Underlayment for porch roof
 

Hope I'm not wearing out my welcome by tapping into the wealth of knowledge here.

I'll be shingling a porch roof 10' x 24'. I'd like to use GAF synthetic underlayment, $83:

https://www.homedepot.com/p/GAF-Felt...0973/205035868

instead of Grace Ice and Water Shield at $150. Sound OK?

Grace all the way from my standpoint....

Because???

It is extremely sticky and adheres to the roof surface extremely well. I have tried other membranes and they failed with ice dams, etc. I had a branch go though the roof after Grace underlayment material and new shingles. Trying to take the Grace off to make a nice repair was difficult, as peeling it off actually pulled some of the plywood fibers. And the Grace actually sealed around the branch because of the material it is made of.

Drive down the road and look at new expensive homes being built...I think you will see Grace.

Another thing...while this is over a porch, you will want 25+ years of protection. Why short the underlayment material to save a few dollars when it is an extremely important part of the roof ? Need to think long term on this stuff, unless you plan to sell soon.

Synthetic underlay is meant to ''breathe'', while the Ice & Water Shield is meant to protect areas with a high risk to building ice dams or wind-driven rain.

GAF, IKO, Certainteed, etc will have learning centers on the web to determine what is best in your situation. But with the low slope of a porch roof, I would surmise that wind-driven rain would be a serious consideration even above an unheated space with good air circulation.

It especially gets tricky were unheated space abuts heated space.
https://www.gaf.com/en-us/roofing-pr...Action=GetGrid

Heh heh! Exactly why I'm proposing GAF.

Well that's a sobering statement from several points of view, raising a number of philosophical questions going beyond porch roofs. ;-)

Two sides of the roof face south and east, where there won't be any wind-driven rain. One short side faces west, which I guess would be exposed to wind-driven rain. There has never been an ice dam on this roof. It's easily reached with a roof rake or shoveled clean from the roof.

I would guess it would be from what direction a storm comes from.
We experience lots of west to east, but a hurricane force storm is likely to come from the south, and the rotation would change the direction as the storm moves.

The importance is what they will warranty.
We moved from IKO Cambridge to IKO Dynasty/Premiums because of the noticeably large effect of wind damage in the area.

The water protection, even in GAF, may be several different products at different price points... and needs to be compared by the coverage.

I know IKO has StormShield, Armourgard, and GoldShield... I would guess that GAF has the same. Our Grace is $149 for a 2 square roll (200 sq ft), so Depot is definitely in the range. Since our Epilay Synthetic is $79 for 10 square (1000 sq ft)... it sounds like the GAF Synthetic is in the ballpark.
We have IKO Stormshield at $78 for 2 square (again 200 sq ft)... I would guess that GAF has a similar product.

If the GAF has a similar product as the StormShield it may be cost effective, especially considering your roof, to use that instead of the synthetic and get the extra protection.

Depending on how the roof connects, it may be the sidewall at the most risk.
A decent roofer can determine on-site what they would suggest.

Ice dams typically do not form on porch roofs over unconditioned (or open) space. They occur when there is too much heat leakage from below, such as by direct thermal conduction through framing, leaks into the attic from wiring penetrations, around pull-down attic stairs, and can lights in the ceiling. Melt water on the roof surface runs down to the overhang and gutter area, where it refreezes, forming the ice dam and backing up melt water. That is why current code requires a waterproof covering, such as Grace Ice & Water Shield, from the edge of the roof going back to a point above two feet inside the exterior wall below.

If you have a sloping intersection between roof and exterior wall of the house, be sure the roofer installs kickout flashing at the lower end, to divert rainwater out and away from the siding. Below is one many diagrams and photos showing different types of kickout flashings; google on that for all sorts of information on the subject.
https://www.howtolookatahouse.com/Bl...FlashingJH.jpg

If the roof is unheated (under) then ordinary felt will work.

If this way my house would use ice and water shield entire roof.
And get the most durable long lasting roof shingles. Keep the receipt.

I have had 2 batches of roof shingle prematurely fail in 2 different decades. Not the same brand either. The warranty is only for the shingles. But it is something.

Next time out driving view roofs. You will see color fade and darkening on some. Just plain poor quality shingles.

