Metal roofing and insulation questions for those in snowy climates

[Jim Mackell]

The shop I volunteer at has a 50 year old metal roof that is failing. Hopefully it will be replaced before next winter. Here's the issue; From the roof peak down to the drip edge is about 50 feet. The last 25 feet are over the heated portion of the shop and is not well insulated. As a result the escaping heat melts the snow which then freezes solid at the drip edge and causes ice jams. I've suggested that when the old roof is stripped off that we lay a plywood deck on the purlins, then lay down some 2 inch foam board, then screw the new metal roofing down through the insulation. In my opinion the insulation provided by the foam board would greatly reduce heat loss, the new metal roof would be slicker than snot and snow would never build up again. Seems simple to me. Am I missing something? Thanks for any input.

[Al Burton]

I am not in a snowy climate(KY) but really with metal roofs you have the same problem and that is condensation in any climate. In your case you want insulation to stop the melting also and to do that the whole roof needs insulated. One of the cheaper fixes is when you have the roof off lay down vinyl backed fiberglass before putting the metal back on. The vinyl is the vapor barrier and goes on facing down. I like this better than foam board because it has a built in vapor barrier. If you go with foam board you still need a vapor barrier unless you buy it with the silver backing. Skip the plywood, it is not worth the expense. There is also the foil bubble type insulation but even though quite a few people like it I have it in my 82x140 barn and I'm not sure I would use it again.

If money isn't a huge issue consider getting a quote for closed cell spray foam on the roof. I don't have it in my 30x40 yet but I'm drooling over getting it done before summer condensation starts. I was too cheap to insulate the building when I built it. From everything I've read and talked to people that have went that route it makes a huge difference. One guy even pulled down his foil insulation to have it sprayed and reduced his heating bill considerably.

[Rudy Schneider]

+1 On the sprayed closed cell foam, I live in Nebraska and have a all metal shop. I had the building sprayed with closed cell foam. It is expensive, but I have not had any problems with condensation or ice. I have had the building heated for the past 3 winters and no problems.

[Ruhi Arslan]

SIP (Structural Insulated Panel) could be a good option too if the entire roof to be redone. Or the spray insulation underneath. I understand that closed cell foam also acts as a moisture barrier. It is $1 per square foot per R-6 (one inch) but that's just the material.

[phil harold]

your method would work

the other way would be to make sure the roof is ventilated and stays cold on the lower half make sure there is an airspace between the insulation and existing roof

+1 on spray insulation

foamboard is vapor retarder...

[Bill Edwards(2)]

What size is the framing under the roof? 2x4 or 2x6

[Halgeir Wold]

greetings from 69 deg N - certainly cold and snowy enough for most people.... :-)

Insulation -That will depend on the construction of the workshop part. From your description, it sounds like the workshop is only occupying about a third of the full width of the building, - or is the roof a single slant roof, and the whole building appx 50' wide??
( I am fairly proficient in english, but unfortunately I don't know the proper english words for all the parts of a building )
The important part is that you don't seem to use - and heat- the full width of the building. If there's an attick above the workshop part, your insulation should go directly on top of the workshop ceiling, and the whole attick kept cold, with proper ventilation to keep it cold, but without letting snow drifting into the attick. I'd suggest fiberglass wool ( or whatever you call it over there ) - 6" or more. The important part is not to have any voids in the wool layer. It also needs to be covered from the top, a windbreaker layer, in order to not have draught into the wool. Heavy craft paper will do, or an attick floor of sorts.
There really should be a moisture barrier directly beneath the insulation, but unless the shop is constantly heated, some sort of breathing barrier is usually recommended over here.

If the shop uses the full height all up to the rafters, you can put the insulation under a plywood decking, as described, but you need to make sure there is proper ventilation under the metal cladding - a well ventilated height of at least 2" is recommended over here. The whole idea is to keep the metal roughly at ambient temperature at all times...
You'd also need some breathing moisture barrier atop of the plywood..
DuPont's "Tyvec" has more or less taken over that market over here -- is it also available over there...?

EDIT: Even if I'm way up north, I live at the coast, or more correctly, on an island. I guess our climate is not very much different from Maine..... roughly down to -10-15C during winter, but lots of wind......and "moving snow"... :-)

[Jim Mackell]

What size is the framing under the roof? 2x4 or 2x6

The purlins are 2 x 12 x 20 on 24 inch centers. There are steel trusses every 20 feet.

