Reasons not to put shingles on top of shingles starts with knowing what asphalt shingles and any roofing material is meant to do first. As a general rule of thumb, if that roofing material isn’t able to serve that purpose anymore, it will cause the roof and home some form of damage.
Asphalt shingles are meant to adhere flat to the roof deck in order to provide the most protection from the outside elements; sun, rain, wind, fire, lightning, debris and storm events. This allows it to:
- easily help water run-off the roof,
- prevent wind from pulling off the shingles from the roof,
- insulate the roof to dry it up quickly (and keep the home’s interior at a moderate temperature)
- and durable enough to prevent debris from breaking through the roof easily.
Depending on the type of shingle, with today’s roofing technology, there are a whole host of more capabilities these shingles can provide that were not discussed here.
Except none of this is possible when shingles are layered on top of one another, defeating their purpose essentially. In how many layers of shingles are allowed, it’s generally accepted to have two layers but at roofing mission (a.k.a “BulletpRoof”) we recommend one layer max. Simply because one layer of shingles does a better job than any number of layers of shingles any day of the week.
Although the short-term cost savings of layering shingles may be enticing, it’s important to realize the numerous reasons why this is a bad idea over the long-term.
Below these reasons are categorized appropriately for the reader:
- Roof Installation Issues
- Roof integrity
- Structural and Home Integrity
- Maintenance Issues
- Building Code Restrictions
- Warranty Issues
- Insurance Issues
- Lowers Real Estate Value
- Conclusion About Not Layering Shingles
Roof Installation Issues
When layering shingles on top of one another, the roofing installer only completes a limited number of steps while skipping other steps; Specifically, they skip the tear-off, disposal of the old shingles and roof deck repair steps. Which are the leading causes for issues with the roof installation.
- Dependent on the Previous Installer’s Workmanship – Current installer depends on how well the previous installer did with their installation of the roof. Trusting that all leak prevention measures were installed correctly. This means all flashing, ice and water barriers, underlayment, drip edge and old shingles have been taken care of. Which is a big “if” from our experience.
- Roof Deck is Never Exposed – A roofer and a homeowner can’t know exactly what kind of damage has been done to the roof deck since the previous roof replacement without tearing off the shingles. Leaving the condition of the roof deck unknown until a future date when it could be too late. When layering shingles, tearing off and disposal of shingles are canceled to save the homeowner costs on the installation.
- Protection between the Shingles and Roof Deck aren’t Replaced – Ice and water barriers, roofing underlayment (synthetic, felt, etc.) and flashing protecting the surfaces may be missing or damaged. These could be or could not be protecting the home currently, it’s unknown, meaning there could already be leaks (minor or major). Without addressing these it’s likely to worsen over time.
- Underlayment Can Be Left Exposed – Underlayment has a 20 year lifespan under properly installed shingles, when exposed this is cut short making it into a brittle paper which offers no protection. An installer who is layering shingles will try to hide this, it’s best to notify a professional when a homeowner notices this issue. Most likely there will be a leak sometime in the future.
- Flashing is Considered to be in “Good Shape” – Flashing on the surface is considered to be in “Good Shape” by the roofer, while it is assumed that the portion of the flashing under the shingles is also in “Good Shape”. Flashing’s purpose is to protect sensitive joints where leaks are most likely to happen in the first place. Meaning at a glance it may look fine but could be leaking already.
- Can’t Install New Flashing – Since there is no tearing off of the shingles, no new flashing can be installed. This goes back to trusting the previous installer but the new installer will try to sweep it under the rug; that new flashing isn’t needed. It sounds minor, but it could become a costly major repair in the future for the homeowner.
- Requires a 4:12 Pitch Roof – This isn’t a steep roof meaning with minimal fastening the new layer of asphalt shingles will generally stay on the roof; Any steeper and there will be missing shingles shortly after installation. The problem is that no matter what the installer does, there will be areas for water to accumulate and this will cause damage to the roof (and home). It’s inevitable.
- No Prep Work, Only Installation – The installer will skip the prep work of protecting parts of the home like they normally would and begin laying the shingles immediately to save time. Meaning in a few short hours the installation will be done at the cost of leaving behind roofing materials and debris that aren’t their problem anymore. A safety hazard for people and vehicles that are completely avoidable.