Not to hijack the thread, but I'm seeing more and more metal roofs going up and it would seem that they might potentially solve a lot of the problems discussed here.

Any thoughts from actual pros or homeowners with real life experience the metal roofs actually work better and how they compare cost-wise and if its worth any extra cost???

Great comments all! Hope I can remember the when its time for my next roof,,,

Note that metal roofs come in varying qualities. Plus installers should be reviewed.

Metal roofs can now look like slate, shakes, - not just plain. Most think that all metal roofs look the same. Not.

The cost of metal roofs usually is sizably more then a shingle roof.

There also can be a snow slide issue for some.
If I were to construct a new home, yes, I would give a metal roof serious consideration.

But yes, having the porch roof metal could be an option for the OP.

Since the OP is looking to spend less... no, metal is not an option.
We can come close with ribbed roofing, but it must have a decent slope, and any sealant should be high-temp.

Once you get into standing seam... the cost becomes considerably more expensive.

An unheated porch mostly likely will have a heated transition to a sidewall... the melt there will form an ice dam. And even open structures, sometimes form icicles, which is a sign of snow melting dripping and then refreezing... it can happen under the structure if the warm air causes the roof decking to warm enough to create melting below the snow blanket. It is mainly a spring affliction, but has become more common with our unusual weather.

https://www.iko.com/na/document-libr...arranty-en.pdf

I would surmise that GAF also has an ''Iron Clad'' period for which it will cover labor costs to replace the shingles.

But the roofer will help determine the costs and lead time for materials acquisition... as GAF Liberty may be the best product depending on the slope and desired look of the porch when the OP's desire for GAF product is taken into consideration.

I went back to the OP and looked at the specific material they are looking at...for a second time. Let's get the money straight. The OP material is $83 for a 1000 sq. ft roll.......which equates to approx. $16 for 200 sq. ft (.08 cents per sq.ft.)....vs. the cost of Ice and water shield of about $150 for 200 sq. ft.(.75 cents per sq. ft).....9 times more expensive). So this material as presented by the OP is in no way comparable. It only compares to old felt roofing material and is a cheaper alternative to that product. It is surely apples and oranges. I suggested a superior overall product for the project (Grace), regardless of whether it is a porch or anything else. You only get what you pay for.

They aren't comparable because they are not used for the same thing.

One is an ice & water shield, the other is a synthetic acting something like a housewrap (Tyvek).

Ice & Water does not allow for transmission in either direction, while the synthetic allows for water vapor to move from one side to the other.

The synthetic underlay is like a high tech felt.

Synthetic is usually used on steeper sloped roughs (5:12 over above) with an ice & water shield applied to the last three feet near the eave. The I&W protects the hot/cold transfer spot were ice dams are most likely to occur.

It can be used on low slope roofs (heated or cold) to stop wind-driven penetrations. But rolled roofing is preferred to prevent shingles from getting wind damage when applied at such a shallow angle. This would be like the GAF Liberty.

But a lot of determining the best product is the slope, what the waste factor will be, and what the final product will look like.

Thank you for the information, Dick. Kickout flashing is on the materials list so I believe the roofer intends to use it on the porch roof, and there is currently kickout flashing up there.

Alright, here's another product: GAF Storm Guard, $87 for 200 sq ft.

https://www.lowes.com/pd/GAF-STORMGU...yment/50353100

It's supposed to be for wind-driven rain.

I'm using GAF Timberline HDZ shingles on the whole house. Don't forget that shingle companies prefer that you use their underlayment for the warranty. I admit I'm looking for a cheaper alternative to Grace Ice and Water Shield. I'm not sure my humble Taj Mahal is worth Grace IWS.

Correct. It's not that I'm resistant to Grace IWS or don't believe it's the best product out there. It's that I need to choose something durable but affordable for the porch.

If it's not too late I should probably mention that the porch current has about 3 layers of rolled roofing on it. I'm not really clear about the difficulty and cost of removing that and how the porch roof should be handled overall.

Much better option than the original stuff.

Even a porch should never have more than two layers.
And an architectural shingle will be considered two layers.

In the past, we would use a three tab - IKO calls them Marathons, not sure what the GAF equivalent is. That would allow a second layer without removing. .

