Problems With Roof Windows, Roof Lights

and Sky Lights


1stAssociated can provide help and advice with regard to surveys, structural surveys, building surveys, independent valuations, specific defects reports on property problems, such as roof problems, window problems, dampness, cracks, movement, etc, or any other property matters.

Please free phone 0800 298 5424 for a friendly chat with an independent surveyor.


What is a roof window?

Barrel sky light A roof window has many other names, such as a roof light, or sky light, but probably the most common name is the trade name of velux or velux windows. It is so popular it is almost generic, such as the word Hoover or Biro pen. We have come across many problems with this type of window over the years when carrying out structural surveys and home buyer reports.
A barrel sky light that we saw on a property on a flat roof. We were pleased to see a barrel roof light as the barrel affect at the top ensures that any water that lands on the roof light then runs off.  


Barrel shaped roof light

We do have the benefit when carrying out a structural survey that we have time to really analyse the problem and ensure we come up with the right solution, as unfortunately often on a home buyers report the surveyors time is very limited and it will have to refer you on a little more than just identifying the problem.

One very basic problem with roof lights on flat roofs is where the roof light itself is flat, as this enables water to sit on the roof light, which can promote condensation and of course if there are any cracks at all in the roof window then the rainwater gets in. The problem with this particular roof light is, as you can see in the first photo, to the right hand side of the barrel roof light water was sitting on the roof. This rainwater was sitting against the roof light and during the course of our structural survey we identified that the flashing around the base of it was leaking, letting in water.

Interior view of barrel shaped roof window  

When a roof window is used on a pitched roof it is inset into a roof and normally follows the pitch of the roof, particularly when it is a flat roof light. When a roof light is on a flat roof it is usually above the level of the material covering the roof. However, it can come in a variety of shapes and sizes such as flat roof windows, domed roof windows, or even barrel shaped.


Problems that can occur with sky lights


Junction of roof window and the roof

The first point we wish to make is that many problems occur at the junction between the roof light and the roof itself, where a flashing should be. We often find the flashings around the roof windows are defective. They were originally installed poorly, or deteriorated over the years, because it is the area that most people tend to miss.


Why does the water sit around the roof light?

Of course the quality of the roof light needs to be taken into consideration as well. We quite frequently find that where the original roof light was quite good quality it has over the years deteriorated and rather than replace it is repaired poorly. In the photo you can see the roof light, if you look closely to the right hand corner (just below the blue sky) and in this case on a lovely Georgian property the roof light has been repaired using plastic corrugated sheeting, which is such a shame. This particular roof light gave light to the top of the stair well. Roof window to pitched roof of poor quality
Poor quality roof light


Another repair that we come across quite often can be seen in the other photo where a flat roof has been re-roofed rather than replace and repair the roof light, it has simply been felted over, as often with that value of job there doesn't seem a budget to repair and replace roof lights. Here we have an example of an asphalt roof, which is normally more expensive, and a better quality flat roof simply asphalting over the roof light. You can see quite clearly the cracks in the top of the asphalt. This is where differential movement has occurred (this is quite simply different movement between the roof structure and the roof light), which is bound to happen if they are made out of different materials. Repairs will soon be necessary to the asphalted over roof light.

In our experience it is more prudent to repair the roof light than to cover it over, but when we say repair it we mean repair it with an equivalent standard, even replacement roof lights are not that expensive.


Roof light to flat roof that has been asphalted over
Asphalted over flat roof light

Defects set in windows in flat roofs

If you can imagine that where a roof window is, part of the roof structure has been taken away. Often in a flat roof situation the structure can be slightly weaker in this area and therefore movement occurs causing a dip in the roof.


Where can I get a good builder to repair my roof window?

We would suggest that the first question should be, what is the problem with my roof? Many builders will solve the effect of the problem but not the actual cause. For example, with a leaking roof light they may well seal the glazed unit or the flashing, but if the leaking roof light is caused by ponding (water sitting on the roof) in the roof, which in turn has been caused by blocked guttering, gutters wrongly discharging on the roof, then the problem will soon reoccur.

Coming back to the question, where do I find a good builder to repair my roof? This probably has to be equivalent to the how long is a piece of string question. First we would say you need to ensure that whoever you use has your best interest at heart rather than their best interest and that they are not simply trying to sell you the most profitable solution to them. Word of mouth is a great way of finding good builders but do be aware that often word of mouth recommendations come via someone who doesn't have any experience or expertise or working with builders.

Therefore the reasons for their word of mouth could be that the builder turned up on the day that he said he would, finished the job on the day that he said he would and charged the price he said he would, which ironically can be a good recommendation, but not if the work carried out was technically wrong or of poor quality. You should also take great care if your property is an old property as it could be a Listed Building or in a conservation area or simply need a builder that knows how to deal with older properties.


Newer properties

Equally, a newer property also has to be dealt with in an appropriate manner, so the experience the builder has is very important. Also, you need to see if you are still covered by a warranty. The NHBC is probably the most common warranty in the country and is generally for ten years, but does have limitations on what it covers. Please see our article on the NHBC.


Defects report on roof windows

We have developed a specific defects report for looking at a specific problem, such as chimneys or problematic roof windows on your property. These originally developed from our engineers report that specifically looked at structural cracks in properties, which then moved onto us giving specific advice on dampness in properties, due to many contracts being involved in this industry simply being there to sell a product rather than to give you best advice.

Large Roof Window Large roof windows

Please see our other article on Roof windows, roof lights and sky lights:


Roof Windows, Roof Lights, Sky Lights and Light Tunnels


If you truly do want an independent expert opinion from a surveyor with regard to roof windows, roof lights, velux roofs, dormer, dormer roofs, roof problems, chimneys, surveys, building surveys, structural reports, engineers reports, specific defects report, structural surveys, home buyers reports or any other property matters please contact 0800 298 5424 for a surveyor to give you a call back.

If you have a commercial leasehold, freehold, etc, then you may wish to look at our Dilaps Website at and for Disputes go to our Disputes Help site .

We hope you found the article of use and if you have any experiences that you feel should be added to this article that would benefit others, or you feel that some of the information that we have put is wrong then please do not hesitate to contact us (we are only human).

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