Installing a Metal Roof - over old shingles?

Your next step will be to determine if you can install your new roof over your old shingles, or if you will have to remove the old shingles before installing your new roof. Again, you will have to refer to the recommendations listed in your manufacturers instructions for which sub surfaces you can install the metal roof over. In some cases, the metal roof can be installed over old asphalt shingles, however this also depends on the condition of the shingles.

Inspection of asphalt shingle roofs must include: The condition of the shingles, such as are they buckled, cracked, or cupped. If so, then they must be removed as metal roofs have to be installed over smooth, flat surfaces. The number of shingle layers already on the roof. If you asphalt roof has more than one layer of shingles, you may have to remove the shingles as the weight constraints of some local building codes may limit the number of layers of old roofing that can be covered.

When removing old tiles, this process is called a tear-off job. Before you begin your tear-off job, make sure that you check your local forecast for any chance of rain. It is always a good idea to have at least two roofing tarps on hand in case of a pop-up shower.

Remove the shingles using a wide, flat shovel, or a roofing shovel. You will also need a claw hammer and pry bar to loosen stubborn nails. You want to first use the pry bar to loosen and remove all of the flashing from around your stacks, vents, and skylights. Next, start at the top of he roof and remove the old shingles in sections. Keep the roofing shovel close against the plywood decking so that you can remove peel off the shingles in large chunks, instead of one at a time. Any tear-off job will create a lot of debris, therefore as you move along you want to sweep the debris off the roof. Before that no one is below you as you sweep and that, you cover any decorative plants first. Loose debris that is left on the roof can create a hazard, especially on a steep roof. It is also advisable that you have someone on the ground that can collect the debris and deposit it in special containers or large trash collects that you can rent. This will prevent the debris from damaging shrubs or flowers planted near the house. In addition, you may also want to perches or rent a roller magnet to pickup all roofing nails. This will reduce the chance of someone from stepping on the nails and the nails from getting into your automobile tires.

After you have removed all the old shingles and asphalt paper that covered the decking, your next step is to carefully inspect the decking for rotting or holes. If any are found, then you must replace the damaged decking. Small holes and gaps can be patched over using pieces of flashing. You also have to ensure that you have the minimal required thickness of decking. Many metal roof manufacturers require a minimum of 1/2-inch decking attached according to local building codes.

Now that you have inspected, replace, and repaired the decking, the next step is to refer to the manufacturers instructions concerning the material and fastening requirements for the roofing underlayment. The purpose of the underlayment is to deflect wind blown spray, condensation, or ice dam backups. The underlayment you purchase must meet or exceed your local building codes and fire requirements, as well as meet the manufacturers requirements. When installing the underlayment a minimum 18 vertical and 6 horizontal lap is usually required, in addition the underlayment should also overhang all the roof edges by at least 1 , and extend up at least 1 on all vent pipes. The underlayment should also extend 6 up all sidewalls. Proper installation of the underlayment can prevent problems in the future such as damage caused by the development of condensation beneath the metal roof during certain weather conditions.

For years, one layer of 30-pound roofing felt has been the standard underlayment. For metal roofs, however, to prevent the felt from sticking to the metal, a slip-sheet of red rosin paper is often installed over the felt paper. However, every year new and better technology is bringing developed. Today, there are many polymer-based underlayment that work better than the standard 30-pound roofing felt and slip-sheet, simple because they serve as their own slip-sheet. However, do not assume that this is what the manufacturer of your metal roof wants you to use. Do not question the manufacturers instructions. Use only what they request you to use.

When it comes to actually installing the actual components of the metal roof, you will have to completely rely on your manufacturers installation instruction. This is no time to get creative, follow the instructions to the letter.

It is important to understand that metal roofing expands and contracts in response to temperature changes, and it is vital that this movement be taken into account during the installation phase. All manufacturers of metal roofs are extremely aware of this movement and do take this into account when writing their installation instructions. For this reason it is critical that you read and follow all of their recommendations to the letter in addition to paying very close attention to the installation of fasteners, fastener length, type, and how they are to be placed. When the metal roofs expands or contracts, if these fasteners are not properly installed, leaks will eventually develop. Because of this expanding and contraction of the metal, many manufacturers of metal roofs allow for this by designing their roofs to float over the clip fasteners. Other manufacturers design their produce to have folds in the metal that behave like accordions allowing the metal to move.

Now, given all the facts on the installation of a metal roof, you can truly see that this is not your average DIY project, but in fact a complicated, professional-grade project. Therefore if you are still set on installing a metal roof, perhaps you may want to first attempt installing one over a smaller structure, such as a porch or shed, before you attempt to re-roof your entire home. This will also give you a chance to test your skills on a manageable, simple installation.

As stated earlier, once you have completed your installation project, do not throw away your manufacturers installation instructions. You may need then if ever you have to replace an entire section of your roof, such as in the event of a serious storm.

Home page

Find a contractor
A free service to locate a contractor.

Why Choose Metal Roofing
Information about the benefits of the metal roof.

Roof Coatings & Accessories
Information about the different types of coatings used for metal roofs.

Repairs and DIY
A look at repairing and doing it yourself.

Misc. information
Stuff we couldn't fit anywhere else.

Disclaimers
Our contact and privacy information.