Grace I&W would need a layer of shingles on the top. If the roof is shallow pitch, that is what will fail. It would need a lot of heat to stick flat and not curl.

Did the roofer give you a materials list? They may be looking at the job as a total... and that could reduce some waste.

Which one are you referring to?

GAF Storm Guard would be better in my opinion than the original recommended stuff. I still prefer Grace, but if you want to save a little money, then the GAF would help, as there is a small difference. However, consider the pricing:

All based on Lowes web site.....

GAF comes only in 200 sq. ft rolls. You said roof was 10X24, so you would need at least 240 sq. ft and probably a little more for overlaps. GAF only comes in 200 ft rolls at Lowes.

2 rolls at $88 each = $176

Grace comes in both 200 and 100 sq. ft rolls. So you would need one of each...

1 @ $149 (200 ft) and 1 @ $80 = $229

Project Savings....$53.

Not sure I can add anything more to the discussion. You have my non-professional opinion. I would go with Grace every time on my own roof, but that is just me. Others on this thread have given you some added info. and opinions. It seems it is now down to a choice for you to weigh. Good luck !!

Now I get your reasoning, thank you, tummyman! Very good points. What you're saying makes sense.

If you are going with GAF, you have to use and follow the directions that GAF has for the slope of that roof... or they will not cover any warranty.
If all the products come from one company, or as recommended by them, applied as they require, you will always be in better shape.

I see more and more of the warranty requests that I make coming back ''non-compliant''.

Roofing, siding, decking, windows, and site-finished doors are notorious for this.

I can't find any indication of roof slope for GAF Storm Guard at the the GAF website. Agree it's best to use GAF products throughout since the shingles are GAF, but others in this thread seem opposed to that.

Anything under a 4:12 is a low slope.

Anything under a 2:12, pretty sure cannot accept an asphalt shingle.

The GAF dealer should have a guide to help with the correct products, and most will have a materials estimator that knows - or can access - the warranty and application guides for their product.

If you can; bring a couple of pictures so they can see the overall design and how it attaches into the main structure. It is the little parts and pieces that can make a big difference.

Interesting thread. I'm building a 14'x14' screen porch this fall and planning a 4/12 pitch roof. I have yet to decide the roofing materials but it will either be metal or rolled roofing, depending on how much I spend on framing. I have a whole budget in mind.
It will be in the back of the house so visual of the roof is not that important.

So glad it's going to be in the back of the hose so it won't get wet! Just teasing. You made me laugh! Thanks.

I believe that you can apply ribbed directly to purlins, as long as the pitch is steep enough and the spacing between the purlins tight enough to accept the snow load.

I was just missing u. :D

You fixed it! It was MUCH more fun the other way!!:laugh:

I listened to the advice here and had a roofer check the slope of the roof (1.5 to 2/12). Looks like I should go with rolled roofing, so back to the drawing board.

That seems really low, but GAF does have Liberty rolled roofing.

You might be better off with a rubber membrane. That's not much pitch at all.

Whew, I spent a couple of hours reading about low-slope roofing materials and couldn't reach any solid conclusion about what's best. There were fervent and contradictory debates among roofers. Not a single product had more fans than others.

This roof needs to hold up to shoveling snow with a plastic shovel and to being walked on for that task plus a metal roof rake. Any recommendations? Links much appreciated!

So what material is on it currently (three tab, roll roofing, etc...???)? How long has it been down? Maybe your answer is right in front of you....with a good ice and water membrane like Grace.

You don't use Grace under rolled roofing.
It would void any warranty.

Low slope is either going to require GAF Liberty *the brand she wants* or EPDM rubber roofing.

GAF Liberty is listed as going from 1/2:12 to 6:12, and should be applied as recommended.
https://www.gaf.com/en-us/document-l...structions.pdf

Two or three layers of rolled roofing. Ancient.

Now the roofers disagree about the slope. One said 1.5-2; another said 4. Any way to measure it?

One foot of run horizontal, measure the rise in inches.
There is also some inexpensive tools made that measure the angle and transfer it to pitch.

With a 2’ carpenter’s level, measure the downhill gap to the roof in inches. Divide by two for your pitch. Easy pease lemon squeezey!