Ask Andy®

Frequently Asked Questions About Roof Cleaning

Straight Forward and Honest Answers about cleaning your roof. We  will clear up misinformation and sales talk, so you can make an informed choice about cleaning your roof.

Is Bio-Shield safe to use on my roof?

Yes, Bio-Shield has been used commercially and safely for over 40 years and on more than 10,000+ roofs in New Zealand. It is not acidic, not a bleach and not abrasive like pressure washing, so won’t cause any damage to the factory coating, skylights, spoutings, vents, solar panels and other fittings or cause water leaks during the application.

How much does Bio-Shield Roof Cleaning cost?

Prices start from $250 for a  small 2-3 Bdm house with a low pitched Colorsteel roof.
Factors that effect price are the size of the roof, the type of growth,  level of these growths, layout of the roof and height.

How quickly will Bio-Shield clean my roof?

Bio-Shield is a gentle, no damage cleaning method that preserves the factory coating.
The length of time taken for rainfall to remove the dead growths and clean the roof will vary from 3 months and up to 12 months.

Factors that will affect the cleaning time are:

  • The age and condition of the roof.
  • The type of substrate, concrete roofs will clean up faster than Colorsteel roofs.
  • The level of growths  present on the surface, thick, heavy and well established growths will take longer to weather away once treated with Bio-Shield
  • The time since the roofs last cleaning treatment, light re-growths on regularly treated roofs will be removed in as little as 3 to 4 weeks.  

The only way to get a roof clean quickly is to water blast it, or use aggressive (corrosive) chemicals. These chemicals should be avoided where possible as they are unlikely to be an approved cleaning method and may void the roofs warranty.

How is Bio-Shield applied to my roof?

Bio-Shield Applicators are trained and experienced at working directly on the roof to apply Bio-Shield.
Application is by low pressure spray – less pressure than a garden hose, and we do not damage the roof with this application method.

Direct application from the roof is best practice, – it ensures accurate application, resulting in a good quailty clean up.  Applications from the ground, without walking on the roof, do not provide for this accuracy and can have excessive overspray, drift and runoff that can cause problems if not dealt with.

Application from the roof also allows the roof to be closely inspected and identify any current or future maintenance issues.  BRANZ has advised consumers that peridoic maintenace and inspection allows early detection of problems and prevents more expensive deterioration and possible leaks.

Spraying from the ground will not provide this valuable insight into your roof condition.

To use an anlogy, if you engaged a contractor to spray your lawn and he arrived and sprayed all the lawn from the driveway, would you think this was a good job?

Will Bio-Shield on my roof void my warranty?

No, Bio-Shield is completely safe to use on any roof.
Roof manufactures all recommend their roofs are kept clean to extend the service life of the protective and decorative coatings and maintain the warranty

Can I still collect rain water from my roof once its been treated with Bio-Shield?

Yes, Bio-Shield is water based, water soluble and bio-degradable so it is safe to use on roofs that collect drinking water. The storage tank must be disconnected before application and can be reconnected after a minimum of 3 to 4 weeks and at least one day of rain has flushed the roof clear of Bio-Shield residue.

A diverter can be installed on the tank inlet pipe, on above ground tanks to isolate the water tank from the roof and make reconnection and any future disconnections a 15 second task. No need to remove down pipes or fit expensive or ineffective diverters to the down pipes

We do not recommended cleaning a roof over the summer months, from January to March in drier areas, as there may not be enough rain to flush the roof and refill the tank after it is reconnected.

How often should my roof be treated with Bio-Shield?

To maintain a roof in a clean condition, apply Bio-Shield every 2 years.  After 2 -3 years spores that have settled on the roof will begin colonize and become visible. If a roof is treated every 3 years, any light re-growths will be be removed quickly, potentially within weeks, not months. Regular Bio-Shield applications will help to preserve the factory protective coating in good condition.

The micro climate around a roof will have a large influence on timing between the maintenance treatments.

If there are trees in proximity to the roof, the roof is steep pitched or birds habitually use the roof to rest or nest, annual or 2 yearly Bio-Shield applications may be required to keep the roof clean.

My roof was treated by another company and it did not clean up. What happened?

Unfortunately some cleaning applications by companies that claim to be ‘experts’ and ‘specialists’ do not work, leaving live growths or a visible residue behind.

This is becoming problematic in the industry as there are long term effects from these failed applications.  Avoid door to door selling and pressure sales tactics – you have a 5 day ‘cooling off’ period to get out of any such contract and get a full refund,  avoid discount online offers and coupons,  get alternate quotes and then check references and online reviews, ask to see other roofs in your area that have been cleaned by your preferred supplier.
Ask if they are members of a professional association such as RANZ or ECIA.
Ask friends, family and work colleagues if they can recommend anyone.
Beware of companies that unlawfully contract out of the Consumer Guarantees Act – check their terms and conditions carefully for the exclusion, and avoid using these companies.