[Jim Mackell]

greetings from 69 deg N - certainly cold and snowy enough for most people.... :-)

Insulation -That will depend on the construction of the workshop part. From your description, it sounds like the workshop is only occupying about a third of the full width of the building, - or is the roof a single slant roof, and the whole building appx 50' wide??
For our purposes, consider the building 50 feet wide with a single slant roof. Only the lower portion of the roof is over a heated space.
The important part is that you don't seem to use - and heat- the full width of the building. If there's an attick above the workshop part, your insulation should go directly on top of the workshop ceiling, and the whole attick kept cold, with proper ventilation to keep it cold, but without letting snow drifting into the attick. I'd suggest fiberglass wool ( or whatever you call it over there ) - 6" or more. The important part is not to have any voids in the wool layer. It also needs to be covered from the top, a windbreaker layer, in order to not have draught into the wool. Heavy craft paper will do, or an attick floor of sorts.
Because of the manner in which the building was constructed it's not possible to insert any more insulation between the ceiling of the workshop and the underside of the roof. That's why I was considering foam board.
There really should be a moisture barrier directly beneath the insulation, but unless the shop is constantly heated, some sort of breathing barrier is usually recommended over here. If the shop uses the full height all up to the rafters, you can put the insulation under a plywood decking, as described, but you need to make sure there is proper ventilation under the metal cladding - a well ventilated height of at least 2" is recommended over here. The whole idea is to keep the metal roughly at ambient temperature at all times...
That's what I was afraid of.
You'd also need some breathing moisture barrier atop of the plywood..
DuPont's "Tyvec" has more or less taken over that market over here -- is it also available over there...? Yes, Tyvek and Typar are readily available.
EDIT: Even if I'm way up north, I live at the coast, or more correctly, on an island. I guess our climate is not very much different from Maine..... roughly down to -10-15C during winter, but lots of wind......and "moving snow"... :-) Thanks for the information.

[Jim Mackell]

While I'd love to use foam, it won't work in this application. First, we can't afford it! Second, because we can't get to the underside of the roof over the heated portion of the building, we can't spray it in place and I don't think it can be sprayed first and then screwed down. The vapor barrier issues concern me. Hadn't really considered them. Theoretically it seems like I'd have to lay down a moisture barrier, then a plywood deck, then the foam board, then the metal roofing. Still scratching my head over this one!

[Al Burton]

So the heated portion is framed and has it's own cieling? I'm just trying to figure out why you can't get to the underside of the roof on the heated portion. Maybe I misunderstood it all but is thier an option of putting in or just insulating the cieling (not roof) of the heated portion? If so you can just lay down fiberglass, blow cellouse etc like you do in traditional houses as long as there is a enough dead space between the cieling and roof. Think plywood flat cieling. I'll assume you can't do that or don't want to for now and need the roof itself insulated.

In my area the vinyl backed fiberglass or foil bubble insulation laid on the purlins with the metal then screwed on would be the best solution in your case. I can't imagine why you would waste the money putting down plywood then foam board right below the metal but I'm not an expert either, just trying to understand what you are really gaining. With the plywood a metal roof and foam board sandwiched close together you are asking for possible moisture problems. For example on a metal roof retrofit on a house you don't put the metal right against the shingles, you use a stand off to help w. condensation. As far as the vinyl backed insulation goes you can get it in 8ft wide rolls and putting it down first you won't have sags etc. The same goes for the foil bubble type insulation with a built on barrier. The foam boards alone with a vapor barrier either attached to the foam(factory) or layed down first seems like a better solution than using the plywood in direct contact. You are suppossed to cover the foam boards for fire rating purposes but that is usually done with a space between the foam boards and barrier.

I would likely call a decent building insulation supply company in your area and tell them what you are thinking about for a second opinion if you have concerns. Hopefully you have one nearby that won't try to push a paticuliar product for thier benifit but if you find out where the guys that build metal buildings in your area buy thier insulation you will get some decent info.

