How can we get a flat roof and satisfy insurance requirements?

We are contemplating a house extension and a flat roof has been proposed by the architect. An alternative is a roof with a 16 per cent (approx) incline. Potentially, the flat roof could amount to 33 per cent of the total roof area.

We have learned that insurance companies are reluctant to insure flat roofs and, while they don't rule it out, will not offer any clarification as to what specifications may be acceptable. To obtain an opinion, our insurance company has requested details such as materials, life expectancy, warranty, manufacturer, contractor and overall per cent of flat roof. These details are only available at tender stage and may change during construction. We also understand that a 16 per cent incline is also deemed to be a flat roof.

Can you advise what material is suitable and how to satisfy insurance company requirements (in advance of tendering)?

Other relevant information: we are keen to know where we stand in advance of tendering / construction as alternatives include refusal of cover, policy exclusions, penalty premiums or periodic roof replacement.

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This is a complex question with numerous sub-sections and I will address these in turn as follows:

Firstly there is the issue of flat versus pitched roofs. This is perhaps a mute point and strictly speaking, no roof should be flat and should be laid to fall to facilitate rainwater drainage. Clearly a roof may look flat, and it is standard industry practice to call a roof with a 5º pitch or less a flat roof. Anything over this, is in our opinion, a pitched roof, albeit potentially a low-pitched roof. It is fair to say that the various tile and slate manufacturers which one would normally associate with pitched roofs have minimum stipulated pitches for their products and typically a slate manufacture requires a minimum 22.5º pitch whereas the tile manufacturers requirements are typically a minimum 17.5º pitch. While the manufactures of slates and tiles do have certain products that allow one down to pitches as low as 12º in certain circumstances, you should remember that a typical roof light manufacturer requires a minimum 15º pitch for their products to work. Hopefully, the above sets the scene and the parameters and your designer should be fully aware of all of the restrictions.

The next issue to consider is what is practical to build given the constraints of the site. Whereas one would like to try and achieve a general minimum pitch of 22.5º to allow for maximum flexibility in the choice of covering type, you could be restricted by issues such as the length of the extension and the height of window cills on the existing rear wall which simply restrict the actual pitch – it sounds like this is the case that you are faced with here and that the maximum available pitch for you is 16º.

Choice of roof covering

This is a low-pitched roof which clearly restricts the choice of roof covering available to you and this rules out most of the normal / typical slates and tiles and you will most likely have to use a typical flat-roof covering which is suitable for low pitches, such as felt, asphalt, fibre glass or metal sheeting products such as mock tile corrugated cladding, or if budgets permit, zinc or copper.

Whatever about the insurance company requirements, which I will touch on below, it is essential that you use a material that is suitable for the low pitch, otherwise you will have problems with leaks in the future and ironically your insurance company probably would not pay out for a claim if and when it comes to light that the “pitched” roof covering was not laid in accordance with the manufacturer’s requirements.

I also note that you seem to have a fear over the issue of changing specification between what is specified and tendered and what is actually used in the building. Whilst I accept that this is typically what happens, one needs to understand why this happens, and this is simply lack of planning and foresight. There is no reason why one should not be able to consider the situation, select the best solution in terms of suitability, availability and costs, specify it and stick to it. Too often, little thought is given to the detail at the start and it is only when one goes to do the job that the builder ends up suggesting or telling you what to do, and whilst this may prove to be effective, it can also be a rushed and inappropriate solution to suit the contractor’s programme. So, in short, do the homework with your design, select a product and stick to it.

As regards the insurance companies’ requirements, unfortunately there appears to be some misconceptions by the insurance companies which is no doubt based on statistics and history of past claims, all of which are based on very basic poor-quality flat roofs of old. Thankfully, the construction industry has moved on in leaps and bounds and there are fantastic roofing products available for flat roofs and a well-designed flat roof will perform every bit as well as a pitched roof. You only have to look around at buildings to see large office blocks, schools, hospitals etc with extensive flat roof areas. So whatever about perception, in reality, insurance companies should have nothing to fear in terms of performance of a flat roof, but as you know, the insurance companies call the shots when it comes to providing insurance and setting premiums.

While we are not insurance experts, we are aware that insurance companies will have problems / concerns over the type of material and this is not only to do with the risk of leaks, but how the material would perform in, say, a fire situation. In this respect, a typical flat roofing membrane would be more combustible in a fire situation and thus in the event of a fire there would be a risk of a greater level of damage with a flat roof than a pitched roof, and this may well explain their rationale.

However, there is no substitute for planning in advance and in this respect, we would recommend that you, with the aid of your designer, identify the most appropriate solutions in the circumstance, draw these to your insurer’s attention, explain the rationale behind your choices and seek confirmation from them as to whether or not they are prepared to offer insurance cover and to identify any specific increase in premium and the reasons for same. This should then assist you to make a final selection on the most appropriate covering in the circumstances. There is no substitute for having the homework done before making your decision.

• Val O'Brien is a Chartered Building Surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie