Flat roof installation and replacing skylights


This guide is based on a PVC flat roof installation that we performed in Quincy, MA. We already covered the rubber roof repair which we did on this roof back in the fall of ’09, and as the roof began to leak in different spots, it was time to replace it. Basically this is a continuation of our previous roof installation review, which we will also use as a guide for homeowners, to help them choose the right roofing contractor and to know what is involved in the flat roof installation.

To read the beginning of this story, refer to our rubber roof repair in Quincy, MA article.

Replacing rubber roof with a new IB PVC flat roofing system:

… As I predicted, the roof started to leak again in the early spring of 2010, but this time it was not the flashing that we installed – the leaking water was coming in at the top of skylights, where rubber flashing was glued to the skylight frame. This time around, homeowners did not want to waste any more money on temporary rubber roof repairs, and wanted to install a lifetime IB PVC roof.

Flat roofing in Quincy Massachusetts

Homeowners chose to install a commercial grade, 80-mil IB flat roofing membrane in red color to match the rest of their roof, which is red asphalt shingles. In the roof specifications we were to remove the old roofing down to the deck – both rubber roof and shingles bellow it. We also installed new skylight curbs for the 4 skylights on the rear portion of the roof – these curbs were designed to increase the slope of the skylights to over 3 in 12, which is the minimum pitch for this type of skylights. The roof was a mechanically attached assembly, over 1/2″ styrofoam insulation. All flashings were color-matching pre-fabbed accessories, using either the same membrane as was used on the roof or the unreinforced 60-mil flashing material.

As we discovered during roof removal, the strong odor in the living roof was caused by the rotting and mold growth in the asphalts shingles layer, underneath the rubber membrane. Once the old roofing was removed, we needed to install the membrane, and also double-flash two skylights the same day, to avoid roof leaks from rains that were forecasted the next day.

The skylights had to be flashed “twice” as they were installed on a curb which was 5 inches wider than than the skylight frame, so we had to bring flashing up, over and then again up to completely seal the skylight, and also install 12 corner flashing on each skylight. This whole procedure was very time consuming, so the first day we worked well into the dark, and had to use flashlights to finish the work that day.

We flashed the skylights to make them watertight, but since skylights were to be replaced, and we were still waiting for new units, we did not install the corner flashings at this point, and used small pieces of unreinforced flashing material to temporary make skylights watertight. Later, as we received the new skylight units, we cut the flashing along the corners, pulled out old units, installed new skylights (which were Velux non-vented units), and reinstalled the corner flashings as well as skylight counter-flashing.

This procedure actually turned the number of skylight flashings to 3, as we had to flash the skylights once again, after swapping old units for new ones. Fortunately, these skylights were already sitting on curbs and had sufficient roof pitch, which allowed water to safely drain down onto the roof bellow it.

Installing IB flat roof on the rear roof section – building and flashing 4 skylight curbs:

All in all, the rear roof was much easier to install than the front roof. To avoid roof leaks between the day when we installed the roof and when we built and installed four skylight curbs and flashings, we simply removed the skylights altogether, leaving a “hole” in the roof, which was covered by a continuous piece of roofing membrane.

Later we just cut out the openings in the membrane and installed the curbs which were build on the ground and also stained from the inside to match the interior trim of the house. This allowed us not to rush with the installation of the curbs and skylights as we knew the roof was watertight.

Once we built all skylight curbs, installed the skylights and flashing, the rear roof was pretty much complete, as well as the rest of the roof. It was now time for some small finishing touches.

We still had to install a PVC-coated steel drip edge, weld a 6″ cover strip to the roof and the drip-edge metal, install all pipe flashing, weld in all inside and outside corners, and re-nail the ceder siding along the bottom of the wall – where roof to wall termination is.

This was a short overview of the flat roof installation and rubber roof repair on this roof in Quincy, MA. However the actual job took more than 7 work days to complete. Between tearing off old roofing, repairing rotten wood, flashing new roof up under the shingles roof, building and installing skylight curbs, flashing 6 skylights and doing the inside trim, this roofing job was very involved. However, we are happy that we spent extra time on this roof – now we know that this roof will not leak in the next 30+ years, and for much longer after that.

To see more flat roof installations that we’ve done in Massachusetts, check out the following roofing job profiles:

Flat roof deck Wellesley, MA – on this roof deck, we installed an 80-mil grey IB roof, flashed multiple railing posts with pre-fabricated post flashing and installed strips of membrane where deck rafters (slippers) will lay, to protect roof from the deck.

Flat & metal roofs in Massachusetts – short reviews of a multitude of flat and metal roof installations in Massachusetts that we installed in 2009 – this review article covers roofs that we installed in Framingham, Westminster, Hingham, Boston, Wellesley, and other cities in MA.


2 thoughts on “Flat roof installation and replacing skylights”

  1. Hello,

    I’m interested in getting two estimates. One is for a roofing structure 14′ tall, 10′ wide in an “L” shape with the long leg being 30′ and the short leg being 20′.

    The second estimate would be for a structure that is 13′ wide and 20′ long and 14′ high.

    We would need these to be capable of supporting snow loads and all the standard New England weather.


  2. existing skylight was coverup with a wooden box and plexiglass. Now the plexiglass cracked. Water in now getting into the skylight and leaking.

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