Roof-Mounted Solar Panels

The ideal orientation for a solar panel installation is facing south where optimum energy production will be achieved.  If your roof faces east or west your overall energy production will typically will be 10 to 25% lower compared to a south-facing.  On sloped roofs, the rack supporting the solar array is usually flush mounted for aesthetic, cost and structural reasons.  The annual energy production is also dependent on the tilt angle of the array (and roof).

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Common Roof Types

Common Roof Types

Tick Tock Energy has installed solar systems on all types of metal and shingle roofs.   The rack for both applications is similar and the main difference is the connection between the rack and the roof surface.  Common roof types in Illinois and surrounding Midwest states are:

  • Shingle roofs
  • Metal – standing seam
  • Metal – panel type (corrugated)

Shingle Roofs – Age Considerations

Shingle Roofs – Age Considerations

If your shingle roof in newer and has many years of life left, it’s a good time for solar now.  If your roof is older and near replacement, you should consider replacing the shingles first or do the solar and roof upgrade at the same time.

However,  With the 30% federal tax credit available (in 2016 through 2019 and then declining in 2020 and beyond) you may want to accelerate your roof replacement project and not delay.  In some markets like Illinois, the solar renewable energy credit (SREC) is something you don’t want to miss out on either.  Don’t let an old roof replacement project hinder your solar plan and the savings you will otherwise miss!

How Solar Panels Are Mounted to a Shingle Roof

How Solar Panels Are Mounted to a Shingle Roof

A common approach is fastening an “L-foot” or elevated block to your roof that is solidly anchored into the center of the truss below the roof deck via lag-bolt.   The L-foot or elevated block forms the structural base and is surrounded by a thin metal flashing system that tucks under a preceding shingle preventing water from reaching the L-foot.  The lag bolt anchoring the L-foot is equipped with a rubberized grommet that compresses around the bolt and around the hole penetrating the roof deck providing a waterproof installation.

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Mounting Solar Panels to Metal Roofs

Metal roofs are common on homes, farm buildings and commercial buildings in many areas of the US.  Mounting a solar array on these types of roofs is similar to a shingle roof with exception of the roof attachment mechanism.  Two major metal roof types exist:

  • Metal standing seam
  • Metal panel or corrugated type

Roof Setback Considerations

Roof Setback Considerations

When planning your roof installation a 3-foot setback around all edges or peaks of the roof is a good practice.  This reduces the overall area available for capturing solar energy but has both structural and fire protection reasons.  Some solar installers will ignore these issues.  Code or no code, we follow this practice.

Fire Code / Access Around Your Solar Array

Fire Code / Access Around Your Solar Array

In some parts of the country, fire codes require a setback from each roof edge for fire safety personnel to access to your rooftop.  This does reduce the available area for solar and can result in a smaller array.  Although your local jurisdiction may have not adopted the current fire code, its good probability they eventually will.

Although some solar companies will encourage building close to the roof perimeter, you may want to reconsider this advice.  Caution!  If your home ever experiences a fire, you don’t want your solar array to hinder the work of fire protection personal.  Furthermore, we also consider that where this code doesn’t currently exist, that one day your insurance company could scrutinize this factor in the future (just like insurance companies now penalize folks with old electrical service panels & wiring).

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Structural Engineering Considerations

Having a setback from the roof edges is also very important for structural engineering reasons too.   In many projects, we’ll have our structural engineer advise on truss loads, reinforcing requirements, and similar matters.

Your rootop solar array installation may be in place up to 30 years and longer.  The solar array (and roof) will take a beating from mother nature) and  must stand up to high wind, hail, rain, snow, sleet, etc.   The perimeter zones around your rooftop are exposed to the greatest forces during high wind and thus areas to try and avoid locating panels.

A 3-foot setback as a general “rule-of-thumb” will generally keep your solar array away from these areas of high wind turbulence and extreme forces.  The figure on the left illustrates the “caution” zones that are determined by a structural engineering analysis.  Placing panels in this area is possible but may require additional reinforcement.

Truss / Roof Reinforcing

Truss / Roof Reinforcing

In metal pole barn and wood-framed building applications, we occasionally need to bolster the trusses with additional lumber.  High winds on a solar array exert positive or negative pressure requiring a strong roof structure to counteract these forces.  The additional weight of a solar array along with positive and downward wind forces may necessitate adding additional lumber to reinforce truss joints, members and attachments.  This is often not required but a consideration.

More frequently required is the need to use metal ties underneath the roof to reinforce the purlin attachment to the truss.  Purlins are usually nailed into the roof trusses and nails alone typically don’t resist the pull-out forces that increase after solar is added to a rooftop under high winds.  A metal tie provides an extra connection to secure the purlin to roof truss.  We typically add one metal tie near each L-foot used for the solar array rack.

Overall, the added reinforcing is a small extra cost but an important factor to protect your roof and solar investment over the long term.

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