# Standing Seam Metal Roof Underlayment



## EIRE

So im having my old roof completely removed and installing a standing seam metal roof 24gauge. 
I’ve heard two different stories regarding underlayment. The first is run ice and water shield 4 feet up and then use 30 pound felt the rest of the way up the roof, or use ice and water shield on the entire roof.

My dilemma is with the 30 pound felt, ive been told during the summer months the felt will heat up and bleed a petroleum product that will stick to the underside of the metal roof causing oil canning. Is there any truth to this statement?

Thanks for the input


----------



## 1985gt

Most areas are I&W shield 2' past the interior walls. Generally this works out to 2 runs or 6' depending on slope of the roof. The steeper the roof the more you will need. In turn if its too low of slope you may want to think about doing the whole thing or using something other then felt the rest of the way.

As far as felt bleeding out and causing oil canning I have never seen this.

Oil canning is the warping of metal. With a 12" or 16" wide profile in 24 ga you should never have oil canning *IF* it is installed right. on a 24" they pans should have minor ribs in the middle to prevent oil canning. 

Now felt that wrinkles up may cause oil canning but I've never seen it.


----------



## Grumpy

I wouldn't use the 30# personally, however I have never heard of oil canning from the use of it. They make specific metal roofing underlayments. There are numerous numerous metal roofing underlayments on the market. Old school specs called for 30# with the use of a "Red rosin paper" above it. Red Rosin paper is basically 30# without the asphalt. 

All ice shield is an option, but only with absolutely perfect or better than perfect ventilation because the ice shield will act as a vapor barrier and any ventilation flaws will immediately show up within a few seasons. However remember most ice shield are asphaltic products as well.


----------



## EIRE

Thanks for the info Grumpy, what underpalyemt other that 30# would you recommend?

Currently the roof has a bunch of turtle vents, the contractor suggested removing those, filling the holes, and install a full length ridge vent. I tend to agree.


----------



## Grumpy

Only install the ridge vent IF there is adequate ridge line, if the roof is all cut up with hips and valleys you may not have adequate ridge line. Also you need very good intake for the ridge vent to work. This intake may need to be added. The thing abotu ridge vent is it works wonderfully when properly installed, usually the improper installation is a design failure on part of the roofer, but it simply will not work without proper intake. 

So which metal roofing underlayment would I recommend? I dunno. I'm not the metal expert, most of our jobs are porches, gazebos, bays etc... so very small areas and in those cases we ice shield the whole thing. However I just got an email today that CertainTeed has released a new product for use under metal roofs. I know nothing about it except that it's fresh in my brain because I read it this morning.

Edit: Sorry, I take it back. I just checked my email and that priduct is a tile roof underlayment, not a metal roof underlayment. See I am def. not the person to ask  There are numerous you will find if you perform a google search.


----------



## EIRE

The house is a 2 story cookie cutter. Basic roof in two sections, both parts are basic A-frame structure… 
No valleys, hips, dormers, etc. It’s a straight shot from the eves to the ridge on all parts of the roof.
If I had to guess, the total square inches of ridge vent would exceed what the turtle vents currently provide.


----------



## Pie in the Sky

Few comments.

1. I never specify Rosin paper under a metal roof. If there is a leak or vapor drive, it gets wet and doesn’t dry out. Its common with Zinc (white rust) but can happen on any metal roof.

2. I have specified and seen many metal roofs with a full covering of Ice and water shield below. A metal roof is a vapor barrier, adding your adding a vapor retarder directly below it, I can’t see it being an issue but you should ALWAYS follow manufacturer instructions. That way if something happens you have recourse. 

3. Ice and water shield under a metal roof has to be of the "High Temp" variety or a slip sheet must be added between the membrane and the metal. The metal heats up to upwards of 180 degrees and melting to the ice and water. Then it cools down, contracts and tears the membrane. Ive never seen it cause oil canning but have seen it bleed through into the building.

I’ve used a lot of this… http://www.interwrap.com/titanium/RPD_PDF/TITANIUM_SPECS_WEB.pdf 

4. I would way rather see a ridge vent unless you’re in a snowy climate, But Grumpys right, you need a full ridge. Gables would work better if its cut up or there’s a lot of snow. Also you may want to consider snow guards in some cases… If you have some Photos in your attic and from the outside that


----------



## 1985gt

Your best bet is to call the manufacture of the panels and ask them. That way if there is any problems in the future your covered. Go ridge vent if at all possible. Low profile vents are not going to be fun to work around if there are a lot of them and likely wont end up in the right spots.