- Skip using Architectural Shingles – Ridge shingles, starter shingles and any pre-bent (fitted) shingles will not be replaced in the installation. These shingles are thicker for protection, help with the ventilation and prevent water from entering sensitive areas. Meaning the original shingle that has deteriorated and is no longer doing its job will be forced to keep going. Spelling trouble in the form of higher energy bills and worse a major repair to the roof’s framing (on the peak and its overhanging drip edge).
- Roof’s Age is Unknown – An experienced roofer can spot signs of damage to the roof and will try to determine the age of the roof, but they will only know by luck. Meaning multiple roofers will provide different estimates and one will eventually recommend a replacement or another layer since the roof looks aged. More of a roofing scam tool used to sell roofs to inexperienced homeowners.
- Layering Shingles isn’t Always Possible – Depending on the roof’s valleys, intersections, steepness, etc. it may not permit a second, third or fourth layer of shingles. Layering shingles may result in missing shingles, leaks, nails and fasteners missing and worse damage to property. Homeowners beware the installers who don’t consider this in their estimate, it’s a safety risk that should be avoided at all costs.
- Shingles are Designed for Flat Surfaces – Reiterating from earlier, shingles aren’t meant to bridge gaps, dips or bumps on the surface below. This only deteriorates the shingle on top faster (shortens its lifespan), allowing water to slip underneath it easier, causing leaks and insulation issues. Which is all bad news for the homeowner because it shouldn’t do that.
- Shingle Fasteners Aren’t Long Enough – Already assuming the roof deck is in “Good Shape”, sturdy enough to hold a nail in place, and that the nails are long enough to reach the roof deck. All this means is that no matter what the installer does, there will be missing shingles, fasteners will fall out of place and there will be exposed old shingles below.
- Mixing Roofing Materials – An installer can install a layer of asphalt shingles on cedar shakes, slate tiles, clay tiles, metal panels, rubber panels, etc. It’s possible and has been seen before, never recommended. As it will trap water even better than shingle on top of shingle, leading to hidden leaks in the roof one day.
- After Installation the Roof Won’t Look New – At the end of the day, the installer is layering new shingles on old shingles so it’s going to be bumpy and there will be exposed old shingles. The homeowner will have to live with a “semi-new ish” roof after the installation is complete.
- Ultimately Delays Tear-Off Costs – When considering going past two layers into the three, four and beyond range it’s highly recommended to tear-off the shingles and go back to one layer. What happens as a homeowner continues to add layers is they are delaying the cost of tearing off the shingles and it gets more expensive with every added layer (both in labor and disposal).
- Forced to Work with Multiple Roofers – After facing one incompetent roofer after the next, its difficult to know the state of a home’s roof and is especially frustrating for the homeowner. Meaning parts of the roof may be up to code, while others are not, until a qualified roofer can complete the installation correctly. Making the installation expensive as each roofer makes their attempt at the roof.
The roof integrity suffers when shingles are layered on top of one another as the shingles are no longer beneficial to the roof’s integrity. Instead it helps to trap water and heat between the layers of shingles which leads to a host of issues with the roof’s integrity; Where it should’ve been helping the roof to insulate properly and act as a barrier against the outside elements, along with helping rain water to easily run-off into the gutters.
- Cuts the Roof’s Lifespan Short – Asphalt shingles are meant to remain cool and dry, when they are layered they remain wet and hot because they trap water and heat between the many layers of shingles. Where the older shingles will help the new shingles to deteriorate faster, halving the life of the new shingles or worse depending on the condition of the roof.
- More Layers, Doesn’t Mean More Waterproof – This is not true, as it compounds the damage under the top layer of shingles making it less and less waterproof. Meaning if there is water damage under the top layer of shingles it will continue to get worse and will make the top layer useless in the end.
- Each Layer adds Weight, it’s like adding a second or third roof; For example, an average 30 square foot roof requires 90 bundles of shingles. Each bundle weighs about 100 lbs, adding roughly 9,000 lbs of additional weight for each layer. It’s concerning as most residential homes can’t handle this weight; Additional stress on the roof from heavy rainfall or snowfall could cause the roof deck to cave-in.
- Multiple layers of shingles traps heat between shingles, instead of insulating and moderating its temperature like it should. This trapped heat promotes condensation under the shingles, together reducing the new shingle layer’s life in half.
- Hide Problems with the Roof – There could be leaks and damage underneath or between the layers of shingles that aren’t visible to the human eye. Slowly these can eat through the roof without any chance for the homeowner or a roofer to pinpoint where the leak even started from.