For your peace of mind   –  Roof Cleaning with Bio-Shield is backed by 37 years of experience, a 2 Year Written Guarantee and RANZ Membership

Does Bio-Shield remove dirt from my roof?

All roofs that are exposed to rainfall are regularly flushed free of atmospheric dirt.
The black marks and discolouration you can see on your roof are actually algae. This algae will be killed and removed with Bio-Shield, leaving your roof clean.
The exception is roofs that are close enough to trees to allow a build up of tree debris.  If not removed, this debris breaks down  into soil and produces slightly acidic conditions that can corrode  steel roofs.

Will Bio-Shield remove pollen?

Pollen is not an organic growth so Bio-Shield will not remove it. The only way to clear pollen is waterblast cleaning – but, this is not necessary as it will clear from the roof naturally with rain. Pollen does get trapped on black algae so a clean roof will not hold as much pollen, and the pollen will clear faster.

Should my roof be waterblast cleaned?

Yes you can , but you should be aware that water blast cleaning uses medium to high pressure – 2000 to 3000 psi, and large volumes of water, between 3000 to 6000L per roof.  Even low pressure water blasting ( soft washing) is 1000 to 1500 psi .
Most roofs are not designed to take this pressure and will leak to some degree during any water blast cleaning or soft washing.
Water blast cleaning is perfect and essential preparation for re-coating as it strips away any loose surface material on your roof, but for just cleaning moss, algae and lichen it’s an expensive way to clean a roof and potentially damaging to the protective coating.

While water blast cleaning gives the appearance of a clean roof, the moss, algae and lichens are not killed and will immediately begin to grow back. Within 12 months your roof could need cleaning again.

Bio-Shield Roof Cleaning is less than 50% the cost of water blast cleaning,  uses 97 % less water and lasts 200 to 300% longer.

Will Bio-Shield kill my plants?

Bio-Shield can not kill plants, it is a surface santizer, not a systemic garden spray or herbicide
It can safely be used on lawns to kill moss and on tree trunks and branches to kill lichen.
In sunny conditions, some delicate leaved plants can get spotting on leaves from contact with Bio-Shield so any affected plants are hosed down after the application.

Edible plants near the roof are always hosed down after the application.
Bio-Shield is fully bio-degradable when in contact with organic matter and soil

Is Bio-Shield harmful to animals and pets?

The active ingredient in Bio-Shield has been safely and continuously used in the the food industry, in hospitals, veterinary clinics and zoos as a hard surface sanitiser for over 60 years.

The only precautions we take are to move feed bowls and toys away from the roof, and flush them out after the application is complete.

Can mould grow inside my roof if its dirty?

No, this is not possible.  Mould does not grow on a roof surface – mould only grows on rotting food or other natural substances that are dead and breaking down, and the genrally dry conditons inside a roof space will not allow mould to grow.  In addition, the type of  algae that grow on the exterior of a roof are not toxic.

Will my roof leak if its not cleaned?

No, it would be very unusual for a roof to leak from being dirty and moss on a roof does not cause leaks.  On concrete and clay tiles, moss in the laps actually reduces wind and water pressure on the lap, stopping intermittent leaks during storms. Longer term erosion of the concrete and clay caused by moss, algae and lichens may eventually cause leaks. If a roof ever gets to this stage, it should be replaced

Will moss and lichen damage the roof structure?

No.  Moss, algae and lichens only grow on the surface of your roof. They do not damage the timber roof frame or structure, they do not cause the timber to rot and they do not move or dislodge roof tiles or ‘jack up’ asphalt shingles

Is Lichen Acidic or Caustic?

Lichen secrets a mild acid to breakdown the substrate it grows on.  This mild acid will affect the surface beneath the growth, leaving visible damage on Colorsteel, Decrabond / Gerard tiles and asphalt shingles and cause longer term damage on alkaline concrete and clay tiles.
Lichen is not caustic (alkaline)

Is there a Guarantee?

When Bio-Shield is applied to any roof we provide a written 2 Year Guarantee on the effectiveness of the application.

This includes all domestic, commercial and industrial roofs.

While there are conditions to this warranty, these conditions are common across all roof treatments and cleaning methods as they relate to the situation, pitch and conditions around the roof, not the quality of the application.

You should be aware of the limitations in keeping any roof clean.
More information is provided in the written quote we supply to you.

Beware of companies that attempt to unlawfully contract out of the Consumer Guarantees Act for domestic roofs – check their contract terms and conditions carefully for the exclusion, and avoid using these companies.