----------



## EIRE

The company seems vague when it comes to underlayment requirements. This paragraph is the all that I could find regarding underlayment.
I’m in Utah and while we do get snow its pretty mild, we hardly ever get any gale force winds that I feel would be powerful enough to push the snow under the ridge vent.

The panels in question will be 18 inches wide

http://www.mbci.com/pdf/design_tech_manuals/LokSeam_Manual.pdf




15. A vapor retarder may be necessary to protect roofing components when high interior humidity is a factor. The need for a
vapor retarder, as well as the type, placement and location should be determined by an architect or engineer. The following​are examples of conditions that may require a vapor retarder: (A) Projects where outside winter temperatures below 40°F
are anticipated and where average winter interior relative humidity of 45% or greater is expected. (B) Building usages with​high humidity interiors, such as indoor swimming pools, textile manufacturing operations, food, paper or other wet-process​industrial plants. (C) Construction elements that may release moisture after the roof is installed, such as interior concrete​and masonry, plaster finishes and fuel burning heaters.


----------



## Pie in the Sky

EIRE said:


> The company seems vague when it comes to underlayment requirements. This paragraph is the all that I could find regarding underlayment.
> I’m in Utah and while we do get snow its pretty mild, we hardly ever get any gale force winds that I feel would be powerful enough to push the snow under the ridge vent.
> 
> The panels in question will be 18 inches wide
> 
> 
> http://www.mbci.com/pdf/design_tech_manuals/LokSeam_Manual.pdf​
> 
> 
> 
> 
> 15. A vapor retarder may be necessary to protect roofing components when high interior humidity is a factor. The need for a
> vapor retarder, as well as the type, placement and location should be determined by an architect or engineer. The following​
> 
> 
> 
> ​​​​are examples of conditions that may require a vapor retarder: (A) Projects where outside winter temperatures below 40°F
> are anticipated and where average winter interior relative humidity of 45% or greater is expected. (B) Building usages with
> high humidity interiors, such as indoor swimming pools, textile manufacturing operations, food, paper or other wet-process
> industrial plants. (C) Construction elements that may release moisture after the roof is installed, such as interior concrete​
> and masonry, plaster finishes and fuel burning heaters.


Interesting. It is a "Structural" metal roof system but it will not resist a hydrostatic head. Honestly to give you a proper recommendation I would need to know more about the Project. Your Ice and Water shield is a vapor retarder but you are not using it as one if I am seeing this correctly. If it were being used as a vapor retarder, it would need to be on the warm side of the insulation. If this is really a concern, I would use the "Titanium UDL" instead of the "PSU" because it can breathe. 

Have you installed alot of metal roofs? I apologize if thats insulting, I dont know your background, this is a difficult roof to install. the details provided are not great and you need to account for expansion coefficients of the steel when installing it. 

Are you planning on securing the panels at the ridge or the eave?

Dustin


----------



## Pie in the Sky

Erie:

Let me ask you a few questions.

1. Is your attic a cold attic? meaning insulation is on the floor and the entire roof deck is exposed?
2. have you done any ventilation calculations? its easy, take 1 square foot of net free ventilation for every 150 square feet of floor space. This should be minimum, I like half at the eaves and half at the ridge then add a few gable vents for good measure. Attic need to ventilate in a system like this.
3. What are your longest run on roof panels?
4. Do you have any photos?
5. is there any existing ventilation problems?


----------



## EIRE

Pie, thanks for taking the time to answer my questions.
Im not an installer, im the home owner. Over the course of the last few months ive been getting quotes on new roofs. They all seem to have a different idea on how the roof should be installed

Im spending a lot of $$$ on this project and I just want to make sure its done correctly.

1. Is your attic a cold attic? Meaning insulation is on the floor and the entire roof deck is exposed? Yes

2. have you done any ventilation calculations? its easy, take 1 square foot of net free ventilation for every 150 square feet of floor space. This should be minimum, I like half at the eaves and half at the ridge then add a few gable vents for good measure. Attic need to ventilate in a system like this. 