- Cheap Shingles Among the Layers – Inexpensive shingle brands are generally thin and easy to damage paired with an inexperienced roofer who selected warped shingles from the bottom of the pallet is a problem. Other than being difficult to install, these shingles will deteriorate faster due to wind, rain and the older shingles underneath it. Making the roof’s age more of an unknown to the next roofer.
- Promote Organic Growth – Trapping water and heat will inevitably lead to moss, mold, algae and rot to set in. It’ll be happening between the layers of shingles, to the roof deck and inside the home. Slowly creating openings for water to creep through right under the homeowner’s nose; Allergies being set off (breathing issues), higher energy bills, black water streaks and/or bulging walls may give hints to the homeowner.
- Wind, Weather and Storm Damage – Insecure shingles and bumpy shingles will catch more wind and water during these weather events. Leading to missing shingles, missing fasteners, leaks and openings for debris to damage the roof. Due to the added weight of the shingle layers, the storm weather could strain the roof to cave in.
- Snow and Ice Dams in Colder Climates – Aside from the snow weight putting more strain on the roof, the snow melt will easily create ice dams on the bumpy roof surface. These ice dams will seep through the old shingles and cause severe water damage if not dealt with as soon as possible.
- Animal Intrusion – More opportunities for animals to dig or chew through the roof, or possibly find a hole to crawl through. Once animals are in the home, there are droppings, the chance of baby animals and worse they will enter into the home through the attic. Range from rodents to small birds, and larger local animals like badgers or raccoons.
- Bats Nesting in the Roof – With the trapped heat and water in the layers of shingles, this creates optimal conditions within the attic for bats to hibernate or make their home for the season. When the homeowner is made aware, speaks with a roofer and a roofer discovers bats they’ll have no choice but to report them to the authorities. Since bat species are on the animal protection list in different areas the roofer will have to stop work and the bats will not be forced to evict; it may be the homeowner that has to leave in some cases.
- Hot Summers or Weather – Layering of shingles, heat and moisture being trapped between the shingles and the sun’s rays are a bad combination to have for your home. Resulting in faster deterioration of the new shingles (fading, becoming more brittle, etc.) and the UV protection will eventually offer no protection from the sun. Only helping to heat up the home excessively in the summertime and easier to damage the roof in a storm event.
- Soft Roof Decking will Show – When the roof deck goes soft it will cause parts of the roof to appear to be sagging which will help water to pool and leak through the top more easily. This is a problem because water damage has already been done to the roof deck and it will only continue to get worse. Unless the top layers of shingles are torn off and the roof deck is replaced.
Structural and Home Integrity
The structural and home integrity relates to the vital systems inside the home that the roof protects from the outside elements. These are the electrical, plumbing, HVAC, framing and foundation of the home which suffer when these outside elements come in contact with them over time. Due to the layering of the shingles, it creates obscure leaks and helps to trap moisture in the attic which helps to break down these other systems.
- Leaks are Worse – Leaks will be difficult to find and be happening unnoticed by the homeowner, but once a leak has become more visible it’s already too late; it means the roof is way past the time to replace it. Replacing the roof is the only solution at this point, along with any of the home’s vital systems that have been damaged too; The home’s vital systems include roofing, framing, electrical, plumbing, HVAC and foundation.
- More Prone to Leaks – Due to the bumpy surface of a layered shingle roof, it will help to accumulate water in different parts of the roof and even redirect it to sensitive areas of the roof which will leak. These can be obscure leaks, least expected, leading to a whole host of issues throughout the home. When there is a musky smell, dark streaks or other signs of a leak, it’s too late already.
- Lack of Insulation – Instead of insulating, layering shingles will trap heat and moisture within the roof. Causing the layers of shingles to deteriorate faster while assisting with deteriorating the attic and roof at the same time; Leading to fluctuating home temperatures, normally in the extremes, and higher energy bills to moderate the temperatures.
- Roof Framing and Home Framing Damage – Leaks, moisture build-up and a lack of insulation will cause issues with the roof and home’s framing. Leading to organic growth and water eating through the home’s trusses, causing the home/roof to sag over time; Potentially leading to a cave-in if not repaired in time.
