Pitched Roofs (Houses) - Part 2 – Moss Growth and Flashings

It is worth spending the time to look closely at a roof, from a maintenance point of view, for those living or occupying a property and from an investment point of view for those thinking of acquiring, disposing of, or leasing property

Source: http://www.mgcltd.co.uk/

In my previous article (Link) I discussed what an important component a roof is to a building and that to be effective it needs to be weather and watertight, and if deterioration starts to occur it can affect many other parts of a building and ultimately, a roof is often one of the most expensive components to repair or replace. It is therefore worth spending the time to look closely at a roof, from a maintenance point of view, for those living or occupying a property and from an investment point of view for those thinking of acquiring, disposing of or leasing property. In last week’s article I discussed sagging roofs and provided some examples of likely causes and what to look for and for the purposes of the remainder of this article I plan to discuss moss growth and flashings and identify some of the things that I would look for when carrying out a survey to a traditional timber pitched roof to a low rise domestic building (for the layperson I am referring to a typical house).

Moss Growth – ‘vegetation’ or ‘deposits’ can appear on the surface of a roof in many forms and the type of vegetation or deposit will be determined by a number of different factors.  Typical terms used to describe these are lichen, algae, fungus or moss growth.  Limited presence or absence of sunlight on a roof surface is often an influencing factor in the amount of moss or lichen growth. Usually there will be less growth if there is regular sunlight, so consequently when there are shady and cool/moist conditions, the presence of moss/lichen growth is more likely.

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Apart from looking a little unsightly the impact of small deposits of moss/lichen on a roof surface are likely to be insignificant.  However, valley gutters, rainwater gutters, downpipes, hoppers and other outlets should be regularly checked to ensure that deposits, which may detach from a roof surface, are not allowed to block the rainwater system. If on the other hand, deposits are allowed to develop and cover larger areas of the roof surface then this can have a more detrimental effect to the building. Moss/lichen growth on roofs in large deposits have the capability of holding surface water and moisture and as such will keep the roof surface moist and cool in the areas where it is present.  This can also result in the internal surface temperature being cooler than it would normally be, creating an environment with an increased possibility of condensation occurring in the internal roof space.  Consequently, this can introduce moisture into a roof space which can be the catalyst for quite a number of other building problems.  You can view my previous article on condensation by following this (Link).  During colder periods of the year and moisture held within moss/lichen deposits may freeze causing expansion (when water freezes it expands and therefore increases in volume).  This can introduce stresses to the roof surface underneath and can damage or even displace roof tiles, particularly where water is trapped in the moss/lichen at the junction or under the ‘lap’ of roof tiles. 

Therefore moss/lichen growth on as roof surface may look innocent enough however it can be seen from the information above that it can be quite problematic if it is not dealt with.  Caution should be taken when removing moss/lichen deposits from a roof from a personal safety perspective (particularly safe access), as well as the method adopted to remove any deposits. After all it would be pointless clearing the deposits and then damaging the roof surface in the process.  The use of a high pressure water jet for example will damage certain types of roof tiles so always carry out some research before deciding on which method to use.

Source: http://metalrooftodays.blogspot.co.uk/

Flashings - When any part of a roof meets a vertical surface or abutment such as an extension, dormer window or a chimney stack etc. the joint between the vertical surface and the roof covering needs to be completely water tight to prevent moisture ingress. Nowadays, lead is commonly used however in older buildings zinc, aluminium, slate, tile and even cement mortar were used in these locations.  Whilst undertaking surveys, flashing are a vulnerable point within a building and it is common to find evidence of damage and deterioration to flashings as well as signs of moisture ingress internally.  It is always worth looking closely inside a building at the underside of where flashings are located externally, looking for historical signs of moisture ingress such as staining in addition to areas that may be visibly damp, peeling/blistering of paint and finishes and other signs that there may be a problem with the flashings.

Things to look for include evidence of temporary repairs around flashings including the use of ‘flashband’, which is basically a bitumous tape.  The use of flashband should never be considered as a permanent solution and in fact it will not be long before moisture ingress starts to re-occur unless a more substantial repair is not carried out quickly.  To a Surveyor, flashband screams out problem!

Source: http://www.1stassociated.co.uk/

The use of cement based mortar as a flashing is also inadequate and should be replaced with something more substantial.  The whole point of a flashing is that it should be watertight.  The problem with using mortar is that it is porous and therefore has the ability to absorb moisture, which can easily find its way through to the surfaces below. As discussed with moss growth above, any water or moisture that is trapped within the mortar will expand if it freezes and this can cause the mortar to crack, move and even fall away. This will expose the junction it is trying to protect to further moisture ingress.  

