Best Methods of Attaching a Roof to an Existing Roof

Connecting a new roof to an existing one can be challenging, especially for home additions or expansions. With over 15 years of roofing experience, this guide provides practical steps and insights, supported by research and personal experiences, to ensure a seamless and effective integration.

If you plan to attach a roof to an existing roof, this article will inform you of the know-how.

Drawing from extensive experience in various roofing projects, I provide trustworthy and practical guidance on the best methods for attaching a new roof to an existing structure.

How to Add a Porch Roof to an Existing Roof

Planning to add a porch to your yard? Make sure to install a porch roof as well. Otherwise, you may have to deal with the hot scorching sun or drenching rain.

attaching a roof to an existing roof

First, to add a porch roof, know how the roof pitch will look. In general, people tend to pick an inclined patio roof to avoid water pooling when it rains. With this in mind, you will also be forced to measure the clearance height.

After you determine the clearance height, here’s what you should do next:

  1. If you plan to place the additional roof on the existing roof, you should consider whether to remove the eaves. You can skip this procedure if you plan to place it under the existing roof.
  1. Pick and determine how many beams, roofing planks, and rafters you need for your roof.
  1. You can stain your wood pieces with protective paints before installing them.
  1. If you plan to place a pillar on your patio roof, work on it first after considering the patio’s height. Make sure to make it perpendicular to the ground.
  1. Install the roofing. Starting from the joist, rafter, and later the beams and planks. Consider adding eaves while installing it.
  1. Now, it’s time to apply the roofing felt to protect the roof’s inner side from moisture and such.
  1. Lastly, shingles are on top of the underlayment, and the outer side of the roof is done.
  1. Cover the inner roof side (the ceiling’s side) with plywood, plasterboard, or anything. Apply some paint to beautify it.

Read also: Installing Wood Stove Pipe through Roof

How to Join Two Roofs Together?

  1. Preparing the area. Clean the affected area from debris, including removing the shingles and underlayments covering the roof. No need to remove it all. Make it to the extent of around 6 inches from the edge of every pitch.
  1. Measure the joint area. Make sure to include the 6-inch edge into the counting.
  1. Prepare the flashing joint. Then, cut the flashing material with metal snips according to the size you obtained.
  1. Place the flashing material at the meeting point. Start by placing it from the higher joint area first.  Remember to slip the flashing material to the roof pitch as well.
  1. Bend the joint with the help of lumber to make the shape suitable for the slope. Take away the lumber after you finish making the bend.
  1. Seal the flashing edges afterward. Prepare two pieces of 1×1 inch lumber and cut them with the length of the flashing itself. Then, slip each lumber piece under the roof pitch to align well with the roof edge. Apply a bead of sealant material along the top and bottom of the lumber piece.
  1. Next, secure the flashing with metal screws with 6-inch spacing between each screw.
  1. Make the flashing cut-edge neat. Then, cover the flashing with shingles that look similar to the surrounding shingles.
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Personal Experience

In a recent project, we extended a roof to cover a new porch area. We used the overlapping method, ensuring that the new shingles matched the existing ones for a seamless look. Proper alignment and sealing were critical to prevent leaks and maintain the roof’s aesthetic.

Research and Case Studies

Research indicates that using metal flashing and proper sealing techniques can significantly extend the lifespan of an attached roof. A case study demonstrated that roofs attached with the interlocking method performed better in high-wind areas due to enhanced stability.

Read also: How to Attach Roof Over Deck From House

“Using metal flashing and ensuring proper sealing are essential for extending the lifespan of an attached roof.”

Common Challenges and Solutions

Alignment IssuesUse a chalk line and level to ensure proper alignment
Leaks at the JointApply high-quality roofing sealant and flashing at all joints
Material CompatibilityEnsure the new roofing materials match the existing ones


Attaching a new roof to an existing one requires careful planning and precise execution. You can achieve a durable and aesthetically pleasing result by following the methods and steps outlined in this guide and leveraging my extensive experience.

Proper preparation, quality materials, and attention to detail are key to a successful project.

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Roofing Expert is an experienced author and roofing expert. With years of practical experience in the field authored several informative articles on various aspects of roofing, including installation, maintenance, and repair.