- Short Circuits and Electrical Damage – The water that is trapped between the layers of shingles is rain water, impure and filled with minerals, which is a good conductor. Meaning a leaky roof can cause electrical problems; When these leaks reach the home’s wiring or worse the circuit breaker it could short circuit the home.
- Piping and Plumbing Damage – With the fluctuating temperatures and added moisture trapped in the home, it will cause the pipes to expand and contract more rapidly. This will result in the pipe joints to become damaged and/or develop cracks along the plumbing system. In odd times, causing sections of plumbing to sit out of place, backed up air bubble sounds or sewer smells to enter into the home; Older homes retrofitted with copper pipes will experience this sooner than newer homes with PVC pipes.
- Water Run-Off will Skip over the Gutters – Water run-off should travel directly into the gutter, with bumpy layered shingles it’s more likely to travel over the gutters. This not only prevents the gutters from doing their job of directing water away from the foundation of the home. While sending more water to the home’s foundation; This will damage the home’s foundation potentially flooding a basement, damaging siding and fascia, damaging landscaping and even allowing water to seep into the home.
- Repurposed Home Increases Incompatibility – Think of it this way a home is designed to handle so much airflow, water flow, electrical current and generally handle a set amount. When the home is repurposed for whatever reason and it isn’t designed to handle those requirements, it will only shorten the life of the home. In combination with layers of shingles, both elements will work against the home to shorten its life in the long-run.
Regular roof maintenance is always a good idea, except when the roof has layers of shingles on top of it because it has many hidden risks associated with it. Potentially making basic maintenance tasks a homeowner can take care of themselves to a degree with some help from a professional here and there. To become a risk of injury that the homeowner should actively avoid.
- Walking on the Roof is Risky – Without a solid roof deck, it’s not recommended for a homeowner to walk or perform maintenance on the roof without safety equipment. They’re risking the roof breaking and injuries that are all avoidable. Keep in mind, the roof deck may be soft where you least expect it. Instead it’s recommended to use binoculars to inspect the roof from afar.
- Inspecting for Leaks from the Attic – Using a flashlight on a rainy day, checking for water dripping, water stains, dark streaks, musty odors, etc. While cleaning out the ventilation systems or addressing malfunctions is recommended. Except it may be difficult to track down the source of the leak due to layered shingles misdirecting the source of the leak. Meaning any minor repairs may be not to the actual place water is leaking from.
- Organic Growth will be Difficult to Remove – Layering shingles makes it easier for mold, moss, algae and rot to grow under the shingles; These are neve supposed to get under the shingles under any circumstances. In any case, washing and scrubbing these off will only damage the shingles more, helping it to get further underneath the shingles. It’s a vicious cycle.
- Only Spot Pressure Wash the Roof – It’s possible to pressure wash the roof on a lower wider setting, except it’s not recommended due to the pressure it puts on the layers of shingles. It will help to loosen the top layer of shingles that are already barely fastened because the nails aren’t long enough to reach through the layered shingles and the roof deck. Unfortunately, this will only help to remove a shingles granules, damage shingles and force water between the shingle layers; Speeding up the deterioration of the new shingles on top.
- Damaged Flashing Can’t Be Replaced Easily – Unless the layers of shingles can be removed, replace the flashing and new shingles can be installed, it’s not possible. Even when the replacement was successful, the new shingles will either be lower or higher than the original layers which will only assist with accumulating water in these areas. Not recommended, as this will cause the flashing area to become more prone to leaks; This goes for valley flashing, roof protrusion flashing and chimney flashing all alike.
- Replacing Damaged Shingles – Normal practice is to replace any curled, cracked or broken shingles, except with layered shingles this isn’t all too helpful. By replacing these shingles, the new shingles will extend the life of the damaged spot of the roof but will quickly deteriorate regardless.
- Homeowner Needs to be More Aware of the Home’s Interior – The home won’t display the most obvious of leaks, instead it’s more likely to show bulging patches on walls, rooms will lose their squareness, musty odors will become prevalent in specific rooms, etc. Water damage will be isolated to specific parts of the home where it has the easiest access and it’s the homeowner’s job to notify a roofer when they see a change. Once a leak becomes visible, it’s too late and a roof replacement is needed.
- Hints of Water Accumulation – Look for ice dams in the winter, water accumulations during rainy months and areas of missing shingles, normally are culprits for water damage. Not as easy when visually inspecting a layered shingle roof as the bumps could literally block water and ice as easily as it could direct it between the layers of shingles; Shingles are meant to lay flat, on a bumpy surface these shingles form bridges for gaps and in turn create gaps for water to enter through.