A Surveyor will also commonly see problems associated with roof flashings which are a result of poor workmanship. The reasons for poor workmanship are wide but will include cutting corners to save money, use of inappropriate materials, lack of knowledge and understanding, ‘getting the job done quickly’, if it’s out of sight, it’s out of mind’ etc.  I used to think I’d seen it all however there was always something new just around the corner that I had not seen before!  Whatever the reason, poor workmanship creates a lot of problems in buildings and something that I am sure will continue to do so in the future.  The photographs below provide some examples of poor workmanship of roof flashings.

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Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Pitched Roofs (Houses) - Part 1 – ‘Sagging’ roofs

If the surface of a pitched roof is not perfectly level or straight then this can give the impression that there is a serious problem.  Whilst this can sometimes be the case it is not true in every situation

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Regardless of an individual’s knowledge of property/construction there is always one part of a building that seems to raise increased concern and that is the roof.  Whilst undertaking surveys I often get asked questions about all sorts of different things however when it comes to the roof there appears to be a great deal of trepidation and anticipation of what I am about to say.  This is likely to be because, firstly the roof is such an important part of the building in as much as it needs to be weather and watertight, and secondly, if it does start to deteriorate it can affect many other parts of the building and ultimately, a roof is often one of the most expensive components of a building to repair or replace. There many different ways of constructing a pitched roof (an angled roof with sloping sides which will shed water) and there are many different forms however for the purposes of the article I plan to discuss some of things I would look for when carrying out a survey to a traditional timber pitched roof to a low rise domestic building (for the layperson I am referring to a typical house).

Over the last few weeks I have discussed how much information can be found by inspecting a roof void (the underside of the roof internally) and within the first article I briefly provided some information about cut timber and trussed roofs. This is important because many of the problems that can occur with roofs often relate to the various components and the manner in which a roof is constructed.  Please take the time to read these articles to understand some of the terminology that will be used through this article. You can view the previous articles by using the following links (Link 1) (Link 2).  Within this and next week’s article, I have selected a number of things a Surveyor will consider when undertaking an inspection of a traditional timber pitched roof to a low rise domestic building.  The items discussed are in no particular order of priority and are far from exhaustive however it is hoped that they will provide a basic understanding of what to look for anyone with an interest in property.  Based on my previous articles it should now go without saying that professional advice should always be sought if something is identified that raises cause for concern.

Source: http://www.redbeacon.com/

‘Sagging’ roof surface – If the surface of a pitched roof is not perfectly level or straight then this can give the impression that there is a serious problem.  Whilst this can sometimes be the case it is not true in every situation.  The main purpose of the roof, as previously discussed, is to ensure that the building remains weather and watertight.  It is therefore quite possible to view a roof that is showing signs of unevenness or sagging on the outside, however on inspection of the inside of the building there are no signs of any water ingress. This raises a key point.  An inspection of a building must be thorough and no assumptions or conclusions should be made until a full comprehensive inspection has been carried out. A Surveyor will have the knowledge and skills to make this assessment at which point, having gathered all of the facts, will be able to provide sound accurate advice. Basically, a sagging roof may appear visually strange or indifferent compared to other roofs however if it is still performing the function it was designed for then it does not mean that it needs to be replaced or indeed repaired immediately?  Having said this, if the inspection identifies something more sinister then works may well be required.  So then, what would cause a roof to sag?

Source: http://clarkehomeimprovements.ie/surveys/

Usually a roof will start to sag if something happens to the timbers which form the roof structure. This could include broken or damages rafters or purlins which can be a result of excessive load on the roof surface, possibly a heavier roof tile has replaced an original lighter roof surface or possibly snow (however a well constructed roof should be designed to accommodate snow load), possibly fungal decay such as wet or dry rot, possibly woodworm, or even possibly damage during repairs or renovation etc.  It is quite easy to damage rafters in a roof space if you do not understand what you are doing. As a Surveyor I regularly see the results of poor DIY where it is clear that the person who carried out the work did not understand that a rafter is one of the main supporting timbers within the roof and that cutting into it or trying to remove it because ‘it is in the way’, is actually going to result in significant problems (believe me, I have seen this!).

The significance of what is causing a roof to sag will clearly be determined by what is causing the problem in the first place, which can occur for a variety of different reasons.  Remedial measures can vary from leaving the roof as it is to repairing or replacing individual components or ultimately removing the roof surface and removing and replacing the roof structure, if for example extensive dry rot is identified.  I have discussed dry rot during a previous article which you can view by using the following (Link). 

To conclude, there are many reasons why a roof may sag, however extensive remedial works are not always required.  In fact it could be argued that in some cases the presence of a sagging roof actually gives a building character. There are numerous examples of buildings that have existed for many hundreds of years which have sagging roofs, which are still performing the function that they were originally designed for.  The roofs may sometimes look odd compared to more modern roofs however to replace these roof would remove a significant feature and the buildings could also lose the charm that makes them interesting in the first place. In part 2 next week I will discuss some other things that a surveyor will consider whilst inspecting a traditional timber pitched roof to a low rise domestic building.