[Bill Edwards(2)]

I'm sure I've missed the point, but I think I have a similar issue with my shop.
The outside edges of my ceiling are the roof, with a dead space in the
middle.

http://www.ilynda.com/shop/images/myshop56.jpg

I'm going to use vent tubes (in blue) to move air from the soffits to the dead
space (which has a peak vent) and use fiberglass insulation. I will have the
advatange of being able to cover the ceiling with sheathing.

http://www.billsid.com/img/roof.jpg

[Jim Mackell]

So the heated portion is framed and has it's own ceiling? I'm just trying to figure out why you can't get to the underside of the roof on the heated portion. Maybe I misunderstood it all but is there an option of putting in or just insulating the ceiling (not roof) of the heated portion? If so you can just lay down fiberglass, blow cellulose etc like you do in traditional houses as long as there is a enough dead space between the ceiling and roof. Think plywood flat ceiling. I'll assume you can't do that or don't want to for now and need the roof itself insulated. Al, you are correct, we can't do that. The underside of the roof was insulated many years ago and then sheetrocked. Since the roofing must be replaced anyway due to deterioration, I was thinking of having the insulation above the purlins.
In my area the vinyl backed fiberglass or foil bubble insulation laid on the purlins with the metal then screwed on would be the best solution in your case. I can't imagine why you would waste the money putting down plywood then foam board right below the metal.......... As far as the vinyl backed insulation goes you can get it in 8ft wide rolls and putting it down first you won't have sags etc. Well, the main reason I posted the question here is to get this kind of real world information and experience. I had not considered vinyl backed fiberglass, didn't even know it existed. The plywood and foam board was a brainstorm to try and solve the problem. I can readily see now that it won't work. Thanks for the ideas.

[Steve Ryan]

I'm sure I've missed the point, but I think I have a similar issue with my shop.
The outside edges of my ceiling are the roof, with a dead space in the
middle.

http://www.ilynda.com/shop/images/myshop56.jpg

I'm going to use vent tubes (in blue) to move air from the soffits to the dead
space (which has a peak vent) and use fiberglass insulation. I will have the
advatange of being able to cover the ceiling with sheathing.



You should seriously look into sprayed on Icynene foam for this space. It will get sprayer directly onto the bottom of the roof sheathing. No air space needed and no condesation problems either. This would allow you to run a central DC line in the space above the ceiling 2Xs. Also allow you to make a few stock racks in the non room portion of the upstairs.
[QUOTE=Jim N Maine;1646044]Al, you are correct, we can't do that. The underside of the roof was insulated many years ago and then sheetrocked. Since the roofing must be replaced anyway due to deterioration, I was thinking of having the insulation above the purlins. Well, the main reason I posted the question here is to get this kind of real world information and experience. I had not considered vinyl backed fiberglass, didn't even know it existed. The plywood and foam board was a brainstorm to try and solve the problem. I can readily see now that it won't work. Thanks for the ideas.
My metal roof leaked after 10 years and the roofing company put down 2" foam with ply over that, and topped it with an EPDM rubber roof that wraps around the edges to a fastening strip.

[Bill Edwards(2)]

You should seriously look into sprayed on Icynene foam for this space. It will get sprayer directly onto the bottom of the roof sheathing. No air space needed and no condesation problems either. This would allow you to run a central DC line in the space above the ceiling 2Xs. Also allow you to make a few stock racks in the non room portion of the upstairs.


I keep looking at spray type insulation and always have to lay down till my
heart starts beating correctly.

I find it to be too pricey for me... even though it would be a good solution.

[Homer Faucett]

While I'd love to use foam, it won't work in this application. First, we can't afford it! Second, because we can't get to the underside of the roof over the heated portion of the building, we can't spray it in place and I don't think it can be sprayed first and then screwed down. The vapor barrier issues concern me. Hadn't really considered them. Theoretically it seems like I'd have to lay down a moisture barrier, then a plywood deck, then the foam board, then the metal roofing. Still scratching my head over this one!

I was able to pick up enough foil backed foam board at this place to insulate my barn at a fraction of the cost of fiberglass from this gentleman in Illinois: http://www.insulationfactoryseconds.com/ . I know this particular outlet won't help you in Maine, but I have seen similar advertisements on CL around in many parts of the country.

[Jim Neeley]

Your area may be different but this is how most do it here in Alaska...

What it sounds like you have is a "hot roof", where the inside ceiling is nailed to joists filled with insulation, topped directly with the metal roofing. The insulation slows but does not stop the flow of heat. The escaping heat melts the snow wich then refreezes, causing problems.

The *best* solution is a "cold roof". To build a cold roof you need a non-sealed air gap between the inside roof and the metal roof. Typically the inside ceiling is nailed to joists which are then filled between with insulation. A vented air gap is then nneded between the insulation and the metal roof. This can be done by using wider ceiling joists than your insulation thickness or by installing firring strips. On the lower end, under the eve is open and a vent is along the top of the roof to let warm air escape. In the winter any heat getting through the insulation slightly warns the air barrier. This warmer air rises, escaping the roof vent and cold makeup air enters the gap under the eve.