- Careful when Cleaning the Gutters – It’s possible water has seeped into the fascia behind the gutter, making it soft and unstable. Making a leaning ladder unsteady to place against it and the person cleaning the gutter can’t apply much force themselves to clean them, without risking the fascia to break. Friendly tip, repairing fascia is a horrible situation to be in, avoid it if possible, and do your best to do this safely.
- Avoid Using Harmful Products to Clean the Roof – An eco-friendly alternative as opposed to a bleach (corrosive) product, as this will only help create additional damage to the roof and home. Water run-off will carry it between the shingle layers, into the roof/home’s framing, and onto the landscaping, damaging them all in the process.
- Careful Clearing Debris – Normally, a garden hose and a leaf blower would do the trick. Unfortunately with layered shingles, we don’t recommend doing this because it’s only loosening the shingles and putting more water between the shingle layers. Remove the large debris if anything and leave the rest to avoid injuring yourself by stepping on a soft section of the roof.
- Inspecting and Cleaning Gutter Downspouts – Due to the unknown age of a layered shingle roof, it’s likely to have shingle granules littered in these areas and may get clogged on occasion. This is telling the homeowner a layer of shingles or all of the layers has reached the end of its life, which is largely unknown; Along with the fact that debris, shingle granules, grime, etc. are clogging the gutter downspout which will lead to water dripping and damaging the home’s siding. Reason being the bumpy shingles on top will help water to run over the edges of the gutter, drip along the sides of these downspouts and eventually loosen their brackets from the siding.
- Applying Coatings will have Limited Effect – When shingle coatings like its UV coating wears off, there are sprays to re-apply this coating to maintain the protection longer otherwise the shingles will need to be replaced sooner; Especially for those living in hotter and sunnier climates, where the sun affects the shingles even more. Except with layered shingles, applying a coating will offer limited protection to both the new and old shingles, inevitably wearing off quickly; This is due to the shingles trapping water and heat between the layers, constantly eating through the shingles.
Building Code Restrictions
Building code binds all contractors to a set of best practices which holds them accountable when the workmanship isn’t done right; As it can result in serious damage or injury if not done correctly. Some roofing contractors choose to ignore them, advising the homeowner that layering shingles is acceptable and complete the job quickly to pocket a few extra bucks. This hurts the homeowner because upon inspection, they will be penalized with having to replace their roof again depending on the home’s building code restrictions.
- International Building Code Requires a Drip Edge on Every Home – Without exposing the roof deck, a roofer can’t assess the drip edge and fascia it protects for damage. This is a serious concern because all water run-off instead of being directed away from the home is now entering the home. Be warned, this is an immense amount of damage that is possible if this happens.
- Local Building Code May Not Allow Layering Shingles – High storm risk areas will have strict building codes against this because high winds or heavy rain could get the roof torn off or caved in.
- Unqualified Roofer Neglects Building Codes – Commercial and residential roofers with the proper certifications, legitimate roofers will know these building codes and get the required documents for you in a timely manner. While there are other roofers who know the trade, uncertified or are unprofessional, will most likely bypass building codes leaving it for the homeowner to deal with it.
A warranty helps a homeowner to request repairs or replacements in the case of the roof getting damaged. Except this is not honored when shingles are layered because it is considered bad practice and the roofing materials aren’t able to perform as well as they should anyways.
- Disqualifies Manufacturer’s Warranty on New Shingles – Disqualifies material warranty, pro rated enhanced warranty and contractor’s workmanship warranty. For example, 3-tab asphalt shingles come with a 25 year warranty, architectural 30 year warranty that’s pro rated 10 years after coverage ends. Further, if a roofer uses all components from one manufacturer the homeowner receives a 50 year non pro rated warranty and contractor’s workmanship warranty.
- Disqualifies Workmanship Warranty – Normally a 5 year workmanship warranty is provided with a new roof, depending on the roofing company. Meaning if there are any problems with the roofing installation, the roofer will take responsibility for the repairs and make sure it’s done right; If not, they will pay for another roofer to handle the repair on their behalf. When layering shingles, it’s a one and done deal unfortunately.
With insurance, providers are specific as to which cases they will cover and to the extent they will cover in the event something does happen to the home and roof. Largely provider dependent but generally they don’t provide coverage if the roof has layers of shingles, which is a problem for the homeowner.
