Flat Roof Guide | Options, Materials and Costs 

By Flatroofs.ie 


Get Leak Free Flat Roofs

For anyone who grew up during the eighties and early nineties, flat roofs had a poor reputation and they were far from leak proof, however those days are behind us and flat roofs today are very problem free and leak free due to the advance of better materials and waterproofing systems.

We’ve always liked them simply because of their simplicity, plenty of ceiling height and low cost in comparison to standard roofing.  Today we like them because of their modern look and clean lines combined with a lot of glass for light making the perfect Irish home.

Flat or Not-Flat

Flat roofs are not technically flat as they require a slope to drain off rainwater, however this is virtually unnoticeable their perfect from homes that require high floor to ceiling heights and often where a pitched roof would be unsuitable.

Regular checks to your roof can minimise potential problems in the long run and making sure you minimise any debris or leaves that may lodge and cause problems.

Poor Workmanship 

Another contributing problem to flat roofs is poor workmanship, the incorrect installation or poor materials has in the past contributed to leaks and a short lifespan of flat roofs.  Check with your contractor that they have the skills and references to carry out such work before hiring them. Also engage with engineers and architects for new installations where possible.  

Flat Roofing Systems – Three Main Types 

There are three main flat roofing systems, these are 1) rubber roofing, 2) fibreglass roofing and 3) torch-on felt.  When we examine these, the obvious question is how do they compare?  

Torch-on Felt

The cheapest and probably the most popular in the past is the torch-on felt flat roof.  This system still has a somewhat poor reputation due to the older application of the rolled felt.  That combined with poor workmanship hasn’t helped it but the newer type is allot more durable and resistant.  This system involves three layers of felt melted together using a torch – torch on felt.  

The surface layer or also called the cap sheet can be made of either black bitumen, a reflective paint or a mineral fleck which comes in a range of colours.  Most of these roofing systems have a 10 year guarantee but can last up to 30 years of maintained, treated and cared for.

Rubber Roofs

Rubber systems are increasing in popularity in recent times.  A rubber system depending on the size of the surface can be installed in one large sheet but for larger roofs rubber joinings can be necessary.  A rubber surface is very light weight, flexible and a strong finish. A well installed rubber surface and last up to 30 years and beyond. The cost of rubber roofing in comparison to torch-on felt is about 25% more expensive.  It can be repaired very easily through a patch system similar to how tyre tubes are repaired.  

Fibreglass Roofing

Fibreglass roofing has been with us for a number of years but is gaining popularity in more recent years and so far has proven itself to be tough and very durable.  This system is layed usually in one layer or two layers with factory made trim finishing. Most guarantees for this surface are in or around 25 years this is not an issue for this surface.  

It’s also the most expensive system of the three and due to materials and labour. It’s the most resistant of the three to damage and is very tough once it’s hardened and cured.  Repairs are practically unnoticeable and easy. Probably the most attractive option of the three.  

Flat Roof V’s Pitched Roof

If you are trying to decide or consider putting on a flat roof or pitched and what are the considerations, there are many and cost is one of those but not the only one.  Flat roofs are suitable for large areas or roofs that have a lot of complicated angles.  

Pitched roofs on the other hand were traditionally built by carpenters allowing to convert later for additional space.  These days most roofs are coming prefabricated to make the build faster. For a final decision on the best roof to put on your building, you’ll obviously need to consult an engineer but here is approximately the rough cost difference of both options.  

Cost difference based on a 139 sqm rectangular building 

Element Qty Rate Total Qty Rate Total
Pitched Flat
Roof Structure €19,500 €14,500
Roof Joists 502 10.40 5,200 360 10.40 3,700
Bridging 301 10.40 3,134 215 10.40 2,200
Ceiling Joists 358 10.40 3,700 0 10.40 0
Bridging 215 10.40 2,300 0 10.40 0
Wall Plate 47 11.25 530 47 11.25 530
Straps 40 10.00 403 40 10 403
Plywood 0 27 139 139 3,700
Insulation 139 28 3,800 139 139 3,800
Ridge Collars  36 8.50 300 0.00 0 0
Costs based on 139 sqm rectangular building.  

Based on a structure size of 139 sqm, the cost difference between a pitched and a flat roof is approximately €5000 give or take.  Please take into consideration the life span of each type of roof, although flat roof lifespan is dramatically improved, pitched roofs traditionally last longer.  

Related Roof Types & Estimated Costs

Flat roofing has come along way in the last ten years since the days of them just being a cheap alternative to a pitch roof and nearly always leaking.  That has changed now and thanks to the development of better materials.  

We live in a climate of consistent damp and wet and all roofing systems need to be able to cope with that certainty not to mention driving winds and unpredictable conditions.  Our wind driven rain will test any roofer worth his salt. “Modern materials, design and ventilation have completely changed flat roofing” see more here, see more info below (Reference) 

Flat roofs which should not not be totally flat as its needs to give a small fall in order to direct water using 1 degree fall to direct water to the gutter.  Flat roofs are popular usually on rear or side extensions avoiding the need for an apex or pitch. With some buildings depending on where the windows are giving better views and vista.  


Torch-on felt is what covers most flat roofs and has come a long way in the last ten years. This is the go-to option, cheap and readily available, it’s usually applied in two or three layers. They can either have a granular finish or a smooth finish  and this can be then painted with solar reflective paint. It usually comes with a materials guarantee of 10-15 years and costs about €55per sqm.


Another alternative is PVC, this is a single ply membrane of usually grey-coloured rubber is fixed to your timber base, making labour costs cheaper than the installation of a two-ply material. When its laid well it can looks very good, it usually costs 20-30 per cent more than a torch-on system and will come with guarantees of around 12-15 years.

Fibre Glass

Then there’s fibreglass, its effectiveness is still a bit undecided but has a reputation of being durable. Its inflexible nature is not suitable for some situations, but advances in materials in recent years have made fibreglass roofing more reliable and very durable.  Costs are around €70 per sq m on domestic-sized roofs and should be able to last for about 15-20 years.

Zinc Roofing

Zinc is growing in popularity and one of our favourites, it’s a slick, smooth, contemporary look that goes on in panels with a standing seam joining each panel.  Its a very modern and durable look impressing the neighbours and visitors.

It is naturally resistant to corrosion, needs minimal to no maintenance due to its natural, self-protecting patina, and is extremely long lasting – 100 years-plus. It can come in a few grey, dark and silvery colours and will maintain its colour throughout its life.

Costs are about €120 per metre by the time up-stands, drips and fascias are taken into account. It is a nice advantage to be able to do your fascias, soffits and rainwater goods in the same material, giving nice continuity and consistency.  

Copper Roofing

Copper has been the more traditional way to go. It is one of the few metals that occur naturally rather than needing to be extracted from ore, thus making it one of the earliest metals to be used.

The covering of choice for well-to-do buildings of the past. The gorgeous green patina it develops after years of oxidation has long been coveted by architects.

A truly beautiful natural product but unfortunately it comes with a truly heavy price tag. Expect to pay in the region of €130 per metre. Like zinc, it is extremely long lasting, around 100 years in this country.

Lead Roofing

Lead, another beautiful and traditional product, is hugely malleable, and mostly used on small areas, over bay windows for example. Cost would be similar to copper at €130 per metre and comes with a material guarantee of 50 years.


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