vented. If you wanted to add more insulation, you are really talking about ripping off the roof deck or dense packing cellulose. You could create an over deck venting situation (i.e. battens) and hope that creates enough of a thermal break and air movement to eliminate some of melting.
ray tartakoff
energy saver in the catskills
8/19/2011
hi that was a good answer for a salesman/marketing type. now, what brand of metal roofing would you recommend or choose that allows for foam insulation?
Todd Miller
Isaiah Industries, Inc.
8/19/2011
Thanks Ray. Honestly, I personally do not recommend any installations over foam. However, there are some manufacturers who are probably okay with it. I really do not know specifically who is and who is not. Sorry. First of all, I think the rooftop is the wrong place to insulate, and second installing over foam can lead to the product interlocks and overlaps being distorted and rendered not watertight. As far as brands of metal roofing ... certainly I am a believer in all of the MRA member manufacturers. ABC, ATAS, Fabral, MBCI, McElroy, and Metal Sales are manufacturers that may offer good fits for what you wnat to do.
Todd Miller
Isaiah Industries, Inc.
8/19/2011
I would also suggest looking for products that meet the Premium certification level of the Metal Construction Association certified metal roofing program.
Eric Novotny
An informed customer is the Best Customer!
8/19/2011
Todd is 100 correct. Installing directly over foam in not recommended regardless of what the manufacturer says in my opinion. It is about 100 times easier to foul up that kind of install and create issues down the road. The roof, if you want to apply foam, should be installed on to a system of battens which will benefit you from both the over deck venting aspect and the structure of the roof (i.e. maintaining proper alignment of the installed system). Foam is not a very resistant to point load deflection and if a fastener is over torqued, the foam will compress and mis-align the fastener and roof. A batten helps displace the load over a larger surface area and is much more resistant to over compression and therefore maintains proper alignment. Todd is not a Salesman or Marketeer. He gives quite freely of his time and is more than available to customer to answer questions and help them navigate the complexities of a metal roof decision process. He also helps out quite a few people with problems when roofs are installed improperly or materials have failed.
ray tartakoff
energy saver in the catskills
8/19/2011
how about something like ice dam shield material directly over entire roof? maybe foil backed. then i dont need battens and the compressibilty wont dimple the screws enough to compromise watertightness. presently i use 100 gallons oil and 4 cords wood. per winter the foamco guy can install 3 inches high density between two by four battens on edge. estimated $3600. for r 35 total. figure $7k for entire job as opposed to $2k for just steel and some type of ice dam over entire roof. not much r but the amortization cost is more than 20 years. i like the ice shield idea. anybody manufacture anything like that? already have a roof vent and rafter mates so ventllation isnt an issue. what materials are out there?
Eric Novotny
An informed customer is the Best Customer!
8/22/2011
Ice and water over the entire roof is a great idea and especially if you consider the fact that you are sealing up the envelope (air barrier) across the roof deck. If you put the 2x4s on end, you should get a 3" foam (will get you an additional R-18) on there and still have a 1/4" above deck airspace. This would be the best of both worlds. Fasten the roof panels the the battens (that is what the 2x4s will be acting as) and you should have little to no melting at that point.
Guest User
8/31/2013
I am getting ready to put a metal roof on my house it presently has 1 layer of shingles on a 6/12 pitch and Iam in florida I am think of putting r-foil under 1 x 4s battens or the styrofoam boards between the battens and also a solar attic fan w/elec option and the metal will be a light color from douglas metal roofing does this sound like a good plan?
Todd Miller
Isaiah Industries, Inc.
8/31/2013
Yes, that sounds reasonable. Make sure that the product you choose to install is accepted / approved for this type of installation. Also, if your ran vertical battens first followed by horizontal you could potentially vent a portion of the chamber, bringing air in at the bottom and exhausting it out at the ridge, This would be very effective for energy efficiency as well. Also, as an option, the metal shingle style modular products create their own integral airspace as a thermal break, even when installed over solid decking.
Guest User
6/11/2014
Todd you are most helpful. I am thinking about a metal roof over shingles on a singlewide trailer. I am looking to hopefuly put the metal roof on an never have to worry about it again. Thanks for all the info.
Todd Miller
Isaiah Industries, Inc.
6/11/2014
Thanks for the kind words, John. I also have an educational site at www.asktoddmiller.com
Eric Novotny
An informed customer is the Best Customer!
6/12/2014
Todd is a great resource and even better person. Always willing to lend a helping hand and thoughtful answer.
Guest User
7/9/2015
Todd, earlier in the post you said you would not recommend foam under metal but here you are telling Steve that 'it sounds reasonable'. I've been told not to put foam under the metal because of the condensation from the metal will deteriorate the foam. I believe there are more burdens than benefits by so doing. Is there any way to insulate when you install metal over existing shingles on a one with 'cathedral' ceilings and with very little existing insulation and therefore a low R-factor. The home owner feels there has to be a way but I have never seen an effective solution. Your thoughts?
Eric Novotny
An informed customer is the Best Customer!
7/10/2015
JD, I don't recall Todd saying that he didn't like insulation, just that metal directly over insulation (i.e. rigid board) can easily be over torqued and mess with panel alignment. I agree to that extent and always recommend a solid deck or some sort of strapping to prevent this. Rigid foam works great and the metal can be installed directly over the top of it. You just need to be careful not to pull/torque the panels when fastening them.
Guest User
7/10/2015
if you are installing a standing seam panel, use a 4" x 4" bearing plate with a rigid foam.
Guest User
7/12/2015
Eric, Thanks for your reply. We are using R-panel and intend to use 1x4 battens. My main concern is whether or not the R-factor gained from using foam board is worth the expense. Do you know what the R-factor is for the foam board? (I can't seem to get accurate answers from anyone locally) Any idea what a realistic monthly savings would be (percentage wise) after foam is installed? From what I've been able to determine the difference between installing r-panel on battens vs the same install but adding the foam board is minimal yet the cost is much greater. Also, Should one expect that condensation might cause damage to the foam over time or is this a myth? Your thoughts?
Eric Novotny
An informed customer is the Best Customer!
7/13/2015
Foam works great. Depending on the foam, you will have an R-Value of anywhere from 3.5 per inch on the low side and 6.5 on the high side. As long as the battens and purlins combo will vent, it will work fine and you can skip the foam. The foam is better for non above deck vented options.
Guest User
4/6/2016
thanks for this forum it really helped me a lot. I want to use the rigid foam under the metal sheet to provide some thermal insulation and i'm planning to use bitumen as a kinda of glue between the metal sheet and the foam; my question is : Can it work? Thanks

If you would like to reply to this thread, please log in. If you do not have an Ask the Experts forum user account, create one here.

Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.