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Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Inspecting Roof Spaces – Part 1 - A 'Rafter' information available

Anyone with an interest in property can learn a great deal from what they find in a roof space as this is one of those places where most people chose to ignore, use is generally limited to storage or access once a year to collect the Christmas tree and then put it back again afterwards!

Source: http://www.loft-conversion-uk.com/

One of the great things about of being a Building Surveyor, is that we get to crawl around and inspect numerous parts of a building that many others would often not dare to venture.  Basements, floor voids, manholes are good examples, however a common place that will tells us a great deal about a building is the roof space (or attic depending on which part of the World you are from).  It is true that some people choose to utilize the roof space to maximize the habitable space as well maximizing the potential of their property and decide to refurbish the area, covering all of the exposed details in the process.  However when we access a roof void which has not been adapted or refurbished we enter a ‘mine' of information because it often allows us to see a building in its barest form.  Anyone with an interest in a property can learn a great deal from what they find in a roof space as this is one of those places where most people chose to ignore, use is generally limited to storage or access once a year to collect the Christmas tree and then put it back again afterwards!

There are a number of different roof types that can be selected depending on design criteria, aesthetics, location and ultimately costs, however for the purposes of this article I will refer to a traditional timber pitched roof, typically found on domestic dwellings in the United Kingdom, United States and other parts of the World.  Certain parts of the World that do not experience excessive rainfall may favour a flat roof, however where there is regular rain and snow a pitched roof will allow more efficient rainwater run-off, as long as the roof is constructed and maintained to a good standard. 

Pitched roofs can either be ‘cut and constructed’ on site or alternatively trusses can be manufactured off site, delivered and installed as a complete component.  Either way both choices ensure that a large amount of timber is installed and concealed with the roof void when a building is completed.  All of this timber has the potential to deteriorate/decay for a whole host of reasons and must be inspected on a regular basis to monitor its condition.  Although inspection of the roof timbers is important, the Inspection of a roof space includes much more than just this. The remaining part of this article will provide some examples of what a Surveyor will look for when inspecting timbers in a roof space and next week in Part 2 I will discuss other things that a Surveyor will consider.

Source: http://www.gopixpic.com/

Roof timbers – There are many different components of a timber cut roof, for which each has its own purpose and function.  A Surveyor will inspect all of the roof timbers carefully looking for signs of damage, deflection, dampness and water presence or possibly decay (wet rot or dry rot), or even woodworm.  Clearly there is a great deal that can affect timber and with it, its ability to maintain the function it was designed for.  The Surveyor will inspect the underside of the roof surface for any indication of water ingress, condensation or possible signs of daylight. This should identify if there are any missing or displaced tiles and where the sarking felt is split or missing. 

One of the primary functions of a roof is to keep the internal environment dry and it is essential that water is kept away from the timber.  In the event that water does come into contact with timber then an environment for wet rot or possibly dry rot may be created if left undetected.  Wet rot requires timber with a very high moisture content (typically 50% to 60%) in order to thrive, so any timber effected by wet rot in a roof void would need to be exposed to moisture over a long period of time. Dry rot requires a lower moisture content than wet rot (typically 25% to 30%), but also prefers much more humid temperature.  In both cases, poor ventilation is also usually a factor. You can read my previous article on dry rot by using the following (Link).

Source: http://www.omegapestcontrol.co.uk/

When inspecting for woodworm the Surveyor will look closely at the timber for ‘flight holes’ these are identifiable as little pin holes. Damage occurs to timber as a result of the larva boring through the wood with the eventual appearance of the adult insect. Different insects have a range of life spans, different flight hole sizes and are active at different times of the year.  In order to try to establish whether there is evidence of recent activity the Surveyor will look for small piles of dust (known as frass) on surfaces adjacent to the flight holes.  The Surveyor will also inspect the timber with a bradawl (similar to a blunt edge screwdriver), to establish the extent and depth of any woodworm attack, by ‘prodding’ the timber at various locations. For completeness woodworm is defined Timberwise (online) as; ‘Woodworm is a generic term that is used to commonly describe the larvae stage of all wood boring beetles. The most common beetle in the UK is known as the Common Furniture Beetle, however there are various other beetles which can make a nuisance of themselves. Other types include Powder Post Beetle, Wood Boring Weevil, Death Watch Beetle and House Longhorn Beetle’ 

Before inspecting a roof space it first worth expressing a note of caution.  Firstly, many roof spaces are accessible with a ladder only and will not have any lighting, so a torch will be required. Also, before entering a roof space always make sure that the environment is safe for you to do so.  Fragile materials, dust, noxious fumes, vermin and live services are some examples of the types of hazards that may be encountered, so if you have any doubts at all about your own health & safety then you should not enter a roof space.  In any event it would always be appropriate to instruct a professional such as a Chartered Building Surveyor to carry out the inspection for you, who will provide you with a comprehensive report, highlighting all issues within the roof void. 

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.