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.

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‘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?

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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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