1. Many town and state building codes do not allow more than two layers maximum.  If you have one layer than you would be allowed to add a second layer;
2. Roof shingles must be intact and not broken or curled. See image below:


3. There should be no existing leaks in the roof.  It is difficult to always trace a leak back to its origin since water will travel in the direction of least resistance;
   
   
4. Chimneys and all other transition walls can not be disturbed;
   
   
5. Roof should have proper Ice & Water Shield on original layer.  (It does not make fundamental sense to strip the first 6 feet to install the Ice & Water, you might as well strip the whole roof.);
   
   
6. The original roof has to be a strip shingle (i.e. 3-Tab or Single Tab).  Can not go over designer shingles, for example, architectural, slate imitation, Country Mansion.  Must have a smooth surface for a base;
   
   
7. Cannot replace drip edge on a go-over.  But we can install a wrap-around drip edge to conceal the first layer.
   
   

All of the above items should be met in order to successfully install a roof over an existing roof.  We recommend that the roof is stripped because of the benefits (explained below) and the requirements needed qualify for a go over

Extra Options
3 Types of Valleys
When making the decision to install a new roof you also have a close on the type of valley and product you can use.  The most common valley is a weaved valley.

This is when we run the shingles up to 3 feet under one another up the valley, layering one over the other, thus creating a double layer system.

Then we have a California cut, also know as, a French cut valley.  This is typically used on an architectural roof and has only one basic layer and the second layer is cut in a straight line from the bottom of the valley to the top.

Strip Roof
Performing a strip roof allows for full inspection of the decking and all transition points.  Leaks are typically found in the weakest part of the roof which tend to be chimneys, skylights, transition walls or any other areas that have junctions.  The lack of ice and water and proper ventilation is also known as the culprit for ice dams and icicles forming on the eaves of a house or building.  Below is a list of items we look at during a strip job.

• The condition of the roof sheathing.  For new homes or buildings this is typically plywood or OSB board and for older homes or buildings it is planking or ledger board (spring board).
  
  
• What type of roof deck is on the house – Plywood, OSB board or Ledger plank boards?  Older homes (over 40 years), tend to have planks.  As the house ages, the planks shrink and the spacing between the plants expands.  When this happens, we recommend going over the roof deck with 3/8” plywood.  This prevents misnailing, which is when the nails hit a hollow spot between the planks.
  
  
• The weakest link in a roof is the transition wall areas.  This is where the roof line meets the siding.  If this area is not flashed properly it will leak.  We recommend stripping the transition and installing new Ice & Water shield with new step flashing.  This guarantees the transitions will be water tight under all conditions, rain, wind-driven rain and snow.

Shingle Type
Choosing the type of shingle for your home is easy.  The most basic shingle is the 25 year 3-Tab shingle.  For years this was the only shingle available on the market.  Today, there are over 20 types of shingles to choose from.  The most popular and most cost effective is the Architectural shingle.  This comes in a 30, 40 and 50 year shingle.  The weight of the shingle determines the number of years of warranty associated with it.  There are many shingle types available, please click on the link to GAF to see more.

This home has been fitted with the standard 30-year architectural shingle.

Warranty
GAF and CertainTeed both have a certified warranty program.  We are certified with both manufacturers and the homeowner may choose to purchase an extended warranty.  There are different types of warranties available.  We typically sell the GAF System Plus.

Company Warranty
We offer a one-year warranty which covers labor, installations and material.  All shingles come with a material warranty based on the type of shingle.  For example, the 25 year shingle comes with a 25 year warranty; 30 year comes with a 30 year warranty, and so on.