metal roof conversion

ionized

I am probably going to have a standing-seam metal roof installed on my house and garage. It will probably be cool roof. I am pretty naive about everything except the difference between standing-seam on the one hand and “r-panels on the other.

The re-roof will include two types of construction. One is replacement of an existing shingle roof. The existing roof deck is planks, not plywood. I plan to spray-foam insulate the underside of the deck and seal the attic.

The other two roofs are flat-roofed additions. There, I plan to frame with minimal rise for the metal roofing. These areas will be sloped in different directions (right angles). One is a lower-slope continuation from one of the gabled roofs. The other will border on that and end at the gable end. The existing roofing has to be removed to eliminate the vapor barrier and that will also be spray-foam insulated before the metal panels go on.

I will appreciate any advice that is offered. I have some specific questions. Are there different options for treating the edges of the roof? What are the choices for underlayment? This roof will be difficult to get onto safely compared to shingles and the flat roof. Is there any practical way to install attachment points for a safety harness? (I am planning on installing both photovoltaic and solar thermal. I have nearly South-facing gable on both the house and garage.)

I understand that the metal is lighter than the shingles that will be removed. The dead load will be less. Do I have to be concerned about the corresponding increase in the live load? This is Gulf of Mexico hurricane zone (New Orleans). I wonder if hurricane ties should be added at this point if it is practical.

Thanks for reading!

Windows on Wash

Where is the home located? If you are in a mixed climate, the reality is that roof color (in metal) will not make that much of a difference in savings.

Metal has a much higher emissivity compared to asphalt so you are going to be much better off in either scenario regardless of color.

Standing seam is the preferable of the two materials with a more bullet proof installation (i.e. hidden fastener) and classic look.

What is the rationale behind the sealing the attic? Spray foaming roof decks are great and work very well with metal (make sure you put down a good underlayment and do not spray the back of the metal) but that is an expensive option unless you are converting that to conditioned space and using it as living space.

If the goal is purely efficiency, you can do a whole lot more on a whole lot less budge with proper air sealing and insulation.

How flat is flat? Mechanically locked standing seam can be run on a 0:12 application and are used in flat roofs that have proper drainage allocations.

Spray foaming flat roofs are a good ideal because they are tough to get good insulation value in via traditional methods. I would recommend thermally breaking the joists via rigid foam in most cases as well.

Do you mean the edge of the roof or the edge of the panel (i.e. edge priming/painting)?

If you are coastal, go with aluminum and most steel panel makers will not warranty them against salt spray or at minimum they will have reduced warranties.

Go with synthetic underlayment and don't worry about the breathable (i.e. Deck armor) stuff. A good woven poly is fine.

Yes, if you are going to routinely be accessing the roof, hide some attachment points under the ridge cap detail.

Metal is considerably lighter than asphalt but I don't think you need to worry about live load reductions. I have never seen a roof held down by the shingles.

The structure of the metal and its increased wind resistance will easily outweigh the benefit of the additional weight of the asphalt. The metal roof should also be screwed down for security and increased strength.

I would absolutely add in the hurricane ties now. You are making for a lifetime (barring mechanical damage) roof and they are cheap. Do it right...and do it once.

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ionized

Thanks for your advice, Windows on Wash. I aim to answer your questions and look forward to your follow-up if you will continue with your generosity. The home is just upriver from New Orleans so salt is not a problem. I guess steel will be the choice. Hurricanes are a big deal and so are tornadoes that spin off of them. We are in a predominantly cooling climate, HVAC-wise. The current, locally proffered, strategy for older homes that were converted to have mechanical cooling, is to seal off the vented attics and insulate the roof deck. Spray foaming will stop the air leaks and slow the heat gain from the roof. Given what my ceilings and roofs look like, it will be very difficult to seal off the top of the house at that level. (One of the flat roofs has a very shallow attic space under it that communicates with the gable roof attics. There are some complex, uninsulated fur-downs as well as the “normal” air leaks introduced by careless work.)

I am a bit up in the air about the cool metal roof. Regular Galvalume or similar is less expensive and after spray foam the marginal improvement is not that great. My understanding of the metal characteristics is that the emissivity really sucks but the reflectance is very high compared to shingles and other materials. The cool metal roofs will allow the house to cool off faster after the sun goes down and will also warm up slower reaching a much lower steady-state than shingle roofs and somewhat lower than the standard metal roofs.

“Flat” is relative to the existing gabled roof. The areas that are currently flat will be framed to a slope that is compatible with the metal roofing. One of the “new” (low) sloped roofs will continue from partway down the existing gable. This one sits in the “L” formed by the two gabled roofs. It will face North. The other will start on the end of the gable and the new roof just described and slope to the West. I wish I were computer competent enough to post a drawing. I may give it a try.

Just to be clear. The existing flat roof area will be foamed here, not the underside of the metal that will cover it.

When asking about the edge of the roof, not the edge of the panels, are there any choices to be made when thinking about how the metal meets the existing exterior walls/trim?

Windows on Wash

Spray foam on the flats where you cannot get a good enough R-Value level via traditional insulation is a great idea.

As a mentioned, converting a traditional attic into a sealed attic just for the purposes of sealing up leaks is an expensive route to go.

Get someone to look at the home that understands energy and envelope issues and much can be done to seal up the envelope prior to spray foaming ($$$$) the whole attic.

If you want to email me more pictures off line or attach them to the thread, I can help you out beyond that.

Feel free to PM me with your information and I will help out where I can.

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ionized

"Get someone to look at the home that understands energy and envelope issues and much can be done to seal up the envelope prior to spray foaming ($$$$) the whole attic"

Done that, but I am always open to another opinion. The first evaluation was to seal gable roofs and in doing so, seal off the flat roof attic at one side leaving one side vented. I thought that would make that roof into a ceiling heater and I was thinking of making it into a sloped roof anyway. I hate flat roofs. I came back to evaluator with the idea of foaming and sealing the flat roofs before raising frame over them for metal installation.

I know that foaming is expensive, but due to the extent of the fur-downs and other holes, it is probably the best way to go. If I took a couple of years of my spare time to fix it all, it would pay. If I have to pay someone to do it, I am better off sealing the attic.

I'll try to attach a (crude) diagram. Both flat roof will be removed, any vapor barrier removed and then the deck insulated. After that the metal roof will be installed. The drawing is really bad. The South gable should be drawn much larger and the flat roofs smaller.

Windows on Wash

I will take a look at the satellite images.

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