I apologize for my poor explanation of this; here's a link to a site with sketches..

http://www.brainerdhomeinspection.com/casest~1.pdf

[Jim Mackell]

What it sounds like you have is a "hot roof", where the inside ceiling is nailed to joists filled with insulation, topped directly with the metal roofing. The insulation slows but does not stop the flow of heat. The escaping heat melts the snow wich then refreezes, causing problems.

I apologize for my poor explanation of this; here's a link to a site with sketches..

http://www.brainerdhomeinspection.com/casest~1.pdf (http://www.brainerdhomeinspection.com/casest%7E1.pdf)

Jim, your explanation is dead on. Since the metal roofing needs to be replaced anyway, the sole question is how best to cool down the portion of roof that runs over the heated space. Thanks for the link!

[Bill ThompsonNM]

+1 for the cold roof. I built my metal roof similar to that used in a "blog cabin" episode a few years ago. Google blog cabin metal roof. Basically I added foam insulation, sheathing, tar paper x 2 then wood nailers to keep the metal 3/4 inch above the tarpaper with eave vents and a continuous ridge vent In my case it lets the metal get hot but not transfer the heat in.. So the roof and metal are independent

[fred klotz]

If you decide to go with the rigid foam, add furring/strapping (1X4, 16" or so O.C.) fastened through the foam to the existing framing, then screw your roofing to the furring. This further ventilates the metal to keep it colder.

[Haley Parker]

Metal roofing can provide a solid, durable and attractive finish to any modern house. Metal roofing (http://bartonroof.com/) coated in granite is one kind, which looks like asphalt shingles. Coated metal roofs are virtually indestructible, 100% recyclable, and will reflect heat instead of absorbing it.

[Jim Andrew]

Closed cell insulation IS a vapor barrier, so you don't need another.

[Tony Joyce]

Closed cell foam can be applied over the metal roof(on top), but must be coated with elastomeric coating to avoid deterioration of the foam and must be re-coated every 10 to 20 years. If you save the cost of re-roofing the foam is very cost effective. Both problems solved.

This is a good short explanation of "spray polyurethane foam roof insulation". http://www.foamroofing.com/aboutSPF.html
I'm am not endorsing any company, just the process. It seem to me to have many benefits, which why I'm using it on my roof. Plus I'm killing two birds with one stone.

Just my .02 cents.

Tony


While I'd love to use foam, it won't work in this application. First, we can't afford it! Second, because we can't get to the underside of the roof over the heated portion of the building, we can't spray it in place and I don't think it can be sprayed first and then screwed down. The vapor barrier issues concern me. Hadn't really considered them. Theoretically it seems like I'd have to lay down a moisture barrier, then a plywood deck, then the foam board, then the metal roofing. Still scratching my head over this one!

[Darcy Forman]

I wouldn't put sheeting or foam on a tin roof. One how are you going to hold the tin to the roof tight enough against foam to prevent leaks over time. Foam is compressable to a degree. In my opinion tin needs to be screwed to solid wood to work and so the screw washers stay tight. Plus foam under tin shouldn't be needed. Your problems can be solved with a properly vapour barriered and insulated ceiling followed by a properly vented roof. Make sure there are vents near the roof ridges. The turbine ones work great on tin roofs. Then I would simply strap the rafters with 1X6 and apply the tin on top. I have built dozens of roofs this way and we have allot of experience with winter and snow in Alberta. One more think if you don't fix the ceiling problem you will continue to have problems even if you replace the roof and insulate it. The heat and moisture excaping the ceiling will frost the underside of your plywood roof and then melt when it gets warm making a mess. If it was my builing I would fix the ceiling. Tin the roof and properly vent the roof and the problem is solved.

[Charles McKinley]

The company I used to work for had insulation that matched to steel roof put on top of the roof then covered the insulation with rubber roofing.

[fred klotz]

Screw purlins over your rigid insulation, then the metal to the new purlins. The air gap between the metal and rigid insulation will mean the metal will remain near the outdoor temps. Snow can build up on a cold metal roof, but if there is any melting, it will slide off en masse, so you might want snow guards in areas where that could be a danger. 50 feet of sliding snow can cause some serious damage.

[Carl Beckett]

+1 on a cold roof. I did this to my house - made a huge difference.

Since you are roofing anyway, you might just leave the current roofing and nail strips over the top of it to attach and entire new roof to (what Fred says). You want some convection in the gap between (and this needs to be sized properly, so some technical consultation is a good idea) which recirculates from the overhang to the ridge vents.

The only way to go imo, if ice damming an issue.