A little about the house: the first floor is more like a cathedral ceiling and has very little attic space, no room for gable vents on the first floor. Second floor is more traditional and has a full attic with 2 gable vents.
All together both sections have 7 turtle vents with probably 1 square foot of vent area per turtle. I would say based on your calculations 7x150 should cover the floor area in those two parts of the house


3. What are your longest run on roof panels?
The longest panel will be 15 feet from eave to ridge, total roof is 17square

4. Do you have any photos? 
Let me see if I can find a few…

5. is there any existing ventilation problems?
Not that im aware of, house is comfortable year round (should be more so in the summer months with a metal roof)


----------



## EIRE

This should give you a general idea of the layout.


----------



## Pie in the Sky

Can I ask why you are going with metal? Tile would look great on this house. 

The fact that the fetch (eave to ridge) on the roof are so short you probably will not have too much of an issue with expansion and contraction of the metal. The Product info you sent is a top of the line metal roof. Its geared towards commercial or High end residences. That doesn’t mean you can’t use it. in fact I think it is great. The system is secured to the roof with concealed cleats. Then as the roof heats up it slides on these cleats. 

Now you can get a metal roof with exposed fasteners, but after maybe 10-15 years in your climate you will start seeing leaks. The exposed fasteners stay in place while the roof moves, slowly elongating these holes. You can fix it by taking the screws out and replacing them with slightly larger screws.

I like the choice you have made on systems as far as metal roofs go. You are not going cheap and I hope you can keep a contractor from convincing you to go cheaper. 

If I were you I would ask all of the Contractors a few simple questions. also you want to get references. This is a good job, they can put a few references together. 

1. Get 3 references of metal roofs with concealed cleats they have done and call them. NOT EXPOSED FASTENER JOBS. The Idea of this question is to see how much they know about your system.
2. Ask if they plan on securing it at the Ridge of the eave and why? Really it doesn’t matter where they secure it as long as they use the correct details, asking Why may see if there BS’ing you or not. 
3. Ask them 
4. to lay out the details they will use from the installation instructions for each of the following: headwall, Eave, ridge, rake, step flashing.
You really need to be careful of the contractor you choose. A commercial contractor may take your job as a filler job, might be worth calling the manufacturer and see who they have used. Are you near Salt Lake?

I personally don’t think metal will look all that good on that house but the roof your considering will last 50 years. so that’s probably why you’re doing it. I could argue concrete tile would be similar in price and look awesome, but you would need a few hundred bucks for a structural evaluation.

PS: you are going to want to install a snow fence over your door....


----------



## EIRE

I’m choosing metal for the longevity, durability, wind resistance, and maybe add some value to the house.
While I think tile would be great if I were in Florida it would just be too out of place here. I can’t ever remember seeing a tile roof here.

The contract in question has been in business for about 30 years and probably has a 50\50 mix of commercial and residential customers. I will make note of you questions and present them to my contractor.
We still have a little snow and ice on the roof so ive decided to hold off on any roof work until late March or April.

The contractor did mention having to remove all the siding where the roof comes in contact with the wall. Makes sense to flash those areas. 
I agree somewhat that the metal roof will look a little out of place with the vinyl siding but when the time comes to replace it im seriously considering cedar siding. Should give a little more of a country appearance and blend better with the metal roof.

This house was built in 98 and other than the electrical and the plumbing all the materials and workmanship ive seen have been absolute garbage. Including the roof.


----------



## Pie in the Sky

Well great man, sounds good, let me know if you have any questions, feel free to post photos when he is doing the work and good luck.

D


----------



## O'Donnell Roofing & Solar

Lest face it, the introduction of plywood has caused many of the venting & mold issues.
I have removed many old tin roofs. Porches, without heat, usually have red rosin installed to separate the steel nails in the deck from causing galvanic corrosion on the underside of the new roof.

Fast forward to the 21st century, Plywood deck, mold growth on the north side, overheating of the deck on the south side, what's a person to do?
With 24ga metal fully sheath in the lower 4' with treated plywood, install ice shield, vent the soffit, 1 x 6 pine battens with 3" spacing, gable venting.


----------



## EIRE

Ok guys here it is, finished a few months ago and thus far im really happy with the job.
Of course after the roof was removed and new felt installed we had rain showers every other day and a wind storm with speeds reaching 60 mph.

Still need to install a snow fence


----------



## LCG

Very nice:thumbup: 

It gives your home a sense of permanence. I'm sure your the envy of the neighborhood.

Good to hear back from from you and good luck in the future.


----------



## Interloc

that looks waaaay better then shingle, wish more ppl would pick metal around here.


----------