- Disqualifies Insurance Coverage for Damages – Depending on the provider, any layering of shingles will not be paid for by the insurance company. Reason being, there is an additional cost of labor to tear off each layer of shingles and replace each layer of shingles.
- Insurance Carriers Require a Roof Inspection – Insurance factors in the age of the roof, the condition of the roof and the cost of replacing it when the time comes. Making a roof inspection mandatory to find this information out for them, but if they find layering of shingles to be indicated they aren’t going to provide coverage. Aside from the additional labor and tear off costs associated with replacing the roof, the rest of the home’s vital systems (roofing, framing, electrical, plumbing, HVAC and foundation) may be at risk too. Making them unwilling to cover every kind of damage that could be involved.
- Expenses for Damage will Come out of the Homeowner’s Pocket – A homeowner will be required to pay for the repair expenses in full in most cases, depending on the carrier and where you live it is subject to change. They will provide specific reasoning as to why each case isn’t covered by the insurance provider, offering limited coverage in cases. Otherwise its expected for the homeowner to find the appropriate contractors and complete the repairs themselves without any help.
Lowers Real Estate Value
Due to the home inspection and visual appearance of the roof after layering shingles on top of one another, this lowers the real estate value of a home; Increasing listing times and the cost of repairs a prospective home buyer would have to incur in order to restore the home real estate value.
- Lack of Curb Appeal – The visible imperfections will stick out like a sore thumb, with both visible bumps from the layering of shingles and old shingles showing through the new shingles. This will only help to deter prospective home buyers and lower the home’s value as a result.
- Home Inspector will Report Multiple Layers – When this is reported, the prospective home buyer will have to add a roof tear down into their cost of buying the home. Along with any other related damage the roof has caused to the home’s framing, electrical, plumbing and/or HVAC systems, in the form of hidden costs. Depending on the homeowner’s level of research into the home, as this is a surface level of everything in the home.
- Requires an Additional Roof Inspection – A general home inspection will reveal a rough estimate of roof related costs, while hiring a specialized roof inspector who will provide an in-depth actual estimate on the entire roof system; a roof inspection on its structure, workmanship, roofing material and the interior of the home. Indicating whether the damage done by layering shingles was caught early enough to replace the shingles with a single layer and not too late that the entire roof’s framing doesn’t need to be rebuilt from the ground up, before any shingles are laid. Lowering the home’s value in order to compensate for these repairs in the process.
- Other Specialized Inspections – A roof protects the rest of the home’s vital systems and when it is compromised due to layering shingles, it puts the other systems at risk; A home’s vital systems are its roofing, framing, electrical, plumbing, HVAC and the foundation. When a roof isn’t insulating and waterproofing the home as it should, it causes leaks that eat through these other interconnected systems and will suffer damage too. Making it necessary to be inspected by specialists to catch the damage as early as possible. These too will lower the home’s value due to the expensive nature of these repairs.
- Relisting a Home – Homes that are on sale a long time or continue returning to a sale status are considered questionable homes as realtors would suggest; Building a negative reputation in the home buyers market. When they are relisted through another real estate agency there are costs associated that the homeowner will incur. While prospective home buyers will actively avoid these listings in favor of a more suitable home even though it may cost them more.
Conclusion About Not Layering Shingles
There are many reasons to not layer shingles, except they all relate back to a roof not being able to insulate and protect the home like it was designed to do. With today’s roofing technology, one layer of shingles is all a roof needs and it is incorrect to think the more layers a roof has, the more protective it will be.
Keep in mind, anytime a roof has an opportunity to accumulate water it will and it will inevitably leak at some point in time.
When new shingles are layered on top of old shingles which are curled or damaged, they become bumpy and form gaps. Helping water to accumulate on top, between and below the layers of shingles, while trapping heat at the same time. Whereas shingles are meant to remain dry and cool to ensure their longevity, that no longer is possible; Shortening the life of the new shingles in the process.
As a result, layering the shingles only damages all of the home’s vital systems in the process; The home’s vital systems include the roofing, framing, electrical, plumbing, HVAC and foundation of the home.
Which is why it isn’t supported by manufacturers, insurance providers, professional roofing contractors, real estate agencies and building code regulations; Depending on where the home is located and their associated parties who are regulating these processes.