Most of the work we do on metal roofs would be on metal building roofs. There are people who will cover existing built up roofs with metal roofs. But that is not a system that we would recommend.
We have done a great deal of restoration of metal roofs for systems that are basically metal building systems. There are some basic concerns that seem to always give problems with metal roofs.
The first area is the bottom edge. When gutter is installed on any other type of structure, good roofing practice is to have the outside edge of the gutter lower than the building side. That way if for some reason the water can’t get out of the gutter fast enough and backs up, it will run over the outside edge and not back into the building. On metal buildings, the gutter is used for a wind break, and the outside edge is higher than the inside edge. When the building is built, there is a formed rubber piece that is installed under the metal roof, and fastened down with the metal roof.
When the rubber starts to age it will dry out and shrink. After a couple of years, the outside edge can start to leak because of the water backing up onto it. There is a cure that does not take long, and very inexpensive.
The next areas that cause problems are rooftop equipment. Rooftop equipment on metal roofs is never a good idea, and should be avoided as much as possible. We have products that will seal around them however, metal roofs were designed to shed water, and any time the equipment will trap water, it can cause problems.
Once the bottom edge is fixed, and any rooftop equipment is dealt with, the next problem makers are the outside rake edges, the ridge vents, the end laps, and the skylights, and fasteners. Usually, the outside rakes only have a fastener every 12″ or so. Our experience is that a lot of times high winds will wreak havoc on them and cause problems. The ridge vents, end, and skylights are handled the same way. They need to be properly secured, sealed, and webbed with a fabric that will hold them together, move with the expansion and contraction, and eliminate water from infiltrating the system.
There are a couple of popular systems that we can install that will seal them, however we have found that there is a mixture of products that will perform a lot better than any one specific system.
We have found that if we must first re-secure or replace all of the fasteners on entire roof. We then add additional fasteners to the skylights, rakes, and end laps. Once all of the fasteners are ready, we use a neoprene product that we have found to perform the best over a 20 year period. We seal every screw head, and we then neoprene and web the rakes, ridge vents, end laps, skylights, and any other pipe or rooftop equipment to make sure everything is sealed. Once everything is secured and sealed, we use an asphalt type coating to protect the entire roof and metal from the elements.
I install elastomeric coatings but I don’t recommend them. PLEASE do not ever allow anyone to coat any time of coating over any skylights! Skylights should either be redesigned, or replaced. I have almost stepped onto skylights that were coated with elastomeric coatings. I don’t care what you have to do to seal the system, NEVER coat over the skylights!
The asphalt coatings will bond to almost anything. The elastomeric won’t. If there is any outside agent, the elastomeric will not bond. The asphalt coating will not blister where the elastomeric will.
I have also found that the neoprene mastic is incredible strong, and although it takes a little care to make sure it is bonded, once bonded, it is almost impossible to break loose.
We have been installing these systems for years, and have had unbelievable success.
If the metal is getting to rusty for the rehab, there are other systems that have performed well of us.
The first option would be to re-skin or replace the existing metal roof. This usually is the easiest option if the roof is over a boat dock, or somewhere that there is no insulation or electrical lines that are tied to the system.
If you wish to save the insulation or electrical, or if there is a fear of completely exposing the inside of the structure to the outside elements during the re-roof, the next option is to recover the metal. There are systems made that will allow you to install spacers that are secured to the original perlins. The new metal system can be secured to these spacers. You can even add additional insulation between the two roof systems at that time.
If there is any rooftop equipment that exists on the roof, you can also change the system over to a conventional system that will allow you to flash all of the equipment in a manner that will perform much better.
If fire rating is not a high priority, we have found that we can install ½” plywood over 2″ by 4″ sleepers that are install sideways to the conventional rafters, but that will allow you to secure the plywood in a manner similar to conventional construction. The 2″ by 4″ sleepers must be secured to the sub framing, and must be install 16″ on center. The outside edge must be trimmed off, and framed to allow for the installation of the perimeter metal. Once this system is in place, the re-roofing costs will be much less that replacing the metal.
The last option is to install commercial roof insulation to the existing deck and install a conventional roofing system. The only mistake that we have seen is to install the insulation between the seams, and then NOT installing a cover insulation to span over the seams. When that is done, the gap will break down and fail. Not to mention if the structure is air conditioned, there is a heat sink right between the insulation gaps. There can be both heat loss, and an opportunity for the area to sweat, and rust out.
If you are considering any of these options, please contact us. We can inspect the property, evaluate the situation, and give you our best recommendation.